使用情景：最近有個需求是統計後臺應用執行時間，如果一個應用在後臺執行超過一定時間就Kill掉程序，達到省電的目的。此時就可以使用PkgUsageStats這個類來實現啦！

通過com.android.internal.os.PkgUsageStats這個類可以得到一個應用程式的啟動次數，執行時間等資訊，功能強大，但是google並沒有將這個類作為API介面提供給開發者，如果在android原始碼下開發，可以通過以下程式碼來使用這個類：

import com.android.internal.app.IUsageStats;
import com.android.internal.os.PkgUsageStats;

//比較兩個應用程式的啟動次數和執行時間
public final int compare(ApplicationInfo a, ApplicationInfo b) {
	ComponentName aName = a.intent.getComponent();
	ComponentName bName = b.intent.getComponent();
	int result = 0;
	// get usagestats service
	IUsageStats mUsageStatsService = IUsageStats.Stub.asInterface(ServiceManager.getService("usagestats"));
	try {
		// get PkgUsageStats
		PkgUsageStats aStats = mUsageStatsService.getPkgUsageStats(aName);
		PkgUsageStats bStats = mUsageStatsService.getPkgUsageStats(bName);
		if (aStats != null && bStats != null) {
			if ((aStats.launchCount > bStats.launchCount) || ((aStats.launchCount == bStats.launchCount) && (aStats.usageTime > bStats.usageTime)))
				result = -1;
			else if ((aStats.launchCount < bStats.launchCount) || ((aStats.launchCount == bStats.launchCount) && (aStats.usageTime < bStats.usageTime)))
				result = 1;
			else {
				result = 0;
			}
		} else if (aStats != null && bStats == null) {
			result = -1;
		} else if (aStats == null && bStats != null) {
			result = 1;
		}
	} catch (RemoteException e) {
		Log.i("TAG", "get package usage stats fail");
	}
	return result;
}
 

public final int compare(ApplicationInfo a, ApplicationInfo b) {
	ComponentName aName = a.intent.getComponent();
	ComponentName bName = b.intent.getComponent();
	int aLaunchCount, bLaunchCount;
	long aUseTime, bUseTime;
	int result = 0;
	try {
		// 獲得ServiceManager類
		Class<?> ServiceManager = Class.forName("android.os.ServiceManager");
		// 獲得ServiceManager的getService方法
		Method getService = ServiceManager.getMethod("getService", java.lang.String.class);
		// 呼叫getService獲取RemoteService
		Object oRemoteService = getService.invoke(null, "usagestats");
		// 獲得IUsageStats.Stub類
		Class<?> cStub = Class.forName("com.android.internal.app.IUsageStats$Stub");
		// 獲得asInterface方法
		Method asInterface = cStub.getMethod("asInterface", android.os.IBinder.class);
		// 呼叫asInterface方法獲取IUsageStats物件
		Object oIUsageStats = asInterface.invoke(null, oRemoteService);
		// 獲得getPkgUsageStats(ComponentName)方法
		Method getPkgUsageStats = oIUsageStats.getClass().getMethod("getPkgUsageStats", ComponentName.class);
		// 呼叫getPkgUsageStats 獲取PkgUsageStats物件
		Object aStats = getPkgUsageStats.invoke(oIUsageStats, aName);
		Object bStats = getPkgUsageStats.invoke(oIUsageStats, bName);
		// 獲得PkgUsageStats類
		Class<?> PkgUsageStats = Class.forName("com.android.internal.os.PkgUsageStats");
		aLaunchCount = PkgUsageStats.getDeclaredField("launchCount").getInt(aStats);
		bLaunchCount = PkgUsageStats.getDeclaredField("launchCount").getInt(bStats);
		aUseTime = PkgUsageStats.getDeclaredField("usageTime").getLong(aStats);
		bUseTime = PkgUsageStats.getDeclaredField("usageTime").getLong(bStats);
		if ((aLaunchCount > bLaunchCount) || ((aLaunchCount == bLaunchCount) && (aUseTime > bUseTime)))
			result = 1;
		else if ((aLaunchCount < bLaunchCount) || ((aLaunchCount == bLaunchCount) && (aUseTime < bUseTime)))
			result = -1;
		else {
			result = 0;
		}
	} catch (Exception e) {
		Log.e("###", e.toString(), e);
	}
	return result;
}
 

如何看自己的android的詳細使用資訊：

import com.android.internal.app.IUsageStats;
import com.android.settings.R;
import android.app.Activity;
import android.content.Context;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.os.Bundle;
import android.os.RemoteException;
import android.os.ServiceManager;
import com.android.internal.os.PkgUsageStats;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;


import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.AdapterView.OnItemSelectedListener;


/**
 * Activity to display package usage statistics.
 */
public class UsageStats extends Activity implements OnItemSelectedListener {
    private static final String TAG="UsageStatsActivity";
    private static final boolean localLOGV = true;
    private Spinner mTypeSpinner;
    private ListView mListView;
    private IUsageStats mUsageStatsService;
    private LayoutInflater mInflater;
    private UsageStatsAdapter mAdapter;
    private PackageManager mPm;
    
    public static class AppNameComparator implements Comparator<PkgUsageStats> {
        Map<String, CharSequence> mAppLabelList;
        AppNameComparator(Map<String, CharSequence> appList) {
            mAppLabelList = appList;
        }
        public final int compare(PkgUsageStats a, PkgUsageStats b) {
            String alabel = mAppLabelList.get(a.packageName).toString();
            String blabel = mAppLabelList.get(b.packageName).toString();
            return alabel.compareTo(blabel);
        }
    }
    
    public static class LaunchCountComparator implements Comparator<PkgUsageStats> {
        public final int compare(PkgUsageStats a, PkgUsageStats b) {
            // return by descending order
            return b.launchCount - a.launchCount;
        }
    }
    
    public static class UsageTimeComparator implements Comparator<PkgUsageStats> {
        public final int compare(PkgUsageStats a, PkgUsageStats b) {
            long ret = a.usageTime-b.usageTime;
            if (ret == 0) {
                return 0;
            }
            if (ret < 0) {
                return 1;
            }
            return -1;
        }
    }
    
     // View Holder used when displaying views
    static class AppViewHolder {
        TextView pkgName;
        TextView launchCount;
        TextView usageTime;
    }
    
    class UsageStatsAdapter extends BaseAdapter {
         // Constants defining order for display order
        private static final int _DISPLAY_ORDER_USAGE_TIME = 0;
        private static final int _DISPLAY_ORDER_LAUNCH_COUNT = 1;
        private static final int _DISPLAY_ORDER_APP_NAME = 2;
        
        private int mDisplayOrder = _DISPLAY_ORDER_USAGE_TIME;
        private List<PkgUsageStats> mUsageStats;
        private LaunchCountComparator mLaunchCountComparator;
        private UsageTimeComparator mUsageTimeComparator;
        private AppNameComparator mAppLabelComparator;
        private HashMap<String, CharSequence> mAppLabelMap;
        
        UsageStatsAdapter() {
            mUsageStats = new ArrayList<PkgUsageStats>();
            mAppLabelMap = new HashMap<String, CharSequence>();
            PkgUsageStats[] stats;
            try {
                stats = mUsageStatsService.getAllPkgUsageStats();
            } catch (RemoteException e) {
                Log.e(TAG, "Failed initializing usage stats service");
                return;
            }
           if (stats == null) {
               return;
           }
           for (PkgUsageStats ps : stats) {
               mUsageStats.add(ps);
               // load application labels for each application
               CharSequence label;
               try {
                   ApplicationInfo appInfo = mPm.getApplicationInfo(ps.packageName, 0);
                   label = appInfo.loadLabel(mPm);
                } catch (NameNotFoundException e) {
                    label = ps.packageName;
                }
                mAppLabelMap.put(ps.packageName, label);
           }
           // Sort list
           mLaunchCountComparator = new LaunchCountComparator();
           mUsageTimeComparator = new UsageTimeComparator();
           mAppLabelComparator = new AppNameComparator(mAppLabelMap);
           sortList();
        }
        public int getCount() {
            return mUsageStats.size();
        }


        public Object getItem(int position) {
            return mUsageStats.get(position);
        }


        public long getItemId(int position) {
            return position;
        }


        public View getView(int position, View convertView, ViewGroup parent) {
            // A ViewHolder keeps references to children views to avoid unneccessary calls
            // to findViewById() on each row.
            AppViewHolder holder;


            // When convertView is not null, we can reuse it directly, there is no need
            // to reinflate it. We only inflate a new View when the convertView supplied
            // by ListView is null.
            if (convertView == null) {
                convertView = mInflater.inflate(R.layout.usage_stats_item, null);


                // Creates a ViewHolder and store references to the two children views
                // we want to bind data to.
                holder = new AppViewHolder();
                holder.pkgName = (TextView) convertView.findViewById(R.id.package_name);
                holder.launchCount = (TextView) convertView.findViewById(R.id.launch_count);
                holder.usageTime = (TextView) convertView.findViewById(R.id.usage_time);
                convertView.setTag(holder);
            } else {
                // Get the ViewHolder back to get fast access to the TextView
                // and the ImageView.
                holder = (AppViewHolder) convertView.getTag();
            }


            // Bind the data efficiently with the holder
            PkgUsageStats pkgStats = mUsageStats.get(position);
            if (pkgStats != null) {
                CharSequence label = mAppLabelMap.get(pkgStats.packageName);
                holder.pkgName.setText(label);
                holder.launchCount.setText(String.valueOf(pkgStats.launchCount));
                holder.usageTime.setText(String.valueOf(pkgStats.usageTime)+" ms");
            } else {
                Log.w(TAG, "No usage stats info for package:" + position);
            }
            return convertView;
        }
        
        void sortList(int sortOrder) {
            if (mDisplayOrder == sortOrder) {
                // do nothing
                return;
            }
            mDisplayOrder= sortOrder;
            sortList();
        }
        private void sortList() {
            if (mDisplayOrder == _DISPLAY_ORDER_USAGE_TIME) {
                if (localLOGV) Log.i(TAG, "Sorting by usage time");
                Collections.sort(mUsageStats, mUsageTimeComparator);
            } else if (mDisplayOrder == _DISPLAY_ORDER_LAUNCH_COUNT) {
                if (localLOGV) Log.i(TAG, "Sorting launch count");
                Collections.sort(mUsageStats, mLaunchCountComparator);
            } else if (mDisplayOrder == _DISPLAY_ORDER_APP_NAME) {
                if (localLOGV) Log.i(TAG, "Sorting by application name");
                Collections.sort(mUsageStats, mAppLabelComparator);
            }
            notifyDataSetChanged();
        }
    }


    /** Called when the activity is first created. */
    protected void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        mUsageStatsService = IUsageStats.Stub.asInterface(ServiceManager.getService("usagestats"));
        if (mUsageStatsService == null) {
            Log.e(TAG, "Failed to retrieve usagestats service");
            return;
        }
        mInflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        mPm = getPackageManager();
        
        setContentView(R.layout.usage_stats);
        mTypeSpinner = (Spinner) findViewById(R.id.typeSpinner);
        mTypeSpinner.setOnItemSelectedListener(this);
        
        mListView = (ListView) findViewById(R.id.pkg_list);
        // Initialize the inflater
        
        mAdapter = new UsageStatsAdapter();
        mListView.setAdapter(mAdapter);
    }


    public void onItemSelected(AdapterView<?> parent, View view, int position,
            long id) {
        mAdapter.sortList(position);
    }


    public void onNothingSelected(AdapterView<?> parent) {
        // do nothing
    }
}