Android5.0 Framework - Activity启动过程（一）

Android5.0 Framework - Activity启动过程（一）

标签（空格分隔）： Android Framework

1. 打开Activity

[code]startActivity(new Intent(MyActivity.this, OtherActivity.class));

2. 进入Activity源码分析

android.app.Activity

[code]    @Override
    //入口
    public void startActivity(Intent intent) {
        this.startActivity(intent, null);
    }

….省略代码…

[code]  @Override
    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.
            //-1表示不需要这个Actvity结束后的返回结果
            startActivityForResult(intent, -1);
        }
    }

….省略代码…

[code]
        public void startActivityForResult(Intent intent, int requestCode) {
        startActivityForResult(intent, requestCode, null);
    }

最终到

startActivityForResult(intent, requestCode, null);

方法处理

[code]  public void startActivityForResult(Intent intent, int requestCode, @Nullable Bundle options) {
        if (mParent == null) {
            //Activity启动执行交由Instrumentation对象去处理
            //ActivityThread mMainThread 是应用程序的主线程
            //Instrumentation mInstrumentation来监控应用程序和系统的交互
            //mToken也是Activity类的成员变量，它是一个Binder对象的远程接口
            Instrumentation.ActivityResult ar =
                mInstrumentation.execStartActivity(
                    this, mMainThread.getApplicationThread(), mToken, this,
                    intent, requestCode, options);
            if (ar != null) {
                //发送结果，即onActivityResult会被调用
                mMainThread.sendActivityResult(
                    mToken, mEmbeddedID, requestCode, ar.getResultCode(),
                    ar.getResultData());
            }
            if (requestCode >= 0) {
                mStartedActivity = true;
            }

            final View decor = mWindow != null ? mWindow.peekDecorView() : null;
            if (decor != null) {
                decor.cancelPendingInputEvents();
            }
            // TODO Consider clearing/flushing other event sources and events for child windows.
        } else {
            //在ActivityGroup内部的Activity调用startActivity的时候会走到这里，内部处理逻辑和上面是类似的
            if (options != null) {
                mParent.startActivityFromChild(this, intent, requestCode, options);
            } else {
                // Note we want to go through this method for compatibility with
                // existing applications that may have overridden it.
                mParent.startActivityFromChild(this, intent, requestCode);
            }
        }
        if (options != null && !isTopOfTask()) {
            mActivityTransitionState.startExitOutTransition(this, options);
        }
    }

主要参数说明:

mInstrumentation:Instrumentation用来辅助Activity完成启动Activity的过程

this:当前对象，也就是上下文

mMainThread.getApplicationThread():ActivityThread是主线程

mToken:是IBinder是远程接口,主要用于数据传输



那么Instrumentation到底如何启动Activity待续…