Android的Activity以后台隐藏

public class MainActivity extends Activity {     /** Called when the activity is first created. */     NotificationManager nm;     Notification notifi;     PendingIntent pi;     @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         nm = (NotificationManager)getSystemService(Context.NOTIFICATION_SERVICE);         notifi = new Notification(R.drawable.ic_launcher,"",System.currentTimeMillis());         Intent intent = new Intent(this,MainActivity.class);         intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP|Intent.FLAG_ACTIVITY_NEW_TASK);         pi = PendingIntent.getActivity(this, 0, intent, 0);         notifi.setLatestEventInfo(this,"别当心", "哥还在", pi);         notifi.flags  = Notification.FLAG_INSISTENT|Notification.FLAG_ONGOING_EVENT;         setContentView(R.layout.main);              }      @Override     public void onBackPressed() {         // TODO Auto-generated method stub         //super.onBackPressed();         AlertDialog.Builder builder = new AlertDialog.Builder(this);         builder.setIcon(R.drawable.ic_launcher);         builder.setTitle("是否退出");         //builder.setMessage("");         builder.setPositiveButton("退出", new DialogInterface.OnClickListener() {                          @Override             public void onClick(DialogInterface dialog, int which) {                 // TODO Auto-generated method stub                 finish();                 android.os.Process.killProcess(android.os.Process.myPid());             }         });         builder.setNeutralButton("隐藏", new DialogInterface.OnClickListener() {                          @Override             public void onClick(DialogInterface dialog, int which) {                 // TODO Auto-generated method stub                 Intent intent = new Intent(Intent.ACTION_MAIN);                 intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);                 intent.addCategory(Intent.CATEGORY_HOME);                 MainActivity.this.startActivity(intent);                              }         });         builder.setNegativeButton("取消", new DialogInterface.OnClickListener() {                          @Override             public void onClick(DialogInterface dialog, int which) {                 // TODO Auto-generated method stub                              }         });                  builder.create().show();     }                     @Override     public void finish() {         // TODO Auto-generated method stub         super.finish();         nm.cancel(R.drawable.ic_launcher);     }      @Override     protected void onDestroy() {         // TODO Auto-generated method stub         super.onDestroy();         Log.e("MainActivity", "onDestroy");         nm.cancelAll();     }      @Override     protected void onStop() {         // TODO Auto-generated method stub         super.onStop();         nm.notify(R.drawable.ic_launcher, notifi);     }

?感谢大神:http://www.cnblogs.com/bvin/archive/2012/08/18/2645584.html