Android 一鍵清理、內存清理功能實現

360桌面、金山清理大師等都提供了一鍵清理、一鍵加速等功能，其實就是殺一些後台進程來達到釋放內存的目的。

基本思路就是列出所有運行的進程，查看其重要值（RunningAppProcessInfo.importance，值越大說明進程重要程度越低），可以設定一個阈值，如果該進程的重要值大於該阈值，就可以殺掉該進程。

進程的重要值有以下幾個等級：

/**  
       * 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;  

需要權限：

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

具體操作代碼如下：

package com.example.demo; 
 
import java.util.List; 
 
import android.app.Activity; 
import android.app.ActivityManager; 
import android.app.ActivityManager.MemoryInfo; 
import android.app.ActivityManager.RunningAppProcessInfo; 
import android.content.Context; 
import android.content.pm.PackageManager; 
import android.content.pm.PackageManager.NameNotFoundException; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.widget.Toast; 
 
public class CleanProcessActivity extends Activity { 
 
  private static final String TAG = "Clean"; 
 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_clean_process); 
  } 
  public void clean(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(this);  
    Log.d(TAG, "-----------before memory info : " + beforeMem);  
    int count = 0;  
    PackageManager pm = getPackageManager(); 
     
    if (infoList != null) {  
      for (int i = 0; i < infoList.size(); ++i) {  
        RunningAppProcessInfo appProcessInfo = infoList.get(i);  
        Log.d(TAG, "process name : " + appProcessInfo.processName);  
        //importance 該進程的重要程度 分為幾個級別，數值越低就越重要。  
        Log.d(TAG, "importance : " + appProcessInfo.importance);  
         
          
 
        // 一般數值大於RunningAppProcessInfo.IMPORTANCE_SERVICE的進程都長時間沒用或者空進程了  
        // 一般數值大於RunningAppProcessInfo.IMPORTANCE_VISIBLE的進程都是非可見進程，也就是在後台運行著  
        if (appProcessInfo.importance > RunningAppProcessInfo.IMPORTANCE_VISIBLE) {  
          String[] pkgList = appProcessInfo.pkgList;  
          for (int j = 0; j < pkgList.length; ++j) {//pkgList 得到該進程下運行的包名  
            String appName = null; 
            try { 
              appName = (String) pm.getApplicationLabel(pm.getApplicationInfo(pkgList[j], 0));  
            } catch (NameNotFoundException e) { 
              // TODO Auto-generated catch block 
              e.printStackTrace(); 
            } 
            Log.d(TAG, "It will be killed, package name : " + pkgList[j]+" -- "+appName );  
            am.killBackgroundProcesses(pkgList[j]);  
            count++;  
          }  
        }  
 
      }  
    }  
 
    long afterMem = getAvailMemory(this);  
    Log.d(TAG, "----------- after memory info : " + afterMem);  
    Toast.makeText(this, "clear " + count + " process, "  
          + (afterMem - beforeMem) + "M", Toast.LENGTH_LONG).show();  
  } 
  private long getAvailMemory(CleanProcessActivity cleanProcessActivity) { 
    // 獲取android當前可用內存大小  
    ActivityManager am = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);  
    MemoryInfo mi = new MemoryInfo();  
    am.getMemoryInfo(mi);  
    //mi.availMem; 當前系統的可用內存  
    //return Formatter.formatFileSize(context, mi.availMem);// 將獲取的內存大小規格化  
    Log.d(TAG, "可用內存---->>>" + mi.availMem / (1024 * 1024));  
    return mi.availMem / (1024 * 1024);  
  }  
} 

注意：

我這裡選擇阈值是IMPORTANCE_VISIBLE級別的，也就是非可見的後台進程和服務會被殺掉（一些系統進程肯定除外）。
清理的效果跟金山清理大師和360桌面的一鍵清理效果差不多。

如果不想殺的太凶，可以選擇IMPORTANCE_SERVICE級別，殺掉那些長時間沒用或者空進程了，這個級別的清理力度不夠大，達不到金山清理大師的效果。

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