Android窗口機(jī)制系列

Android窗口機(jī)制（一）初識(shí)Android的窗口結(jié)構(gòu)
Android窗口機(jī)制（二）Window瑞凑，PhoneWindow，DecorView概页，setContentView源碼理解
Android窗口機(jī)制（三）Window和WindowManager的創(chuàng)建與Activity
Android窗口機(jī)制（四）ViewRootImpl與View和WindowManager
Android窗口機(jī)制（五）最終章：WindowManager.LayoutParams和Token以及其他窗口Dialog籽御，Toast

前篇文章中出現(xiàn)了PhoneWindow，DecorView這些類绰沥，如果是第一次見過(guò)的話篱蝇，肯定會(huì)覺(jué)得陌生。這篇文章主要跟大家講解Window徽曲，PhoneWindow，DecorView他們的理解以及他們之間的聯(lián)系

Window

我們來(lái)看下源碼里面的說(shuō)明

/**
 * Abstract base class for a top-level window look and behavior policy.  An
 * instance of this class should be used as the top-level view added to the
 * window manager. It provides standard UI policies such as a background, title
 * area, default key processing, etc.
 *
 * <p>The only existing implementation of this abstract class is
 * android.view.PhoneWindow, which you should instantiate when needing a
 * Window.
 */
public abstract class Window {
    ...
    @Nullable
    public View findViewById(@IdRes int id) {
        return getDecorView().findViewById(id);
    }

/**
 * Convenience for * {@link #setContentView(View, android.view.ViewGroup.LayoutParams)}
 * to set the screen content from a layout resource.  The resource will be * inflated, adding all top-level views to the screen. * * @param layoutResID Resource ID to be inflated.
 * @see #setContentView(View, android.view.ViewGroup.LayoutParams)
 */
     public abstract void setContentView(@LayoutRes int layoutResID);
     ...
}

一個(gè)頂級(jí)窗口查看和行為的一個(gè)抽象基類麸塞。這個(gè)類的實(shí)例作為一個(gè)頂級(jí)View添加到Window Manager秃臣。它提供了一套標(biāo)準(zhǔn)的UI方法，比如添加背景哪工，標(biāo)題等等奥此。當(dāng)你需要用到Window的時(shí)候，你應(yīng)該使用它的唯一實(shí)現(xiàn)類PhoneWindow雁比≈苫ⅲ可以看到，Window是一個(gè)抽象基類偎捎，它提供了一系列窗口的方法蠢终，比如設(shè)置背景，標(biāo)題等等茴她，而它的唯一實(shí)現(xiàn)類則是PhoneWindow

PhoneWindow

Window的唯一實(shí)現(xiàn)類

public class PhoneWindow extends Window implements MenuBuilder.Callback {

    private final static String TAG = "PhoneWindow";

    ...

    // This is the top-level view of the window, containing the window decor.
    private DecorView mDecor;

    // This is the view in which the window contents are placed. It is either
    // mDecor itself, or a child of mDecor where the contents go.
    private ViewGroup mContentParent;

    private ViewGroup mContentRoot;
    ...
}

可以看到寻拂，在PhoneWindow里面，出現(xiàn)了成員變量DecorView的而這里丈牢，DecorView則是PhoneWindow里面的一個(gè)內(nèi)部類祭钉，它是繼承與FrameLayout

 private final class DecorView extends FrameLayout implements RootViewSurfaceTaker {

        /* package */int mDefaultOpacity = PixelFormat.OPAQUE;

        /** The feature ID of the panel, or -1 if this is the application's DecorView */
        private final int mFeatureId;

        private final Rect mDrawingBounds = new Rect();

        private final Rect mBackgroundPadding = new Rect();

        private final Rect mFramePadding = new Rect();

        private final Rect mFrameOffsets = new Rect();
        ....
 }

既然是FrameLayout，也就可以加載布局文件己沛，也就是說(shuō)慌核，我們那些標(biāo)題欄，內(nèi)容欄申尼，頂級(jí)上看是加載在DecorView上的垮卓。而DecorView則是由PhoneWindow負(fù)責(zé)添加

兩者關(guān)系以及setContentView源碼流程

接下我們就從一個(gè)常見的方法中去認(rèn)知他們之間的關(guān)系，那就是activity里面的setContentView晶姊，就是我們平常把布局內(nèi)容顯示到界面上的一個(gè)方法扒接。點(diǎn)擊activity.setContentView時(shí)

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

里面方法調(diào)用了getWindow().setContentView，而這個(gè)getWindow方法獲取的就是Activity上的Window

/**
     * Retrieve the current {@link android.view.Window} for the activity.
     * This can be used to directly access parts of the Window API that
     * are not available through Activity/Screen.
     *
     * @return Window The current window, or null if the activity is not
     *         visual.
     */
    public Window getWindow() {
        return mWindow;
    }

可以看到如果當(dāng)前mWindow為null的話，則表示當(dāng)前Activity不在窗口上钾怔，這里的mWindow.setContentView碱呼，實(shí)際上調(diào)用到的是它的實(shí)現(xiàn)類方法phoneWindow.setContentView

 @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) {
            //創(chuàng)建DecorView，并添加到mContentParent上
            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 {
            //將要加載的資源添加到mContentParent上
            mLayoutInflater.inflate(layoutResID, mContentParent);
        }
        mContentParent.requestApplyInsets();
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            //回調(diào)通知表示完成界面加載
            cb.onContentChanged();
        }
    }

如果當(dāng)前內(nèi)容還未放置到窗口宗侦，此時(shí)mContentParent==null,也就是第一次調(diào)用的時(shí)候愚臀，調(diào)用那個(gè)installDecor方法。FEATURE_CONTENT_TRANSITIONS矾利，則是標(biāo)記當(dāng)前內(nèi)容加載有沒(méi)有使用過(guò)度動(dòng)畫姑裂，也就是轉(zhuǎn)場(chǎng)動(dòng)畫。如果內(nèi)容已經(jīng)加載過(guò)男旗，并且不需要?jiǎng)赢嫴案瑒t會(huì)調(diào)用removeAllViews。添加完Content后如有設(shè)置了FEATURE_CONTENT_TRANSITIONS則添加Scene來(lái)過(guò)度啟動(dòng)察皇。否則mLayoutInflater.inflate(layoutResID, mContentParent);將我們的資源文件通過(guò)LayoutInflater對(duì)象轉(zhuǎn)換為View樹茴厉，并且添加至mContentParent視圖中。既然是第一次啟動(dòng)則會(huì)調(diào)用到installDecor什荣，從字面上看可以知道該方法用來(lái)添加DecorView矾缓，看下里面說(shuō)明

private void installDecor() {
        if (mDecor == null) {
        //調(diào)用該方法創(chuàng)建new一個(gè)DecorView
            mDecor = generateDecor();
            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
            mDecor.setIsRootNamespace(true);
            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
            }
        }
        //一開始DecorView未加載到mContentParent，所以此時(shí)mContentParent=null
        if (mContentParent == null) {
        //該方法將mDecorView添加到Window上綁定布局
            mContentParent = generateLayout(mDecor);

            // Set up decor part of UI to ignore fitsSystemWindows if appropriate.
            mDecor.makeOptionalFitsSystemWindows();

            final DecorContentParent decorContentParent = (DecorContentParent) mDecor.findViewById(
                    R.id.decor_content_parent);
                
                ...//添加其他資源
                ...//設(shè)置轉(zhuǎn)場(chǎng)動(dòng)畫
        }
    }

可以看到該方法稻爬，先通過(guò)吊桶generateDecor創(chuàng)建DecorView

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

創(chuàng)建完后再通過(guò)調(diào)用generateLayout將setContentView的內(nèi)容賦值到mContentParent嗜闻，這個(gè)方法有點(diǎn)長(zhǎng)，我們看下

 protected ViewGroup generateLayout(DecorView decor) {
        // Apply data from current theme.
        //根據(jù)當(dāng)前設(shè)置的主題來(lái)加載默認(rèn)布局
        TypedArray a = getWindowStyle();
        //如果你在theme中設(shè)置了window_windowNoTitle桅锄，則這里會(huì)調(diào)用到琉雳，其他方法同理，
        //這里是根據(jù)你在theme中的設(shè)置去設(shè)置的
        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);
        }
        //是否有設(shè)置全屏
        if (a.getBoolean(R.styleable.Window_windowFullscreen, false)) {
            setFlags(FLAG_FULLSCREEN, FLAG_FULLSCREEN & (~getForcedWindowFlags()));
        }
        
        ...//省略其他加載資源
        
        // 添加布局到DecorView竞滓，前面說(shuō)到咐吼，DecorView是繼承與FrameLayout，它本身也是一個(gè)ViewGroup商佑，而我們前面創(chuàng)建它的時(shí)候锯茄，只是調(diào)用了new DecorView，此時(shí)里面并無(wú)什么東西茶没。而下面的步奏則是根據(jù)用戶設(shè)置的Feature來(lái)創(chuàng)建相應(yīng)的默認(rèn)布局主題肌幽。舉個(gè)例子，如果我在setContentView之前調(diào)用了requestWindowFeature(Window.FEATURE_NO_TITLE)抓半，這里則會(huì)通過(guò)getLocalFeatures來(lái)獲取你設(shè)置的feature喂急，進(jìn)而選擇加載對(duì)應(yīng)的布局，此時(shí)則是加載沒(méi)有標(biāo)題欄的主題笛求，對(duì)應(yīng)的就是R.layout.screen_simple

        int layoutResource;
        int features = getLocalFeatures();
        // System.out.println("Features: 0x" + Integer.toHexString(features));
        if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
            layoutResource = R.layout.screen_swipe_dismiss;
        } ... //省略其他判斷方法
        } else {
            // Embedded, so no decoration is needed.
            layoutResource = R.layout.screen_simple;
            // System.out.println("Simple!");
        }

        mDecor.startChanging();
        //選擇對(duì)應(yīng)布局創(chuàng)建添加到DecorView中
        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);
        ...
        return contentParent;
    }

首先generateLayout會(huì)根據(jù)當(dāng)前用戶設(shè)置的主題去設(shè)置對(duì)應(yīng)的Feature廊移，接著糕簿，根據(jù)對(duì)應(yīng)的Feature來(lái)選擇加載對(duì)應(yīng)的布局文件，(Window.FEATURE_NO_TITLE)接下來(lái)通過(guò)getLocalFeatures來(lái)獲取你設(shè)置的feature狡孔，進(jìn)而選擇加載對(duì)應(yīng)的布局懂诗，這也就是為什么我們要在setContentView之前調(diào)用requesetFeature的原因。此時(shí)則是加載沒(méi)有標(biāo)題欄的主題苗膝，對(duì)應(yīng)的就是R.layout.screen_simple殃恒，我們看下里面的布局

<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"
              android:theme="?attr/actionBarTheme" />
    <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>

可以看到是LinearLayout里面包含了兩個(gè)，因?yàn)樵O(shè)置可NoTitle辱揭，所以上面只有一個(gè)ViewStub离唐，否則還有一個(gè)FrameLayout。也證明前面第一篇中說(shuō)的问窃，“DecorView只有一個(gè)子元素為L(zhǎng)inearLayout亥鬓。代表整個(gè)Window界面，包含通知欄泡躯，標(biāo)題欄贮竟，內(nèi)容顯示欄三塊區(qū)域〗咸辏”注意FrameLayout里面的id，@android:id/content 技健，我們setContentView的內(nèi)容就是添加到這個(gè)FrameLayout中写穴。

generateLayout的返回是contentParent，而它的獲取則是ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);`

public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;

正是id為content的FrameLayout雌贱。之后我們setContentView則是添加在mContentParent上面了啊送。回到前面剛開始的方法

 @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) {
            //創(chuàng)建DecorView欣孤，并添加到mContentParent上
            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 {
            //將要加載的資源添加到mContentParent上
            mLayoutInflater.inflate(layoutResID, mContentParent);
        }
        mContentParent.requestApplyInsets();
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            //回調(diào)通知表示完成界面改變
            cb.onContentChanged();
        }
    }

此時(shí)已經(jīng)創(chuàng)建完DecorView并且獲取到mContentParent馋没，接著就是將你setContentView的內(nèi)容添加到mContentParent中，也就是

 mLayoutInflater.inflate(layoutResID, mContentParent);
 或者
 mContentParent.addView(view, params);

最后調(diào)用Callback來(lái)通知界面發(fā)生改變降传。Callback是Window里面的一個(gè)接口篷朵，里面聲明了當(dāng)界面更改觸摸時(shí)調(diào)用的各種方法。這里的話婆排，我們看下onContentChanged声旺，在PhoneWindow里面并沒(méi)有看到onContentChanged的實(shí)現(xiàn)類，而我們又知道Activity本身又是加載在Window上的段只，我們看下Activity

public class Activity extends ContextThemeWrapper
        implements LayoutInflater.Factory2,
        Window.Callback, KeyEvent.Callback,
        OnCreateContextMenuListener, ComponentCallbacks2,
        Window.OnWindowDismissedCallback { ... }

可以看到Activity里面實(shí)現(xiàn)了Window.Callback接口而里面onContentChanged則是空的腮猖，也就是我們可以通過(guò)重寫該方法來(lái)監(jiān)聽布局內(nèi)容的改變了

 public void onContentChanged() {
    }

小結(jié)

• Window是一個(gè)抽象類，提供了各種窗口操作的方法赞枕，比如設(shè)置背景標(biāo)題ContentView等等
• PhoneWindow則是Window的唯一實(shí)現(xiàn)類澈缺，它里面實(shí)現(xiàn)了各種添加背景主題ContentView的方法坪创，內(nèi)部通過(guò)DecorView來(lái)添加頂級(jí)視圖
• 每一個(gè)Activity上面都有一個(gè)Window，可以通過(guò)getWindow獲取
• DecorView姐赡，頂級(jí)視圖莱预，繼承與FramentLayout，setContentView則是添加在它里面的@id/content里
• setContentView里面創(chuàng)建了DecorView雏吭，根據(jù)Theme锁施，F(xiàn)eature添加了對(duì)應(yīng)的布局文件
• 當(dāng)setContentView設(shè)置顯示后會(huì)回調(diào)Activity的onContentChanged方法

回顧

再看一下前一篇文章的結(jié)構(gòu)圖，是不是就更好理解了呢杖们。

Paste_Image.png

下一篇文章
Android窗口機(jī)制（三）Window和WindowManager的創(chuàng)建與Activity
http://www.reibang.com/p/6afb0c17df43