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ActivityManager

与系统中所有的Activity进行交互的类。官网一句话解释了这个东西，但是有点随意了。ActivityManager的作用很多，我们通过它获得内存信息，进程信息，还可以终止某个进程。当然啦，只能终止用户的进程，系统的进程是杀死不了的。下面我通过实例，一步一步学习它的具体作用，我也是刚学，不能从宏观的角度给大家解释清楚它的具体作用。希望通过程序一步一步的写下去，其每个方法的作用也就清楚了，从而我们就知道它能干什么啦。语言组织能力差，所以就用代码来解释吧。

首先我们创建一个程序，在入口Activity里的onCreate()方法里，我们来创建ActivityManager.

ActivityManager activityManager = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);

从系统服务里得到我们的ActivityManger对象.在官方文档中，并没有提供构造方法，所以我们不能通过new的方式创建该对象，由于ActivityManager是核心服务，所以android从系统服务里得到它的实例。

获取手机的内存信息MemoryInfo

MemoryInfo memInfo = new MemoryInfo();//存放内存信息的对象
activityManager.getMemoryInfo(memInfo);//传入参数，将获得数据保存在memInfo对象中
long availMem = memInfo.availMem/1000000;//可用内存
boolean isLowMem = memInfo.lowMemory;//是否达到最低内存
long threshold = memInfo.threshold/1000000;//临界值，达到这个值，进程就要被杀死
long totalMem = memInfo.totalMem/1000000;//总内存
Log.i(TAG, "avail:" + availMem + ",isLowMem:" + isLowMem + ",threshold:" + threshold + ",totalMem:" + totalMem);

在ActivityManager的getMemoryInfo的方法中需要传入一个MemoryInfo类，该类为ActivityManager内部类，手机的内存信息就保存在这个类中。然后通过MemoryInfo类中的方法，获得我们想要的信息。运行程序输出结果如下：

Android中ActivityManager学习笔记(1)-MemoryInfo「建议收藏」

然后我们在调用一下清楚用户数据的方法：

activityManager.clearApplicationUserData()//清楚当前应用的用户数据

放在刚才获取内存的数据前面，我们看看清除当前应用的用户数据以后，我们的内存大小：

Android中ActivityManager学习笔记(1)-MemoryInfo「建议收藏」

可以看出我们清除了1M的用户数据。

系统各个进程的信息RunningAppProcessInfo

List<RunningAppProcessInfo> list1 = activityManager.getRunningAppProcesses();
for(RunningAppProcessInfo info :list1){
int importance = info.importance;//通过给进程标值来给进程分类，越重要的进程，那么数值就越低
Log.i(TAG, "importance: "+importance);
int importanceReasonCode = info.importanceReasonCode;//重要性的原因，也是通过数值去判断。
Log.i(TAG, "importanceReasonCode: "+importanceReasonCode);
ComponentName impoartanceReasonComponent = info.importanceReasonComponent;//重要性原因的组件，返回一个ComponentName的对象。
Log.i(TAG, "impoartanceReasonComponent: "+impoartanceReasonComponent);
int importanceReasonPid = info.importanceReasonPid;//其他客户端进程的进程id号，如果没有其他进程返回0
Log.i(TAG, "importanceReasonPid : "+importanceReasonPid);
int lastTrimLevel = info.lastTrimLevel;//提供给ComponentCallbacks2.onTrimMemory(int)方法的参数。上一次提交给进程的内饰水平
Log.i(TAG, "lastTrimLevel: "+lastTrimLevel);
int lru = info.lru;//在一个特殊的进程中，提供更精细密度的衡量值，目前只维护IMPORTANCE_BACKGROUND
Log.i(TAG, "lru ："+lru);
int pid = info.pid;//进程id
Log.i(TAG, "pid ："+pid);
String proName = info.processName;//进程名
Log.i(TAG, "proName : " + proName);
int uid = info.uid;//用户id
Log.i(TAG, "uid : " + uid);
Log.i(TAG, "================================");  }

运行程序得到输出，截取一部分如下：

03-27 14:24:54.460: I/MainActivity(7647): importance: 100
03-27 14:24:54.460: I/MainActivity(7647): importanceReasonCode: 0
03-27 14:24:54.460: I/MainActivity(7647): impoartanceReasonComponent: null
03-27 14:24:54.460: I/MainActivity(7647): importanceReasonPid : 0
03-27 14:24:54.460: I/MainActivity(7647): lastTrimLevel: 0
03-27 14:24:54.460: I/MainActivity(7647): lru ：0
03-27 14:24:54.460: I/MainActivity(7647): pid ：7647
03-27 14:24:54.460: I/MainActivity(7647): proName : com.ibm.activitymanager
03-27 14:24:54.470: I/MainActivity(7647): uid : 10072
03-27 14:24:54.470: I/MainActivity(7647): ================================
03-27 14:24:54.470: I/MainActivity(7647): importance: 130
03-27 14:24:54.470: I/MainActivity(7647): importanceReasonCode: 0
03-27 14:24:54.470: I/MainActivity(7647): impoartanceReasonComponent: null
03-27 14:24:54.470: I/MainActivity(7647): importanceReasonPid : 0
03-27 14:24:54.480: I/MainActivity(7647): lastTrimLevel: 0
03-27 14:24:54.480: I/MainActivity(7647): lru ：0
03-27 14:24:54.480: I/MainActivity(7647): pid ：836
03-27 14:24:54.480: I/MainActivity(7647): proName : com.android.launcher3
03-27 14:24:54.480: I/MainActivity(7647): uid : 10053
03-27 14:24:54.480: I/MainActivity(7647): ================================
03-27 14:24:54.480: I/MainActivity(7647): importance: 400
03-27 14:24:54.480: I/MainActivity(7647): importanceReasonCode: 0
03-27 14:24:54.480: I/MainActivity(7647): impoartanceReasonComponent: null
03-27 14:24:54.480: I/MainActivity(7647): importanceReasonPid : 0
03-27 14:24:54.480: I/MainActivity(7647): lastTrimLevel: 0
03-27 14:24:54.480: I/MainActivity(7647): lru ：0
03-27 14:24:54.490: I/MainActivity(7647): pid ：770
03-27 14:24:54.490: I/MainActivity(7647): proName : com.android.settings
03-27 14:24:54.490: I/MainActivity(7647): uid : 1000
03-27 14:24:54.490: I/MainActivity(7647): ================================
03-27 14:24:54.490: I/MainActivity(7647): importance: 400
03-27 14:24:54.490: I/MainActivity(7647): importanceReasonCode: 0
03-27 14:24:54.490: I/MainActivity(7647): impoartanceReasonComponent: null
03-27 14:24:54.500: I/MainActivity(7647): importanceReasonPid : 0
03-27 14:24:54.500: I/MainActivity(7647): lastTrimLevel: 0
03-27 14:24:54.500: I/MainActivity(7647): lru ：1
03-27 14:24:54.500: I/MainActivity(7647): pid ：1092
03-27 14:24:54.500: I/MainActivity(7647): proName : com.android.mms
03-27 14:24:54.500: I/MainActivity(7647): uid : 10009
03-27 14:24:54.500: I/MainActivity(7647): ================================
03-27 14:24:54.500: I/MainActivity(7647): importance: 400
03-27 14:24:54.500: I/MainActivity(7647): importanceReasonCode: 0
03-27 14:24:54.500: I/MainActivity(7647): impoartanceReasonComponent: null
03-27 14:24:54.500: I/MainActivity(7647): importanceReasonPid : 0
03-27 14:24:54.500: I/MainActivity(7647): lastTrimLevel: 0
03-27 14:24:54.500: I/MainActivity(7647): lru ：1
03-27 14:24:54.500: I/MainActivity(7647): pid ：1353
03-27 14:24:54.500: I/MainActivity(7647): proName : com.baidu.appsearch
03-27 14:24:54.500: I/MainActivity(7647): uid : 10073
03-27 14:24:54.500: I/MainActivity(7647): ================================
03-27 14:24:54.510: I/MainActivity(7647): importance: 400
03-27 14:24:54.510: I/MainActivity(7647): importanceReasonCode: 0
03-27 14:24:54.510: I/MainActivity(7647): impoartanceReasonComponent: null
03-27 14:24:54.510: I/MainActivity(7647): importanceReasonPid : 0
03-27 14:24:54.510: I/MainActivity(7647): lastTrimLevel: 0
03-27 14:24:54.510: I/MainActivity(7647): lru ：1
03-27 14:24:54.510: I/MainActivity(7647): pid ：2131
03-27 14:24:54.510: I/MainActivity(7647): proName : com.android.defcontainer
03-27 14:24:54.510: I/MainActivity(7647): uid : 10004
03-27 14:24:54.510: I/MainActivity(7647): ================================
03-27 14:24:54.520: I/MainActivity(7647): importance: 300
03-27 14:24:54.520: I/MainActivity(7647): importanceReasonCode: 0
03-27 14:24:54.530: I/MainActivity(7647): impoartanceReasonComponent: null
03-27 14:24:54.530: I/MainActivity(7647): importanceReasonPid : 0
03-27 14:24:54.530: I/MainActivity(7647): lastTrimLevel: 0
03-27 14:24:54.530: I/MainActivity(7647): lru ：0
03-27 14:24:54.530: I/MainActivity(7647): pid ：979
03-27 14:24:54.530: I/MainActivity(7647): proName : com.infinit.wostore.ui
03-27 14:24:54.540: I/MainActivity(7647): uid : 10071
03-27 14:24:54.540: I/MainActivity(7647): ================================
03-27 14:24:54.540: I/MainActivity(7647): importance: 400
03-27 14:24:54.540: I/MainActivity(7647): importanceReasonCode: 0
03-27 14:24:54.550: I/MainActivity(7647): impoartanceReasonComponent: null
03-27 14:24:54.550: I/MainActivity(7647): importanceReasonPid : 0
03-27 14:24:54.550: I/MainActivity(7647): lastTrimLevel: 0
03-27 14:24:54.550: I/MainActivity(7647): lru ：3
03-27 14:24:54.550: I/MainActivity(7647): pid ：1712
03-27 14:24:54.550: I/MainActivity(7647): proName : com.android.quicksearchbox
03-27 14:24:54.550: I/MainActivity(7647): uid : 10054
03-27 14:24:54.550: I/MainActivity(7647): ================================

获取进程中的错误信息ProcessErrorStateInfo

List<ProcessErrorStateInfo> list2 = activityManager.getProcessesInErrorState();
if (list2 != null) {
for (ProcessErrorStateInfo info : list2) {
int condition = info.condition;// 进程进入的条件
Log.i(TAG, "condition: " + condition);
byte[] data = info.crashData;// crash数据
if (data != null) {
Log.i(TAG, "data: " + data.toString());
} else {
Log.i(TAG, "data: null");
}
String longMsg = info.longMsg;// 对条件condition的描述
Log.i(TAG, "longMsg: " + longMsg);
int pid = info.pid;// 进程id
Log.i(TAG, "pid: " + pid);
String proName = info.processName;// 进程名
Log.i(TAG, "proName: " + proName);
String shortMsg = info.shortMsg;
Log.i(TAG, "shortMsg: " + shortMsg);
String sTrace = info.stackTrace;// 堆栈追踪到的信息
Log.i(TAG, "sTrace: " + sTrace);
String tag = info.tag;// activity名是否与错误有关联
Log.i(TAG, "tag: " + tag);
int uid = info.uid;
Log.i(TAG, "uid: " + uid);
int describeContents = info.describeContents();// 数据包裹的描述
Log.i(TAG, "describeContents: " + describeContents);
	}
}

可惜，获得信息为空，也就无法打印信息查看。

获取任务信息RunningTaskInfo

List<RunningTaskInfo> list3 = activityManager.getRunningTasks(10);
		if (list3 != null) {
			for (RunningTaskInfo info : list3) {
				ComponentName baseActivity = info.baseActivity;//任务主activity名
				Log.i(TAG, "baseActivity: " + baseActivity);
				CharSequence description = info.description;//任务的描述
				if(description!=null){
					Log.i(TAG, "description: " + description.toString());
				}else{
					Log.i(TAG, "description: null" );
				}
				int id = info.id;//任务的id号
				Log.i(TAG, "id: " + id);
				int numActivity = info.numActivities;//该任务的activity的数量
				Log.i(TAG, "numActivity: " + numActivity);
				int numRunning = info.numRunning;//当前活动的activity数量
				Log.i(TAG, "numRunning: " + numRunning);
				Bitmap bitmap = info.thumbnail;//缩略图
				Log.i(TAG, "bitmap: " + bitmap);
				ComponentName topActivity = info.topActivity;//当前活动activity中处于最顶端的activity
				Log.i(TAG, "topActivity: " + topActivity);
				int content = info.describeContents();//描述文本
				Log.i(TAG, "content: " + content);
				Log.i(TAG, "================================");
			}
		}

获取任务的方法需要添加权限：

<uses-permission android:name="android.permission.GET_TASKS"/>

运行程序输出信息如下：

03-27 16:05:18.990: I/MainActivity(10997): baseActivity: ComponentInfo{com.ibm.activitymanager/com.ibm.activitymanager.MainActivity}
03-27 16:05:18.990: I/MainActivity(10997): description: null
03-27 16:05:18.990: I/MainActivity(10997): id: 43
03-27 16:05:18.990: I/MainActivity(10997): numActivity: 1
03-27 16:05:18.990: I/MainActivity(10997): numRunning: 1
03-27 16:05:18.990: I/MainActivity(10997): bitmap: null
03-27 16:05:18.990: I/MainActivity(10997): topActivity: ComponentInfo{com.ibm.activitymanager/com.ibm.activitymanager.MainActivity}
03-27 16:05:18.990: I/MainActivity(10997): content: 0
03-27 16:05:18.990: I/MainActivity(10997): ================================
03-27 16:05:18.990: I/MainActivity(10997): baseActivity: ComponentInfo{com.android.launcher3/com.android.launcher3.Launcher}
03-27 16:05:18.990: I/MainActivity(10997): description: null
03-27 16:05:18.990: I/MainActivity(10997): id: 1
03-27 16:05:18.990: I/MainActivity(10997): numActivity: 1
03-27 16:05:18.990: I/MainActivity(10997): numRunning: 1
03-27 16:05:18.990: I/MainActivity(10997): bitmap: null
03-27 16:05:19.000: I/MainActivity(10997): topActivity: ComponentInfo{com.android.launcher3/com.android.launcher3.Launcher}
03-27 16:05:19.000: I/MainActivity(10997): content: 0
03-27 16:05:19.000: I/MainActivity(10997): ================================
03-27 16:05:19.000: I/MainActivity(10997): baseActivity: ComponentInfo{com.sohu.newsclient/com.sohu.newsclient.app.SplashActivity}
03-27 16:05:19.000: I/MainActivity(10997): description: null
03-27 16:05:19.000: I/MainActivity(10997): id: 39
03-27 16:05:19.000: I/MainActivity(10997): numActivity: 2
03-27 16:05:19.000: I/MainActivity(10997): numRunning: 2
03-27 16:05:19.000: I/MainActivity(10997): bitmap: null
03-27 16:05:19.000: I/MainActivity(10997): topActivity: ComponentInfo{com.sohu.newsclient/com.sohu.newsclient.app.NewsTabActivity}
03-27 16:05:19.000: I/MainActivity(10997): content: 0
03-27 16:05:19.000: I/MainActivity(10997): ================================
03-27 16:05:19.000: I/MainActivity(10997): baseActivity: ComponentInfo{com.android.settings/com.android.settings.Settings}
03-27 16:05:19.000: I/MainActivity(10997): description: null
03-27 16:05:19.000: I/MainActivity(10997): id: 14
03-27 16:05:19.000: I/MainActivity(10997): numActivity: 1
03-27 16:05:19.000: I/MainActivity(10997): numRunning: 1
03-27 16:05:19.000: I/MainActivity(10997): bitmap: null
03-27 16:05:19.000: I/MainActivity(10997): topActivity: ComponentInfo{com.android.settings/com.android.settings.Settings}
03-27 16:05:19.000: I/MainActivity(10997): content: 0
03-27 16:05:19.000: I/MainActivity(10997): ================================

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