Android之 FLAG_ACTIVITY_CLEAR_TASK

FLAG_ACTIVITY_CLEAR_TASK :如果在调用Context.startActivity时传递这个标记，将会导致任何用来放置该activity的已经存在的task里面的已经存在

的activity先清空，然后该activity再在该task中启动，也就是说，这个新启动的activity变为了这个空tas的根activity.所有老的activity都结束掉。

该标志必须和FLAG_ACTIVITY_NEW_TASK一起使用。

示例：

我们有三个activity:MainActivity、ActivityA、ActivityB. 依次从MainActivity中启动ActivityA，从ActivityA中启动ActivityB.

首先我们所有的都使用缺省的，也即没有设置taskAffinity、launchMode，启动activity时Intent也不带标记，我们看一下启动B之后的堆栈：

  

   

    

     

    
    

     

      ACTIVITY MANAGER ACTIVITIES (dumpsys activity activities) 
     
    
   

    

     

    
    

     

        Main stack: 
     
    
   

    

     

    
    

     

       TaskRecord{4199dd68 #56 A com.leaves.ipanel U 0} 
     
    
   

    

     

    
    

     

       Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.leaves.ipanel/.MainActivity } 
     
    
   

    

     

    
    

     

       Hist #3: ActivityRecord{4140fdf8 u0 com.leaves.ipanel/.ActivityB} 
     
    
   

    

     

    
    

     

       Intent { act=com.leaves.ipanel.ActivityB cmp=com.leaves.ipanel/.ActivityB } 
     
    
   

    

     

    
    

     

       ProcessRecord{41517e80 13350:com.leaves.ipanel/u0a10061} 
     
    
   

    

     

    
    

     

       Hist #2: ActivityRecord{413ff7e8 u0 com.leaves.ipanel/.ActivityA} 
     
    
   

    

     

    
    

     

       Intent { act=com.leaves.ipanel.ActivityA cmp=com.leaves.ipanel/.ActivityA } 
     
    
   

    

     

    
    

     

       ProcessRecord{41517e80 13350:com.leaves.ipanel/u0a10061} 
     
    
   

    

     

    
    

     

       Hist #1: ActivityRecord{413f8b28 u0 com.leaves.ipanel/.MainActivity} 
     
    
   

    

     

    
    

     

       Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.leaves.ipanel/.MainActivity } 
     
    
   

    

     

    
    

     

       ProcessRecord{41517e80 13350:com.leaves.ipanel/u0a10061} 
     
    
   

    

     

    
    

     

       TaskRecord{41350f60 #2 A com.android.launcher U 0} 
     
    
   

    

     

    
    

     

       Intent { act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10600000 cmp=com.android.launcher/com.android.launcher2.Launcher } 
     
    
   

    

     

    
    

     

       Hist #0: ActivityRecord{41616790 u0 com.android.launcher/com.android.launcher2.Launcher} 
     
    
   

    

     

    
    

     

       Intent { act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10000000 cmp=com.android.launcher/com.android.launcher2.Launcher } 
     
    
   

    

     

    
    

     

       ProcessRecord{41615818 628:com.android.launcher/1000}   
     
    
  
 

接下来我们在启动ActivityB时添加FLAG_ACTIVITY_CLEAR_TASK和FLAG_ACTIVITY_NEW_TASK

  

   

    

     

    
    

     

      public void onClick(View v) { 
     
    
   

    

     

    
    

     

       // TODO Auto-generated method stub 
     
    
   

    

     

    
    

     

       Log.i(TAG, "--onClick--task id = " + getCurrentTaskId()); 
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

       Intent intent = new Intent("com.leaves.ipanel.ActivityB"); 
     
    
   

    

     

    
    

     

       intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK); 
     
    
   

    

     

    
    

     

       startActivity(intent); 
     
    
   

    

     

    
    

     

      }  
     
    
  
 

  

   

    

     

    
    

     

       ACTIVITY MANAGER ACTIVITIES (dumpsys activity activities) 
     
    
   

    

     

    
    

     

       Main stack: 
     
    
   

    

     

    
    

     

       TaskRecord{4245bd10 #57 A com.leaves.ipanel U 0} 
     
    
   

    

     

    
    

     

       Intent { act=com.leaves.ipanel.ActivityB flg=0x10008000 cmp=com.leaves.ipanel/.ActivityB } 
     
    
   

    

     

    
    

     

       Hist #1: ActivityRecord{413f8b28 u0 com.leaves.ipanel/.ActivityB} 
     
    
   

    

     

    
    

     

       Intent { act=com.leaves.ipanel.ActivityB flg=0x10008000 cmp=com.leaves.ipanel/.ActivityB } 
     
    
   

    

     

    
    

     

       ProcessRecord{41413010 13441:com.leaves.ipanel/u0a10061} 
     
    
   

    

     

    
    

     

       TaskRecord{41350f60 #2 A com.android.launcher U 0} 
     
    
   

    

     

    
    

     

       Intent { act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10600000 cmp=com.android.launcher/com.android.launcher2.Launcher } 
     
    
   

    

     

    
    

     

       Hist #0: ActivityRecord{41616790 u0 com.android.launcher/com.android.launcher2.Launcher} 
     
    
   

    

     

    
    

     

       Intent { act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10000000 cmp=com.android.launcher/com.android.launcher2.Launcher } 
     
    
   

    

     

    
    

     

       ProcessRecord{41615818 628:com.android.launcher/1000} 
     
    
  
 

文章来源: chenyu.blog.csdn.net，作者：chen.yu，版权归原作者所有，如需转载，请联系作者。

原文链接：chenyu.blog.csdn.net/article/details/51786525