http://blog.school51.com/show_diary.asp?uid=84890&logid=622777
solution:
在AndroidManifest.xml中对应的Activity中找到“android:excludeFromRecents”，把值改为false，或直接去掉该项。
e.g.
AndroidManifest.xml
<activity android:icon="@drawable/ic_launcher_fmradio"
android:name=".FMRadio"
android:label="@string/app_name"
android:taskAffinity=""
android:launchMode="singleTop"
android:screenOrientation="portrait">
<!-- android:excludeFromRecents="true"
-->
-->
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
<intent-filter>
<action android:name="com.quicinc.fmradio.FMRADIO_ACTIVITY" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
android:excludeFromRecents the list of recent apps. "
true" if the task should beexcluded from the list; "false" if it should be included. The default value is "false".
============================
相反，如果要不出现在近期任务里面，可以增加android:excludeFromRecents="true"，但貌似要apk中所有activity都加上才有用。