Android 一键清理、内存清理功能实现

   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：

/**
         * 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：

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。