Android 百分比布局库 percent support lib 解析与扩展

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一、概述

周末游戏打得过猛，于是周天熬夜码代码，周一早上浑浑噩噩的发现android-percent-support-lib-sample这个项目，Google终于开始支持百分比的方式布局了，瞬间脉动回来，啊咧咧。对于这种历史性的时刻，不出篇博客难以表达我内心的激动。

还记得不久前，发了篇博客：Android 屏幕适配方案，这篇博客以Web页面设计引出一种适配方案，最终的目的就是可以通过百分比控制控件的大小。当然了，存在一些问题，比如：

对于没有考虑到屏幕尺寸，可能会出现意外的情况；
apk的大小会增加；

当然了android-percent-support这个库，基本可以解决上述问题，是不是有点小激动，稍等，我们先描述下这个support-lib。

这个库提供了：

两种布局供大家使用：
PercentRelativeLayout、PercentFrameLayout，通过名字就可以看出，这是继承自FrameLayout和RelativeLayout两个容器类；
支持的属性有：

layout_widthPercent、layout_heightPercent、
layout_marginPercent、layout_marginLeftPercent、
layout_marginTopPercent、layout_marginRightPercent、
layout_marginBottomPercent、layout_marginStartPercent、layout_marginEndPercent。

可以看到支持宽高，以及margin。

也就是说，大家只要在开发过程中使用PercentRelativeLayout、PercentFrameLayout替换FrameLayout、RelativeLayout即可。

是不是很简单，不过貌似没有LinearLayout，有人会说LinearLayout有weight属性呀。但是，weight属性只能支持一个方向呀~~哈，没事，刚好给我们一个机会去自定义一个PercentLinearLayout。

好了，本文分为3个部分：

PercentRelativeLayout、PercentFrameLayout的使用
对上述控件源码分析
自定义PercentLinearLayout

二、使用

关于使用，其实及其简单，并且github上也有例子，android-percent-support-lib-sample。我们就简单过一下：

首先记得在build.gradle添加：

 compile 'com.android.support:percent:22.2.0'

（一）PercentFrameLayout

<?xml version="1.0" encoding="utf-8"?><android.support.percent.PercentFrameLayout    xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:app="http://schemas.android.com/apk/res-auto"    android:layout_width="match_parent"    android:layout_height="match_parent">    <TextView        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_gravity="left|top"        android:background="#44ff0000"        android:text="width:30%,height:20%"        app:layout_heightPercent="20%"        android:gravity="center"        app:layout_widthPercent="30%"/>    <TextView        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_gravity="right|top"        android:gravity="center"        android:background="#4400ff00"        android:text="width:70%,height:20%"        app:layout_heightPercent="20%"        app:layout_widthPercent="70%"/>    <TextView        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_gravity="bottom"        android:background="#770000ff"        android:text="width:100%,height:10%"        android:gravity="center"        app:layout_heightPercent="10%"        app:layout_widthPercent="100%"/></android.support.percent.PercentFrameLayout>

3个TextView，很简单，直接看效果图：

Android 百分比布局库 percent support lib 解析与扩展

(二) PercentRelativeLayout

<?xml version="1.0" encoding="utf-8"?><android.support.percent.PercentRelativeLayout    xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:app="http://schemas.android.com/apk/res-auto"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:clickable="true">    <TextView        android:id="@+id/row_one_item_one"        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_alignParentTop="true"        android:background="#7700ff00"        android:text="w:70%,h:20%"        android:gravity="center"        app:layout_heightPercent="20%"        app:layout_widthPercent="70%"/>    <TextView        android:id="@+id/row_one_item_two"        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_toRightOf="@+id/row_one_item_one"        android:background="#396190"        android:text="w:30%,h:20%"        app:layout_heightPercent="20%"        android:gravity="center"        app:layout_widthPercent="30%"/>    <ImageView        android:id="@+id/row_two_item_one"        android:layout_width="match_parent"        android:layout_height="0dp"        android:src="@drawable/tangyan"        android:scaleType="centerCrop"        android:layout_below="@+id/row_one_item_one"        android:background="#d89695"        app:layout_heightPercent="70%"/>    <TextView        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_below="@id/row_two_item_one"        android:background="#770000ff"        android:gravity="center"        android:text="width:100%,height:10%"        app:layout_heightPercent="10%"        app:layout_widthPercent="100%"/></android.support.percent.PercentRelativeLayout>

ok，依然是直接看效果图:

Android 百分比布局库 percent support lib 解析与扩展

使用没什么好说的，就是直观的看一下。

三、源码分析

其实细想一下，Google只是对我们原本熟悉的RelativeLayout和FrameLayout进行的功能的扩展，使其支持了percent相关的属性。

那么，我们考虑下，如果是我们添加这种扩展，我们会怎么做：

通过LayoutParams获取child设置的percent相关属性的值
onMeasure的时候，将child的width,height的值，通过获取的自定义属性的值进行计算（eg:容器的宽 * fraction ），计算后传入给child.measure(w,h);

ok，有了上面的猜想，我们直接看PercentFrameLayout的源码。

public class PercentFrameLayout extends FrameLayout {    private final PercentLayoutHelper mHelper = new PercentLayoutHelper(this);    //省略了，两个构造方法    public PercentFrameLayout(Context context, AttributeSet attrs) {        super(context, attrs);    }    @Override    public LayoutParams generateLayoutParams(AttributeSet attrs) {        return new LayoutParams(getContext(), attrs);    }    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec);        super.onMeasure(widthMeasureSpec, heightMeasureSpec);        if (mHelper.handleMeasuredStateTooSmall()) {            super.onMeasure(widthMeasureSpec, heightMeasureSpec);        }    }    @Override    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {        super.onLayout(changed, left, top, right, bottom);        mHelper.restoreOriginalParams();    }    public static class LayoutParams extends FrameLayout.LayoutParams            implements PercentLayoutHelper.PercentLayoutParams {        private PercentLayoutHelper.PercentLayoutInfo mPercentLayoutInfo;        public LayoutParams(Context c, AttributeSet attrs) {            super(c, attrs);            mPercentLayoutInfo = PercentLayoutHelper.getPercentLayoutInfo(c, attrs);        }        //省略了一些代码...        @Override        public PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo() {            return mPercentLayoutInfo;        }        @Override        protected void setBaseAttributes(TypedArray a, int widthAttr, int heightAttr) {            PercentLayoutHelper.fetchWidthAndHeight(this, a, widthAttr, heightAttr);        }    }}

代码是相当的短，可以看到PercentFrameLayout里面首先重写了generateLayoutParams方法，当然了，由于支持了一些新的layout_属性，那么肯定需要定义对应的LayoutParams。

（一）percent相关属性的获取

可以看到PercentFrameLayout.LayoutParams在原有的FrameLayout.LayoutParams基础上，实现了PercentLayoutHelper.PercentLayoutParams接口。

这个接口很简单，只有一个方法：

public interface PercentLayoutParams {        PercentLayoutInfo getPercentLayoutInfo();    }

而，这个方法的实现呢，也只有一行：return mPercentLayoutInfo;，那么这个mPercentLayoutInfo在哪完成赋值呢？

看PercentFrameLayout.LayoutParams的构造方法：

public LayoutParams(Context c, AttributeSet attrs) {            super(c, attrs);            mPercentLayoutInfo = PercentLayoutHelper.getPercentLayoutInfo(c, attrs);        }

可以看到，将attrs传入给getPercentLayoutInfo方法，那么不用说，这个方法的内部，肯定是获取自定义属性的值，然后将其封装到PercentLayoutInfo对象中，最后返回。

代码如下：

public static PercentLayoutInfo getPercentLayoutInfo(Context context,            AttributeSet attrs) {        PercentLayoutInfo info = null;        TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.PercentLayout_Layout);        float value = array.getFraction(R.styleable.PercentLayout_Layout_layout_widthPercent, 1, 1,                -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent width: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.widthPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_heightPercent, 1, 1, -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent height: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.heightPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginPercent, 1, 1, -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent margin: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.leftMarginPercent = value;            info.topMarginPercent = value;            info.rightMarginPercent = value;            info.bottomMarginPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginLeftPercent, 1, 1,                -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent left margin: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.leftMarginPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginTopPercent, 1, 1,                -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent top margin: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.topMarginPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginRightPercent, 1, 1,                -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent right margin: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.rightMarginPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginBottomPercent, 1, 1,                -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent bottom margin: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.bottomMarginPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginStartPercent, 1, 1,                -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent start margin: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.startMarginPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginEndPercent, 1, 1,                -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent end margin: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.endMarginPercent = value;        }        array.recycle();        if (Log.isLoggable(TAG, Log.DEBUG)) {            Log.d(TAG, "constructed: " + info);        }        return info;    }

是不是和我们平时的取值很类似，所有的值最终封装到PercentLayoutInfo对象中。

ok，到此我们的属性获取就介绍完成，有了这些属性，是不是onMeasure里面要进行使用呢？

(二) onMeasue中重新计算child的尺寸

@Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec);        super.onMeasure(widthMeasureSpec, heightMeasureSpec);        if (mHelper.handleMeasuredStateTooSmall()) {            super.onMeasure(widthMeasureSpec, heightMeasureSpec);        }    }

可以看到onMeasure中的代码页很少，看来核心的代码都被封装在mHelper的方法中，我们直接看mHelper.adjustChildren方法。

/**     * Iterates over children and changes their width and height to one calculated from percentage     * values.     * @param widthMeasureSpec Width MeasureSpec of the parent ViewGroup.     * @param heightMeasureSpec Height MeasureSpec of the parent ViewGroup.     */    public void adjustChildren(int widthMeasureSpec, int heightMeasureSpec) {        //...        int widthHint = View.MeasureSpec.getSize(widthMeasureSpec);        int heightHint = View.MeasureSpec.getSize(heightMeasureSpec);        for (int i = 0, N = mHost.getChildCount(); i < N; i++) {            View view = mHost.getChildAt(i);            ViewGroup.LayoutParams params = view.getLayoutParams();            if (params instanceof PercentLayoutParams) {                PercentLayoutInfo info =                        ((PercentLayoutParams) params).getPercentLayoutInfo();                if (Log.isLoggable(TAG, Log.DEBUG)) {                    Log.d(TAG, "using " + info);                }                if (info != null) {                    if (params instanceof ViewGroup.MarginLayoutParams) {                        info.fillMarginLayoutParams((ViewGroup.MarginLayoutParams) params,                                widthHint, heightHint);                    } else {                        info.fillLayoutParams(params, widthHint, heightHint);                    }                }            }        }    }

通过注释也能看出，此方法中遍历所有的孩子，通过百分比的属性重新设置其宽度和高度。

首先在widthHint、heightHint保存容器的宽、高，然后遍历所有的孩子，判断其LayoutParams是否是PercentLayoutParams类型，如果是，通过params.getPercentLayoutInfo拿出info对象。

是否还记得，上面的分析中，PercentLayoutInfo保存了percent相关属性的值。

如果info不为null，则判断是否需要处理margin；我们直接看fillLayoutParams方法（处理margin也是类似的）。

 /**         * Fills {@code ViewGroup.LayoutParams} dimensions based on percentage values.         */        public void fillLayoutParams(ViewGroup.LayoutParams params, int widthHint,                int heightHint) {            // Preserve the original layout params, so we can restore them after the measure step.            mPreservedParams.width = params.width;            mPreservedParams.height = params.height;            if (widthPercent >= 0) {                params.width = (int) (widthHint * widthPercent);            }            if (heightPercent >= 0) {                params.height = (int) (heightHint * heightPercent);            }            if (Log.isLoggable(TAG, Log.DEBUG)) {                Log.d(TAG, "after fillLayoutParams: (" + params.width + ", " + params.height + ")");            }        }

首先保存原本的width和height，然后重置params的width和height为(int) (widthHint * widthPercent)和(int) (heightHint * heightPercent);。

到此，其实我们的百分比转换就结束了，理论上就已经实现了对于百分比的支持，不过Google还考虑了一些细节。

我们回到onMeasure方法：

@Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec);        super.onMeasure(widthMeasureSpec, heightMeasureSpec);        if (mHelper.handleMeasuredStateTooSmall()) {            super.onMeasure(widthMeasureSpec, heightMeasureSpec);        }    }

下面还有个mHelper.handleMeasuredStateTooSmall的判断，也就是说，如果你设置的百分比，最终计算出来的MeasuredSize过小的话，会进行一些操作。
代码如下：

public boolean handleMeasuredStateTooSmall() {        boolean needsSecondMeasure = false;        for (int i = 0, N = mHost.getChildCount(); i < N; i++) {            View view = mHost.getChildAt(i);            ViewGroup.LayoutParams params = view.getLayoutParams();            if (Log.isLoggable(TAG, Log.DEBUG)) {                Log.d(TAG, "should handle measured state too small " + view + " " + params);            }            if (params instanceof PercentLayoutParams) {                PercentLayoutInfo info =                        ((PercentLayoutParams) params).getPercentLayoutInfo();                if (info != null) {                    if (shouldHandleMeasuredWidthTooSmall(view, info)) {                        needsSecondMeasure = true;                        params.width = ViewGroup.LayoutParams.WRAP_CONTENT;                    }                    if (shouldHandleMeasuredHeightTooSmall(view, info)) {                        needsSecondMeasure = true;                        params.height = ViewGroup.LayoutParams.WRAP_CONTENT;                    }                }            }        }        if (Log.isLoggable(TAG, Log.DEBUG)) {            Log.d(TAG, "should trigger second measure pass: " + needsSecondMeasure);        }        return needsSecondMeasure;    }

首先遍历所有的孩子，拿出孩子的layoutparams，如果是PercentLayoutParams实例，则取出info。如果info不为null，调用shouldHandleMeasuredWidthTooSmall判断：

private static boolean shouldHandleMeasuredWidthTooSmall(View view, PercentLayoutInfo info) {        int state = ViewCompat.getMeasuredWidthAndState(view) & ViewCompat.MEASURED_STATE_MASK;        return state == ViewCompat.MEASURED_STATE_TOO_SMALL && info.widthPercent >= 0 &&                info.mPreservedParams.width == ViewGroup.LayoutParams.WRAP_CONTENT;    }

给我老师的人工智能教程打call！http://blog.csdn.net/jiangjunshow

Android 百分比布局库 percent support lib 解析与扩展

转载请标明出处：
http://blog.csdn.net/lmj623565791/article/details/46695347；
本文出自:【张鸿洋的博客】

一、概述

对于没有考虑到屏幕尺寸，可能会出现意外的情况；
apk的大小会增加；

当然了android-percent-support这个库，基本可以解决上述问题，是不是有点小激动，稍等，我们先描述下这个support-lib。

这个库提供了：

两种布局供大家使用：
PercentRelativeLayout、PercentFrameLayout，通过名字就可以看出，这是继承自FrameLayout和RelativeLayout两个容器类；
支持的属性有：

可以看到支持宽高，以及margin。

也就是说，大家只要在开发过程中使用PercentRelativeLayout、PercentFrameLayout替换FrameLayout、RelativeLayout即可。

好了，本文分为3个部分：

PercentRelativeLayout、PercentFrameLayout的使用
对上述控件源码分析
自定义PercentLinearLayout

二、使用

关于使用，其实及其简单，并且github上也有例子，android-percent-support-lib-sample。我们就简单过一下：

首先记得在build.gradle添加：

 compile 'com.android.support:percent:22.2.0'

（一）PercentFrameLayout

<?xml version="1.0" encoding="utf-8"?><android.support.percent.PercentFrameLayout    xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:app="http://schemas.android.com/apk/res-auto"    android:layout_width="match_parent"    android:layout_height="match_parent">    <TextView        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_gravity="left|top"        android:background="#44ff0000"        android:text="width:30%,height:20%"        app:layout_heightPercent="20%"        android:gravity="center"        app:layout_widthPercent="30%"/>    <TextView        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_gravity="right|top"        android:gravity="center"        android:background="#4400ff00"        android:text="width:70%,height:20%"        app:layout_heightPercent="20%"        app:layout_widthPercent="70%"/>    <TextView        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_gravity="bottom"        android:background="#770000ff"        android:text="width:100%,height:10%"        android:gravity="center"        app:layout_heightPercent="10%"        app:layout_widthPercent="100%"/></android.support.percent.PercentFrameLayout>

3个TextView，很简单，直接看效果图：

Android 百分比布局库 percent support lib 解析与扩展

(二) PercentRelativeLayout

<?xml version="1.0" encoding="utf-8"?><android.support.percent.PercentRelativeLayout    xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:app="http://schemas.android.com/apk/res-auto"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:clickable="true">    <TextView        android:id="@+id/row_one_item_one"        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_alignParentTop="true"        android:background="#7700ff00"        android:text="w:70%,h:20%"        android:gravity="center"        app:layout_heightPercent="20%"        app:layout_widthPercent="70%"/>    <TextView        android:id="@+id/row_one_item_two"        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_toRightOf="@+id/row_one_item_one"        android:background="#396190"        android:text="w:30%,h:20%"        app:layout_heightPercent="20%"        android:gravity="center"        app:layout_widthPercent="30%"/>    <ImageView        android:id="@+id/row_two_item_one"        android:layout_width="match_parent"        android:layout_height="0dp"        android:src="@drawable/tangyan"        android:scaleType="centerCrop"        android:layout_below="@+id/row_one_item_one"        android:background="#d89695"        app:layout_heightPercent="70%"/>    <TextView        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_below="@id/row_two_item_one"        android:background="#770000ff"        android:gravity="center"        android:text="width:100%,height:10%"        app:layout_heightPercent="10%"        app:layout_widthPercent="100%"/></android.support.percent.PercentRelativeLayout>

ok，依然是直接看效果图:

Android 百分比布局库 percent support lib 解析与扩展

使用没什么好说的，就是直观的看一下。

三、源码分析

其实细想一下，Google只是对我们原本熟悉的RelativeLayout和FrameLayout进行的功能的扩展，使其支持了percent相关的属性。

那么，我们考虑下，如果是我们添加这种扩展，我们会怎么做：

通过LayoutParams获取child设置的percent相关属性的值
onMeasure的时候，将child的width,height的值，通过获取的自定义属性的值进行计算（eg:容器的宽 * fraction ），计算后传入给child.measure(w,h);

ok，有了上面的猜想，我们直接看PercentFrameLayout的源码。

public class PercentFrameLayout extends FrameLayout {    private final PercentLayoutHelper mHelper = new PercentLayoutHelper(this);    //省略了，两个构造方法    public PercentFrameLayout(Context context, AttributeSet attrs) {        super(context, attrs);    }    @Override    public LayoutParams generateLayoutParams(AttributeSet attrs) {        return new LayoutParams(getContext(), attrs);    }    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec);        super.onMeasure(widthMeasureSpec, heightMeasureSpec);        if (mHelper.handleMeasuredStateTooSmall()) {            super.onMeasure(widthMeasureSpec, heightMeasureSpec);        }    }    @Override    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {        super.onLayout(changed, left, top, right, bottom);        mHelper.restoreOriginalParams();    }    public static class LayoutParams extends FrameLayout.LayoutParams            implements PercentLayoutHelper.PercentLayoutParams {        private PercentLayoutHelper.PercentLayoutInfo mPercentLayoutInfo;        public LayoutParams(Context c, AttributeSet attrs) {            super(c, attrs);            mPercentLayoutInfo = PercentLayoutHelper.getPercentLayoutInfo(c, attrs);        }        //省略了一些代码...        @Override        public PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo() {            return mPercentLayoutInfo;        }        @Override        protected void setBaseAttributes(TypedArray a, int widthAttr, int heightAttr) {            PercentLayoutHelper.fetchWidthAndHeight(this, a, widthAttr, heightAttr);        }    }}

（一）percent相关属性的获取

可以看到PercentFrameLayout.LayoutParams在原有的FrameLayout.LayoutParams基础上，实现了PercentLayoutHelper.PercentLayoutParams接口。

这个接口很简单，只有一个方法：

public interface PercentLayoutParams {        PercentLayoutInfo getPercentLayoutInfo();    }

而，这个方法的实现呢，也只有一行：return mPercentLayoutInfo;，那么这个mPercentLayoutInfo在哪完成赋值呢？

看PercentFrameLayout.LayoutParams的构造方法：

public LayoutParams(Context c, AttributeSet attrs) {            super(c, attrs);            mPercentLayoutInfo = PercentLayoutHelper.getPercentLayoutInfo(c, attrs);        }

代码如下：

public static PercentLayoutInfo getPercentLayoutInfo(Context context,            AttributeSet attrs) {        PercentLayoutInfo info = null;        TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.PercentLayout_Layout);        float value = array.getFraction(R.styleable.PercentLayout_Layout_layout_widthPercent, 1, 1,                -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent width: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.widthPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_heightPercent, 1, 1, -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent height: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.heightPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginPercent, 1, 1, -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent margin: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.leftMarginPercent = value;            info.topMarginPercent = value;            info.rightMarginPercent = value;            info.bottomMarginPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginLeftPercent, 1, 1,                -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent left margin: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.leftMarginPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginTopPercent, 1, 1,                -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent top margin: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.topMarginPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginRightPercent, 1, 1,                -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent right margin: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.rightMarginPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginBottomPercent, 1, 1,                -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent bottom margin: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.bottomMarginPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginStartPercent, 1, 1,                -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent start margin: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.startMarginPercent = value;        }        value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginEndPercent, 1, 1,                -1f);        if (value != -1f) {            if (Log.isLoggable(TAG, Log.VERBOSE)) {                Log.v(TAG, "percent end margin: " + value);            }            info = info != null ? info : new PercentLayoutInfo();            info.endMarginPercent = value;        }        array.recycle();        if (Log.isLoggable(TAG, Log.DEBUG)) {            Log.d(TAG, "constructed: " + info);        }        return info;    }

是不是和我们平时的取值很类似，所有的值最终封装到PercentLayoutInfo对象中。

ok，到此我们的属性获取就介绍完成，有了这些属性，是不是onMeasure里面要进行使用呢？

(二) onMeasue中重新计算child的尺寸

@Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec);        super.onMeasure(widthMeasureSpec, heightMeasureSpec);        if (mHelper.handleMeasuredStateTooSmall()) {            super.onMeasure(widthMeasureSpec, heightMeasureSpec);        }    }

可以看到onMeasure中的代码页很少，看来核心的代码都被封装在mHelper的方法中，我们直接看mHelper.adjustChildren方法。

/**     * Iterates over children and changes their width and height to one calculated from percentage     * values.     * @param widthMeasureSpec Width MeasureSpec of the parent ViewGroup.     * @param heightMeasureSpec Height MeasureSpec of the parent ViewGroup.     */    public void adjustChildren(int widthMeasureSpec, int heightMeasureSpec) {        //...        int widthHint = View.MeasureSpec.getSize(widthMeasureSpec);        int heightHint = View.MeasureSpec.getSize(heightMeasureSpec);        for (int i = 0, N = mHost.getChildCount(); i < N; i++) {            View view = mHost.getChildAt(i);            ViewGroup.LayoutParams params = view.getLayoutParams();            if (params instanceof PercentLayoutParams) {                PercentLayoutInfo info =                        ((PercentLayoutParams) params).getPercentLayoutInfo();                if (Log.isLoggable(TAG, Log.DEBUG)) {                    Log.d(TAG, "using " + info);                }                if (info != null) {                    if (params instanceof ViewGroup.MarginLayoutParams) {                        info.fillMarginLayoutParams((ViewGroup.MarginLayoutParams) params,                                widthHint, heightHint);                    } else {                        info.fillLayoutParams(params, widthHint, heightHint);                    }                }            }        }    }

通过注释也能看出，此方法中遍历所有的孩子，通过百分比的属性重新设置其宽度和高度。

是否还记得，上面的分析中，PercentLayoutInfo保存了percent相关属性的值。

如果info不为null，则判断是否需要处理margin；我们直接看fillLayoutParams方法（处理margin也是类似的）。

 /**         * Fills {@code ViewGroup.LayoutParams} dimensions based on percentage values.         */        public void fillLayoutParams(ViewGroup.LayoutParams params, int widthHint,                int heightHint) {            // Preserve the original layout params, so we can restore them after the measure step.            mPreservedParams.width = params.width;            mPreservedParams.height = params.height;            if (widthPercent >= 0) {                params.width = (int) (widthHint * widthPercent);            }            if (heightPercent >= 0) {                params.height = (int) (heightHint * heightPercent);            }            if (Log.isLoggable(TAG, Log.DEBUG)) {                Log.d(TAG, "after fillLayoutParams: (" + params.width + ", " + params.height + ")");            }        }

首先保存原本的width和height，然后重置params的width和height为(int) (widthHint * widthPercent)和(int) (heightHint * heightPercent);。

到此，其实我们的百分比转换就结束了，理论上就已经实现了对于百分比的支持，不过Google还考虑了一些细节。

我们回到onMeasure方法：

@Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec);        super.onMeasure(widthMeasureSpec, heightMeasureSpec);        if (mHelper.handleMeasuredStateTooSmall()) {            super.onMeasure(widthMeasureSpec, heightMeasureSpec);        }    }

下面还有个mHelper.handleMeasuredStateTooSmall的判断，也就是说，如果你设置的百分比，最终计算出来的MeasuredSize过小的话，会进行一些操作。
代码如下：

public boolean handleMeasuredStateTooSmall() {        boolean needsSecondMeasure = false;        for (int i = 0, N = mHost.getChildCount(); i < N; i++) {            View view = mHost.getChildAt(i);            ViewGroup.LayoutParams params = view.getLayoutParams();            if (Log.isLoggable(TAG, Log.DEBUG)) {                Log.d(TAG, "should handle measured state too small " + view + " " + params);            }            if (params instanceof PercentLayoutParams) {                PercentLayoutInfo info =                        ((PercentLayoutParams) params).getPercentLayoutInfo();                if (info != null) {                    if (shouldHandleMeasuredWidthTooSmall(view, info)) {                        needsSecondMeasure = true;                        params.width = ViewGroup.LayoutParams.WRAP_CONTENT;                    }                    if (shouldHandleMeasuredHeightTooSmall(view, info)) {                        needsSecondMeasure = true;                        params.height = ViewGroup.LayoutParams.WRAP_CONTENT;                    }                }            }        }        if (Log.isLoggable(TAG, Log.DEBUG)) {            Log.d(TAG, "should trigger second measure pass: " + needsSecondMeasure);        }        return needsSecondMeasure;    }

首先遍历所有的孩子，拿出孩子的layoutparams，如果是PercentLayoutParams实例，则取出info。如果info不为null，调用shouldHandleMeasuredWidthTooSmall判断：

private static boolean shouldHandleMeasuredWidthTooSmall(View view, PercentLayoutInfo info) {        int state = ViewCompat.getMeasuredWidthAndState(view) & ViewCompat.MEASURED_STATE_MASK;        return state == ViewCompat.MEASURED_STATE_TOO_SMALL && info.widthPercent >= 0 &&                info.mPreservedParams.width == ViewGroup.LayoutParams.WRAP_CONTENT;    }

Android 百分比布局库 percent support lib 解析与扩展

一、概述

二、使用

（一）PercentFrameLayout

(二) PercentRelativeLayout

三、源码分析

（一）percent相关属性的获取

(二) onMeasue中重新计算child的尺寸

给我老师的人工智能教程打call！http://blog.csdn.net/jiangjunshow

一、概述

二、使用

（一）PercentFrameLayout

(二) PercentRelativeLayout

三、源码分析

（一）percent相关属性的获取

(二) onMeasue中重新计算child的尺寸

给我老师的人工智能教程打call！http://blog.csdn.net/jiangjunshow

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