Android源码分析-深入理解setContentView方法
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一般我们都是这样使用setContentView:
@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); }但setContentView是怎么把我们的布局加载显示到界面上的呢？我们进去setContentView看一下：
public void setContentView(int layoutResID) { getWindow().setContentView(layoutResID); initWindowDecorActionBar(); }这里的getWindow返回一个Window对象mWindow，然后调用其setContentView方法，不过Window是一个抽象类，因此这个mWindow一定是Window的某个子类对象（你可以打印它的Class对象直接看是什么类型），它在Activity的attach方法（这个方法在ActivityThread启动Activity时会被调用）中被初始化：
final void attach(Context context, ActivityThread aThread, Instrumentation instr, IBinder token, int ident, ...... mWindow = PolicyManager.makeNewWindow(this); ......再看PolicyManager的makeNewWindow方法：
public static Window makeNewWindow(Context context) { return sPolicy.makeNewWindow(context); }这个sPolicy是通过反射创建的，是一个com.android.internal.policy.impl.Policy对象，它的makeNewWindow方法：
public Window makeNewWindow(Context context) { return new PhoneWindow(context); }到这里就可以确定Activity的getWindow()返回的其实是一个PhoneWindow对象，注意PhoneWindow所在的包为com.android.internal.policy.impl。也就是说getWindow().setContentView(layoutResID);调用的就是PhoneWindow的setContentView方法：
@Override public void setContentView(int layoutResID) { if (mContentParent == null) { installDecor(); } else { mContentParent.removeAllViews(); } //把我们的布局添加到mContentParent中 mLayoutInflater.inflate(layoutResID, mContentParent); //这个cb其实就是我们的Activity对象 final Callback cb = getCallback(); if (cb != null && !isDestroyed()) { cb.onContentChanged(); } }代码逻辑并不复杂，就是把我们的布局添加到mContentParent（ViewGroup对象）中。它的赋值是在installDecor中进行的：
private void installDecor() { if (mDecor == null) { mDecor = generateDecor(); ...... } if (mContentParent == null) { mContentParent = generateLayout(mDecor); ...... } }先看mDecor是一个什么东西：
protected DecorView generateDecor() { return new DecorView(getContext(), -1); }原来是一个DecorView对象，DecorView类继承自FrameLayout，它是PhoneWindow的内部类。
再来看generateLayout方法：
protected ViewGroup generateLayout(DecorView decor) { // Apply data from current theme. TypedArray a = getWindowStyle(); if (false) { System.out.println("From style:"); String s = "Attrs:"; for (int i = 0; i < com.android.internal.R.styleable.Window.length; i++) { s = s + " " + Integer.toHexString(com.android.internal.R.styleable.Window[i]) + "=" + a.getString(i); } System.out.println(s); } mIsFloating = a.getBoolean(com.android.internal.R.styleable.Window_windowIsFloating, false); int flagsToUpdate = (FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR) & (~getForcedWindowFlags()); if (mIsFloating) { setLayout(WRAP_CONTENT, WRAP_CONTENT); setFlags(0, flagsToUpdate); } else { setFlags(FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR, flagsToUpdate); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowNoTitle, false)) { requestFeature(FEATURE_NO_TITLE); } else if (a.getBoolean(com.android.internal.R.styleable.Window_windowActionBar, false)) { // Don't allow an action bar if there is no title. requestFeature(FEATURE_ACTION_BAR); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowActionBarOverlay, false)) { requestFeature(FEATURE_ACTION_BAR_OVERLAY); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowActionModeOverlay, false)) { requestFeature(FEATURE_ACTION_MODE_OVERLAY); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowFullscreen, false)) { setFlags(FLAG_FULLSCREEN, FLAG_FULLSCREEN & (~getForcedWindowFlags())); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowTranslucentStatus, false)) { setFlags(FLAG_TRANSLUCENT_STATUS, FLAG_TRANSLUCENT_STATUS & (~getForcedWindowFlags())); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowTranslucentNavigation, false)) { setFlags(FLAG_TRANSLUCENT_NAVIGATION, FLAG_TRANSLUCENT_NAVIGATION & (~getForcedWindowFlags())); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowOverscan, false)) { setFlags(FLAG_LAYOUT_IN_OVERSCAN, FLAG_LAYOUT_IN_OVERSCAN&(~getForcedWindowFlags())); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowShowWallpaper, false)) { setFlags(FLAG_SHOW_WALLPAPER, FLAG_SHOW_WALLPAPER&(~getForcedWindowFlags())); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowEnableSplitTouch, getContext().getApplicationInfo().targetSdkVersion >= android.os.Build.VERSION_CODES.HONEYCOMB)) { setFlags(FLAG_SPLIT_TOUCH, FLAG_SPLIT_TOUCH&(~getForcedWindowFlags())); } a.getValue(com.android.internal.R.styleable.Window_windowMinWidthMajor, mMinWidthMajor); a.getValue(com.android.internal.R.styleable.Window_windowMinWidthMinor, mMinWidthMinor); if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedWidthMajor)) { if (mFixedWidthMajor == null) mFixedWidthMajor = new TypedValue(); a.getValue(com.android.internal.R.styleable.Window_windowFixedWidthMajor, mFixedWidthMajor); } if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedWidthMinor)) { if (mFixedWidthMinor == null) mFixedWidthMinor = new TypedValue(); a.getValue(com.android.internal.R.styleable.Window_windowFixedWidthMinor, mFixedWidthMinor); } if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedHeightMajor)) { if (mFixedHeightMajor == null) mFixedHeightMajor = new TypedValue(); a.getValue(com.android.internal.R.styleable.Window_windowFixedHeightMajor, mFixedHeightMajor); } if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedHeightMinor)) { if (mFixedHeightMinor == null) mFixedHeightMinor = new TypedValue(); a.getValue(com.android.internal.R.styleable.Window_windowFixedHeightMinor, mFixedHeightMinor); } final Context context = getContext(); final int targetSdk = context.getApplicationInfo().targetSdkVersion; final boolean targetPreHoneycomb = targetSdk < android.os.Build.VERSION_CODES.HONEYCOMB; final boolean targetPreIcs = targetSdk < android.os.Build.VERSION_CODES.ICE_CREAM_SANDWICH; final boolean targetHcNeedsOptions = context.getResources().getBoolean( com.android.internal.R.bool.target_honeycomb_needs_options_menu); final boolean noActionBar = !hasFeature(FEATURE_ACTION_BAR) || hasFeature(FEATURE_NO_TITLE); if (targetPreHoneycomb || (targetPreIcs && targetHcNeedsOptions && noActionBar)) { addFlags(WindowManager.LayoutParams.FLAG_NEEDS_MENU_KEY); } else { clearFlags(WindowManager.LayoutParams.FLAG_NEEDS_MENU_KEY); } if (mAlwaysReadCloseOnTouchAttr || getContext().getApplicationInfo().targetSdkVersion >= android.os.Build.VERSION_CODES.HONEYCOMB) { if (a.getBoolean( com.android.internal.R.styleable.Window_windowCloseOnTouchOutside, false)) { setCloseOnTouchOutsideIfNotSet(true); } } WindowManager.LayoutParams params = getAttributes(); if (!hasSoftInputMode()) { params.softInputMode = a.getInt( com.android.internal.R.styleable.Window_windowSoftInputMode, params.softInputMode); } if (a.getBoolean(com.android.internal.R.styleable.Window_backgroundDimEnabled, mIsFloating)) { /* All dialogs should have the window dimmed */ if ((getForcedWindowFlags()&WindowManager.LayoutParams.FLAG_DIM_BEHIND) == 0) { params.flags |= WindowManager.LayoutParams.FLAG_DIM_BEHIND; } if (!haveDimAmount()) { params.dimAmount = a.getFloat( android.R.styleable.Window_backgroundDimAmount, 0.5f); } } if (params.windowAnimations == 0) { params.windowAnimations = a.getResourceId( com.android.internal.R.styleable.Window_windowAnimationStyle, 0); } // The rest are only done if this window is not embedded; otherwise, // the values are inherited from our container. if (getContainer() == null) { if (mBackgroundDrawable == null) { if (mBackgroundResource == 0) { mBackgroundResource = a.getResourceId( com.android.internal.R.styleable.Window_windowBackground, 0); } if (mFrameResource == 0) { mFrameResource = a.getResourceId(com.android.internal.R.styleable.Window_windowFrame, 0); } if (false) { System.out.println("Background: " + Integer.toHexString(mBackgroundResource) + " Frame: " + Integer.toHexString(mFrameResource)); } } mTextColor = a.getColor(com.android.internal.R.styleable.Window_textColor, 0xFF000000); } // Inflate the window decor. int layoutResource; int features = getLocalFeatures(); // System.out.println("Features: 0x" + Integer.toHexString(features)); if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) { if (mIsFloating) { TypedValue res = new TypedValue(); getContext().getTheme().resolveAttribute( com.android.internal.R.attr.dialogTitleIconsDecorLayout, res, true); layoutResource = res.resourceId; } else { layoutResource = com.android.internal.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 = com.android.internal.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( com.android.internal.R.attr.dialogCustomTitleDecorLayout, res, true); layoutResource = res.resourceId; } else { layoutResource = com.android.internal.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( com.android.internal.R.attr.dialogTitleDecorLayout, res, true); layoutResource = res.resourceId; } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) { layoutResource = com.android.internal.R.layout.screen_action_bar; } else { layoutResource = com.android.internal.R.layout.screen_title; } // System.out.println("Title!"); } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) { layoutResource = com.android.internal.R.layout.screen_simple_overlay_action_mode; } else { // Embedded, so no decoration is needed. layoutResource = com.android.internal.R.layout.screen_simple; // System.out.println("Simple!"); } mDecor.startChanging(); View in = mLayoutInflater.inflate(layoutResource, null); decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT)); ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT); if (contentParent == null) { throw new RuntimeException("Window couldn't find content container view"); } if ((features & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) { ProgressBar progress = getCircularProgressBar(false); if (progress != null) { progress.setIndeterminate(true); } } // Remaining setup -- of background and title -- that only applies // to top-level windows. if (getContainer() == null) { Drawable drawable = mBackgroundDrawable; if (mBackgroundResource != 0) { drawable = getContext().getResources().getDrawable(mBackgroundResource); } mDecor.setWindowBackground(drawable); drawable = null; if (mFrameResource != 0) { drawable = getContext().getResources().getDrawable(mFrameResource); } mDecor.setWindowFrame(drawable); // System.out.println("Text=" + Integer.toHexString(mTextColor) + // " Sel=" + Integer.toHexString(mTextSelectedColor) + // " Title=" + Integer.toHexString(mTitleColor)); if (mTitleColor == 0) { mTitleColor = mTextColor; } if (mTitle != null) { setTitle(mTitle); } setTitleColor(mTitleColor); } mDecor.finishChanging(); return contentParent; }这个方法主要做两件事：
1.设置当前窗口的主题样式
2.查找适当的布局作为mDecor的子View，Android中定义了许多这种布局，在~\sdk\platforms\android-19\data\res\layout目录下可以找到，比如一般使用的screen_simple.xml：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:fitsSystemWindows="true" android:orientation="vertical"> <ViewStub android:id="@+id/action_mode_bar_stub" android:inflatedId="@+id/action_mode_bar" android:layout="@layout/action_mode_bar" android:layout_width="match_parent" android:layout_height="wrap_content" /> <!-- 这个就是mContentParent,我们的布局添加做为它的子View --> <FrameLayout android:id="@android:id/content" android:layout_width="match_parent" android:layout_height="match_parent" android:foregroundInsidePadding="false" android:foregroundGravity="fill_horizontal|top" android:foreground="?android:attr/windowContentOverlay" /></LinearLayout>因此平时我们调用setContentView设置显示我们的布局，实际的布局会是这样子：
实际的xml布局文件（采用screen_simple.xml为例）：
<com.android.internal.policy.impl.PhoneWindow$DecorView android:layout_width="match_parent" android:layout_height="match_parent"> <!-- screen_simple.xml --> <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:fitsSystemWindows="true" android:orientation="vertical"> <ViewStub android:id="@+id/action_mode_bar_stub" android:inflatedId="@+id/action_mode_bar" android:layout="@layout/action_mode_bar" android:layout_width="match_parent" android:layout_height="wrap_content" /> <!-- mContentParent实际就是这个FrameLayout --> <FrameLayout android:id="@android:id/content" android:layout_width="match_parent" android:layout_height="match_parent" android:foregroundInsidePadding="false" android:foregroundGravity="fill_horizontal|top" android:foreground="?android:attr/windowContentOverlay"> <!-- 我们的activity_main.xml --> <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="hello world"/> </LinearLayout> </FrameLayout> </LinearLayout> </com.android.internal.policy.impl.PhoneWindow>setContentView时序图：
转载请注明出处：http://blog.csdn.net/u012619640/article/details/50722306
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