Activity的启动流程(基于Android 10.0源码)

Activity的启动一般分为普通Activity的启动,根Activity的启动.而根Activity是指应用启动的第一个Activity过程,所以也可以理解为应用的启动过程.

相关内容链接：android系统启动流程

Activity的启动过程(应用的启动流程)

应用的启动流程大致分为如下四个阶段:

一.应用进程(Launcher)调用ATMS系统进程的过程

二.ActivityTaskManagerService到ApplicationThread的调用过程

三.AMS向Zygote发送启动应用进程的过程

四.ActivityThread启动Activity的过程

Activity启动过程涉及到进程之间的关系:

一.应用进程(Launcher)调用ATMS系统进程的过程

启动Activity时,无论是点击桌面图标还是自己写的startActivity,都是调用Activity的startActivity方法,而该方法内部又会调用startActivityForResult具体如下:

    // android-29\android\app\Activity.java
    public void startActivity(Intent intent, @Nullable Bundle options) {
        if (options != null) {
            startActivityForResult(intent, -1, options);
        } else {
            // Note we want to go through this call for compatibility with
            // applications that may have overridden the method.
            startActivityForResult(intent, -1);
        }
    }

源码调用如下:

类名: android.app.Activity:

1. startActivity(Intent)

2. startActivity(Intent, Bundle)

3. startActivityForResult(Intent, int, Bundle)

类名: android.app.Instrumentation:

Instrumentation主要用来监控应用程序和系统的交互

4. execStartActivity(android.content.Context, android.os.IBinder, android.os.IBinder, android.app.Activity, android.content.Intent, int, android.os.Bundle)

注释1的getService方法调用了IActivityTaskManagerSingleton的get方法,而它是一个Singleton类,在重写的create方法中获取Context.ACTIVITY_TASK_SERVICE的IBinder引用,然后转换成IActivityTaskManager类型的对象.这段代码是AIDL的写法,IActivityTaskManager类是AIDL工具在编译时自动生成,IActivityTaskManager文件的路径为framework/base/core/java/android/app/IActivityTaskManager.aidl. 要实现进程间通信,服务端也就是ActivityTaskManagerService只需要继承IActivityTaskManager.Stub类并实现相应的方法就可以了(在Android7.0使用的是ActivityManagerProxy代理模式来实现的Binder通信)

// android-29\android/app/Instrumentation.java
    public ActivityResult execStartActivity(
        Context who, IBinder contextThread, IBinder token, String target,
        Intent intent, int requestCode, Bundle options) {
        // ... ...
        try {
            intent.migrateExtraStreamToClipData();
            intent.prepareToLeaveProcess(who);
            int result = ActivityTaskManager.getService()   // 注释1
                .startActivity(whoThread, who.getBasePackageName(), intent,
                        intent.resolveTypeIfNeeded(who.getContentResolver()),
                        token, target, requestCode, 0, null, options);
            checkStartActivityResult(result, intent);
        } catch (RemoteException e) {
            throw new RuntimeException("Failure from system", e);
        }
        return null;
    }

    // android-29\android\app\ActivityTaskManager.java
    /** @hide */
    public static IActivityTaskManager getService() {
        return IActivityTaskManagerSingleton.get();
    }

    @UnsupportedAppUsage(trackingBug = 129726065)
    private static final Singleton IActivityTaskManagerSingleton =
            new Singleton() {
                @Override
                protected IActivityTaskManager create() {
                    final IBinder b = ServiceManager.getService(Context.ACTIVITY_TASK_SERVICE);
                    return IActivityTaskManager.Stub.asInterface(b);
                }
            };
            
    // android-29\android\content\Context.java  
    /**
     * Use with {@link #getSystemService(String)} to retrieve a
     * {@link android.app.ActivityTaskManager} for interacting with the global system state.
     *
     * @see #getSystemService(String)
     * @see android.app.ActivityTaskManager
     * @hide
     */
    public static final String ACTIVITY_TASK_SERVICE = "activity_task";