(源码阅读)我们经常用的setContentView()，到底做了什么。
既然是源码阅读，那我们就果断上源码吧，首先就是Activity下的setContentView().嘿嘿，首先来看下一张比较经典的图，可能这里话的比较丑~~hhh
/** * Set the activity content from a layout resource. The resource will be * inflated, adding all top-level views to the activity. * * @param layoutResID Resource ID to be inflated. * * @see #setContentView(android.view.View) * @see #setContentView(android.view.View, android.view.ViewGroup.LayoutParams) */ public void setContentView(@LayoutRes int layoutResID) { getWindow().setContentView(layoutResID); initWindowDecorActionBar(); }
我们可以看到有用就只有，getWindow().setContentView()，这行代码了，点进去之后发现又是一个抽象方法。
当我们看到的抽象发现确实比较的头疼，不知道从哪里去找。 不过，这里我window对象调用的setContentView()，所以我们通过mWindow找到mWindow = new PhoneWindow().这么一行代码，我们来到PhoneWindow这个类找到setContentView();
public void setContentView(int layoutResID) { // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window // decor, when theme attributes and the like are crystalized. Do not check the feature // before this happens. if (mContentParent == null) { installDecor(); } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) { mContentParent.removeAllViews(); } if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) { final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID, getContext()); transitionTo(newScene); } else { mLayoutInflater.inflate(layoutResID, mContentParent); } mContentParent.requestApplyInsets(); final Callback cb = getCallback(); if (cb != null && !isDestroyed()) { cb.onContentChanged(); } }先从上面来看，判断了是否为空，执行了installDecor();
private void installDecor() { if (mDecor == null) { mDecor = generateDecor(); //方法一 mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS); mDecor.setIsRootNamespace(true); if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) { mDecor.postOnAnimation(mInvalidatePanelMenuRunnable); } } if (mContentParent == null) { mContentParent = generateLayout(mDecor); //方法二 ............................. } }installDecore()方法太长了，这里也只是截了一部分的，中间的一部分省略了，这里只有重要的俩个方法了。
protected DecorView generateDecor() { return new DecorView(getContext(), -1); }
我们可以看到第一个方法，也只是new了一个DecorView()。那么我们来看第二个。%>_<%这也是一个巨长的方法。
protected ViewGroup generateLayout(DecorView decor) { // Apply data from current theme. TypedArray a = getWindowStyle(); ................................... // Inflate the window decor. int layoutResource; //resId int features = getLocalFeatures(); // System.out.println("Features: 0x" + Integer.toHexString(features)); if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) { layoutResource = R.layout.screen_swipe_dismiss; } else if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) { if (mIsFloating) { TypedValue res = new TypedValue(); getContext().getTheme().resolveAttribute( R.attr.dialogTitleIconsDecorLayout, res, true); layoutResource = res.resourceId; } else { layoutResource = R.layout.screen_title_icons; } // XXX Remove this once action bar supports these features. removeFeature(FEATURE_ACTION_BAR); // System.out.println("Title Icons!"); } else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0 && (features & (1 << FEATURE_ACTION_BAR)) == 0) { // Special case for a window with only a progress bar (and title). // XXX Need to have a no-title version of embedded windows. layoutResource = R.layout.screen_progress; // System.out.println("Progress!"); } else if ((features & (1 << FEATURE_CUSTOM_TITLE)) != 0) { // Special case for a window with a custom title. // If the window is floating, we need a dialog layout if (mIsFloating) { TypedValue res = new TypedValue(); getContext().getTheme().resolveAttribute( R.attr.dialogCustomTitleDecorLayout, res, true); layoutResource = res.resourceId; } else { layoutResource = R.layout.screen_custom_title; } // XXX Remove this once action bar supports these features. removeFeature(FEATURE_ACTION_BAR); } else if ((features & (1 << FEATURE_NO_TITLE)) == 0) { // If no other features and not embedded, only need a title. // If the window is floating, we need a dialog layout if (mIsFloating) { TypedValue res = new TypedValue(); getContext().getTheme().resolveAttribute( R.attr.dialogTitleDecorLayout, res, true); layoutResource = res.resourceId; } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) { layoutResource = a.getResourceId( R.styleable.Window_windowActionBarFullscreenDecorLayout, R.layout.screen_action_bar); } else { layoutResource = R.layout.screen_title; } // System.out.println("Title!"); } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) { layoutResource = R.layout.screen_simple_overlay_action_mode; } else { // Embedded, so no decoration is needed. layoutResource = R.layout.screen_simple; //这个布局是Android自带的 // System.out.println("Simple!"); } mDecor.startChanging(); View in = mLayoutInflater.inflate(layoutResource, null); //o通过inflate去加载对应的一系列判断下来的resId decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT)); mContentRoot = (ViewGroup) in; ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT); //去拿到Android自带的一个布局文件 ，里面只有一个LinearLayout if (contentParent == null) { throw new RuntimeException("Window couldn't find content container view"); } mDecor.finishChanging(); return contentParent; //最终将拿到的布局文件返回回去。 }
/** * The ID that the main layout in the XML layout file should have. */ public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;
这个时候我们再回来在phoneWindow里面看到的setContentView()方法，我们发现下面去.inflate(layoutResID,mContentParent);
if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) { final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID, getContext()); transitionTo(newScene); } else { mLayoutInflater.inflate(layoutResID, mContentParent); } mContentParent.requestApplyInsets(); final Callback cb = getCallback(); if (cb != null && !isDestroyed()) { cb.onContentChanged(); }这里其实也就是去把我们在setContentView()时，设置的resId的布局解析到我们在generateLayout方法所加载的R.id.content的布局上面。
到这里，所看的源码也基本上结束了，中间还有很多的判断或许对大家有用，需要大家去阅读。
看了一些源码之后，本人也get到一些技能了，当不会写的时候就根据Android的源码去写。