前言
Android在DialogFragment推出后，就已经不推荐继续使用Dialog，可替换为DialogFragment，其实DialogFragment只不过是对增加一层看不到的Fragment，用于监听生命周期，在Activity退出的时候会自动回收Dialog弹窗
基础概念
- Activity：活动。控制生命周期和处理事件，统筹视图的添加与显示，控制Window和View的交互
- Window：窗口。在Android中是个虚拟的概念，不是View，是承载View的载体，具体实现是PhoneWindow，承载着DecorView
- WindowManager：窗口管理者。管理Window视图的添加或移除等，具体实现是WindowManagerService（wms）
- DecorView：窗口根视图。本身是FrameLayout，是Window上真正的根布局，其包含两部分，标题和内容
- TitleView：标题。作为DecorView的子View，其Id为@android:id/content
- ContentViews：内容。作为DecorView的子View，其Id为@android:id/content
- ViewRoot：连接wms和DecorView的纽带，View的measure、layout、draw均通过ViewRoot来完成，具体实现是ViewRootImpl
Dialog
在平时中，简单的弹出Dialog只需要这句话
new Dialog(MainActivity.this).show();
一、Dialog的显示
1、Dialog
Dialog的构造方法有多个，但最后都会调用这个构造方法
Dialog(@NonNull Context context, @StyleRes int themeResId, boolean createContextThemeWrapper) {
if (createContextThemeWrapper) {
if (themeResId == 0) {
//如果没有主题，则使用默认主题
final TypedValue outValue = new TypedValue();
context.getTheme().resolveAttribute(R.attr.dialogTheme, outValue, true);
themeResId = outValue.resourceId;
}
//包裹主题的Context
mContext = new ContextThemeWrapper(context, themeResId);
} else {
mContext = context;
}
//获取windowManager服务
mWindowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
//创建新的Window
final Window w = new PhoneWindow(mContext);
mWindow = w;
//设置callback
w.setCallback(this);
w.setOnWindowDismissedCallback(this);
w.setWindowManager(mWindowManager, null, null);
w.setGravity(Gravity.CENTER);
mListenersHandler = new ListenersHandler(this);
}
从Dialog的构造方法中可以看出，Dialog实质上是个Window，其显示和隐藏也是借助WindowManager去控制的
2、Dialog.show
public void show() {
//如果之前已经show过后，就让视图显示即可
if (mShowing) {
if (mDecor != null) {
if (mWindow.hasFeature(Window.FEATURE_ACTION_BAR)) {
mWindow.invalidatePanelMenu(Window.FEATURE_ACTION_BAR);
}
mDecor.setVisibility(View.VISIBLE);
}
return;
}
mCanceled = false;
//如果没有create则会调用dispatchOncreate，该方法最终会调用dialog的onCreate方法
if (!mCreated) {
dispatchOnCreate(null);
}
//dialog的onstart回调
onStart();
//获取decorView
mDecor = mWindow.getDecorView();
//如果需要ActionBar，则创建出来
if (mActionBar == null && mWindow.hasFeature(Window.FEATURE_ACTION_BAR)) {
final ApplicationInfo info = mContext.getApplicationInfo();
mWindow.setDefaultIcon(info.icon);
mWindow.setDefaultLogo(info.logo);
mActionBar = new WindowDecorActionBar(this);
}
//window参数的设置
WindowManager.LayoutParams l = mWindow.getAttributes();
if ((l.softInputMode
& WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION) == 0) {
WindowManager.LayoutParams nl = new WindowManager.LayoutParams();
nl.copyFrom(l);
nl.softInputMode |=
WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION;
l = nl;
}
try {
//windowManager将decorView加入视图
mWindowManager.addView(mDecor, l);
mShowing = true;
sendShowMessage();
} finally {
}
}
show()其实就是走Dialog的生命周期，然后做初始化工作，获取Window上的DecorView后，将DecorView添加到视图上，这里需要注意的是在show()之后才执行onCreate()
3、Dialog.dispatchOnCreate
void dispatchOnCreate(Bundle savedInstanceState) {
if (!mCreated) {
onCreate(savedInstanceState); //回调onCreate()
mCreated = true;
}
}
protected void onCreate(Bundle savedInstanceState) {
//由开发者实现
}
Dialog的初始化其实就是让用户去初始化自己的视图，平时我们是这么写的
public class RxDialog extends Dialog {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//设置视图
setContentView(mView);
}
}
具体的逻辑还是回到setContentView()设置Dialog的视图
4、Dialog.setContentView
public void setContentView(View view) {
//调用mWindow进行视图设置，mWindow实际上就是构造方法中的PhoneWindow
mWindow.setContentView(view);
}
mWindow则是在构造方法创建的PhoneWindow
5、PhoneWindow.setContentView
@Override
public void setContentView(View view) {
//默认MATCH_PARENT
setContentView(view, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}
@Override
public void setContentView(View view, ViewGroup.LayoutParams params) {
if (mContentParent == null) {
installDecor(); //创建应用程序窗口视图对象
} else {
mContentParent.removeAllViews(); //重新设置应用程序窗口的视图
}
if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
view.setLayoutParams(params);
final Scene newScene = new Scene(mContentParent, view);
transitionTo(newScene);
} else {
mContentParent.addView(view, params); //将我们传递进来的view添加布局上
}
mContentParent.requestApplyInsets();
final Callback cb = getCallback();
if (cb != null && !isDestroyed()) {
cb.onContentChanged();
}
......
}
PhoneWindow.setContentView()不仅在Dialog中存在，在Activity的setContentView也是走到这里。mContentParent指的是依附于DecorView上的R.id.content中的view。到这里只是将Dialog设置的View加载到PhoneWindow的ContentView上，其实更主要的还是PhoneWindow添加到我们的手机屏幕上，代码回溯到show()的mWindowManager.addView(mDecor, l)
6、WindowManagerImpl.addView
WindowManager本质上是对View进行管理，但是WindowManager显然依然是个接口，其具体实现是WindowManagerImpl，最后还是委托给WindowManagerGlobal实例mGlobal处理
@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
//委托给mGlobal来进行实现
mGlobal.addView(view, params, mDisplay, mParentWindow);
}
7、WindowManagerGlobal.addView
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, then hardware acceleration for this view is
// set from the application's hardware acceleration setting.
final Context context = view.getContext();
if (context != null
&& (context.getApplicationInfo().flags
& ApplicationInfo.FLAG_HARDWARE_ACCELERATED) != 0) {
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);
}
}
}
//创建ViewRootImpl，ViewRootImpl是view和window中的连接纽带
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
//存储相关View的信息，会在Remove的时候移除，相当于缓存
mViews.add(view);//mViews：存储的是所有Window对应的View，本质是个List
mRoots.add(root);//mRoots：存储的是所有Window所对应的ViewRootImpl，本质是个List
mParams.add(wparams);//mParams：存储所有window对应的布局参数，本质是个List
}
// do this last because it fires off messages to start doing things
try {
//最终由root去实现最终的视图显示
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;
}
}
将视图添加到窗口上的工作交给root.setView()，root就是ViewRootImpl
8、ViewRootImpl.setView
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
synchronized (this) {
if (mView == null) {
......
requestLayout(); //真正完成视图的异步刷新请求
......
//这里调用了mWindowSession的addToDisplay方法，在WindowManagerService层通过IPC机制完成真正的window添加
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(),
mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
mAttachInfo.mOutsets, mInputChannel);
}
}
}
@Override
public void requestLayout() {
if (!mHandlingLayoutInLayoutRequest) {
checkThread();
mLayoutRequested = true;
scheduleTraversals(); //真正的去走Measure、Layout、Draw
}
}
在添加view之前，会走requestLayout()，真正实现View绘制的三部曲Measure、Layout、Draw。mWindowSession类型是IWindowSession，它是个Binder对象，真正的实现类是Session，window的添加过程实际上是一次ipc的调用，最后在WindowManagerService层通过IPC机制去实现的
总结
在这读完这里源码后，我们知道Window是个相对虚拟的对象，真正的操作是对Window中的DecorView进行addView()操作，而且在addView()之前，会先走onCreate()、onStart()、setContentView()操作，而在setContentView()过程中，会经过ViewRootImpl对象进行setView，并且在ViewRootImpl对象中会实现View绘制的三步曲，Measure、Layout、Draw操作，最后再将绘制好的view通过IWindowSession的ipc调用添加到界面上
- Dialog本质上是个Window，具体是通过Window的DecorView进行显示的
-
Dialog是在show()之后走的onCreate()、onStart()、setContentView()等回调
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