新建佈局檔案activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/btnOk"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="開始計時"
        android:textSize="15dp" />

    <TextView
        android:id="@+id/tvTime"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="15dp" />


</LinearLayout>

新建MainActivity.java

package com.example.administrator.timer;

import android.os.Bundle;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private Button btnOk;
    private TextView tvTime;

    private boolean bStart=false;
    private Handler mHander=new Handler();
    private int mCount=0;

    private Runnable mCounter=new Runnable() {
        @Override
        public void run() {
            mCount++;
            tvTime.setText("當前計數值:"+mCount);
            mHander.postDelayed(this,1000);
        }
    };

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

    private void initView() {
        btnOk = (Button) findViewById(R.id.btnOk);
        tvTime = (TextView) findViewById(R.id.tvTime);

        btnOk.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.btnOk:
                if (bStart==false){
                    btnOk.setText("停止計時");
                    mHander.post(mCounter);
                }else{
                    btnOk.setText("開始計時");
                    mHander.removeCallbacks(mCounter);
                }
                bStart=!bStart;
                break;
        }
    }
}

發中經常利用Handler啟動任務。下面是Handler處理Runnable任務的常見方法說明:

●post: 立即啟動Runnable任務。

●postDelayed:延遲若干時間後啟動Runnable任務。

●postAtTime:在指定時間啟動Runnable任務。

●removeCallbacks: 移除指定的Runnable任務。

原文：https://www.cnblogs.com/ldy731729142/p/12608820.html