這篇文章距離現(xiàn)在已經(jīng)兩年的時間了。當(dāng)初自己剛畢業(yè)工作不久，才開始接觸Android，有一天中午和同事一起吃飯的時候，一個大牛問我你思考過Activity的setContentView是怎么執(zhí)行的么。當(dāng)初就因?yàn)檫@個問題我接入到了Android源碼。兩年時間過去了現(xiàn)在回過頭來看，感覺自己寫得有很多的不足，本次再補(bǔ)充一下。

前言

這幾天正在進(jìn)行初級自定義組件的學(xué)習(xí)，一不小心想到了view到底是怎么加載到屏幕上面的。每一個Activity中都有一個方法setContentView,我們可以加載自己想要的界面布局，展示在手機(jī)屏幕上。但到底內(nèi)部是怎么實(shí)現(xiàn)的呢？（PS:源碼基于Android5.1，cm12.1）

Activity的onContentView

首先查看Activity的onContentView的方法：

//Activity.java
public void setContentView(int layoutResID) {
     getWindow().setContentView(layoutResID);
     initActionBar();
}
public void setContentView(View view) {
    getWindow().setContentView(view);
    initActionBar();
}
public void setContentView(View view, ViewGroup.LayoutParams params) {
    getWindow().setContentView(view, params);
    initActionBar();
}

Activity一共重載了三個setContentView方法，其中第一個setContentView(int layoutResID)方法是我們常用的。

public void setContentView(int layoutResID) {
     //getWindow()獲取activity內(nèi)部對象mWindow并調(diào)用它的setContentView方法
      getWindow().setContentView(layoutResID);
      initActionBar(); //這是初始化actionBar，我們不關(guān)注它
}
public Window getWindow() {
    return mWindow;
}

Activity的setContentView方法實(shí)際還是調(diào)用mWindow的setContentView方法，接下看我們試看看mWindow的相關(guān)代碼。

mWindow對象

查看Activity源碼，找到在attach方法中對mWindow做了賦值。

final void attach(Context context, ActivityThread aThread,
           Instrumentation instr, IBinder token, int ident,
           Application application, Intent intent, ActivityInfo info,
           CharSequence title, Activity parent, String id,
           NonConfigurationInstances lastNonConfigurationInstances,
           Configuration config) {
    attachBaseContext(context);
    
    mFragments.attachActivity(this, mContainer, null);
    
    mWindow = PolicyManager.makeNewWindow(this);
    mWindow.setCallback(this);
    /…部分代碼省略…/
}

那么Activity的attach方法是Activity生命周期的第一個方法，它是ActivityThread中performLaunchActivity方法調(diào)用的，這是通過AMS(ActivityManagerService)的startActivity調(diào)用ActivityTrack的startActivityMayWait來調(diào)用的。

attach字面意思就是“使依附；貼上；系上”，也就是點(diǎn)擊activity進(jìn)行啟動的時候之執(zhí)行的。

private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
    /*******部分代碼省略********/
    try {
        java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
        activity = mInstrumentation.newActivity(
                cl, component.getClassName(), r.intent);
        StrictMode.incrementExpectedActivityCount(activity.getClass());
        r.intent.setExtrasClassLoader(cl);
        r.intent.prepareToEnterProcess();
        if (r.state != null) {
            r.state.setClassLoader(cl);
        }
    } catch (Exception e) {
        if (!mInstrumentation.onException(activity, e)) {
            throw new RuntimeException(
                "Unable to instantiate activity " + component
                + ": " + e.toString(), e);
        }
    }

    try {
        Application app = r.packageInfo.makeApplication(false, mInstrumentation);

        /*******部分代碼省略********/

        if (activity != null) {
            Context appContext = createBaseContextForActivity(r, activity);
            CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
            Configuration config = new Configuration(mCompatConfiguration);
            if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity "
                    + r.activityInfo.name + " with config " + config);
            activity.attach(appContext, this, getInstrumentation(), r.token,
                    r.ident, app, r.intent, r.activityInfo, title, r.parent,
                    r.embeddedID, r.lastNonConfigurationInstances, config,
                    r.referrer, r.voiceInteractor);

            /*******部分代碼省略********/
}

如述源代碼當(dāng)中就是在啟動Activity的時候執(zhí)行其attach：

ApplicationThread#scheduleLaunchActivity

ActivityThread#handleLaunchActivity

ActivityThread#performLaunchActivity

Activity#attach

PolicyManager獲取Window對象

public final class PolicyManager {
    private static final String POLICY_IMPL_CLASS_NAME =
        "com.android.internal.policy.impl.Policy";

    private static final IPolicy sPolicy;

    static {
        // Pull in the actual implementation of the policy at run-time
        try {
            Class policyClass = Class.forName(POLICY_IMPL_CLASS_NAME);
            sPolicy = (IPolicy)policyClass.newInstance();
        } catch (ClassNotFoundException ex) {
            throw new RuntimeException(
                    POLICY_IMPL_CLASS_NAME + " could not be loaded", ex);
        } catch (InstantiationException ex) {
            throw new RuntimeException(
                    POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
        } catch (IllegalAccessException ex) {
            throw new RuntimeException(
                    POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
        }
    }

    // Cannot instantiate this class
    private PolicyManager() {}

    // The static methods to spawn new policy-specific objects
    public static Window makeNewWindow(Context context) {
        return sPolicy.makeNewWindow(context);
    }
    /*******部分代碼省略********/
}

PolicyManager.makeNewWindow方法實(shí)際是通過反射機(jī)制調(diào)用了"com.android.internal.policy.impl.Policy"的makeNewWindow方法。

public class Policy implements IPolicy {
    private static final String TAG = "PhonePolicy";

    private static final String[] preload_classes = {
        "com.android.internal.policy.impl.PhoneLayoutInflater",
        "com.android.internal.policy.impl.PhoneWindow",
        "com.android.internal.policy.impl.PhoneWindow$1",
        "com.android.internal.policy.impl.PhoneWindow$DialogMenuCallback",
        "com.android.internal.policy.impl.PhoneWindow$DecorView",
        "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState",
        "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState$SavedState",
    };

    static {
        // For performance reasons, preload some policy specific classes when
        // the policy gets loaded.
        for (String s : preload_classes) {
            try {
                Class.forName(s);
            } catch (ClassNotFoundException ex) {
                Log.e(TAG, "Could not preload class for phone policy: " + s);
            }
        }
    }

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

    /*******部分代碼省略********/
}

Policy的makeNewWindow方法實(shí)際是返回一個PhoneWindow對象。

PhoneWindow.setContentView

public class PhoneWindow extends Window implements MenuBuilder.Callback {
    /*******部分代碼省略********/
    @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) {
            //構(gòu)造DecorView對象并賦值給mDecor，并進(jìn)行mContentParent的初始化
            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 {
            //將附帶params屬性的view對象添加在mContentParent中
            mContentParent.addView(view, params);
        }
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            cb.onContentChanged();
        }
    }
    @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 {
            //將Resource對于的id等于layoutResID的xml布局文件，add到mContentParent中
            mLayoutInflater.inflate(layoutResID, mContentParent);
        }
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            cb.onContentChanged();
        }
    }
    /*******部分代碼省略********/
}

setContentView主要做了兩件事：

初始化整個界面（即：DecorView）

將setContentView的參數(shù)對于的View，add到mContentParent中。

addView

setContentView方法有兩種在界面添加View的方法。

調(diào)用mContentParent的add方法，將目標(biāo)View添加進(jìn)去。
調(diào)用LayoutInfater.inflate方法將資源xml解析并轉(zhuǎn)化為View，添加到mContentParent中。

installDecor

在看installDecor方法的源代碼的時候，我先讓大家看一個Android手機(jī)界面的布局文件的分析圖。

Android手機(jī)界面的布局

PhoneWindow

PhoneWindow.java部分代碼

protected DecorView generateDecor() {
    return new DecorView(getContext(), -1);
}
private void installDecor() {
    if (mDecor == null) {
        //構(gòu)造mDecor對象DecorView
        mDecor = generateDecor();
        mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
        mDecor.setIsRootNamespace(true);
        if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
            mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
        }
    }
    if (mContentParent == null) {
        //構(gòu)造mContentParent
        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);

        if (decorContentParent != null) {
            //mDecorContentParent賦值R.id.decor_content_parent
            mDecorContentParent = decorContentParent;
            mDecorContentParent.setWindowCallback(getCallback());
            if (mDecorContentParent.getTitle() == null) {
                mDecorContentParent.setWindowTitle(mTitle);
            }   
   /*******部分代碼省略********/
}

mDecorContentParent為mDecor中的R.id.decor_content_parent

installDecor先構(gòu)造mDecor，然后通過mDecor執(zhí)行g(shù)enerateLayout()方法初始化mContentParent。

protected ViewGroup generateLayout(DecorView decor) {
     /*******部分代碼省略********/
    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");
    }
     /*******部分代碼省略********/
    return contentParent; 
}

mContentRoot為decor的content，經(jīng)測試(mContentRoot == mDecorContentParent)為true。
generateLayout(DecorView decor)方法構(gòu)造出來的mContentParent為ID_ANDROID_CONTENT，即mDecor中的R.id.content。

從代碼中可以看出顯示獲取當(dāng)前窗口的根ViewGroup（mDecor），然后往這個ViewGroup中添加view。

最終我們要展示在Activity中的View已經(jīng)構(gòu)造好了，那么在Activity的onResume 方法之后，在 ActivityThread#handleResumeActivity 方法中會將該View通過WindowManager添加在Activity所掛在的Window上進(jìn)行展現(xiàn)。

mDecor是什么可以參考博客：DecorView淺析

好了學(xué)習(xí)過程到此結(jié)束~！
下邊介紹在我學(xué)習(xí)過程中膜拜的博客，感覺這些大牛就是點(diǎn)亮我前行的燈塔，哈哈哈。
Android View的加載過程
 Android應(yīng)用setContentView與LayoutInflater加載解析機(jī)制源碼分析
 android的窗口機(jī)制分析------UI管理系統(tǒng)

文章到這里就全部講述完啦，若有其他需要交流的可以留言哦~！~！

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Activity中的Window的setContentView

Activity中的Window的setContentView

前言

Activity的onContentView

mWindow對象

PolicyManager獲取Window對象

PhoneWindow.setContentView

addView

installDecor

相關(guān)閱讀更多精彩內(nèi)容

友情鏈接更多精彩內(nèi)容

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Activity中的Window的setContentView

前言

Activity的onContentView

mWindow對象

PolicyManager獲取Window對象

PhoneWindow.setContentView

addView

installDecor

相關(guān)閱讀更多精彩內(nèi)容

友情鏈接更多精彩內(nèi)容

色偷偷精品伊人,欧洲久久精品,欧美综合婷婷骚逼,国产AV主播,国产最新探花在线,九色在线视频一区,伊人大交九欧美,1769亚洲,黄色成人av