android ViewSwitcher的用法介绍

    ViewSwitcher 的作用简单来说就是：在两个视图间转换时显示动画

它的两个子类应该很熟悉，ImageSwitcher：转换图片时增加动画效果;TextSwitcher：转换文字时增加动画效果;其实例见apidemos中ImageSwitcher实例和TextSwitcher实例

但不要忽略ViewSwicher,在一些场合还是很有用的

在android里视图切换是一个很常见的需求，比如说加载view和后台背景，当后台加载数据时，loding view显示，数据View隐藏，加载完成，反向此过程。使用ViewSwicher提供了简单的逻辑，产生更可读的代码。

举个最常见的例子，模拟点击LoadMoreItems按钮或得更多数据。

<?xml version= "1.0" encoding= "utf-8" ?>
<Button xmlns:android= "http://schemas.android.com/apk/res/android"
    android:id= "@+id/btn_loadmorecontacts"
    android:text= "Load More Items"
    android:layout_width= "fill_parent"
    android:layout_height= "wrap_content"
    android:textAppearance= "?android:attr/textAppearanceLarge"
    android:minHeight= "?android:attr/listPreferredItemHeight"
    android:textColor= "#FFFFFF"
    android:background= "@android:drawable/list_selector_background"
    android:clickable= "true"
    android:onClick= "onClick" />

大致是这样子

 

 

加载中视图：

<?xml version= "1.0" encoding= "utf-8" ?>
<RelativeLayout xmlns:android= "http://schemas.android.com/apk/res/android"
    android:layout_width= "wrap_content"
    android:layout_height= "wrap_content"
    android:gravity= "center_horizontal"
    android:minHeight= "?android:attr/listPreferredItemHeight" >

    <ProgressBar
        android:id= "@+id/progressbar"
        android:layout_width= "wrap_content"
        android:layout_height= "wrap_content"
        android:layout_centerVertical= "true" />

    <TextView
        android:text= "Loading…"
        android:textAppearance= "?android:attr/textAppearanceLarge"
        android:layout_height= "wrap_content"
        android:layout_width= "wrap_content"
        android:layout_toRightOf= "@+id/progressbar"
        android:layout_centerVertical= "true"
        android:gravity= "center"
        android:padding= "10dip"
        android:textColor= "#FFFFFF" />
</RelativeLayout>

 

 

 

 

public class ViewSwitcherExample extends ListActivity
                 implements OnClickListener {

    //sample list items
    static final String[] ITEMS = new String[]
          { "List Item 1" , "List Item 2" ,
            "List Item 3" , "List Item 4" ,
            "List Item 5" , "List Item 6" ,
            "List Item 7" , "List Item 8" ,
            "List Item 9" , "List Item 10" };

    //the ViewSwitcher
    private ViewSwitcher switcher;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
      super .onCreate(savedInstanceState);

      //no window title
      requestWindowFeature(Window.FEATURE_NO_TITLE);

      //create the ViewSwitcher in the current context
      switcher = new ViewSwitcher( this );

      //footer Button: see XML1
      Button footer = (Button)View.inflate( this , R.layout.btn_loadmore, null );

      //progress View: see XML2
      View progress = View.inflate( this , R.layout.loading_footer, null );

      //add the views (first added will show first)
      switcher.addView(footer);
      switcher.addView(progress);

      //add the ViewSwitcher to the footer
      getListView().addFooterView(switcher);

      //add items to the ListView
      setListAdapter( new ArrayAdapter( this ,
              android.R.layout.simple_list_item_1, ITEMS));
    }

    @Override /* Load More Button Was Clicked */
    public void onClick(View arg0) {
        //first view is showing, show the second progress view
        switcher.showNext();
        //and start background work
        new getMoreItems().execute();
    }

    /** Background Task To Get More Items**/
    private class getMoreItems extends AsyncTask {
        @Override
        protected Object doInBackground(Void… params) {
            //code to add more items
            //...
            try {
                Thread.sleep(3000); //only to demonstrate
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return null ;
        }

        @Override /* Background Task is Done */
        protected void onPostExecute(Object result) {
            //go back to the first view
            switcher.showPrevious();
                        //update the ListView
        }
    }
}

当然你也可以使用xml形式构造ViewSwicher,这里加上了系统自带的切换效果@android:anim/slide_in_left和@android:anim/slide_out_right

<?xmlversion= "1.0" encoding= "utf-8" ?>
<ViewSwitcherxmlns:android= "http://schemas.android.com/apk/res/android"

android:id= "@+id/profileSwitcher"
android:layout_width= "fill_parent"

android:layout_height= "fill_parent"
android:inAnimation= "@android:anim/slide_in_left"

android:outAnimation= "@android:anim/slide_out_right" >
<RelativeLayout

android:layout_width= "wrap_content"
android:layout_height= "wrap_content" >

<ProgressBar
android:id= "@+id/progressbar"

android:layout_width= "wrap_content"
android:layout_height= "wrap_content"

android:layout_centerVertical= "true" />
<TextView

android:text= "Loading…"
android:layout_height= "wrap_content"

android:layout_width= "wrap_content"
android:layout_toRightOf= "@+id/progressbar"

android:gravity= "center" />
</RelativeLayout>


<RelativeLayout

android:layout_width= "wrap_content"
android:layout_height= "wrap_content"

android:gravity= "center_horizontal" >
<TextView

android:text= "Finished!"
android:layout_height= "wrap_content"

android:layout_width= "wrap_content"
android:layout_centerVertical= "true" />

</RelativeLayout>


</ViewSwitcher>