Activity初步

首先我们先创建一个Activity，所谓的Activity，就是平时WEB开发中经常接触到的页面（Page），我们可以这样来理解

1、在src文件夹的包下面，创建MainActivity.java

 1 package com.example.helloworld;
 2 
 3 import android.os.Bundle;
 4 import android.app.Activity;
 5 import android.view.Menu;
 6 import android.view.MenuItem;
 7 import android.widget.Button;
 8 import android.widget.TextView;
 9 import android.support.v4.app.NavUtils;
10 
11 
12 public class MainActivity extends Activity {
13 
14     @Override
15     public void onCreate(Bundle savedInstanceState) {
16         super.onCreate(savedInstanceState);
17         setContentView(R.layout.activity_main);
18         TextView myTextView=(TextView)findViewById(R.id.myTextView);
19         Button myButton=(Button)findViewById(R.id.myButton);
20         myTextView.setText("我的第一个Android程序");
21         myButton.setText("确定");
22     }
23 
24     @Override
25     public boolean onCreateOptionsMenu(Menu menu) {
26         getMenuInflater().inflate(R.menu.activity_main, menu);
27         return true;
28     }
29 
30    
31 }

2、在res目录下面创建MainActivity.java的布局文件，activity_main.xml

 1 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 2     xmlns:tools="http://schemas.android.com/tools"
 3     android:layout_width="fill_parent"
 4     android:layout_height="fill_parent" >
 5 
 6     <TextView
 7         android:id="@+id/myTextView"
 8         android:layout_width="fill_parent"
 9         android:layout_height="wrap_content"
10         android:layout_centerHorizontal="true"
11         android:layout_centerVertical="true"
12         android:padding="@dimen/padding_medium"
13         tools:context=".MainActivity" />
14 
15         <Button
16             android:id="@+id/myButton"
17            android:layout_width="fill_parent"
18          android:layout_height="wrap_content"/>
19 </RelativeLayout>

3、gen下面的R.java是工具自动帮我们生成的一个全局性文件，如果工程里面有任何一个错误，都会导致R.java生成失败。

 1 package com.example.helloworld;
 2 
 3 public final class R {
 4     public static final class attr {
 5     }
 6     public static final class dimen {
 7         public static final int padding_large=0x7f040002;
 8         public static final int padding_medium=0x7f040001;
 9         public static final int padding_small=0x7f040000;
10     }
11     public static final class drawable {
12         public static final int ic_action_search=0x7f020000;
13         public static final int ic_launcher=0x7f020001;
14     }
15     public static final class id {
16         public static final int menu_settings=0x7f080002;
17         public static final int myButton=0x7f080001;
18         public static final int myTextView=0x7f080000;
19     }
20     public static final class layout {
21         public static final int activity_main=0x7f030000;
22     }
23     public static final class menu {
24         public static final int activity_main=0x7f070000;
25     }
26     public static final class string {
27         public static final int app_name=0x7f050000;
28         public static final int hello_world=0x7f050001;
29         public static final int menu_settings=0x7f050002;
30         public static final int title_activity_main=0x7f050003;
31     }
32     public static final class style {
33         public static final int AppTheme=0x7f060000;
34     }
35 }

4、工程主目录下面的AndroidManifest.xml，注册这样的一个Activity

 1 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
 2     package="com.example.helloworld"
 3     android:versionCode="1"
 4     android:versionName="1.0" >
 5 
 6     <uses-sdk
 7         android:minSdkVersion="4"
 8         android:targetSdkVersion="15" />
 9 
10     <application
11         android:icon="@drawable/ic_launcher"
12         android:label="@string/app_name"
13         android:theme="@style/AppTheme" >
14         <activity
15             android:name=".MainActivity"
16             android:label="@string/title_activity_main" >
17             <intent-filter>
18                 <action android:name="android.intent.action.MAIN" />
19 
20                 <category android:name="android.intent.category.LAUNCHER" />
21             </intent-filter>
22         </activity>
23     </application>
24 
25 </manifest>

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顺势而为