初学Android做计时器和代码

今天做的第一个程序是Head First Android development的Chapter4做一个计时app.

Android开发分为layout和activity开发，当然这样说肯定不合理，就先这么理解，为了继续学习。简化问题是一个不错的学习方式，但是会造成眼高手低的毛病。下面是layout开发

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout<!--线性布局方式-->

        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" 

        android:paddingBottom="16dp" 

        android:paddingLeft="16dp" 

        android:paddingRight="16dp"

        android:paddingTop="16dp" 

        tools:context="com.example.a17315.stopwatch.StopwatchActivity" 

        android:orientation="vertical"<!--子控件TextView，Button垂直排列--> 

        android:gravity="center_horizontal"<!--内部元素TextView，Button居中方式-->>

    <TextView 

        android:id="@+id/time_view" 

        android:layout_width="wrap_content" 

        android:layout_height="wrap_content" 

        android:layout_alignParentTop="true" 

        android:layout_centerHorizontal="true" 

        android:layout_marginTop="0dp" 

        android:text="" 

        android:textAppearance="?android:attr/textAppearanceLarge" 

        android:textSize="92sp" />

<Button 

       android:id="@+id/start_button" 

       android:layout_width="wrap_content" 

       android:layout_height="wrap_content" 

       android:layout_below="@+id/time_view" 

       android:layout_marginTop="20dp" 

       android:layout_centerHorizontal="true" 

       android:onClick="onClickStart"<!--Android 的 activity里面要实现的方法--> 

       android:text="@string/start" /><!--在res文件夹下的values下的string.xml中需要添加的值如下图-->

<Button 

       android:id="@+id/stop_button" 

       android:layout_width="wrap_content" 

       android:layout_height="wrap_content" 

       android:layout_below="@+id/start_button" 

       android:layout_marginTop="10dp" 

       android:layout_centerHorizontal="true" 

       android:onClick="onClickStop" 

       android:text="@string/stop" />

<Button 

       android:id="@+id/rest_button" 

       android:layout_width="wrap_content" 

       android:layout_height="wrap_content" 

       android:layout_below="@id/stop_button" 

       android:layout_marginTop="10dp" 

       android:layout_centerHorizontal="true" 

       android:onClick="onClickReset" 

       android:text="@string/reset" /></LinearLayout>

String.xml中的内容

                        

下面就是StopwatchActivity.java

        

package com.example.a17315.stopwatch;

import android.os.Handler;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.app.Activity;

import android.view.View;

import android.widget.TextView;

public class StopwatchActivity extends AppCompatActivity {

//Numbers of seconds displayed in the stopwatch 

   private int seconds = 0;

//Is the stopwatch running 

   private boolean running;

@Override protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState); setContentView(R.layout.activity_stopwatch);

runTimer();

}

//Start the stopwatch running when the Start button is clicked 

   public void onClickStart(View view){ running = true;

}

//Stop the stopwatch running when the Stop button is clicked 

   public void onClickStop(View view){

running = false;

}

//Reset the stopwatch running when the Reset button is clicked 

   public void onClickReset(View view){

running = false; seconds = 0;

}

private void runTimer(){

final TextView timeView = (TextView)findViewById(R.id.time_view);

final Handler handler = new Handler(); handler.post(new Runnable() {

@Override 

         public void run() {

int hours = seconds/3600;

int minutes = (seconds%3600)/60;

int secs = seconds%60; String time = String.format("%d:%02d:%02d",hours,minutes,secs);

timeView.setText(time);

if(running){

seconds++;

}

handler.postDelayed(this,1000);

}

});

}

}