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1、AndroidActivity的启动过程Activity的启动过程真的很复杂，先看一张图大概了解一下，其中用灰色背景框起来的是在同一个类的方法，如下图：那接下来就从源码的角度来分析Activity的启动过程。当然是从Activity的startActivity方法开始的，@OverridepublicvoidstartActivity(Intentintent){this.startActivity(intent,null);}使用this关键字调用了startActivity方法的两个参数的重载。如下：@OverridepublicvoidstartActivity(Intentin
2、tent,@NullableBundleoptions){if(options!=null){startActivityForResult(intent,-1,options);}else{//Notewewanttogothroughthiscallforcompatibilitywith//applicationsthatmayhaveoverriddenthemethod.startActivityForResult(intent,-1);}}不管怎样，都会调用startActivityForResult方法。并将intent传进。publicvoidstartActivityF
3、orResult(Intentintent,intrequestCode){startActivityForResult(intent,requestCode,null);}转到了startActivityForResult三个参数的重载方法，那就跟进瞧瞧，源码如下：publicvoidstartActivityForResult(Intentintent,intrequestCode,@NullableBundleoptions){if(mParent==null){Instrumentation.ActivityResultar=mInstrumentation.execStart
4、Activity(this,mMainThread.getApplicationThread(),mToken,this,intent,requestCode,options);if(ar!=null){mMainThread.sendActivityResult(mToken,mEmbeddedID,requestCode,ar.getResultCode(),ar.getResultData());}if(requestCode>=0){//Ifthisstartisrequestingaresult,wecanavoidmaking//theactivityvisibleunti
5、ltheresultisreceived.Setting//thiscodeduringonCreate(BundlesavedInstanceState)oronResume()willkeepthe//activityhiddenduringthistime,toavoidflickering.//Thiscanonlybedonewhenaresultisrequestedbecause//thatguaranteeswewillgetinformationbackwhenthe//activityisfinished,nomatterwhathappenstoit.mStart
6、edActivity=true;}cancelInputsAndStartExitTransition(options);//TODOConsiderclearing/flushingothereventsourcesandeventsforchildwindows.}else{if(options!=null){mParent.startActivityFromChild(this,intent,requestCode,options);}else{//代码省略}}}先是判断mParent是否为空。那么mParent是什么呢？Activity中有一个isChild方法如下：/**Is
7、thisactivityembeddedinsideofanotheractivity?*/publicfinalbooleanisChild(){returnmParent!=null;}从注释中可以知道mParent是一个ActivityGroup来的，可以嵌入子Activity的，这个我没用过。在我刚学Android的时候Fragment已经很流行了。那我们回到startActivityForResult方法直接看到mParent==nu
