android.intent.action.MAIN和singleTask模式一起使用导致每次进入应用都会进入该Activity

亦凉 2023-10-16 22:43 7阅读 0赞

如果将android.intent.action.MAIN和singleTask模式一起使用，会导致无论在该应用的哪么Activity 按下返回键退出或按下Home键，然后在进入该应用，都会进入入口Activity(设为action android:name="android.intent.action.MAIN"和category android:name="android.intent.category.LAUNCHER"和android:launchMode="singleTask"的那个Activity)，具体原因在这片文章中找到 [链接地址][Link 1]

在Android设计中遇到这样一个问题：

Activity A，在AndroidManifest.xml中设置它的一个<inter-filter>为

Java代码 [![收藏代码][19180430_1HZ9.png]][19180430_1HZ9.png]

[?][Link 2]

<table style="width:687px; padding:0px!important; margin:0px!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; font-size:1em!important; min-height:inherit!important; background:none!important"> 
 <tbody style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; background:none!important"> 
  <tr style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; background:none!important"> 
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      1 
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      2 
    </div> 
    <div style="padding:0px 0.5em 0px 1em!important; margin:0px!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important">
      3 
    </div> 
    <div style="padding:0px 0.5em 0px 1em!important; margin:0px!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important">
      4 
    </div> </td> 
   <td style="width:658px; padding:0px!important; margin:0px!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; font-size:1em!important; min-height:inherit!important; background:none!important"> 
    <div style="padding:0px!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:relative!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; background:none!important"> 
     <div style="padding:0px 1em!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important"> 
      <code style="padding:0px!important; margin:0px!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; background:none!important">&lt;intent-filter&gt;&nbsp;&nbsp;</code> 
     </div> 
     <div style="padding:0px 1em!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important"> 
      <code style="color:red; padding:0px!important; margin:0px!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; background:none!important">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="padding:0px!important; margin:0px!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; background:none!important">&lt;action&nbsp;android:name=</code> 
      <code style="padding:0px!important; margin:0px!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; color:blue!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; background:none!important">"android.intent.action.MAIN"</code>&nbsp; 
      <code style="padding:0px!important; margin:0px!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; background:none!important">/&gt;&nbsp;&nbsp;</code> 
     </div> 
     <div style="padding:0px 1em!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important"> 
      <code style="color:red; padding:0px!important; margin:0px!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; background:none!important">&nbsp;</code> 
      <code style="padding:0px!important; margin:0px!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; background:none!important">&lt;category&nbsp;android:name=</code> 
      <code style="padding:0px!important; margin:0px!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; color:blue!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; background:none!important">"android.intent.category.LAUNCHER"</code>&nbsp; 
      <code style="padding:0px!important; margin:0px!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; background:none!important">/&gt;&nbsp;&nbsp;</code> 
     </div> 
     <div style="padding:0px 1em!important; margin:0px!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important"> 
      <code style="padding:0px!important; margin:0px!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; background:none!important">&lt;/intent-filter&gt;</code> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

A的launchMode为“singleTask”。

Activity B，设置launchMode为“standard”。

这样，A作为启动应用的入口Activity；在A中进行某个操作可以跳转到B。

如果此时，点击‘Home’键返回到Home Screen后，再次点击应用图标进入应用，出现的界面为A，而非B。通过一些测试，发现，在重新进入应用时，在Back stack中，位于A之上的其他Activity均被销毁了。

开发的时候，由于用到了singleTask用法不当，造成了一些不必要的麻烦，现总结如下：

现有Activity：A,B,C,D;启动顺序是A->B->C->D,其中，B是singleTask的。

A到B后，A finish掉；B到C后，B不finish；C到D后，C不finish；在D启动B，就可以一下子将C、D kill掉，只保留B。但是，

这个时候你从B退出(整个程序退出了)，长按Home键启动，进来的第一个是B，而不是A，这就已经不对了; 而且， 刚才就算你不退出，从B再进到C，按Home，再长按Home进入，回来的是B而不是C。

解决方案如下：

将singleTask改成singleTop。

这样以来，刚才从D启动B的时候，就要用intent.setFlags(Intent.FLAG\_ACTIVITY\_CLEAR\_TOP);

也就是说，singleTask会自动执行clear top, 而singleTop需要手动；而从Home键启动，如果是singleTask的话就自动clear top了，所以到不了想要到的Activity。

这样就解决了问题，但是上面的说法是个人的理解。

至此，我们总结一下，设置了"singleTask"启动模式的Activity的特点：

1. 设置了"singleTask"启动模式的Activity，它在启动的时候，会先在系统中查找属性值affinity等于它的属性值 taskAffinity的任务存在；如果存在这样的任务，它就会在这个任务中启动，否则就会在新任务中启动。因此，如果我们想要设置 了"singleTask"启动模式的Activity在新的任务中启动，就要为它设置一个独立的taskAffinity属性值。

2. 如果设置了"singleTask"启动模式的Activity不是在新的任务中启动时，它会在已有的任务中查看是否已经存在相应的Activity实 例，如果存在，就会把位于这个Activity实例上面的Activity全部结束掉，即最终这个Activity实例会位于任务的堆栈顶端中。

[Link 1]: http://my.oschina.net/u/242041/blog/209748
[19180430_1HZ9.png]: http://static.oschina.net/uploads/img/201403/19180430_1HZ9.png
[Link 2]: http://my.oschina.net/u/242041/blog/209748#