360桌面、金山清理大师等都提供了一键清理、一键加速等功能，其实就是杀一些后台进程来达到释放内存的目的。
基本思路就是列出所有运行的进程，查看其重要值（RunningAppProcessInfo.importance，值越大说明进程重要程度越低），可以设定一个阈值，
如果该进程的重要值大于该阈值，就可以杀掉该进程。
进程的重要值有以下几个等级：
[java] view plain copy /** * Constant for {@link #importance}: this is a persistent process. * Only used when reporting to process observers. * @hide */ public static final int IMPORTANCE_PERSISTENT = 50; /** * Constant for {@link #importance}: this process is running the * foreground UI. */ public static final int IMPORTANCE_FOREGROUND = 100; /** * Constant for {@link #importance}: this process is running something * that is actively visible to the user, though not in the immediate * foreground. */ public static final int IMPORTANCE_VISIBLE = 200; /** * Constant for {@link #importance}: this process is running something * that is considered to be actively perceptible to the user. An * example would be an application performing background music playback. */ public static final int IMPORTANCE_PERCEPTIBLE = 130; /** * Constant for {@link #importance}: this process is running an * application that can not save its state, and thus can't be killed * while in the background. * @hide */ public static final int IMPORTANCE_CANT_SAVE_STATE = 170; /** * Constant for {@link #importance}: this process is contains services * that should remain running. */ public static final int IMPORTANCE_SERVICE = 300; /** * Constant for {@link #importance}: this process process contains * background code that is expendable. */ public static final int IMPORTANCE_BACKGROUND = 400; /** * Constant for {@link #importance}: this process is empty of any * actively running code. */ public static final int IMPORTANCE_EMPTY = 500; 直接上代码： [java] view plain copy package com.android.clearmemory; import android.app.Activity; import android.app.ActivityManager; import android.app.ActivityManager.MemoryInfo; import android.app.ActivityManager.RunningAppProcessInfo; import android.content.Context; import android.os.Bundle; import android.util.Log; import android.view.View; import android.widget.Button; import android.widget.Toast; import java.util.List; public class ClearMemoryActivity extends Activity { private static final String TAG = "ClearMemoryActivity"; /** * Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Button clear = (Button) findViewById(R.id.clear); clear.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { //To change body of implemented methods use File | Settings | File Templates. ActivityManager am = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE); List<RunningAppProcessInfo> infoList = am.getRunningAppProcesses(); List<ActivityManager.RunningServiceInfo> serviceInfos = am.getRunningServices(100); long beforeMem = getAvailMemory(ClearMemoryActivity.this); Log.d(TAG, "-----------before memory info : " + beforeMem); int count = 0; if (infoList != null) { for (int i = 0; i < infoList.size(); ++i) { RunningAppProcessInfo appProcessInfo = infoList.get(i); Log.d(TAG, "process name : " + appProcessInfo.processName); //importance 该进程的重要程度 分为几个级别，数值越低就越重要。 Log.d(TAG, "importance : " + appProcessInfo.importance); // 一般数值大于RunningAppProcessInfo.IMPORTANCE_SERVICE的进程都长时间没用或者空进程了 // 一般数值大于RunningAppProcessInfo.IMPORTANCE_VISIBLE的进程都是非可见进程，也就是在后台运行着 if (appProcessInfo.importance > RunningAppProcessInfo.IMPORTANCE_VISIBLE) { String[] pkgList = appProcessInfo.pkgList; for (int j = 0; j < pkgList.length; ++j) {//pkgList 得到该进程下运行的包名 Log.d(TAG, "It will be killed, package name : " + pkgList[j]); am.killBackgroundProcesses(pkgList[j]); count++; } } } } long afterMem = getAvailMemory(ClearMemoryActivity.this); Log.d(TAG, "----------- after memory info : " + afterMem); Toast.makeText(ClearMemoryActivity.this, "clear " + count + " process, " + (afterMem - beforeMem) + "M", Toast.LENGTH_LONG).show(); } }); ClearMemoryFloatView.instance(getApplicationContext()).createView(); } //获取可用内存大小 private long getAvailMemory(Context context) { // 获取android当前可用内存大小 ActivityManager am = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE); MemoryInfo mi = new MemoryInfo(); am.getMemoryInfo(mi); //mi.availMem; 当前系统的可用内存 //return Formatter.formatFileSize(context, mi.availMem);// 将获取的内存大小规格化 Log.d(TAG, "可用内存---->>>" + mi.availMem / (1024 * 1024)); return mi.availMem / (1024 * 1024); } }注意：
我这里选择阈值是IMPORTANCE_VISIBLE级别的，也就是非可见的后台进程和服务会被杀掉（一些系统进程肯定除外）。
清理的效果跟金山清理大师和360桌面的一键清理效果差不多。
如果不想杀的太凶，可以选择IMPORTANCE_SERVICE级别，杀掉那些长时间没用或者空进程了，
这个级别的清理力度不够大，达不到金山清理大师的效果。
