Dialog显示和消失流程分析

本文所引用的代码为Android 5.0（API 22）版本

Dialog类实现了DialogInterface, Window.Callback, KeyEvent.Callback, OnCreateContextMenuListener, Window.OnWindowDismissedCallback这个五个接口。比较常用到的三个接口：Window.Callback是接收屏幕touch事件；KeyEvent.Callback为接收键盘按键事件和实体键消息；Window.OnWindowDismissedCallback为接收窗口消失回调。

本文从Dialog的创建，隐藏，显示和移除步骤来分析相关的代码流程。最后补充了几个常见的异常分析。

请尊重博主劳动成果，转载请标明出处。

创建

看看构造方法代码：

    //提供给外部调用人口    public Dialog(Context context) {        this(context, 0, true);    }    //提供给外部调用人口    public Dialog(Context context, int theme) {        this(context, theme, true);    }    //真正执行初始化的构造方法    Dialog(Context context, int theme, boolean createContextThemeWrapper) {        if (createContextThemeWrapper) {            if (theme == 0) {                TypedValue outValue = new TypedValue();                context.getTheme().resolveAttribute(com.android.internal.R.attr.dialogTheme, outValue, true);                theme = outValue.resourceId;            }            mContext = new ContextThemeWrapper(context, theme);        } else {            mContext = context;        }        //获取WindowManagerImpl对象，这个对象一般为Activity的windowManger        mWindowManager = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);        //创建PhoneWindow对象        Window w = PolicyManager.makeNewWindow(mContext);        //赋值，mWindow即PhoneWindow对象，不是WindowManger        mWindow = w;        设置Window.Callback回调        w.setCallback(this);        //window dismiss回调        w.setOnWindowDismissedCallback(this);        //调用Window的setWindowManager创建PhoneWindow内部的WindowMangerImpl        w.setWindowManager(mWindowManager, null, null);        //默认设置为居中        w.setGravity(Gravity.CENTER);        //接收异步消息的Handler        mListenersHandler = new ListenersHandler(this);    }

PolicyManager#makeNewWindow相关代码：
路径：/sources/android-22/com/android/internal/policy/PolicyManager.java

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

sPolicy为Policy类的对象：
路径：/sources/android-22/com/android/internal/policy/impl/Policy.java

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

Window的setWindowManager方法相关代码：

    public void setWindowManager(WindowManager wm, IBinder appToken, String appName) {        setWindowManager(wm, appToken, appName, false);    }    public void setWindowManager(WindowManager wm, IBinder appToken, String appName, boolean hardwareAccelerated) {        mAppToken = appToken;        mAppName = appName;        mHardwareAccelerated = hardwareAccelerated                || SystemProperties.getBoolean(PROPERTY_HARDWARE_UI, false);        if (wm == null) {            wm = (WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE);        }        mWindowManager = ((WindowManagerImpl)wm).createLocalWindowManager(this);    }

显示

show方法代码：

    public void show() {        if (mShowing) {//dialog已调用过show方法，调用dismiss会设置为false            if (mDecor != null) {                if (mWindow.hasFeature(Window.FEATURE_ACTION_BAR)) {                    mWindow.invalidatePanelMenu(Window.FEATURE_ACTION_BAR);                }                //显示Dialog的根View，即Dialog便可见                mDecor.setVisibility(View.VISIBLE);            }            return;        }        mCanceled = false;        if (!mCreated) {            dispatchOnCreate(null);        }        onStart();        //创建DecorView        mDecor = mWindow.getDecorView();        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);        }        //设置布局参数        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 {            //添加到当前显示的窗口，便可以看见dialog            mWindowManager.addView(mDecor, l);            mShowing = true;            //发送dialog显示消息            sendShowMessage();        } finally {        }    }

mDecor为DecorView对象，DecorView继承了FrameLayout。在Android 6.0以下版本，DecorView为PhoneWindow的内部类；6.0及以上版本，则被抽出，为一个独立的类。

我们在使用Dialog调用findViewById和setContentView方法，其实都是PhoneWindow中的方法在执行相应的操作。
Dialog中相关方法的代码：

    public View findViewById(int id) {        return mWindow.findViewById(id);    }    public void setContentView(int layoutResID) {        mWindow.setContentView(layoutResID);    }    public void setContentView(View view) {        mWindow.setContentView(view);    }    public void setContentView(View view, ViewGroup.LayoutParams params) {        mWindow.setContentView(view, params);    }    public void addContentView(View view, ViewGroup.LayoutParams params) {        mWindow.addContentView(view, params);    }

再看看PhoneWindow中的相关代码：

    //获取DecorView    @Override    public final View getDecorView() {        if (mDecor == null || mForceDecorInstall) {            //如果没有，则创建            installDecor();        }        return mDecor;    }    //创建和初始化DecorView    private void installDecor() {        if (mDecor == null) {//如果为null，则创建            mDecor = generateDecor();            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);            mDecor.setIsRootNamespace(true);            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);            }        }        ...//省略部分代码    }    //创建DecorView对象    protected DecorView generateDecor() {        //创建DecorView，-1为布局资源id，即不解析xml布局文件        return new DecorView(getContext(), -1);    }    @Override    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);        }        //在Dialog的mWindow中，cb为Dialog本身        final Callback cb = getCallback();        if (cb != null && !isDestroyed()) {            cb.onContentChanged();        }    }    @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();        }    }    @Override    public void addContentView(View view, ViewGroup.LayoutParams params) {        if (mContentParent == null) {            installDecor();        }        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {            // TODO Augment the scenes/transitions API to support this.            Log.v(TAG, "addContentView does not support content transitions");        }        mContentParent.addView(view, params);        final Callback cb = getCallback();        if (cb != null && !isDestroyed()) {            cb.onContentChanged();        }    }

这里就不细讲DecorView是如何被创建的，有兴趣的可以去看看源码，或看这篇博客：Android应用setContentView与LayoutInflater加载解析机制源码分析。

再看看mWindowManager.addView(mDecor, l)这步操作。从创建这一节的分析可知mWindowManager为WindowMangerImpl的对象。
先介绍下WindowMangerImpl代码：

public final class WindowManagerImpl implements WindowManager {    private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();    //    private final Display mDisplay;    private final Window mParentWindow;    private IBinder mDefaultToken;    ...//省略部分代码    //添加View    public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {        applyDefaultToken(params);        mGlobal.addView(view, params, mDisplay, mParentWindow);    }    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;            }        }    }    ...//省略部分代码    //移除View，后面的dimiss会调用到这个方法    public void removeViewImmediate(View view) {        //true为立即移除        mGlobal.removeView(view, true);    }    ...//省略部分代码}

继续看WindowManagerGobal的addView方法代码：

    public void addView(View view, ViewGroup.LayoutParams params,            Display display, Window parentWindow) {        ...//省略        //ViewRootImpl接收接收底层服务发送来的屏幕触摸事件，然后将这些事件传递给DecorView，        //并返回结果（true或false）给底层服务。        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);                    }                }            }            //创建对象            root = new ViewRootImpl(view.getContext(), display);            //设置布局属性            view.setLayoutParams(wparams);            //添加到记录集合，方便以后查找和移除            mViews.add(view);            mRoots.add(root);            mParams.add(wparams);        }        // do this last because it fires off messages to start doing things        try {            //添加DecorView到ViewRootView，执行完这一步，dialog便能接收屏幕事件            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;        }    }

关于ViewRootImpl如何接收和传递屏幕事件，可以阅读Activity touch事件传递流程分析。
经历了setContent和show，漂亮的Dialog便显示在手机上。

隐藏和消失

隐藏调用的是hide方法。如果dialog在当前页面被频繁调用，则可以用这个方法。它不会将Dialog的根视图mDecor从当前移除，仅仅是将其设置为不可见。
hide方法代码

    public void hide() {        if (mDecor != null) {            mDecor.setVisibility(View.GONE);        }    }

当我们调用代码dismiss，点击back键或点击dialog外部区域，便可以将dialog隐藏。

    //提供给外部调用的方法    public void dismiss() {        if (Looper.myLooper() == mHandler.getLooper()) {            //在主线程，则直接调用            dismissDialog();        } else {            //非主线程，则发送消息，让mListenersHandler处理            mHandler.post(mDismissAction);        }    }    //真正执行dismiss的方法    void dismissDialog() {        //如果mDecor为null或dismiss的，则返回        if (mDecor == null || !mShowing) {            return;        }        //如果PhoneWindow被销毁，则返回        if (mWindow.isDestroyed()) {            Log.e(TAG, "Tried to dismissDialog() but the Dialog's window was already destroyed!");            return;        }        try {            //移除mDecor，其实是mWindowManager的内部WindowManagerGlobal对象执行移除操作            mWindowManager.removeViewImmediate(mDecor);        } finally {            if (mActionMode != null) {                mActionMode.finish();            }            mDecor = null;//置为null，释放            mWindow.closeAllPanels();            onStop();            mShowing = false;//修改标志为false            //发送dismiss事件            sendDismissMessage();        }    }

这个方法里最重要的操作为mWindowManager.removeViewImmediate(mDecor)，这步操作将Dialog直接从当前视图移除，并销毁释放。所以在页面中被频繁显示的的dialog采用hide比dimiss更高效。

继续看WindowManagerGlobal代码：

    public void removeView(View view, boolean immediate) {        if (view == null) {            throw new IllegalArgumentException("view must not be null");        }        synchronized (mLock) {            //查找当前View在记录集合中的位置            int index = findViewLocked(view, true);            View curView = mRoots.get(index).getView();            //移除ViewRootImpl            removeViewLocked(index, immediate);            if (curView == view) {                return;            }            //如果要移除的View与记录中的不同，则抛出异常            throw new IllegalStateException("Calling with view " + view                    + " but the ViewAncestor is attached to " + curView);        }    }    //查找位置    private int findViewLocked(View view, boolean required) {        final int index = mViews.indexOf(view);        if (required && index < 0) {            //如果该View已被移除，则抛出异常            throw new IllegalArgumentException("View=" + view + " not attached to window manager");        }        return index;    }    private void removeViewLocked(int index, boolean immediate) {        ViewRootImpl root = mRoots.get(index);        View view = root.getView();        if (view != null) {//断开键盘与当前View的关联            InputMethodManager imm = InputMethodManager.getInstance();            if (imm != null) {                imm.windowDismissed(mViews.get(index).getWindowToken());            }        }        //ViewRootImpl执行die操作        boolean deferred = root.die(immediate);        if (view != null) {            view.assignParent(null);            if (deferred) {                mDyingViews.add(view);            }        }    }

经过以上三个步骤的分析，我们清楚知道了Dialog是如何创建，显示和消失移除。

补充：常见的异常分析

工作中可能会出现的一些异常，现在就分析下它们出现的原因。

WindowLeaked

异常信息：

android.view.WindowLeaked: Activity xx.xxActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{3e7fbc08 V.E..... R.....I. 0,0-960,231} that was originally added hereat android.view.ViewRootImpl.<init>(ViewRootImpl.java:462)at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:278)at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:85)at android.app.Dialog.show(Dialog.java:311)

这个是在Activity执行destroy时，dialog还没有被执行dismiss操作而抛出的。需要在onPause()或onStop()中调用dismiss释放dialog窗口。

如果跟着日志显示的类去查找，估计会转晕。其实，它在ActivityThread执行handleDestroyActivity操作时抛出的。如果跟着代码显示的日志，该异常出现在onDestroy的日志后面。
相关代码：

    //ActivityThread的handleDestroyActivity方法代码    private void handleDestroyActivity(IBinder token, boolean finishing,            int configChanges, boolean getNonConfigInstance) {        ActivityClientRecord r = performDestroyActivity(token, finishing,                configChanges, getNonConfigInstance);        if (r != null) {            cleanUpPendingRemoveWindows(r);            WindowManager wm = r.activity.getWindowManager();            View v = r.activity.mDecor;            if (v != null) {                if (r.activity.mVisibleFromServer) {                    mNumVisibleActivities--;                }                //当前Activity的window token，                IBinder wtoken = v.getWindowToken();                if (r.activity.mWindowAdded) {                    if (r.onlyLocalRequest) {                        // Hold off on removing this until the new activity's                        // window is being added.                        r.mPendingRemoveWindow = v;                        r.mPendingRemoveWindowManager = wm;                    } else {                        wm.removeViewImmediate(v);                    }                }                if (wtoken != null && r.mPendingRemoveWindow == null) {                    //关闭所有与wtoken相关的所有DecorView                    WindowManagerGlobal.getInstance().closeAll(wtoken,                            r.activity.getClass().getName(), "Activity");                }                r.activity.mDecor = null;            }            if (r.mPendingRemoveWindow == null) {                // If we are delaying the removal of the activity window, then                // we can't clean up all windows here.  Note that we can't do                // so later either, which means any windows that aren't closed                // by the app will leak.  Well we try to warning them a lot                // about leaking windows, because that is a bug, so if they are                // using this recreate facility then they get to live with leaks.                //关闭所有与token相关的所有DecorView                WindowManagerGlobal.getInstance().closeAll(token,                        r.activity.getClass().getName(), "Activity");            }            …//省略代码        }        …//省略代码    }    //WindowManagerGlobal的closeAll方法    public void closeAll(IBinder token, String who, String what) {        synchronized (mLock) {            int count = mViews.size();            //Log.i("foo", "Closing all windows of " + token);            //遍历DecorView，对比token            for (int i = 0; i < count; i++) {                //Log.i("foo", "@ " + i + " token " + mParams[i].token                //        + " view " + mRoots[i].getView());                //如果当前传入的token为null，或DecorView的token与之相同                if (token == null || mParams.get(i).token == token) {                    ViewRootImpl root = mRoots.get(i);                    //Log.i("foo", "Force closing " + root);                    //当前传入的who为‘Activity’                    if (who != null) {                        //即这个窗口没有被移除，出现泄漏了                        WindowLeaked leak = new WindowLeaked(                                what + " " + who + " has leaked window "                                + root.getView() + " that was originally added here");                        leak.setStackTrace(root.getLocation().getStackTrace());                        Log.e(TAG, "", leak);                    }                    //将其移除                    removeViewLocked(i, false);                }            }        }    }

IllegalArgumentException

这个异常调用dismiss时出现的，常出现在WindowLeaked之后。在长时间的异步操作后，Activity可能被回收或调用finish释放，再在主线程调用dismiss时可能会出现这个异常。主要出现在网络请求结束关闭加载框时。解决方法：在dismiss前使用isFinishing()判断当前Activity是否被finish，或者在onStop()或onPaus()方法中调用dismiss，再在onStart方法中判断是否需要显示。
异常信息：

java.lang.IllegalArgumentException: View=com.android.internal.policy.impl.PhoneWindow$DecorView{3e7fbc08 V.E..... R.....I. 0,0-960,231} not attached to window managerat android.view.WindowManagerGlobal.findViewLocked(WindowManagerGlobal.java:416)at android.view.WindowManagerGlobal.removeView(WindowManagerGlobal.java:342)at android.view.WindowManagerImpl.removeViewImmediate(WindowManagerImpl.java:116)at android.app.Dialog.dismissDialog(Dialog.java:354)at android.app.Dialog.dismiss(Dialog.java:337)

抛出异常的代码在隐藏和消失这节的WindowManagerGlobal的findViewLocked方法中。因为mDecor已经被移除了，而dialog又没有收到关闭消息，因此dialog认为mDecor还在当前视图中，所以再次remove便报错了。

BadTokenException

这个异常是使用new创建Dialog是没有传入Activity对象，而是其它的Context。导致token验证没有通过，而抛出异常。如果具有系统权限，则可以以其它的Context创建。

android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running?at android.view.ViewRootImpl.setView(ViewRootImpl.java:685)at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:289)at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:85)at android.app.Dialog.show(Dialog.java:311)

ViewRootImpl.setView的代码：

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {        synchronized (this) {            if (mView == null) {                mView = view;                …//省略                int res; /* = WindowManagerImpl.ADD_OKAY; */                …//省略                try {                    mOrigWindowType = mWindowAttributes.type;                    mAttachInfo.mRecomputeGlobalAttributes = true;                    collectViewAttributes();                    //验证token                    res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,                            getHostVisibility(), mDisplay.getDisplayId(),                            mAttachInfo.mContentInsets, mAttachInfo.mStableInsets, mInputChannel);                } catch (RemoteException e) {                    …//省略                } finally {                    …//省略                }                …//省略                //判断token是否可用                if (res < WindowManagerGlobal.ADD_OKAY) {                    mAttachInfo.mRootView = null;                    mAdded = false;                    mFallbackEventHandler.setView(null);                    unscheduleTraversals();                    setAccessibilityFocus(null, null);                    switch (res) {                        case WindowManagerGlobal.ADD_BAD_APP_TOKEN:                        case WindowManagerGlobal.ADD_BAD_SUBWINDOW_TOKEN:                            throw new WindowManager.BadTokenException(                                    "Unable to add window -- token " + attrs.token                                    + " is not valid; is your activity running?");                        …//省略                    }                    throw new RuntimeException(                            "Unable to add window -- unknown error code " + res);                }                …//省略            }        }    }