android activy加载

最新推荐文章于 2025-04-09 16:39:25 发布

smiky

最新推荐文章于 2025-04-09 16:39:25 发布

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分类专栏： android study note 文章标签：移动开发 java ui

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本文详细解析了Android中Looper的工作原理及其与Activity启动过程的关系。从主线程的初始化到Looper循环，再到Activity的创建和加载，揭示了Android应用运行背后的秘密。

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Looper这个东东很重要，线程之间的通信全靠它，Activity能运行起来也是因为它

下面是启动时的方法调用：

Instrumentation.callActivityOnCreate(Activity, Bundle) line: 1079	
ActivityThread.performLaunchActivity(ActivityThread$ActivityClientRecord, Intent) line: 2023	
ActivityThread.handleLaunchActivity(ActivityThread$ActivityClientRecord, Intent) line: 2084	
ActivityThread.access$600(ActivityThread, ActivityThread$ActivityClientRecord, Intent) line: 130	
ActivityThread$H.handleMessage(Message) line: 1195	
ActivityThread$H(Handler).dispatchMessage(Message) line: 99	
Looper.loop() line: 137	
ActivityThread.main(String[]) line: 4745

ThradActivity:

 public static void main(String[] args) {
        SamplingProfilerIntegration.start();

        // CloseGuard defaults to true and can be quite spammy.  We
        // disable it here, but selectively enable it later (via
        // StrictMode) on debug builds, but using DropBox, not logs.
        CloseGuard.setEnabled(false);

        Process.setArgV0("<pre-initialized>");

        Looper.prepareMainLooper();
        if (sMainThreadHandler == null) {
            sMainThreadHandler = new Handler();
        }
	//这里的线程应该就是所谓的UI线程，每个线程有自己的Looper, 用Handler的sendMessage可以向Looper的
//消息队列加消息，Handler在初始化里会找到当前的线程并加与之对应的Looper的消息队列取到，
//这样其它线程就可以给它发送消息，而Looper里面的loop方法会不停的执行处理消息，这样来处理线程之间的通信

        ActivityThread thread = new ActivityThread();
        thread.attach(false);//这里完成部分初始化

        AsyncTask.init();

        if (false) {
            Looper.myLooper().setMessageLogging(new
                    LogPrinter(Log.DEBUG, "ActivityThread"));
        }

        Looper.loop();//这是个死循环，它里面有个消息队列，它不停的遍历并处理消息,它会触发主Activity的加载

        throw new RuntimeException("Main thread loop unexpectedly exited");
    }

public void handleMessage(Message msg) {
            if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));
            switch (msg.what) {
                case LAUNCH_ACTIVITY: {
                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
                    ActivityClientRecord r = (ActivityClientRecord)msg.obj;

                    r.packageInfo = getPackageInfoNoCheck(
                            r.activityInfo.applicationInfo, r.compatInfo);
                    handleLaunchActivity(r, null);//处理启动Activity
                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
                } break;

performLaunchActivity会完成Activity的加载

 Activity activity = null;
        try {
            java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
//加载Activity
            activity = mInstrumentation.newActivity(
                    cl, component.getClassName(), r.intent);
            StrictMode.incrementExpectedActivityCount(activity.getClass());
            r.intent.setExtrasClassLoader(cl);
            if (r.state != null) {
                r.state.setClassLoader(cl);
            }
        } 


attach方法会完成Activity主窗口的创建
activity.attach(appContext, this, getInstrumentation(), r.token,
                        r.ident, app, r.intent, r.activityInfo, title, r.parent,
                        r.embeddedID, r.lastNonConfigurationInstances, config);

activity.mCalled = false;
                mInstrumentation.callActivityOnCreate(activity, r.state);会触发Activity的onCreate事件

Activity:

 mWindow = PolicyManager.makeNewWindow(this);

View之类的组件是在setContentView时才开始绘的

下面以PhoneWindow为例：

  public void setContentView(View view, ViewGroup.LayoutParams params) {
        if (mContentParent == null) {
            installDecor();//这里才是用于显示的窗，decor它是一个FrameLayout,可以看下里面的chrild
        } else {
            mContentParent.removeAllViews();
        }
        mContentParent.addView(view, params);
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            cb.onContentChanged();
        }
    }