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:

Android关于Task的一些实践之SingleTask, SingleInstance和TaskAffinity_第1张图片

 Android关于Task的一些实践之SingleTask, SingleInstance和TaskAffinity_第2张图片

Android关于Task的一些实践之SingleTask, SingleInstance和TaskAffinity_第3张图片

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:

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.lms.taskdemo.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="com.lms.taskdemo.SecondActivity">
        </activity>
        <activity android:name="com.lms.taskdemo.ThirdActivity" >
        </activity>
    </application>
顺序打开三个Activity,看看结果:

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:

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.lms.taskdemo.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="com.lms.taskdemo.SecondActivity"
            android:launchMode="singleTask">
        </activity>
        <activity android:name="com.lms.taskdemo.ThirdActivity" >
        </activity>
    </application>

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:

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.lms.taskdemo.MainActivity"
            android:label="@string/app_name"
            android:taskAffinity="com.lms.taskdemo.MainActivity" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="com.lms.taskdemo.SecondActivity"
            android:launchMode="singleTask"
            android:taskAffinity="com.lms.taskdemo.SecondActivity" >
        </activity>
        <activity android:name="com.lms.taskdemo.ThirdActivity" >
        </activity>
    </application>

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:
    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.lms.taskdemo.MainActivity"
            android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="com.lms.taskdemo.SecondActivity"
            android:launchMode="singleInstance">
        </activity>
        <activity android:name="com.lms.taskdemo.ThirdActivity" >
        </activity>
    </application>

下面是结果:
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: 1
可以看到启动Second Activity的时候,是在新的Task中,而当启动Third Activity的时候,它又跑回原来的Task中去了,这是跟文档描述中符合的,的确是新建的Task中只能有且仅有一个Activity。而由于我们没有定义Task Affinity,所以当启动Third Activity的时候,它就会去找相同Affinity的task,所以就会找到原来的Task,也即是说,如果定义了TaskAffinity的话,那以Third Activity就应该在新的Task中创建了,下面就来验证一下。

5)Single Instance Different Affinity

在配置文件中定义如下:
    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.lms.taskdemo.MainActivity"
            android:label="@string/app_name"
            android:taskAffinity="com.lms.taskdemo.MainActivity" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="com.lms.taskdemo.SecondActivity"
            android:launchMode="singleInstance"
            android:taskAffinity="com.lms.taskdemo.SecondActivity" >
        </activity>
        <activity android:name="com.lms.taskdemo.ThirdActivity" >
        </activity>
    </application>

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。

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