AndroidのActivity之后台隐藏

 1 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);
    }