Android Activity的启动过程.doc

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){(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(Intentintent,***@NullableBundleoptions){if(options!=null){startActivityForResult(intent,-1,options);}else{//patibilitywith//(intent,-1);}}不管怎样,都会调用startActivityForResult方法。并将intent传进。publicvoidstartActivityForResult(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){=(this,(),mToken,this,intent,requestCode,options);if(ar!=null){(mToken,mEmbeddedID,requestCode,(),());}if(requestCode>=0){//Ifthisstartisrequestingaresult,wecanavoidmaking////thiscodeduringonCreate(BundlesavedInstanceState)oronResume()willkeepthe//activityhiddenduringthistime,toavoidflickering.//Thiscanonlybedonewhenaresultisrequestedbecause//thatguaranteeswewillgetinformationbackwhenthe//activityisfinished,=true;}cancelInputsAndStartExitTransition(options);//TODOConsiderclearing/flushingothereventsourcesandeventsforchildwindows.}else{if(options!=null){(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:/**Isthisactivityembeddedinsideofanotheractivity?*/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==null的情况即可。可以看到内部调用了Instrumentation的execStartActivity方法,从字