<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"   xmlns:tools="http://schemas.android.com/tools"   android:layout_width="match_parent"   android:layout_height="match_parent"   android:paddingBottom="@dimen/activity_vertical_margin"   android:paddingLeft="@dimen/activity_horizontal_margin"   android:paddingRight="@dimen/activity_horizontal_margin"   android:paddingTop="@dimen/activity_vertical_margin"   tools:context=".MainActivity">    <Button     android:id="@+id/start_system_clock_bt"     android:layout_width="match_parent"     android:layout_height="wrap_content"     android:text="啟動系統鬧鐘" />  </RelativeLayout> 

package com.demo.cxc.systemclocksample;  import android.content.Intent; import android.content.pm.ApplicationInfo; import android.content.pm.PackageInfo; import android.os.Bundle; import android.os.Handler; import android.os.Message; import android.support.v7.app.AppCompatActivity; import android.util.Log; import android.view.View; import android.widget.Button; import android.widget.Toast;  import java.util.ArrayList; import java.util.List;  public class MainActivity extends AppCompatActivity {   private Button startSystemClockButton = null;     private List<PackageInfo> allPackageInfos;//系統安裝所有軟件   private List<PackageInfo> clockPackageInfos;//系統時鐘軟件    private static final int HANDLE_MESSAGE_KEY = 1001;   private Handler myHandler = new Handler() {     @Override     public void handleMessage(Message msg) {       super.handleMessage(msg);       if (msg != null) {         switch (msg.what) {           case HANDLE_MESSAGE_KEY:             Toast.makeText(getApplicationContext(), "--app scan over--", Toast.LENGTH_SHORT).show();             Log.d("CXC", "--app scan over--");             break;            default:             break;          }        }      }   };    @Override   protected void onCreate(Bundle savedInstanceState) {     super.onCreate(savedInstanceState);     setContentView(R.layout.activity_main);     initViews();     initData();      //begin scan installed applications;     //// TODO: 16/1/15     new Thread(new ScanInstalledAppsRunnable()).start();   }    private void initViews() {     startSystemClockButton = (Button) findViewById(R.id.start_system_clock_bt);     startSystemClockButton.setOnClickListener(new View.OnClickListener() {       @Override       public void onClick(View v) {         //// TODO: 16/1/15         startSystemClock();       }     });   }    private void initData() {     clockPackageInfos = new ArrayList<PackageInfo>();   }     class ScanInstalledAppsRunnable implements Runnable {     @Override     public void run() {       allPackageInfos = getPackageManager()           .getInstalledPackages(0);        if (allPackageInfos == null || allPackageInfos.size() == 0) {         //// TODO: 16/1/15 todo nothing         return;       }        if (clockPackageInfos == null) {         clockPackageInfos = new ArrayList<PackageInfo>();       }        PackageInfo tempPackageInfo = null;       for (int i = 0; i < allPackageInfos.size(); i++) {         tempPackageInfo = allPackageInfos.get(i);         if (tempPackageInfo != null) {            if (isSystemApplication(tempPackageInfo.applicationInfo) &&               isClockApplication(tempPackageInfo.packageName)) {             clockPackageInfos.add(tempPackageInfo);           }          }       }         Message message = myHandler.obtainMessage();       message.what = MainActivity.HANDLE_MESSAGE_KEY;       myHandler.sendMessage(message);     }   }     private boolean isSystemApplication(ApplicationInfo applicationInfo) {     boolean isSystemApp = false;     if (applicationInfo != null) {       if ((applicationInfo.flags & ApplicationInfo.FLAG_UPDATED_SYSTEM_APP) != 0           || (applicationInfo.flags & ApplicationInfo.FLAG_SYSTEM) != 0) {         isSystemApp = true;        }     }     return isSystemApp;   }     private boolean isClockApplication(String packageName) {     boolean isClockApp = false;     if (packageName != null && packageName.contains("clock") && !packageName.contains("widget")) {       isClockApp = true;     }     return isClockApp;   }    private void startSystemClock() {     if (clockPackageInfos == null || clockPackageInfos.size() == 0) {       Toast.makeText(getApplicationContext(), "--啟動系統鬧鐘失敗1--", Toast.LENGTH_SHORT).show();       return;     }      Log.d("CXC", "---clock package size :" + clockPackageInfos.size());     Log.d("CXC", "---clock package [0] :" + clockPackageInfos.get(0).packageName);     try {       Intent startSysClockIntent = getPackageManager().getLaunchIntentForPackage(clockPackageInfos.get(0).packageName);       startActivity(startSysClockIntent);     } catch (Exception e) {       Toast.makeText(getApplicationContext(), "--啟動系統鬧鐘失敗2--", Toast.LENGTH_SHORT).show();     }     }  }