消息handler message 线程通信 空消息

空消息的使用

private Handler handler = new Handler(){
        public void handleMessage(android.os.Message msg) {
            //得到当前显示的数值
            int number = Integer.parseInt(tv_demo_number.getText().toString());
            switch (msg.what) {
            case WHAT_INCREASE:
                //限制number<=20
                if(number==20) {
                    //设置暂停不能操作
                    btn_demo_pause.setEnabled(false);
                    Toast.makeText(HandlerDemoActivity.this, "已经达到最大值", 0).show();
                    return;
                }

                number++;
                tv_demo_number.setText(number+"");
                //发送增加的延迟消息
                handler.sendEmptyMessageDelayed(WHAT_INCREASE, 1000);
                break;
            case WHAT_DECREASE:
                //限制number>=1
                if(number==1) {
                    //设置暂停不能操作
                    btn_demo_pause.setEnabled(false);
                    Toast.makeText(HandlerDemoActivity.this, "已经达到最小值", 0).show();
                    return;
                }
                number--;
                tv_demo_number.setText(number+"");
                //发送减少的延迟消息
                handler.sendEmptyMessageDelayed(WHAT_DECREASE, 1000);
                break;
            default:
                break;
            }
        }
    };

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

    private void init() {
        tv_demo_number = (TextView) findViewById(R.id.tv_demo_number);
        btn_demo_increase = (Button) findViewById(R.id.btn_demo_increase);
        btn_demo_decrease = (Button) findViewById(R.id.btn_demo_decrease);
        btn_demo_pause = (Button) findViewById(R.id.btn_demo_pause);

        btn_demo_increase.setOnClickListener(this);
        btn_demo_decrease.setOnClickListener(this);
        btn_demo_pause.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        if(v==btn_demo_increase) {//自动增加  what =1
            //限制Button可操作性
            btn_demo_increase.setEnabled(false);
            btn_demo_decrease.setEnabled(true);
            btn_demo_pause.setEnabled(true);

            //停止减少(移除未处理的减少的消息)
            handler.removeMessages(WHAT_DECREASE);
            //发消息(增加)
            handler.sendEmptyMessage(WHAT_INCREASE);
        } else if(v==btn_demo_decrease) {//自动减少 what=2
            //限制Button可操作性
            btn_demo_increase.setEnabled(true);
            btn_demo_decrease.setEnabled(false);
            btn_demo_pause.setEnabled(true);

            //停止增加(移除未处理的增加的消息)
            handler.removeMessages(WHAT_INCREASE);

            //发消息(减少)
            handler.sendEmptyMessage(WHAT_DECREASE);
        } else if(v==btn_demo_pause) {//暂停

            //限制Button可操作性
            btn_demo_increase.setEnabled(true);
            btn_demo_decrease.setEnabled(true);
            btn_demo_pause.setEnabled(false);

            //停止增加/减少(移除未处理的减少/增加的消息)
            handler.removeMessages(WHAT_INCREASE);
            handler.removeMessages(WHAT_DECREASE);
        }
    }