android学习之TransitionDrawable …

Drawable的例子，体现出Drawable的强大功能。Android SDK中说明了Drawable主要的作用是：在XML中定义各种动画，然后把 XML当作Drawable资源来读取，通过Drawable显示动画。

下面举个使用TransitionDrawable 的例子，创建一个Android工程，然后再这个工程的基础上修改，修改过程如下：
1、去掉layout/main.xml中的TextView，增加ImagView，如下：

<ImageView
 android:layout_width=”wrap_content”
 android:layout_height=”wrap_content”
 android:tint=”#55ff0000″
 android:src=”@drawable/my_image”/>2、创建一个XML文件，命名为expand_collapse.xml，内容如下：
 <?xml version=”1.0″ encoding=”UTF-8″?>
 <transition xmlns:android=”http://schemas.android.com/apk/res/android”>
 <item android:drawable=”@drawable/image_expand”/>
 <item android:drawable=”@drawable/image_collapse”/>
 </transition>
 需要3张png图片，存放到res\drawable目录下，3张图片分别命名为：my_image.png、image_expand.png、image_collapse.png。3、修改Activity中的代码，内容如下：
 LinearLayout mLinearLayout;
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 mLinearLayout = new LinearLayout(this);
 ImageView i = new ImageView(this);
 i.setAdjustViewBounds(true);
 i.setLayoutParams(new Gallery.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
 mLinearLayout.addView(i);
 setContentView(mLinearLayout);
 Resources res = getResources();
 TransitionDrawable transition =
 (TransitionDrawable) res.getDrawable(R.drawable.expand_collapse);
 i.setImageDrawable(transition);
 ansition.startTransition(10000);}

4、如果修改的没有错误，运行程序，结果显示如下：
初始图片

屏幕上动画显示的是：从图片image_expand.png过渡到image_collapse.png，也就是我们在expand_collapse.xml中定义的一个transition动画。看完这个例子，你对Drawable的理解是否又深入些？这里提供这个程序的源代码，供大家下载，可以在这个例子的基础上去体会其他的Drawable，来加深对Drawable的理解。

总结说明

通过以上2个例子程序，相信对Drawable会有一定的认识了，在以后的篇幅中会介绍更多的例子，更加深入的学习和理解Drawable。具体还有哪些Drawable，大家到Android SDK去深入学习吧。

实现上图效果:

xml部份文件:
<SlidingDrawer  
      android:id="@+id/slidingdrawer" 
      android:layout_width="fill_parent" 
      android:layout_height="fill_parent" 
      android:orientation="horizontal" 
      android:handle="@+id/handle" 
      android:content="@+id/content">  
      <ImageView  
               android:id="@+id/handle" 
               android:layout_width="56dip"
               android:layout_height="fill_parent"
              android:background="@drawable/handle"                 
               android:focusable="true"
               android:clickable="true"
                 
               android:scaleType="center"    
              android:src="@drawable/handle_icon"         />  
      <LinearLayout  
          android:id="@+id/content" 
          android:layout_width="fill_parent" 
          android:layout_height="fill_parent" 
          android:background="#778899">  
          <Button  
              android:id="@+id/button" 
              android:layout_width="wrap_content" 
              android:layout_height="wrap_content" 
              android:text="Button" 
          />  
          <EditText  
              android:id="@+id/editText" 
              android:layout_width="fill_parent" 
              android:layout_height="wrap_content" 
          />  
      </LinearLayout>  
  </SlidingDrawer>   
hand_icon.xml
<?xml version="1.0" encoding="utf-8"?>
 <transition xmlns:android="http://schemas.android.com/apk/res/android">
     <item android:drawable="@drawable/ic_tray_expand"  />
     <item android:drawable="@drawable/ic_tray_collapse"  />
 </transition>
hand.xml
<?xml version="1.0" encoding="utf-8"?>
 <selector xmlns:android="http://schemas.android.com/apk/res/android">
     <item android:state_window_focused="false" android:state_enabled="true" android:drawable="@drawable/tray_handle_normal" />
     <item android:state_pressed="true" android:drawable="@drawable/tray_handle_pressed" />
     <item android:state_focused="true" android:state_enabled="true" android:drawable="@drawable/tray_handle_selected" />
     <item android:state_enabled="true" android:drawable="@drawable/tray_handle_normal" />
     <item android:state_focused="true" android:drawable="@drawable/tray_handle_selected" />
 </selector> 代码部份:
 mDrawer = (SlidingDrawer) findViewById(R.id.slidingdrawer);
   final SlidingDrawer drawer = mDrawer; mLinearLayout = (LinearLayout) drawer.getContent();
   final LinearLayout grid = mLinearLayout;
 mImageView = (ImageView) drawer.findViewById(R.id.handle);
 mHandleIcon = (TransitionDrawable) mImageView.getDrawable();
   mHandleIcon.setCrossFadeEnabled(true);
 final DrawerManager drawerManager = new DrawerManager();
   drawer.setOnDrawerOpenListener(drawerManager);
   drawer.setOnDrawerCloseListener(drawerManager);
   drawer.setOnDrawerScrollListener(drawerManager);
private class DrawerManager implements SlidingDrawer.OnDrawerOpenListener,
    SlidingDrawer.OnDrawerCloseListener,
    SlidingDrawer.OnDrawerScrollListener {
   private boolean mOpen; public void onDrawerOpened() {
    Log.v(tag, "onDrawerOpened");
    if (!mOpen) {
    mHandleIcon.reverseTransition(150);    mOpen = true;
    }
   } private void offsetBoundsToDragLayer(Rect bounds, View view) {
    view.getDrawingRect(bounds);
    Log.v(tag, "offsetBoundsToDragLayer");
   } public void onDrawerClosed() {
    Log.v(tag, "onDrawerClosed");
    if (mOpen) {
     mHandleIcon.reverseTransition(150);    mOpen = false;
    } }
 public void onScrollStarted() {
    if (PROFILE_DRAWER) {
     android.os.Debug.startMethodTracing("/sdcard/launcher-drawer");
    }
   } public void onScrollEnded() {
    if (PROFILE_DRAWER) {
     android.os.Debug.stopMethodTracing();
    }
   }
  }