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Activity显示到界面流程

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之前分析过Activity的启动流程，虽然Activity启动了，但是显示在界面上的并不是Activity，接下来将分析Activity显示到界面的流程。

首先看看各个相关类的关系图
Window初始化
View的生成过程

1.Activity.attach

在Activity启动流程的35步中，我们可以看到Activity的实例化，然后调用Activity.attach初始化所有的数据。 

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final void attach(Context context, ActivityThread aThread,
            Instrumentation instr, IBinder token, int ident,
            Application application, Intent intent, ActivityInfo info,
            CharSequence title, Activity parent, String id,
            Object lastNonConfigurationInstance,
            HashMap<String,Object> lastNonConfigurationChildInstances,
            Configuration config) {
	attachBaseContext(context);

	mWindow = PolicyManager.makeNewWindow(this);
	mWindow.setCallback(this);
	if (info.softInputMode != WindowManager.LayoutParams.SOFT_INPUT_STATE_UNSPECIFIED) {
		mWindow.setSoftInputMode(info.softInputMode);
	}
	mUiThread = Thread.currentThread();

	mMainThread = aThread;
	mInstrumentation = instr;
	mToken = token;
	mIdent = ident;
	mApplication = application;
	mIntent = intent;
	mComponent = intent.getComponent();
	mActivityInfo = info;
	mTitle = title;
	mParent = parent;
	mEmbeddedID = id;
	mLastNonConfigurationInstance = lastNonConfigurationInstance;
	mLastNonConfigurationChildInstances = lastNonConfigurationChildInstances;

	mWindow.setWindowManager(null, mToken, mComponent.flattenToString());
	if (mParent != null) {
		mWindow.setContainer(mParent.getWindow());
	}
	mWindowManager = mWindow.getWindowManager();
	mCurrentConfig = config;
}

里面实际就是初始化一些值，新建了一个window对象。

2. PolicyManager.makeNewWindow

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public static Window makeNewWindow(Context context) {
	return sPolicy.makeNewWindow(context);
}

public PhoneWindow makeNewWindow(Context context) {  
	return new PhoneWindow(context);  
}  

public PhoneWindow(Context context) {
	super(context);
	mLayoutInflater = LayoutInflater.from(context);
}

3. PhoneWindow.setCallback

这个很重要，后面接受键盘和触屏时间都是回调 Window.CallBack,所以Activity能接受到键盘和触屏事件

4. Window.setWindowManager

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public void setWindowManager(WindowManager wm,
		IBinder appToken, String appName) {
	mAppToken = appToken;
	mAppName = appName;
	if (wm == null) {
		wm = WindowManagerImpl.getDefault();
	}
	mWindowManager = new LocalWindowManager(wm);
}

5. WindowManagerImpl.getDefault

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private static WindowManagerImpl mWindowManager = new WindowManagerImpl();  

public static WindowManagerImpl getDefault()
{
	return mWindowManager;
}

6. new LocalWindowManager(wm)

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private class LocalWindowManager implements WindowManager {  
	LocalWindowManager(WindowManager wm) {  
		mWindowManager = wm;  
		mDefaultDisplay = mContext.getResources().getDefaultDisplay(  
				mWindowManager.getDefaultDisplay());  
	}  

	......  

	private final WindowManager mWindowManager;  

	private final Display mDefaultDisplay;  
}

以上就是Activity中Window的创建和初始化过程。

7. Activity.setContentView

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public void setContentView(int layoutResID) {
	getWindow().setContentView(layoutResID);
}

8. PhoneWindow.setContentView

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@Override
public void setContentView(int layoutResID) {
	if (mContentParent == null) {
		installDecor();
	} else {
		mContentParent.removeAllViews();
	}
	mLayoutInflater.inflate(layoutResID, mContentParent);
	final Callback cb = getCallback();
	if (cb != null) {
		cb.onContentChanged();
	}
}

9. PhoneWindow.installDecor

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private void installDecor() {
	if (mDecor == null) {
		mDecor = generateDecor();
		mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
		mDecor.setIsRootNamespace(true);
	}
	if (mContentParent == null) {
		mContentParent = generateLayout(mDecor);

		mTitleView = (TextView)findViewById(com.android.internal.R.id.title);
		if (mTitleView != null) {
			if ((getLocalFeatures() & (1 << FEATURE_NO_TITLE)) != 0) {
				View titleContainer = findViewById(com.android.internal.R.id.title_container);
				if (titleContainer != null) {
					titleContainer.setVisibility(View.GONE);
				} else {
					mTitleView.setVisibility(View.GONE);
				}
				if (mContentParent instanceof FrameLayout) {
					((FrameLayout)mContentParent).setForeground(null);
				}
			} else {
				mTitleView.setText(mTitle);
			}
		}
	}
}

10. PhoneWindow.generateDecor

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protected DecorView generateDecor() {
	return new DecorView(getContext(), -1);
}

private final class DecorView extends FrameLayout implements RootViewSurfaceTaker {

	public DecorView(Context context, int featureId) {
		super(context);
		mFeatureId = featureId;
	}

}

这里就是新建一个DecorView，DecorView是继承FrameLayout，是根View。

11. PhoneWindow.generateLayout

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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);
	}

	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_windowShowWallpaper, false)) {
		setFlags(FLAG_SHOW_WALLPAPER, FLAG_SHOW_WALLPAPER&(~getForcedWindowFlags()));
	}

	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;
		}
		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) {
			layoutResource = com.android.internal.R.layout.dialog_title_icons;
		} else {
			layoutResource = com.android.internal.R.layout.screen_title_icons;
		}
		// System.out.println("Title Icons!");
	} else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0) {
		layoutResource = com.android.internal.R.layout.screen_progress;
	} else if ((features & (1 << FEATURE_CUSTOM_TITLE)) != 0) {
		if (mIsFloating) {
			layoutResource = com.android.internal.R.layout.dialog_custom_title;
		} else {
			layoutResource = com.android.internal.R.layout.screen_custom_title;
		}
	} 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) {
			layoutResource = com.android.internal.R.layout.dialog_title;
		} else {
			layoutResource = com.android.internal.R.layout.screen_title;
		}
		// System.out.println("Title!");
	} 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;
}

虽然这里的代码很多，其实就是设置Activity主题、ActionBar等内容，然后将显示content的ViewGroup返回。

12. ActivityThread.handleResumeActivity

在Activity启动流程的34步，在Activity 初始化和create，调用handleResumeActivity

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final void handleResumeActivity(IBinder token, boolean clearHide, boolean isForward) {
	// If we are getting ready to gc after going to the background, well
	// we are back active so skip it.
	unscheduleGcIdler();

	ActivityClientRecord r = performResumeActivity(token, clearHide);

	if (r != null) {
		final Activity a = r.activity;

		final int forwardBit = isForward ?
				WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION : 0;

		// If the window hasn't yet been added to the window manager,
		// and this guy didn't finish itself or start another activity,
		// then go ahead and add the window.
		boolean willBeVisible = !a.mStartedActivity;
		if (!willBeVisible) {
			try {
				willBeVisible = ActivityManagerNative.getDefault().willActivityBeVisible(
						a.getActivityToken());
			} catch (RemoteException e) {
			}
		}
		if (r.window == null && !a.mFinished && willBeVisible) {
			r.window = r.activity.getWindow();
			View decor = r.window.getDecorView();
			decor.setVisibility(View.INVISIBLE);
			ViewManager wm = a.getWindowManager();
			WindowManager.LayoutParams l = r.window.getAttributes();
			a.mDecor = decor;
			l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
			l.softInputMode |= forwardBit;
			if (a.mVisibleFromClient) {
				a.mWindowAdded = true;
				wm.addView(decor, l);
			}
		}

	} else {

	}
}

这里的getWindowManager就是第六步设置的LocalWindowManager

13. LocalWindowManager.addView

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public final void addView(View view, ViewGroup.LayoutParams params) {
	....
	mWindowManager.addView(view, params);
}

14. WindowManagerImpl.addView

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private void addView(View view, ViewGroup.LayoutParams params, boolean nest)
{
	if (Config.LOGV) Log.v("WindowManager", "addView view=" + view);

	if (!(params instanceof WindowManager.LayoutParams)) {
		throw new IllegalArgumentException(
				"Params must be WindowManager.LayoutParams");
	}

	final WindowManager.LayoutParams wparams
			= (WindowManager.LayoutParams)params;
	
	ViewRoot root;
	View panelParentView = null;
	
	synchronized (this) {
		// Here's an odd/questionable case: if someone tries to add a
		// view multiple times, then we simply bump up a nesting count
		// and they need to remove the view the corresponding number of
		// times to have it actually removed from the window manager.
		// This is useful specifically for the notification manager,
		// which can continually add/remove the same view as a
		// notification gets updated.
		int index = findViewLocked(view, false);
		if (index >= 0) {
			if (!nest) {
				throw new IllegalStateException("View " + view
						+ " has already been added to the window manager.");
			}
			root = mRoots[index];
			root.mAddNesting++;
			// Update layout parameters.
			view.setLayoutParams(wparams);
			root.setLayoutParams(wparams, true);
			return;
		}
		
		// If this is a panel window, then find the window it is being
		// attached to for future reference.
		if (wparams.type >= WindowManager.LayoutParams.FIRST_SUB_WINDOW &&
				wparams.type <= WindowManager.LayoutParams.LAST_SUB_WINDOW) {
			final int count = mViews != null ? mViews.length : 0;
			for (int i=0; i<count; i++) {
				if (mRoots[i].mWindow.asBinder() == wparams.token) {
					panelParentView = mViews[i];
				}
			}
		}
		
		root = new ViewRoot(view.getContext());
		root.mAddNesting = 1;

		view.setLayoutParams(wparams);
		
		if (mViews == null) {
			index = 1;
			mViews = new View[1];
			mRoots = new ViewRoot[1];
			mParams = new WindowManager.LayoutParams[1];
		} else {
			index = mViews.length + 1;
			Object[] old = mViews;
			mViews = new View[index];
			System.arraycopy(old, 0, mViews, 0, index-1);
			old = mRoots;
			mRoots = new ViewRoot[index];
			System.arraycopy(old, 0, mRoots, 0, index-1);
			old = mParams;
			mParams = new WindowManager.LayoutParams[index];
			System.arraycopy(old, 0, mParams, 0, index-1);
		}
		index--;

		mViews[index] = view;
		mRoots[index] = root;
		mParams[index] = wparams;
	}
	// do this last because it fires off messages to start doing things
	root.setView(view, wparams, panelParentView);
}

WindowManagerImpl类有三个成员变量mViews、mRoots和mParams，它们分别是类型为View、ViewRoot和WindowManager.LayoutParams的数组。这三个数组的大小是始终保持相等的。
这样， 有关联关系的View对象、ViewRoot对象和WindowManager.LayoutParams对象就会分别保存在数组mViews、mRoots和mParams的相同位置上，也就是说，
mViews[i]、mRoots[i]和mParams[i]所描述的View对象、ViewRoot对象和WindowManager.LayoutParams对象是具有关联关系的。因此，WindowManagerImpl类的三个参数版本的成员函数addView在关联一个View对象、
一个ViewRoot对象和一个WindowManager.LayoutParams对象的时候，只要分别将它们放在数组mViews、mRoots和mParams的相同位置上就可以了。

15. ViewRoot.setView

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public void setView(View view, WindowManager.LayoutParams attrs,
            View panelParentView) {
	synchronized (this) {
		if (mView == null) {
			mView = view;
			mWindowAttributes.copyFrom(attrs);
			attrs = mWindowAttributes;
			if (view instanceof RootViewSurfaceTaker) {
				mSurfaceHolderCallback =
						((RootViewSurfaceTaker)view).willYouTakeTheSurface();
				if (mSurfaceHolderCallback != null) {
					mSurfaceHolder = new TakenSurfaceHolder();
					mSurfaceHolder.setFormat(PixelFormat.UNKNOWN);
				}
			}
			Resources resources = mView.getContext().getResources();
			CompatibilityInfo compatibilityInfo = resources.getCompatibilityInfo();
			mTranslator = compatibilityInfo.getTranslator();

			boolean restore = false;
			if (mTranslator != null) {
				restore = true;
				attrs.backup();
				mTranslator.translateWindowLayout(attrs);
			}
			if (DEBUG_LAYOUT) Log.d(TAG, "WindowLayout in setView:" + attrs);

			if (!compatibilityInfo.supportsScreen()) {
				attrs.flags |= WindowManager.LayoutParams.FLAG_COMPATIBLE_WINDOW;
			}

			mSoftInputMode = attrs.softInputMode;
			mWindowAttributesChanged = true;
			mAttachInfo.mRootView = view;
			mAttachInfo.mScalingRequired = mTranslator != null;
			mAttachInfo.mApplicationScale =
					mTranslator == null ? 1.0f : mTranslator.applicationScale;
			if (panelParentView != null) {
				mAttachInfo.mPanelParentWindowToken
						= panelParentView.getApplicationWindowToken();
			}
			mAdded = true;
			int res; /* = WindowManagerImpl.ADD_OKAY; */

			// Schedule the first layout -before- adding to the window
			// manager, to make sure we do the relayout before receiving
			// any other events from the system.
			requestLayout();
			mInputChannel = new InputChannel();
			try {
				res = sWindowSession.add(mWindow, mWindowAttributes,
						getHostVisibility(), mAttachInfo.mContentInsets,
						mInputChannel);
			} catch (RemoteException e) {

			} finally {
				if (restore) {
					attrs.restore();
				}
			}
		}
	}
}

这里会请求Layout计算视图的大小，然后通过sWindowSession通知WindowManagerService添加视图，sWindowSession是Binder对象。

16. 总结

首先是Activity的初始化会创建一个Window对象，初始化window对象中的数据，然后调用生命周期onCreate方法，然后设置ContentView，其实调用的是Window中的ContentView，Window对象中会新建DecorView（根布局），
然后将自定义的View添加到DecorView中，然后ActivityThread调用到handleResumeActivity,将DecorView添加到ViewRoot中，ViewRoot中含有WindowManagerService的远程Binder对象，然后调用WindowManagerService
将DecorView显示在界面中。