二期Android项目 - TabHost界面

        在该项目中首先是做一个TabHost界面,本来对Android知识都不是很了解,现在只有查询SDK来开始学习Tab选项。一步一步的学习……

1、TabHost用法

HelloTabWidget.java:

public class HelloTabWidget extends TabActivity {

    public void onCreate(Bundle savedInstanceState) {

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

        Resources res = getResources(); // Resource object to get Drawables
        TabHost tabHost = getTabHost(); // The activity TabHost.取得TablHost引用
    
        // Resusable TabSpec for each tab.对于每一个tab,TabHost.TabSpec被用来定义tab属性
        TabHost.TabSpec spec;
        Intent intent; // Reusable Intent for each tab

        // Create an Intent to launch an Activity for the tab (to be reused)
        intent = new Intent().setClass(this, ArtistsActivity.class);

        /* *
         * Initialize a TabSpec for each tab and add it to the TabHost
         * newTabSpec(String) 创建一个新的TabHost.TabSpec实例
         * setIndicator(CharSequence, Drawable) 设置标签的文本和图标
         * */
       spec = tabHost.newTabSpec("artists")
        .setIndicator("Artists",
                res.getDrawable(R.drawable.ic_tab_artists))
        .setContent(intent);//打开Activity
        tabHost.addTab(spec);//加入TabHost

        // Do the same for the other tabs
        intent = new Intent().setClass(this, AlbumsActivity.class);
        spec = tabHost
                .newTabSpec("albums")
                .setIndicator("Albums",
                        res.getDrawable(R.drawable.ic_tab_artists))
                .setContent(intent);
        tabHost.addTab(spec);

        intent = new Intent().setClass(this, SongsActivity.class);
        spec = tabHost
                .newTabSpec("songs")
                .setIndicator("Songs",
                        res.getDrawable(R.drawable.ic_tab_artists))
                .setContent(intent);
        tabHost.addTab(spec);
        //在最后,打开一个Tab显示为默认:setCurrentTab(int),int是要打开的Tab的索引值 
        tabHost.setCurrentTab(2);
        /*
         * 需要注意:
         * Notice that not once was the TabWidget object referenced. 
         * This is because a TabWidget must always be a child of a TabHost, 
         * which is what you use for almost all interaction with the tabs. 
         * So when a tab is added to the TabHost, 
         * it's automatically added to the child TabWidget.
         */
    }
}
对应的布局文件:main.xml

<?xml version="1.0" encoding="utf-8"?>
<TabHost xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@android:id/tabhost"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <LinearLayout
        android:orientation="vertical"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:padding="5dp">
        <TabWidget
            android:id="@android:id/tabs"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content" />
        <FrameLayout
            android:id="@android:id/tabcontent"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:padding="5dp" />
    </LinearLayout>
</TabHost>
res/drawable/ic_tab_artists.xml:

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

<selector xmlns:android="http://schemas.android.com/apk/res/android">
 <!-- When selected, use grey -->
    <item android:drawable="@drawable/ic_tab_artists_grey"
          android:state_selected="true" />
    <!-- When not selected, use white-->
    <item android:drawable="@drawable/ic_tab_artists_white" />
</selector>
AlbumsActivity.java、ArtistsActivity.java、SongsActivity.java代码与下面的内容类似,只不过是改下TextView的内容

public class SongsActivity extends Activity {
	
    @Override
    public void onCreate(Bundle savedInstanceState) {
    	 super.onCreate(savedInstanceState);

         TextView textview = new TextView(this);
         textview.setText("SongsActivity tab");
         setContentView(textview);

    }
}
在这个二期项目中上述有一点不明白的是:res/drawable/ic_tab_artists.xml:这个文件的运行机理是什么?


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