【希望大家分享一下对这两个flag的用法、谢谢】
先看一下这两个的官方解释
一、FLAG_ACTIVITY_SINGLE_TOP
/**
* If set, the activity will not be launched if it is already running
* at the top of the history stack.
*/
public static final int FLAG_ACTIVITY_SINGLE_TOP = 0x20000000;
个人理解为：
startActivity如果设置flag为 FLAG_ACTIVITY_SINGLE_TOP
当目标activity在stack的顶部的时候 不会重新被创建
二、FLAG_ACTIVITY_CLEAR_TOP
看官方解释
如果设置了FLAG_ACTIVITY_CLEAR_TOP 并且。目标Activity已经在当前的task中启动。那么不会launch一个新的Activity实例。
同时目标Activity之上的所有Activity将会被destroy 并且目标Activity会接受一个新的intent
？？？？？？？？？？？？？可是用过之后感觉我理解错了。。。。
/**
* If set, and the activity being launched is already running in the
* current task, then instead of launching a new instance of that activity,
* all of the other activities on top of it will be closed and this Intent
* will be delivered to the (now on top) old activity as a new Intent.
*
* <p>For example, consider a task consisting of the activities: A, B, C, D.
* If D calls startActivity() with an Intent that resolves to the component
* of activity B, then C and D will be finished and B receive the given
* Intent, resulting in the stack now being: A, B.
*
* <p>The currently running instance of activity B in the above example will
* either receive the new intent you are starting here in its
* onNewIntent() method, or be itself finished and restarted with the
* new intent. If it has declared its launch mode to be "multiple" (the
* default) and you have not set {@link #FLAG_ACTIVITY_SINGLE_TOP} in
* the same intent, then it will be finished and re-created; for all other
* launch modes or if {@link #FLAG_ACTIVITY_SINGLE_TOP} is set then this
* Intent will be delivered to the current instance's onNewIntent().
*
* <p>This launch mode can also be used to good effect in conjunction with
* {@link #FLAG_ACTIVITY_NEW_TASK}: if used to start the root activity
* of a task, it will bring any currently running instance of that task
* to the foreground, and then clear it to its root state. This is
* especially useful, for example, when launching an activity from the
* notification manager.
*
* <p>See
* <a href="{@docRoot}guide/topics/fundamentals/tasks-and-back-stack.html">Tasks and Back
* Stack</a> for more information about tasks.
*/
public static final int FLAG_ACTIVITY_CLEAR_TOP = 0x04000000;
假设三个Activity A B C
如果A启动B B启动C。此时 task中的顺序 ABC 栈顶是C
如果在后台一个Service中启动B
Intent intent = new Intent(); intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK); //intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); intent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP); intent.setClass(BeatService.this, Activity_B.class); startActivity(intent);
我最开始的理解是 task中 由 ABC 变成 ACB
但是调试发现 此时重新创建了一个B
task中变成 ABCB
如果此时在service中再次启动B 则不会重新创建，仅仅执行onResume
11-03 14:44:52.410: D/activity(26579): onCreate Activity_A 11-03 14:44:52.410: D/activity(26579): onResume Activity_A 11-03 14:44:53.490: D/activity(26579): onCreate Activity_B 11-03 14:44:53.490: D/activity(26579): onResume Activity_B 11-03 14:44:53.760: D/activity(26579): onStop Activity_A 11-03 14:44:54.350: D/activity(26579): onCreate Activity_C 11-03 14:44:54.350: D/activity(26579): onResume Activity_C 11-03 14:44:54.630: D/activity(26579): onStop Activity_B 11-03 14:44:56.050: D/activity(26579): onCreate Activity_B /// 在service中启动B 11-03 14:44:56.050: D/activity(26579): onResume Activity_B 11-03 14:44:56.330: D/activity(26579): onStop Activity_C 11-03 14:44:58.540: D/activity(26579): onResume Activity_B // B在栈顶，此时仅仅执行onResume
二、FLAG_ACTIVITY_CLEAR_TOP 启动模式
假设task中三个activity ABC
此时后台Service中启动B。代码如下
Intent intent = new Intent(); intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK); intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); //intent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP); intent.setClass(BeatService.this, Activity_B.class); startActivity(intent);
task中activity的变化为 ABC -- 销毁B 创建B 销毁C
此时task中剩下AB 如果再次启动B
则会创建B 销毁B 此时task中还是AB
两种情况B的创建、销毁顺序是不一样的。
11-03 14:47:47.430: D/activity(27722): onCreate Activity_A //启动A 11-03 14:47:47.430: D/activity(27722): onResume Activity_A 11-03 14:47:51.190: D/activity(27722): onCreate Activity_B //A中启动B 11-03 14:47:51.200: D/activity(27722): onResume Activity_B 11-03 14:47:51.460: D/activity(27722): onStop Activity_A 11-03 14:47:52.040: D/activity(27722): onCreate Activity_C //B中启动C 11-03 14:47:52.040: D/activity(27722): onResume Activity_C 11-03 14:47:52.500: D/activity(27722): onStop Activity_B 11-03 14:47:54.630: D/activity(27722): onDestroy Activity_B // Service中启动B 11-03 14:47:54.680: D/activity(27722): onCreate Activity_B 11-03 14:47:54.680: D/activity(27722): onResume Activity_B 11-03 14:47:55.040: D/activity(27722): onStop Activity_C 11-03 14:47:55.040: D/activity(27722): onDestroy Activity_C // Service中启动B 结束 11-03 14:47:57.650: D/activity(27722): onCreate Activity_B //service中再次启动B 11-03 14:47:57.650: D/activity(27722): onResume Activity_B 11-03 14:47:57.920: D/activity(27722): onStop Activity_B 11-03 14:47:57.920: D/activity(27722): onDestroy Activity_B
demo的代码上传在
https://github.com/droidcoffee/yolanda/tree/master/yolanda_Android