37、自定义控件详解（二）-- View和ViewGroup

width = right - left
height = bottom - top

x = left + translationX
y = top + translationY

public static class MeasureSpec {
    private static final int MODE_SHIFT = 30;
    private static final int MODE_MASK  = 0x3 << MODE_SHIFT;
    public static final int UNSPECIFIED = 0 << MODE_SHIFT;
    public static final int EXACTLY     = 1 << MODE_SHIFT;
    public static final int AT_MOST     = 2 << MODE_SHIFT;
    public static int makeMeasureSpec(int size, int mode) {
        if (sUseBrokenMakeMeasureSpec) {
            return size + mode;
        } else {
            return (size & ~MODE_MASK) | (mode & MODE_MASK);
        }
    }
    public static int getMode(int measureSpec) {
        return (measureSpec & MODE_MASK);
    }
    public static int getSize(int measureSpec) {
        return (measureSpec & ~MODE_MASK);
    }
    .....
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    setMeasuredDimension(measureWidth(widthMeasureSpec), measureHeight(heightMeasureSpec));
}

/**测量宽度的模板代码*/
private int measureWidth(int measureSpec){
    int result = 0;
    int specMode = MeasureSpec.getMode(measureSpec);
    int specSize = MeasureSpec.getSize(measureSpec);
    
    if(specMode == MeasureSpec.EXACTLY){    // 精确数值
        result = specSize;
    }else{                                    // 非精确数值
        result = 200;
        if(specMode == MeasureSpec.AT_MOST){// 自动包含
            result = Math.min(result, specSize);// 取出指定大小与specSize中最小一个作为最后测量值。
        }
    }
    return result;
}

/**测量高度的模板代码*/
private int measureHeight(int measureSpec){
    int result = 0;
    int specMode = MeasureSpec.getMode(measureSpec);
    int specSize = MeasureSpec.getSize(measureSpec);
    
    if(specMode == MeasureSpec.EXACTLY){
        result = specSize;
    }else{
        result = 200;
        if(specMode == MeasureSpec.AT_MOST){
            result = Math.min(result, specSize);
        }
    }
    return result;
}

Canvas canvas = new Canvas();   或    Canvas canvas = new Canvas(bitmap);

/*
  * Draw traversal performs several drawing steps which must be executed
  * in the appropriate order:
  *
  *  1. Draw the background  （绘制控件设置的背景，系统已在view.draw()中绘制，只要在xml中指定背景即可）
  *  2. If necessary, save the canvas' layers to prepare for fading  
  *  3. Draw view's content  (可以重写， onDraw(canvas);)
  *  4. Draw children      (可重写，用来分发canvas到子控件，具体看ViewGroup。
  *                        对应方法dispatchDraw(canvas);此方法依次调用了子控件的draw()方法)
  *  5. If necessary, draw the fading edges and restore layers （绘制控件四周的阴影渐变效果）
  *  6. Draw decorations (scrollbars for instance) （用来绘制滚动条，对应方法onDrawScrollBars(canvas);。
  *      onDrawHorizontalScrollBar()和onDrawVerticalScrollBar()被隐藏了无法重写，也许有其他方法重写滚动条）
  */

// measureChild(View, int, int)为子组件添加Padding   
measureChild(child, parentWidthMeasureSpec, parentHeightMeasureSpec);
// measureChildren(int, int)根据指定的高和宽来测量所有子View中显示参数非GONE的组件。  
measureChildren(widthMeasureSpec, heightMeasureSpec);
// measureChildWithMargins(View, int, int, int, int)测量指定的子组件，为子组件添加Padding和Margin。
measureChildWithMargins(child, parentWidthMeasureSpec, widthUsed, parentHeightMeasureSpec, heightUsed);

onFinishInflate -> onMeasure() -> onMeasure() -> onSizeChange() -> onLayout()  -> onMeasure() -> onMeasure() -> onLayout() -> onDraw()
之后的操作会一直onDraw()去重绘

ViewConfiguration.get(this).getScaledTouchSlop();

VelocityTracker velocityTracker = VelocityTracker.obtain();
velocityTracker.addMovement(event);

VelocityTracker velocityTracker = VelocityTracker.obtain();
velocityTracker.addMovement(event);
velocityTracker.computeCurrentVelocity(1000);
int xVelocity = (int) velocityTracker.getXVelocity();
int yVelocity = (int) velocityTracker.getYVelocity();

速度 = （终点位置 - 起点位置）/ 时间段

velocityTracker.clear();
velocityTracker.recycle();

<?xml version="1.0" encoding="utf-8"?>
<translate xmlns:android="http://schemas.android.com/apk/res/android"
    android:fromXDelta="100%"
    android:toXDelta="0"
    android:fromYDelta="0"
    android:toYDelta="0"
    android:duration="300">
</translate>

<?xml version="1.0" encoding="utf-8"?>
<translate xmlns:android="http://schemas.android.com/apk/res/android"
    android:fromXDelta="0"
    android:toXDelta="-100%"
    android:fromYDelta="0"
    android:toYDelta="0"
    android:duration="300">
</translate>

<?xml version="1.0" encoding="utf-8"?>
<translate xmlns:android="http://schemas.android.com/apk/res/android"
    android:fromXDelta="-100%"
    android:toXDelta="0"
    android:fromYDelta="0"
    android:toYDelta="0"
    android:duration="300">
</translate>

<?xml version="1.0" encoding="utf-8"?>
<translate xmlns:android="http://schemas.android.com/apk/res/android"
    android:fromXDelta="0"
    android:toXDelta="100%"
    android:fromYDelta="0"
    android:toYDelta="0"
    android:duration="300">
</translate>

//两个参数表示进入和退出的动画,要写在startactivity的后面生效
overridePendingTransition(R.anim.trans_next_in, R.anim.trans_next_out);

//该方法最好做成成员变量可以响应下方的触摸动作
GestureDetector gestureDetector = new GestureDetector(this,new GestureDetector.SimpleOnGestureListener(){
    //手指在屏幕上滑动
    //e1,e2:手指的事件:手指第一次触摸屏幕触发->手指离开屏幕触发
    //vX vY:水平和垂直方向的速度
    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2,float velocityX, float velocityY) {
        //过滤掉Y的移动
        if(Math.abs(e1.getRawY()-e2.getRawY())>100){
            //ToastUtils.show(SetupBaseActivity.this,"动作不合法");
            return true;
        }
        
        if(e1.getRawX()-e2.getRawX()>150){
            //从右向左滑，显示下一个界面
            //showNext();
            overridePendingTransition(R.anim.trans_next_in, R.anim.trans_next_out);
            return true;
        }else if (e2.getRawX()-e1.getRawX()>150) {
            //从左向右滑，显示上一个界面
            //showPre();
            overridePendingTransition(R.anim.trans_pre_in, R.anim.trans_pre_out);
            return true;
        }
        return super.onFling(e1, e2, velocityX, velocityY);
    }
});

//3.使用手势识别器去识别用户的动作
@Override
public boolean onTouchEvent(MotionEvent event) {
    //将手势事件传递给手势识别器
    gestureDetector.onTouchEvent(event);
    return super.onTouchEvent(event);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    float downX = 0, downY = 0, upX, upY;
    //继承了Activity的onTouchEvent方法，直接监听点击事件
    if(event.getAction() == MotionEvent.ACTION_DOWN) {
        //当手指按下的时候
        downX = event.getX();
        downY = event.getY();
    }
    if(event.getAction() == MotionEvent.ACTION_UP) {
        //当手指离开的时候
        upX = event.getX();
        upY = event.getY();
        if((downY - upY > 50) && (Math.abs(upX - downX) <= ( downY - upY))) {
            Toast.makeText(TaskToMoneyActivity.this, "向上滑", Toast.LENGTH_SHORT).show();
        } else if((upY - downY > 50) && (Math.abs(upX - downX) <= (upY - downY))) {
            Toast.makeText(TaskToMoneyActivity.this, "向下滑", Toast.LENGTH_SHORT).show();
        } else if((downX - upX>50) && (Math.abs(upY - downY) < (downX - upX))) {
            Toast.makeText(TaskToMoneyActivity.this, "向左滑", Toast.LENGTH_SHORT).show();
        } else if((upX - downX>50) && (Math.abs(upY - downY) < (upX - downX))) {
            Toast.makeText(TaskToMoneyActivity.this, "向右滑", Toast.LENGTH_SHORT).show();
        }
    }
    return super.onTouchEvent(event);
}

Scroller mScroller = new Scroller(getContext());
// 缓慢滚动到指定位置
private void smoothScrollTo(int destX , int destY){
    int scrollX = getScrollX();
    int scrollY = getScrollY();
    int delta = destX - scrollX;
    // 1000ms内滑向destX，缓慢移动
    mScroller.startScroll(scrollX, 0, delta, 0, 1000);
    invalidate();
}
@Override
public void computeScroll() {
    super.computeScroll();
    if(mScroller.computeScrollOffset()){
        scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
        postInvalidate();
    }
}