android ViewSwitcher

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，列表底部加载

Button more

<?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);
	  
	  //底部 Button: see XML1
	  Button footer = (Button)View.inflate(this, R.layout.btn_loadmore, null);
	  
	  //进度条View: see XML2
	  View progress = View.inflate(this, R.layout.loading_footer, null);
	  
	  //向viewSwitcher加入view (first added will show first)
	  switcher.addView(footer);
	  switcher.addView(progress);
	  
	  //listview底部加入swicher
	  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
		}
	}
}

switcher.showNext();  // Switches to the next view
switcher.showPrevious();  // Switches to the previous view

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

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

你喜欢的话可以加入动画效果，使用View gone、Visible方式还是ViewSwicher还是看自己喜好了