（Android学习系列）一，用按钮实现时间的显示

我们先用AndroidStudio新建一个项目，选择空白模板，然后像其中拖入两个Button，将他们的id分别命名为btDate(显示日期)，btTime(显示时间)，他的模板

 1 <??> 2 <RelativeLayout ="http://schemas.android.com/apk/res/android" 3   ="http://schemas.android.com/tools" 4   android:layout_width="match_parent" 5   android:layout_height="match_parent" 6   android:paddingBottom="@dimen/activity_vertical_margin" 7   android:paddingLeft="@dimen/activity_horizontal_margin" 8   android:paddingRight="@dimen/activity_horizontal_margin" 9   android:paddingTop="@dimen/activity_vertical_margin"10   tools:context="com.neil.ad01.MainActivity">11 12 13   <Button14     android:layout_width="wrap_content"15     android:layout_height="wrap_content"16     android:text="显示当前日期"17     android:id="@+id/btDate"18     android:layout_alignParentLeft="true"19     android:layout_alignParentStart="true"20     android:layout_alignParentTop="true" />21 22   <Button23     android:layout_width="wrap_content"24     android:layout_height="wrap_content"25     android:text="显示当前时间"26     android:id="@+id/btTime"27     android:layout_below="@+id/btDate"28     android:layout_alignParentLeft="true"29     android:layout_alignParentStart="true" />30 </RelativeLayout>

如图所示

images/loading.gif' 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

一个标准的Android应用程序窗口类需要继承android.app.Activity类，至少实现onCreate方法来初始化这个窗口。接下来实现方法

 1 package com.neil.ad01; 2  3 import android.app.Activity; 4 import android.app.AlertDialog; 5 import android.content.Intent; 6 import android.os.Bundle; 7 import android.view.View; 8 import android.widget.Button; 9 10 import java.text.SimpleDateFormat;11 import java.util.Date;12 13 public class MainActivity extends Activity implements View.OnClickListener14 {15 16   private void showDialog(String title,String msg)17   {18     AlertDialog.Builder builder=new AlertDialog.Builder(this);19     //设置对话框的图标20     builder.setIcon(android.R.drawable.ic_dialog_info);21     //设置对话框的标题22     builder.setTitle(title);23     //设置对话框的信息24     builder.setMessage(msg);25     //设置对话框的按钮26     builder.setPositiveButton("确定",null);27     //显示对话框28     builder.create().show();29 30     Intent intent;31   }32   //初始化窗口33   @Override34   protected void onCreate(Bundle savedInstanceState) {35     super.onCreate(savedInstanceState);36     //装载了View(刚才编写的37     setContentView(R.layout.activity_main);38     //获得两个按钮对象的实例39     Button btDate=(Button)findViewById(R.id.btDate);40     Button btTime=(Button)findViewById(R.id.btTime);41     //为两个按钮添加单击事件的监听（实现了OnClickListener接口的对象）42     btDate.setOnClickListener(this);43     btTime.setOnClickListener(this);44   }45 46   //两个按钮共用一个单击事件，通过按钮的id区分单击了哪个按钮47   @Override48   public void onClick(View v) {49     switch (v.getId())50     {51       case R.id.btDate: {52         SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");53         //显示当前日期54         showDialog("当前日期", sdf.format(new Date()));55         break;56       }57       case R.id.btTime: {58         SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");59         //显示当前日期60         showDialog("当前时间", sdf.format(new Date()));61         break;62       }63     }64   }65 }

注：1，AlertDialog可用于显示对话框

　　2，如果多个控件共用一个事件方法，必须在布局文件中指定控件标签的android:id属性，并且每个控件的id属性不能相同

　　3.res(resource)目录中的每一个资源文件都会在gen目录下的R类中生成一个int类型的变量，用于标识当前资源文件。所以在onCreate方法中可以通过R.layout.activity_main引用activity_main.

其中还可以在string.

<resources>  <string name="app_name">显示日期时间</string>  <string name="title_activity_main">显示日期时间</string></resources>

至此，代码部分全部写完。

　　然后点击运行按钮，在模拟器中生成app,如图