Android走进Framework之AppCompatActivity.setContentView

转载请标明出处: http://weyye.me/detail/framework-appcompatactivity-setcontentview/
本文出自:【Wey Ye的博客】

前言

在上一篇Android走进Framework之app是如何被启动的中讲到了从我们点击app一直到调用Activity.onCreate()的整个流程,今天来研究下我们最熟悉的一行代码setContentView()。网上也有很多关于setContentView的源码解析,但是都是基于Activity源码,而我们现在都是继承的AppCompatActivity,看源码发现改动还不少,所以我打算来研究下AppCompatActivity里是如何把我们的布局添加进去的。你是否也曾有过同样的疑惑,为什么创建Activity就要在onCreate()里面调用setContentView()?那就让我们来RTFSC (Read the fucking source code )。

学前疑惑

  • setContentView中到底做了什么?为什么我们调用后就可以显示到我们想到的布局?
  • PhoneWindow是个什么鬼?Window和它又有什么关系?
  • DecorView什么干嘛的?和我们的布局有什么联系?
  • 在我们调用requestFeature的时候为什么要在setContentView之前?

接下来,我们就来解决这些疑惑!以下源码基于Api24

AppCompatActivity.setContentView

我们先来看下AppCompatActivitysetContentView中做了什么
AppCompatActivity.java

    //这个是我们最常用的
    @Override
    public void setContentView(@LayoutRes int layoutResID) {
        getDelegate().setContentView(layoutResID);
    }

    @Override
    public void setContentView(View view) {
        getDelegate().setContentView(view);
    }

    @Override
    public void setContentView(View view, ViewGroup.LayoutParams params) {
        getDelegate().setContentView(view, params);
    }

可以看到3个重载的方法都调用getDelegate(),而其他的方法也都是调用了getDelegate(),很显然这个是代理模式。那么这个getDelegate()返回的是什么呢?

AppCompatActivity.java

    /**
     * @return The {@link AppCompatDelegate} being used by this Activity.
     */
    @NonNull
    public AppCompatDelegate getDelegate() {
        if (mDelegate == null) {
            //第一次为空,创建了AppCompatDelegate
            mDelegate = AppCompatDelegate.create(this, this);
        }
        return mDelegate;
    }

我们来看下AppCompatDelegate是怎么创建的

AppCompatDelegate.java

    private static AppCompatDelegate create(Context context, Window window,
            AppCompatCallback callback) {
        final int sdk = Build.VERSION.SDK_INT;
        if (BuildCompat.isAtLeastN()) {
            //7.0以及7.0以上创建AppCompatDelegateImplN
            return new AppCompatDelegateImplN(context, window, callback);
        } else if (sdk >= 23) {
            //6.0创建AppCompatDelegateImplV23
            return new AppCompatDelegateImplV23(context, window, callback);
        } else if (sdk >= 14) {
            //...
            return new AppCompatDelegateImplV14(context, window, callback);
        } else if (sdk >= 11) {
            //...
            return new AppCompatDelegateImplV11(context, window, callback);
        } else {
            return new AppCompatDelegateImplV9(context, window, callback);
        }
    }

哦~原来根据不同的api版本返回不同的Delegate,我们先来看看AppCompatDelegateImplN,里面是否有setContentView

AppCompatDelegateImplN.java

@RequiresApi(24)
@TargetApi(24)
class AppCompatDelegateImplN extends AppCompatDelegateImplV23 {

    AppCompatDelegateImplN(Context context, Window window, AppCompatCallback callback) {
        super(context, window, callback);
    }

    @Override
    Window.Callback wrapWindowCallback(Window.Callback callback) {
        return new AppCompatWindowCallbackN(callback);
    }

    class AppCompatWindowCallbackN extends AppCompatWindowCallbackV23 {
        AppCompatWindowCallbackN(Window.Callback callback) {
            super(callback);
        }

        @Override
        public void onProvideKeyboardShortcuts(
                List<KeyboardShortcutGroup> data, Menu menu, int deviceId) {
            final PanelFeatureState panel = getPanelState(Window.FEATURE_OPTIONS_PANEL, true);
            if (panel != null && panel.menu != null) {
                // The menu provided is one created by PhoneWindow which we don't actually use.
                // Instead we'll pass through our own...
                super.onProvideKeyboardShortcuts(data, panel.menu, deviceId);
            } else {
                // If we don't have a menu, jump pass through the original instead
                super.onProvideKeyboardShortcuts(data, menu, deviceId);
            }
        }
    }
}

发现并没有setContentView,那么肯定在父类。诶,它继承AppCompatDelegateImplV23,而AppCompatDelegateImplV23又继承AppCompatDelegateImplV14,AppCompatDelegateImplV14又继承AppCompatDelegateImplV11,AppCompatDelegateImplV11又继承AppCompatDelegateImplV9,好,知道关系后我有点懵逼了,搞什么鬼?客官别急,我们先来画个图

类继承关系
ok,最后我在V9里找到setContentView,我们来看下

AppCompatDelegateImplV9.java

    @Override
    public void setContentView(int resId) {
        //这个很关键,稍后会讲
        ensureSubDecor();
        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();
        //把我们的布局放到contentParent里面
        LayoutInflater.from(mContext).inflate(resId, contentParent);
        mOriginalWindowCallback.onContentChanged();
    }

    @Override
    public void setContentView(View v) {
        ensureSubDecor();
        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();
        contentParent.addView(v);
        mOriginalWindowCallback.onContentChanged();
    }

    @Override
    public void setContentView(View v, ViewGroup.LayoutParams lp) {
        ensureSubDecor();
        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();
        contentParent.addView(v, lp);
        mOriginalWindowCallback.onContentChanged();
    }

这是对应的3个实现的方法,发现都会调用ensureSubDecor();并且都会找到contentParent,然后把我们的布局放入进去

ok,到这里我们来捋一捋流程。

大致流程

    private void ensureSubDecor() {
        if (!mSubDecorInstalled) {

            //这个mSubDecor其实就ViewGroup,调用createSubDecor()后,此时存放我们的布局的容器已经准备好了
            mSubDecor = createSubDecor();//核心代码!

            // If a title was set before we installed the decor, propagate it now
            CharSequence title = getTitle();
            if (!TextUtils.isEmpty(title)) {
                onTitleChanged(title);
            }

            applyFixedSizeWindow();
            //SubDecor 安装后的回调
            onSubDecorInstalled(mSubDecor);
            //设置标记位
            mSubDecorInstalled = true;

            // Invalidate if the panel menu hasn't been created before this.
            // Panel menu invalidation is deferred avoiding application onCreateOptionsMenu
            // being called in the middle of onCreate or similar.
            // A pending invalidation will typically be resolved before the posted message
            // would run normally in order to satisfy instance state restoration.
            PanelFeatureState st = getPanelState(FEATURE_OPTIONS_PANEL, false);
            if (!isDestroyed() && (st == null || st.menu == null)) {
                invalidatePanelMenu(FEATURE_SUPPORT_ACTION_BAR);
            }
        }
    }

调用了createSubDecor(),看字面意思创建了一个SubDecor,看似跟DecorView有联系。我们看下里面做了什么操作

    private ViewGroup createSubDecor() {
        TypedArray a = mContext.obtainStyledAttributes(R.styleable.AppCompatTheme);

        if (!a.hasValue(R.styleable.AppCompatTheme_windowActionBar)) {
            a.recycle();
            //还记得我们使用AppCompatActivity如果不设置AppCompat主题报的错误吗?就是在这里抛出来的
            throw new IllegalStateException(
                    "You need to use a Theme.AppCompat theme (or descendant) with this activity.");
        }
        //初始化相关特征标志
        if (a.getBoolean(R.styleable.AppCompatTheme_windowNoTitle, false)) {
            //一般我们的主题默认都是NoTitle
            requestWindowFeature(Window.FEATURE_NO_TITLE);
        } else if (a.getBoolean(R.styleable.AppCompatTheme_windowActionBar, false)) {
            // Don't allow an action bar if there is no title.
            requestWindowFeature(FEATURE_SUPPORT_ACTION_BAR);
        }
        if (a.getBoolean(R.styleable.AppCompatTheme_windowActionBarOverlay, false)) {
            requestWindowFeature(FEATURE_SUPPORT_ACTION_BAR_OVERLAY);
        }
        if (a.getBoolean(R.styleable.AppCompatTheme_windowActionModeOverlay, false)) {
            requestWindowFeature(FEATURE_ACTION_MODE_OVERLAY);
        }
        mIsFloating = a.getBoolean(R.styleable.AppCompatTheme_android_windowIsFloating, false);
        a.recycle();

        //重点!在这里就创建DecorView,至于DecorView到底是什么以及如何创建的,稍后会讲到
        mWindow.getDecorView();

        final LayoutInflater inflater = LayoutInflater.from(mContext);
        //可以看到其实就是个ViewGroup,我们接着往下看,跟DecorView到底有啥关系
        ViewGroup subDecor = null;


        if (!mWindowNoTitle) {
            //上面说了主题默认都是NoTitle,所以不会走里面的方法
            if (mIsFloating) {
                // If we're floating, inflate the dialog title decor
                subDecor = (ViewGroup) inflater.inflate(
                        R.layout.abc_dialog_title_material, null);

                ...
            } else if (mHasActionBar) {

                TypedValue outValue = new TypedValue();
                mContext.getTheme().resolveAttribute(R.attr.actionBarTheme, outValue, true);

                ...

                // Now inflate the view using the themed context and set it as the content view
                subDecor = (ViewGroup) LayoutInflater.from(themedContext)
                        .inflate(R.layout.abc_screen_toolbar, null);

                /**
                 * Propagate features to DecorContentParent
                 */
                if (mOverlayActionBar) {
                    mDecorContentParent.initFeature(FEATURE_SUPPORT_ACTION_BAR_OVERLAY);
                }
                if (mFeatureProgress) {
                    mDecorContentParent.initFeature(Window.FEATURE_PROGRESS);
                }
                if (mFeatureIndeterminateProgress) {
                    mDecorContentParent.initFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
                }
            }
        } else {
            //我们进入else
            if (mOverlayActionMode) {
                //调用了requestWindowFeature(FEATURE_ACTION_MODE_OVERLAY)会走进来
                subDecor = (ViewGroup) inflater.inflate(
                        R.layout.abc_screen_simple_overlay_action_mode, null);
            } else {
                //ok,所以如果这些我们都没设置,默认就走到这里来了,在这里映射出了subDecor,稍后我们来看下这个布局是啥
                subDecor = (ViewGroup) inflater.inflate(R.layout.abc_screen_simple, null);
            }

            ...
        }

        if (subDecor == null) {
            throw new IllegalArgumentException(
                    "AppCompat does not support the current theme features: { "
                            + "windowActionBar: " + mHasActionBar
                            + ", windowActionBarOverlay: "+ mOverlayActionBar
                            + ", android:windowIsFloating: " + mIsFloating
                            + ", windowActionModeOverlay: " + mOverlayActionMode
                            + ", windowNoTitle: " + mWindowNoTitle
                            + " }");
        }

        if (mDecorContentParent == null) {
            mTitleView = (TextView) subDecor.findViewById(R.id.title);
        }

        // Make the decor optionally fit system windows, like the window's decor
        ViewUtils.makeOptionalFitsSystemWindows(subDecor);
        //这个contentView很重要,是我们布局的父容器,你可以把它直接当成FrameLayout
        final ContentFrameLayout contentView = (ContentFrameLayout) subDecor.findViewById(
                R.id.action_bar_activity_content);
        //看过相关知识的同学应该知道android.R.id.content这个Id在以前是我们布局的父容器的Id
        final ViewGroup windowContentView = (ViewGroup) mWindow.findViewById(android.R.id.content);
        if (windowContentView != null) {
            // There might be Views already added to the Window's content view so we need to
            // migrate them to our content view
            while (windowContentView.getChildCount() > 0) {
                final View child = windowContentView.getChildAt(0);
                windowContentView.removeViewAt(0);
                contentView.addView(child);
            }

            //注意!原来windowContentView的Id是android.R.id.content,现在设置成NO_ID
            windowContentView.setId(View.NO_ID);
            //在之前这个id是我们的父容器,现在将contentView设置成android.R.id.content,那么可以初步判定,这个contentView将会是我的父容器
            contentView.setId(android.R.id.content);

            // The decorContent may have a foreground drawable set (windowContentOverlay).
            // Remove this as we handle it ourselves
            if (windowContentView instanceof FrameLayout) {
                ((FrameLayout) windowContentView).setForeground(null);
            }
        }

        // Now set the Window's content view with the decor
        //注意!重要!将subDecor放入到了这个Window里面,这个Window是个抽象类,其实现类是PhoneWindow,稍后会讲到
        mWindow.setContentView(subDecor);

        ....

        return subDecor;
    }

看到了requestWindowFeature是不是很熟悉?还记得我们是怎么让Activity全屏的吗?

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FILL_PARENT
        ,WindowManager.LayoutParams.FILL_PARENT);
        setContentView(R.layout.activity_test);
    }

而且这两行代码必须在setContentView()之前调用,知道为啥了吧?因为在这里就把Window的相关特征标志给初始化了,在setContentView()之后调用就不起作用了!

在代码里其他比较重要的地方已写了注释,我们来看下这个abc_screen_simple.xml的布局到底是什么样子的

abc_screen_simple.xml

<android.support.v7.internal.widget.FitWindowsLinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/action_bar_root"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:fitsSystemWindows="true">

    <android.support.v7.internal.widget.ViewStubCompat
        android:id="@+id/action_mode_bar_stub"
        android:inflatedId="@+id/action_mode_bar"
        android:layout="@layout/abc_action_mode_bar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <include layout="@layout/abc_screen_content_include" />

</android.support.v7.internal.widget.FitWindowsLinearLayout>

abc_screen_content_include.xml

<merge xmlns:android="http://schemas.android.com/apk/res/android">

    <android.support.v7.internal.widget.ContentFrameLayout
            android:id="@id/action_bar_activity_content"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:foregroundGravity="fill_horizontal|top"
            android:foreground="?android:attr/windowContentOverlay" />

</merge>

原来这个subDecor就是FitWindowsLinearLayout

看到这2个布局,我们先把这2个布局用图画出来。

布局结构
(图不在美,能懂就行~)

从AppCompatActivity到现在布局,在我的脑海里浮现出这样的的画面。。。

那这是不是我们app最终的布局呢?当然不是,因为我们还没讲到非常重要的两行代码

mWindow.getDecorView();
mWindow.setContentView(subDecor);

注释中说道Window是个抽象类,其实现类是PhoneWindow。那么我们先来看PhoneWindow的getDecorView做了什么

PhoneWindow.java

public class PhoneWindow extends Window implements MenuBuilder.Callback {
    @Override
    public final View getDecorView() {
        if (mDecor == null || mForceDecorInstall) {
            installDecor();
        }
        return mDecor;
    }
    private void installDecor() {
        //mDecor是DecorView,第一次mDecor=null,所以调用generateDecor
        if (mDecor == null) {
            mDecor = generateDecor();
               ...
         }
         //第一次mContentParent也等于null
        if (mContentParent == null) {
            //可以看到把DecorView传入进去了
            mContentParent = generateLayout(mDecor);
        }

    }

}

在generateDecor()做了什么?其实返回了一个DecorView对象。

    protected DecorView generateDecor(int featureId) {
        // System process doesn't have application context and in that case we need to directly use
        // the context we have. Otherwise we want the application context, so we don't cling to the
        // activity.
        Context context;
        if (mUseDecorContext) {
            Context applicationContext = getContext().getApplicationContext();
            if (applicationContext == null) {
                context = getContext();
            } else {
                context = new DecorContext(applicationContext, getContext().getResources());
                if (mTheme != -1) {
                    context.setTheme(mTheme);
                }
            }
        } else {
            context = getContext();
        }
        return new DecorView(context, featureId, this, getAttributes());
    }

DecorView是啥呢?

public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks {
    ...
}

哦~原来继承FrameLayout,起到了装饰的作用。

我们在来看看generateLayout()做了什么。

    protected ViewGroup generateLayout(DecorView decor) {
        TypedArray a = getWindowStyle();
        //设置一堆标志位...
        ...
        if (!mForcedStatusBarColor) {
            //获取主题状态栏的颜色
            mStatusBarColor = a.getColor(R.styleable.Window_statusBarColor, 0xFF000000);
        }
        if (!mForcedNavigationBarColor) {
            //获取底部NavigationBar颜色
            mNavigationBarColor = a.getColor(R.styleable.Window_navigationBarColor, 0xFF000000);
        }

        //获取主题一些资源
       ...

        // Inflate the window decor.

        int layoutResource;
        int features = getLocalFeatures();
        // System.out.println("Features: 0x" + Integer.toHexString(features));
        if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
            ...我们设置不同的主题以及样式,会采用不同的布局文件...
        } else {
            //记住这个布局,之后我们会来验证下布局的结构
            layoutResource = R.layout.screen_simple;
            // System.out.println("Simple!");
        }
        //要开始更改mDecor啦~
        mDecor.startChanging();
        //注意,此时把screen_simple放到了DecorView里面
        mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
        //这里的ID_ANDROID_CONTENT就是R.id.content;
        ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
        if (contentParent == null) {
            throw new RuntimeException("Window couldn't find content container view");
        }

        ...


        //这里的getContainer()返回的是个Window类,也就是父Window,一般为空
        if (getContainer() == null) {
            final Drawable background;
            if (mBackgroundResource != 0) {
                background = getContext().getDrawable(mBackgroundResource);
            } else {
                background = mBackgroundDrawable;
            }
            //设置背景
            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;
    }

可以看到根据不同主题属性使用的不同的布局,然后返回了这个布局contentParent

我们来看看这个screen_simple.xml布局是什么样子的

<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" />
    <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>

咦,这个布局结构跟subDecor好相似啊。。

好了,到目前为止我们知道了,当我们调用mWindow.getDecorView();的时候里面创建DecorView,然后又根据不同主题属性添加不同布局放到DecorView下,然后找到这个布局的R.id.content,也就是mContentParent。ok,搞清楚mWindow.getDecorView();之后,我们在来看看mWindow.setContentView(subDecor);(注意:此时把subDecor传入进去)

    @Override
    public void setContentView(View view) {
        //调用下面的重载方法
        setContentView(view, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
    }

    @Override
    public void setContentView(View view, ViewGroup.LayoutParams params) {
        //在mWindow.getDecorView()已经创建了mContentParent
        if (mContentParent == null) {
            installDecor();
        } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            mContentParent.removeAllViews();
        }
        //是否有transitions动画。没有,进入else
        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            view.setLayoutParams(params);
            final Scene newScene = new Scene(mContentParent, view);
            transitionTo(newScene);
        } else {
            //重要!!将这个subDecor也就是FitWindowsLinearLayout添加到这个mContentParent里面了
            //mContentParent是FrameLayout,在之前设置的View.NO_ID
            mContentParent.addView(view, params);
        }
        mContentParent.requestApplyInsets();
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            cb.onContentChanged();
        }
        mContentParentExplicitlySet = true;
    }

当调用了mWindow.getDecorView();创建了DecorView以及mContentParent,并且把subDecor放到了mContentParent里面。我们再来回头看看AppCompatDelegateImplV9,还记得它吗?当我们在AppCompatActivitysetContentView的时候会去调用AppCompatDelegateImplV9setContentView

AppCompatDelegateImplV9.java

@Override
    public void setContentView(View v) {
        //此时DecorView和subDecor都创建好了
        ensureSubDecor();
        //还记得调用createSubDecor的时候把原本是R.id.content的windowContentView设置成了NO_ID
        //并且将contentView也就是ContentFrameLayout设置成了R.id.content吗?
        //也就是说此时的contentParent就是ContentFrameLayout
        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();
        //将我的布局放到contentParent里面
        contentParent.addView(v);
        mOriginalWindowCallback.onContentChanged();
    }

    @Override
    public void setContentView(int resId) {
        ensureSubDecor();
        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();
        //将我们的布局id映射成View并且放到contentParent下
        LayoutInflater.from(mContext).inflate(resId, contentParent);
        mOriginalWindowCallback.onContentChanged();
    }

    @Override
    public void setContentView(View v, ViewGroup.LayoutParams lp) {
        ensureSubDecor();
        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();
        contentParent.addView(v, lp);
        mOriginalWindowCallback.onContentChanged();
    }

完整布局

ok,看到这里,想必大家在脑海里也有个大致布局了吧,我们再来把整个app初始布局画出来

不喜勿喷...

验证布局

接下来我们来验证下我们布局结构是否正确

新建一个Activity

    public class TestAcitivty extends AppCompatActivity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test);
    }
}

主题

<!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
        <item name="android:listDivider">@color/divider_dddddd</item>
    </style>

为了演示布局非常简单,就是一个textview

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
          android:id="@+id/textView"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:orientation="vertical">

</TextView>

运行后,我们在用hierarchyviewer查看下

这里写图片描述

看来我们的脑补的布局是对的!

学后总结

整个流程就是这样。看到这里我们明白了,当我们调用setContentView的时候加载了2次系统布局,在PhoneWindow里面创建了DecorView,DecorView是我们的最底层的View,并且将我们的布局放入到一个ContentFrameLayout里,我们还知道在setContentView的时候进行了相关特征标志初始化,所以在它之后调用requestWindowFeature就会不起作用然后报错。

setContentView时序图

知道这些之后我们不妨用时序图来梳理下整个调用的流程

setContentView时序图

查看高清无码大图

致谢

【凯子哥带你学Framework】Activity界面显示全解析(上)

结语

当然,在这篇文章中,因为篇幅问题,也有许多没有讲的重要知识点,比如:

  • PhoneWindow在哪里初始化?它做了哪些事?
  • view树是如何被管理的?
  • findViewById到底是怎么找到对应的View的?
  • 为什么说setContentViewonResume在对用户可见?
  • 等等…

在下一篇中我会详细讲解这些问题。

最后

如果你觉得不错,点下喜欢呗~当做是对我的鼓励( ^_^ )
文中如有错误,希望大家指出!

博主整理不易,转载请注明出处:
http://weyye.me/detail/framework-appcompatactivity-setcontentview/