Activity 是安卓的四大组件之一，同时也是我们在开发中使用的最多的组件。Activity 实际就是界面。通常我们最简单的方式即在 Activity 的 onCreate 方法中 setContentView 运行起来，就能看到我们最简单的一个界面了。
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}
而实际 Activity 在创建界面过程中，关联到了一个Window ，并将我们想要创建的 View 关联到 Window 中，最终才是我们看到的手机屏幕上呈现出来的样子。他们的关系如下图所示。
关系图.png
在 Activity 初始化过程中会创建一个 Window，而 PhoneWindow 为 Window 的实际实现类，最终将 View 则在附在 Window 上面。
接下来，我们就从 Activity 中的 setContenView 来看起，看看他们之间是如何绑定并进行工作的。
public void setContentView(int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
getWindow 返回的是一个 Window 对象，setContentView 方法会调用 Window 的 setContentView 方法，Window 的实现类为 PhoneWindow ，进入 PhoneWindow 进行查看
@Override
public void setContentView(View view) {
setContentView(view, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}
@Override
public void setContentView(View view, ViewGroup.LayoutParams params) {
// 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)) {
view.setLayoutParams(params);
final Scene newScene = new Scene(mContentParent, view);
transitionTo(newScene);
} else {
mContentParent.addView(view, params);
}
final Callback cb = getCallback();
if (cb != null && !isDestroyed()) {
cb.onContentChanged();
}
}
这里去主要看下 installDecor() 方法：
private void installDecor() {
if (mDecor == null) {
mDecor = generateDecor();
mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
mDecor.setIsRootNamespace(true);
if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
}
}
if (mContentParent == null) {
mContentParent = generateLayout(mDecor);
......
}
installDecor 主要去初始化 mDecor ，然后去执行 generateLayout(mDecor) 方法初始化 mContentParent 。
先看下 generateDecor 方法：
protected DecorView generateDecor() {
return new DecorView(getContext(), -1);
}
public DecorView(Context context, int featureId) {
super(context);
mFeatureId = featureId;
mShowInterpolator = AnimationUtils.loadInterpolator(context,
android.R.interpolator.linear_out_slow_in);
mHideInterpolator = AnimationUtils.loadInterpolator(context,
android.R.interpolator.fast_out_linear_in);
mBarEnterExitDuration = context.getResources().getInteger(
R.integer.dock_enter_exit_duration);
}
generateDecor 就是初始化了 DecorView 实例，同时赋值了默认的动画。
接下来继续看下 generateLayout 方法：
protected ViewGroup generateLayout(DecorView decor) {
// Apply data from current theme.
TypedArray a = getWindowStyle();
......
if (a.getBoolean(R.styleable.Window_windowNoTitle, false)) {
requestFeature(FEATURE_NO_TITLE);
} else if (a.getBoolean(R.styleable.Window_windowActionBar, false)) {
// Don't allow an action bar if there is no title.
requestFeature(FEATURE_ACTION_BAR);
}
if (a.getBoolean(R.styleable.Window_windowTranslucentNavigation,
false)) {
setFlags(FLAG_TRANSLUCENT_NAVIGATION, FLAG_TRANSLUCENT_NAVIGATION
& (~getForcedWindowFlags()));
}
......
final WindowManager windowService = (WindowManager) getContext().getSystemService(
Context.WINDOW_SERVICE);
if (windowService != null) {
final Display display = windowService.getDefaultDisplay();
final boolean shouldUseBottomOutset =
display.getDisplayId() == Display.DEFAULT_DISPLAY
|| (getForcedWindowFlags() & FLAG_FULLSCREEN) != 0;
if (shouldUseBottomOutset && a.hasValue(R.styleable.Window_windowOutsetBottom)) {
if (mOutsetBottom == null) mOutsetBottom = new TypedValue();
a.getValue(R.styleable.Window_windowOutsetBottom,
mOutsetBottom);
}
}
if (!mForcedStatusBarColor) {
mStatusBarColor = a.getColor(R.styleable.Window_statusBarColor, 0xFF000000);
}
if (!hasSoftInputMode()) {
params.softInputMode = a.getInt(
R.styleable.Window_windowSoftInputMode,
params.softInputMode);
}
......
View in = mLayoutInflater.inflate(layoutResource, null);
decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
mContentRoot = (ViewGroup) in;
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
if (contentParent == null) {
throw new RuntimeException("Window couldn't find content container view");
}
// Remaining setup -- of background and title -- that only applies
// to top-level windows.
if (getContainer() == null) {
final Drawable background;
if (mBackgroundResource != 0) {
background = getContext().getDrawable(mBackgroundResource);
} else {
background = mBackgroundDrawable;
}
mDecor.setWindowBackground(background);
final Drawable frame;
if (mFrameResource != 0) {
frame = getContext().getDrawable(mFrameResource);
} else {
frame = null;
}
mDecor.setWindowFrame(frame);
mDecor.setElevation(mElevation);
mDecor.setClipToOutline(mClipToOutline);
if (mTitle != null) {
setTitle(mTitle);
}
if (mTitleColor == 0) {
mTitleColor = mTextColor;
}
setTitleColor(mTitleColor);
}
mDecor.finishChanging();
return contentParent;
}
generateLayout 主要做了以下事情：
1 根据 Window 的样式设置 View 的样式以及设置状态栏。
2 设置系统键盘。
3 初始化 mContentParent 返回；
总结 setContentView 方法：
1 调用到 PhoneWindow 的 setContentView 方法；
2 初始化 DectorView；
3 设置 Window 的主题，设置状态栏，系统键盘等。
4 DectorView 实际上内部维护的 mContentParent，而 mContentParent 则包含了 Title 和 setContentView 里面的 xml 布局。
Window 和 DectorView 的关联
上面说到 Activity 的 setContentView 方法调用到 Window 内部，并且创建了DectorView 实例。接下来我们继续看 DectorView 如何和 Window 关联起来。
我们这边直接定位到 ActivityThread 的 handleResumeActivity 方法，其实就是对 Activity onResume 方法的处理，我们同时可以发现 Window 和 DectorView 的相关处理：
final void handleResumeActivity(IBinder token,
boolean clearHide, boolean isForward, boolean reallyResume) {
......
if (r != null) {
......
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);
}
......
// The window is now visible if it has been added, we are not
// simply finishing, and we are not starting another activity.
if (!r.activity.mFinished && willBeVisible
&& r.activity.mDecor != null && !r.hideForNow) {
if (r.newConfig != null) {
if (DEBUG_CONFIGURATION) Slog.v(TAG, "Resuming activity "
+ r.activityInfo.name + " with newConfig " + r.newConfig);
performConfigurationChanged(r.activity, r.newConfig);
freeTextLayoutCachesIfNeeded(r.activity.mCurrentConfig.diff(r.newConfig));
r.newConfig = null;
}
if (localLOGV) Slog.v(TAG, "Resuming " + r + " with isForward="
+ isForward);
WindowManager.LayoutParams l = r.window.getAttributes();
if ((l.softInputMode
& WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION)
!= forwardBit) {
l.softInputMode = (l.softInputMode
& (~WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION))
| forwardBit;
if (r.activity.mVisibleFromClient) {
ViewManager wm = a.getWindowManager();
View decor = r.window.getDecorView();
wm.updateViewLayout(decor, l);
}
}
}
......
}
这里通过 ViewManager wm = a.getWindowManager(); 获取到 ViewManager 对象，同时 wm.addView(decor, l); 将 DectorView 和 ViewManager 进行了绑定。
WindowManager 是 ViewManager 的父类，而 WindowManager 的实现类是 WindowManagerImpl 类，所以添加 DectorView 的方法最终将是在 WindowManagerImpl 实现的。
@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.addView(view, params, mDisplay, mParentWindow);
}
@Override
public void updateViewLayout(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.updateViewLayout(view, params);
}
private void applyDefaultToken(@NonNull ViewGroup.LayoutParams params) {
// Only use the default token if we don't have a parent window.
if (mDefaultToken != null && mParentWindow == null) {
if (!(params instanceof WindowManager.LayoutParams)) {
throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
}
// Only use the default token if we don't already have a token.
final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
if (wparams.token == null) {
wparams.token = mDefaultToken;
}
}
}
@Override
public void removeView(View view) {
mGlobal.removeView(view, false);
}
@Override
public void removeViewImmediate(View view) {
mGlobal.removeView(view, true);
}
WindowManagerImpl 又会委托给 mGlobal 进行添加 View，同时可以看到 WindowManagerImpl 定义了 updateViewLayout 、removeView等操作方法。mGlobal 则是 WindowManagerGlobal 的实例对象。
public void addView(View view, ViewGroup.LayoutParams params,
Display display, Window parentWindow) {
.....
final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;
if (parentWindow != null) {
parentWindow.adjustLayoutParamsForSubWindow(wparams);
} else {
// If there's no parent and we're running on L or above (or in the
// system context), assume we want hardware acceleration.
final Context context = view.getContext();
if (context != null
&& context.getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.LOLLIPOP) {
wparams.flags |= WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;
}
}
ViewRootImpl root;
View panelParentView = null;
synchronized (mLock) {
// Start watching for system property changes.
if (mSystemPropertyUpdater == null) {
mSystemPropertyUpdater = new Runnable() {
@Override public void run() {
synchronized (mLock) {
for (int i = mRoots.size() - 1; i >= 0; --i) {
mRoots.get(i).loadSystemProperties();
}
}
}
};
SystemProperties.addChangeCallback(mSystemPropertyUpdater);
}
int index = findViewLocked(view, false);
if (index >= 0) {
if (mDyingViews.contains(view)) {
// Don't wait for MSG_DIE to make it's way through root's queue.
mRoots.get(index).doDie();
} else {
throw new IllegalStateException("View " + view
+ " has already been added to the window manager.");
}
// The previous removeView() had not completed executing. Now it has.
}
// 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.size();
for (int i = 0; i < count; i++) {
if (mRoots.get(i).mWindow.asBinder() == wparams.token) {
panelParentView = mViews.get(i);
}
}
}
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
mViews.add(view);
mRoots.add(root);
mParams.add(wparams);
}
// do this last because it fires off messages to start doing things
try {
root.setView(view, wparams, panelParentView);
} catch (RuntimeException e) {
// BadTokenException or InvalidDisplayException, clean up.
synchronized (mLock) {
final int index = findViewLocked(view, false);
if (index >= 0) {
removeViewLocked(index, true);
}
}
throw e;
}
}
WindowManagerGlobal 的 addView 方法，创建了 ViewRootImpl 。同时将 ViewRootImpl 、View 以及 Window 的 LayoutParams 放入到了一组集合当中。可以看到 ViewRootImpl 和 View 也进行了绑定操作， * root.setView(view, wparams, panelParentView);* ViewRootImpl 同时也做了相关的设置工作。
ViewManager、WindowManager、WindowManagerImpl和WindowManagerGlobal.png
上面知道 addView 方法会创建 ViewRootImpl ，ViewRootImpl 绑定了 View，ViewRootImpl 则是这里组件联系的核心，接下来看下 ViewRootImpl 的 setView 方法做了些什么事情。
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
synchronized (this) {
if (mView == null) {
mView = view;
......
//获取 window 的配置
mWindowAttributes.copyFrom(attrs);
if (mWindowAttributes.packageName == null) {
mWindowAttributes.packageName = mBasePackageName;
}
attrs = mWindowAttributes;
......
// 软键盘配置
mSoftInputMode = attrs.softInputMode;
mWindowAttributesChanged = true;
mWindowAttributesChangesFlag = WindowManager.LayoutParams.EVERYTHING_CHANGED;
.......
// 绘制界面
requestLayout();
if ((mWindowAttributes.inputFeatures
& WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
mInputChannel = new InputChannel();
}
try {
mOrigWindowType = mWindowAttributes.type;
mAttachInfo.mRecomputeGlobalAttributes = true;
collectViewAttributes();
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(),
mAttachInfo.mContentInsets, mAttachInfo.mStableInsets, mInputChannel);
} catch (RemoteException e) {
mAdded = false;
mView = null;
mAttachInfo.mRootView = null;
mInputChannel = null;
mFallbackEventHandler.setView(null);
unscheduleTraversals();
setAccessibilityFocus(null, null);
throw new RuntimeException("Adding window failed", e);
} finally {
if (restore) {
attrs.restore();
}
}
.....
// 窗口输入事件
if (mInputChannel != null) {
if (mInputQueueCallback != null) {
mInputQueue = new InputQueue();
mInputQueueCallback.onInputQueueCreated(mInputQueue);
}
mInputEventReceiver = new WindowInputEventReceiver(mInputChannel,
Looper.myLooper());
}
view.assignParent(this);
mAddedTouchMode = (res & WindowManagerGlobal.ADD_FLAG_IN_TOUCH_MODE) != 0;
mAppVisible = (res & WindowManagerGlobal.ADD_FLAG_APP_VISIBLE) != 0;
if (mAccessibilityManager.isEnabled()) {
mAccessibilityInteractionConnectionManager.ensureConnection();
}
if (view.getImportantForAccessibility() == View.IMPORTANT_FOR_ACCESSIBILITY_AUTO) {
view.setImportantForAccessibility(View.IMPORTANT_FOR_ACCESSIBILITY_YES);
}
}
}
}
setView 方法这里 requestLayout() 方法。这个方法即将对页面进行绘制。
@Override
public void requestLayout() {
if (!mHandlingLayoutInLayoutRequest) {
checkThread();
mLayoutRequested = true;
scheduleTraversals();
}
}
void scheduleTraversals() {
if (!mTraversalScheduled) {
mTraversalScheduled = true;
mTraversalBarrier = mHandler.getLooper().postSyncBarrier();
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
if (!mUnbufferedInputDispatch) {
scheduleConsumeBatchedInput();
}
notifyRendererOfFramePending();
}
}
final class TraversalRunnable implements Runnable {
@Override
public void run() {
doTraversal();
}
}
void doTraversal() {
if (mTraversalScheduled) {
mTraversalScheduled = false;
mHandler.getLooper().removeSyncBarrier(mTraversalBarrier);
if (mProfile) {
Debug.startMethodTracing("ViewAncestor");
}
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "performTraversals");
try {
// 绘制界面
performTraversals();
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
if (mProfile) {
Debug.stopMethodTracing();
mProfile = false;
}
}
}
即通过 root.requestLayout() --> root.scheduleTraversals() --> doTraversal() --> root. performTraversals() 最终去完成 View 的绘制工作。
private void performTraversals() {
......
if (!mStopped) {
boolean focusChangedDueToTouchMode = ensureTouchModeLocally(
(relayoutResult & WindowManagerGlobal.RELAYOUT_RES_IN_TOUCH_MODE) != 0);
if (focusChangedDueToTouchMode || mWidth != host.getMeasuredWidth()
|| mHeight != host.getMeasuredHeight() || contentInsetsChanged) {
int childWidthMeasureSpec = getRootMeasureSpec(mWidth, lp.width);
int childHeightMeasureSpec = getRootMeasureSpec(mHeight, lp.height);
if (DEBUG_LAYOUT) Log.v(TAG, "Ooops, something changed! mWidth="
+ mWidth + " measuredWidth=" + host.getMeasuredWidth()
+ " mHeight=" + mHeight
+ " measuredHeight=" + host.getMeasuredHeight()
+ " coveredInsetsChanged=" + contentInsetsChanged);
// Ask host how big it wants to be
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
// Implementation of weights from WindowManager.LayoutParams
// We just grow the dimensions as needed and re-measure if
// needs be
int width = host.getMeasuredWidth();
int height = host.getMeasuredHeight();
boolean measureAgain = false;
if (lp.horizontalWeight > 0.0f) {
width += (int) ((mWidth - width) * lp.horizontalWeight);
childWidthMeasureSpec = View.MeasureSpec.makeMeasureSpec(width,
View.MeasureSpec.EXACTLY);
measureAgain = true;
}
if (lp.verticalWeight > 0.0f) {
height += (int) ((mHeight - height) * lp.verticalWeight);
childHeightMeasureSpec = View.MeasureSpec.makeMeasureSpec(height,
View.MeasureSpec.EXACTLY);
measureAgain = true;
}
if (measureAgain) {
if (DEBUG_LAYOUT) Log.v(TAG,
"And hey let's measure once more: width=" + width
+ " height=" + height);
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
}
layoutRequested = true;
}
}
......
performLayout(lp, desiredWindowWidth, desiredWindowHeight);
......
performDraw();
}
调用 Activity 的 setContentView 方法，我们最终会调用到 performTraversals 方法，最终去完成了 View 的测量，布局，绘制过程。
上述过程由 WindowManagerGlobal 类的 addView 发起，最终通过中间件 ViewRootImpl 的 setView 方法完成了 View 的绘制工作，同理，查看 update 和 remove 方法：
public void updateViewLayout(View view, ViewGroup.LayoutParams params) {
if (view == null) {
throw new IllegalArgumentException("view must not be null");
}
if (!(params instanceof WindowManager.LayoutParams)) {
throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
}
final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;
view.setLayoutParams(wparams);
synchronized (mLock) {
int index = findViewLocked(view, true);
ViewRootImpl root = mRoots.get(index);
mParams.remove(index);
mParams.add(index, wparams);
root.setLayoutParams(wparams, false);
}
}
public void removeView(View view, boolean immediate) {
if (view == null) {
throw new IllegalArgumentException("view must not be null");
}
synchronized (mLock) {
int index = findViewLocked(view, true);
View curView = mRoots.get(index).getView();
removeViewLocked(index, immediate);
if (curView == view) {
return;
}
throw new IllegalStateException("Calling with view " + view
+ " but the ViewAncestor is attached to " + curView);
}
}
private void removeViewLocked(int index, boolean immediate) {
ViewRootImpl root = mRoots.get(index);
View view = root.getView();
if (view != null) {
InputMethodManager imm = InputMethodManager.getInstance();
if (imm != null) {
imm.windowDismissed(mViews.get(index).getWindowToken());
}
}
boolean deferred = root.die(immediate);
if (view != null) {
view.assignParent(null);
if (deferred) {
mDyingViews.add(view);
}
}
}
相应地对集合中的元素进行相关操作后，viewRootImpl 的 setLayoutParams 方法同样会对这个界面进行重新的测量以及绘制工作，viewRootImpl 的 die 方法 同样会去释放 window 的对象并对 Surface 资源进行释放：
void doDie() {
checkThread();
if (LOCAL_LOGV) Log.v(TAG, "DIE in " + this + " of " + mSurface);
synchronized (this) {
if (mRemoved) {
return;
}
mRemoved = true;
if (mAdded) {
dispatchDetachedFromWindow();
}
if (mAdded && !mFirst) {
destroyHardwareRenderer();
if (mView != null) {
int viewVisibility = mView.getVisibility();
boolean viewVisibilityChanged = mViewVisibility != viewVisibility;
if (mWindowAttributesChanged || viewVisibilityChanged) {
// If layout params have been changed, first give them
// to the window manager to make sure it has the correct
// animation info.
try {
if ((relayoutWindow(mWindowAttributes, viewVisibility, false)
& WindowManagerGlobal.RELAYOUT_RES_FIRST_TIME) != 0) {
mWindowSession.finishDrawing(mWindow);
}
} catch (RemoteException e) {
}
}
mSurface.release();
}
}
mAdded = false;
}
WindowManagerGlobal.getInstance().doRemoveView(this);
}
总结
本文主要通过 Activity 的 setContentView 方法，阐述了 Activity Window View 之间的关联，同时在此过程中 ViewRootImpl 扮演了一个重要的中间类。
相关类关系图.png
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