handler更新UI主线程

示例：下面代码的功能是修改UI主线程TextView的内容

public class MainActivity extends Activity {
    private Button btn_start;
    private TextView numTxtView;
    int i = 2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        numTxtView = (TextView) this.findViewById(R.id.numTxtView);
        btn_start = (Button)this.findViewById(R.id.btn_start);
        final Handler handler = new Handler() {
            @Override
            public void handleMessage(Message msg) {
                if (msg.what == 0x1233) {
                    //修改主线程中TextView所显示的内容
                    numTxtView.setText("" + i);
                    i++;
                }
            }
        };
        btn_start.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //定义一个计时器，让改计时器周期性地执行指定任务
                new Timer().schedule(new TimerTask() {
                    @Override
                    public void run() {
                        //发送空消息
                        handler.sendEmptyMessage(0x1233);
                    }
                }, 0,1000);
            }
        });

    }

}