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

        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" 

        android:gravity="center_horizontal">

    < 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 :text= "@string/start" />

< 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);

t imeView.setText(time);

if( running){

seconds++;

}

handler.postDelayed( this, 1000);

}

});

}

}