Android关于Task的一些实践之SingleTask, SingleInstance和TaskAffinity
上一篇文章粗略地介绍了一下关于Android中Task的基本知识，不过实践才是检验真理的唯一标准，所以，今天就来试验一下Task中的launchMode是否真的实现了文档所说的那样。
首先，定义三个Activity，MainActivity打开SecondActivity，SecondActivity打开ThirdActivity，如下所示：
下面，我们定义Second Activity的Launch Mode，分别有下面几种情况：
1）Standard（即不定义）
首先是默认情况下，什么都不定义，如下：
04-21 15:23:28.373: V/com.lms.taskdemo(20473): Task : 70
04-21 15:23:28.373: V/com.lms.taskdemo(20473): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-21 15:23:28.373: V/com.lms.taskdemo(20473): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-21 15:23:28.373: V/com.lms.taskdemo(20473): Number of activities : 1
04-21 15:23:28.373: V/com.lms.taskdemo(20473): Number of running activities: 1
04-21 15:23:31.336: V/com.lms.taskdemo(20473): Task : 70
04-21 15:23:31.336: V/com.lms.taskdemo(20473): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-21 15:23:31.336: V/com.lms.taskdemo(20473): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.SecondActivity}
04-21 15:23:31.336: V/com.lms.taskdemo(20473): Number of activities : 2
04-21 15:23:31.336: V/com.lms.taskdemo(20473): Number of running activities: 2
04-21 15:23:33.999: V/com.lms.taskdemo(20473): Task : 70
04-21 15:23:33.999: V/com.lms.taskdemo(20473): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-21 15:23:33.999: V/com.lms.taskdemo(20473): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.ThirdActivity}
04-21 15:23:33.999: V/com.lms.taskdemo(20473): Number of activities : 3
04-21 15:23:33.999: V/com.lms.taskdemo(20473): Number of running activities: 3可以看到三个Activity，都是在同个Task中的。
2）SingleTask
为Second Activity，定义其launch mode 为 “singleTask”，如下：
再来看看其结果，如下：
04-22 10:31:26.197: V/com.lms.taskdemo(924): Task : 162
04-22 10:31:26.217: V/com.lms.taskdemo(924): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-22 10:31:26.217: V/com.lms.taskdemo(924): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-22 10:31:26.217: V/com.lms.taskdemo(924): Number of activities : 1
04-22 10:31:26.217: V/com.lms.taskdemo(924): Number of running activities: 1
04-22 10:31:31.112: V/com.lms.taskdemo(924): Task : 162
04-22 10:31:31.112: V/com.lms.taskdemo(924): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-22 10:31:31.112: V/com.lms.taskdemo(924): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.SecondActivity}
04-22 10:31:31.112: V/com.lms.taskdemo(924): Number of activities : 2
04-22 10:31:31.112: V/com.lms.taskdemo(924): Number of running activities: 2
04-22 10:31:32.884: V/com.lms.taskdemo(924): Task : 162
04-22 10:31:32.884: V/com.lms.taskdemo(924): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-22 10:31:32.884: V/com.lms.taskdemo(924): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.ThirdActivity}
04-22 10:31:32.884: V/com.lms.taskdemo(924): Number of activities : 3
04-22 10:31:32.884: V/com.lms.taskdemo(924): Number of running activities: 2发现虽然定义了SingleTask，但Second Activity和Main Activity还是在同一个Task中，这跟我们期望的不符，原因其实在于，设置了launchMode = SingleTask启动的Activity，在启动的时候，会去查找跟它的taskAffinity相同的task，如果存在这样一个task，就在这个task中启动，如果不存在这样一个task，才创建一个新的task，并在新task中启动。
而在这里，因为没有为各个activity定义taskAffinity，那么默认的affinity值就是包名，那么几个Activity都是一样的，所以就在同样的Task中启动了。
3）Single Task Different Task Affinity
下面，我们分别为Main Activity和 Second Activity设置不同的TaskAffinity值，如下：
下面是结果，启动的顺序是Main Activity->Second Activity->Main Activity -> Second Activity -> Third Activity
04-22 10:26:27.818: V/com.lms.taskdemo(32677): Task : 151
04-22 10:26:27.818: V/com.lms.taskdemo(32677): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-22 10:26:27.818: V/com.lms.taskdemo(32677): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-22 10:26:27.818: V/com.lms.taskdemo(32677): Number of activities : 1
04-22 10:26:27.818: V/com.lms.taskdemo(32677): Number of running activities: 1
04-22 10:26:31.362: V/com.lms.taskdemo(32677): Task : 152
04-22 10:26:31.362: V/com.lms.taskdemo(32677): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.SecondActivity}
04-22 10:26:31.362: V/com.lms.taskdemo(32677): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.SecondActivity}
04-22 10:26:31.372: V/com.lms.taskdemo(32677): Number of activities : 1
04-22 10:26:31.372: V/com.lms.taskdemo(32677): Number of running activities: 1
04-22 10:26:36.558: V/com.lms.taskdemo(32677): Task : 151
04-22 10:26:36.558: V/com.lms.taskdemo(32677): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-22 10:26:36.558: V/com.lms.taskdemo(32677): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-22 10:26:36.558: V/com.lms.taskdemo(32677): Number of activities : 1
04-22 10:26:36.558: V/com.lms.taskdemo(32677): Number of running activities: 1
04-22 10:26:39.401: V/com.lms.taskdemo(32677): Task : 153
04-22 10:26:39.401: V/com.lms.taskdemo(32677): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.SecondActivity}
04-22 10:26:39.401: V/com.lms.taskdemo(32677): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.SecondActivity}
04-22 10:26:39.401: V/com.lms.taskdemo(32677): Number of activities : 1
04-22 10:26:39.401: V/com.lms.taskdemo(32677): Number of running activities: 1
04-22 10:26:41.123: V/com.lms.taskdemo(32677): Task : 153
04-22 10:26:41.123: V/com.lms.taskdemo(32677): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.SecondActivity}
04-22 10:26:41.123: V/com.lms.taskdemo(32677): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.ThirdActivity}
04-22 10:26:41.123: V/com.lms.taskdemo(32677): Number of activities : 2
04-22 10:26:41.123: V/com.lms.taskdemo(32677): Number of running activities: 2在上面的结果中，可以看到在启动Second Activity的时候，的确是在一个新的Task中启动了，Second Activity是这个Task中的根Activity，而由Second Activity启动的Third Activity也是在这个Task中启动的。
4）Single Instance
下面，我们再来看看Single Instance，同样的，先不定义Task Affinity，在AndroidManifest文件中定义如下：
04-22 10:29:43.207: V/com.lms.taskdemo(682): Task : 159
04-22 10:29:43.207: V/com.lms.taskdemo(682): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-22 10:29:43.207: V/com.lms.taskdemo(682): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-22 10:29:43.207: V/com.lms.taskdemo(682): Number of activities : 1
04-22 10:29:43.207: V/com.lms.taskdemo(682): Number of running activities: 1
04-22 10:29:46.580: V/com.lms.taskdemo(682): Task : 160
04-22 10:29:46.580: V/com.lms.taskdemo(682): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.SecondActivity}
04-22 10:29:46.580: V/com.lms.taskdemo(682): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.SecondActivity}
04-22 10:29:46.580: V/com.lms.taskdemo(682): Number of activities : 1
04-22 10:29:46.580: V/com.lms.taskdemo(682): Number of running activities: 1
04-22 10:29:48.202: V/com.lms.taskdemo(682): Task : 159
04-22 10:29:48.202: V/com.lms.taskdemo(682): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-22 10:29:48.202: V/com.lms.taskdemo(682): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.ThirdActivity}
04-22 10:29:48.202: V/com.lms.taskdemo(682): Number of activities : 2
04-22 10:29:48.202: V/com.lms.taskdemo(682): Number of running activities: 1
04-22 10:29:57.112: V/com.lms.taskdemo(682): Task : 160
04-22 10:29:57.112: V/com.lms.taskdemo(682): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.SecondActivity}
04-22 10:29:57.112: V/com.lms.taskdemo(682): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.SecondActivity}
04-22 10:29:57.112: V/com.lms.taskdemo(682): Number of activities : 1
04-22 10:29:57.112: V/com.lms.taskdemo(682): Number of running activities: 15）Single Instance Different Affinity
在配置文件中定义如下：
下面来看看结果，如下：
04-22 10:27:58.866: V/com.lms.taskdemo(391): Task : 155
04-22 10:27:58.866: V/com.lms.taskdemo(391): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-22 10:27:58.866: V/com.lms.taskdemo(391): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.MainActivity}
04-22 10:27:58.866: V/com.lms.taskdemo(391): Number of activities : 1
04-22 10:27:58.866: V/com.lms.taskdemo(391): Number of running activities: 1
04-22 10:28:00.677: V/com.lms.taskdemo(391): Task : 156
04-22 10:28:00.677: V/com.lms.taskdemo(391): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.SecondActivity}
04-22 10:28:00.677: V/com.lms.taskdemo(391): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.SecondActivity}
04-22 10:28:00.677: V/com.lms.taskdemo(391): Number of activities : 1
04-22 10:28:00.677: V/com.lms.taskdemo(391): Number of running activities: 1
04-22 10:28:02.309: V/com.lms.taskdemo(391): Task : 157
04-22 10:28:02.309: V/com.lms.taskdemo(391): Base activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.ThirdActivity}
04-22 10:28:02.309: V/com.lms.taskdemo(391): Current activity : ComponentInfo{com.lms.taskdemo/com.lms.taskdemo.ThirdActivity}
04-22 10:28:02.309: V/com.lms.taskdemo(391): Number of activities : 1
04-22 10:28:02.309: V/com.lms.taskdemo(391): Number of running activities: 1果然，如我们期望的那样，都是在一个新的Task中启动当前的Activity的。
总结：
当使用Launch Mode 来改变系统默认的任务调度的时候，如果是用到Single Task或者Single Instance的时候，还要注意到Affinity的使用，要跟Affinity配合使用，可能才能达到我们期望中的效果。而Affinity，其实是Android提供的一个表从属意义的参数，类似于一个Tag值，它表明当前Activity属于哪一个Tag，相当的Affinity值的Activity，如果不使用其他的标志，如Single Instance之类，那么都会在存在于同一个task中。一般情况下，我们并不定义Task Affinity值，则其默认的值就是当前App的包名。
结束。