FLAG_ACTIVITY_SINGLE_TOP :如果当前栈顶的activity就是要启动的activity,则不会再启动一个新的activity

实例：

我们有一个apk，apk中包含两个Activity:MainActivity和ActivityA，点击MainActivity启动ActivityA,点击ActivityA还是启动ActivityA，但我们设置FLAG_ACTIVITY_SINGLE_TOP标记：

[java] view plain copy
print?

    public void onClick(View v) {  
        // TODO Auto-generated method stub  
        Log.i(TAG, "--onClick--task id = " + getCurrentTaskId());     
          
        Intent intent = new Intent("com.leaves.ipanel.ActivityA");    
        //intent.setFlags( Intent.FLAG_ACTIVITY_NEW_TASK);  
        intent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);  
        startActivity(intent);   
    }  
         

启动动ActivityA，随便我们怎么再点击，都只有一个ActivityA实例，堆栈：

[plain] view plain copy
print?

    ACTIVITY MANAGER ACTIVITIES (dumpsys activity activities)  
      Main stack:  
        TaskRecord{438f1ed8 #9 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 #2: ActivityRecord{4265b1b0 u0 com.leaves.ipanel/.ActivityA}  
            Intent { act=com.leaves.ipanel.ActivityA flg=0x20000000 cmp=com.leaves.ipanel/.ActivityA }  
            ProcessRecord{4292a550 2115:com.leaves.ipanel/u0a10061}  
          Hist #1: ActivityRecord{42485758 u0 com.leaves.ipanel/.MainActivity}  
            Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.leaves.ipanel/.MainActivity }  
            ProcessRecord{4292a550 2115:com.leaves.ipanel/u0a10061}  
        TaskRecord{426f4820 #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{4291c7b0 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{4267f0b8 636:com.android.launcher/1000}