Android为ViewPager添加切换动画——自己定义ViewPager

我们在这个案例模仿上篇博客中的DepthPageTransformer动画效果吧。我们自己定义两种动画。一个Scale动画和一个Translate动画，使两个动画交替一起运行就能够模仿出DepthPageTransformer这种平移缩放的动画效果出来，代码非常easy，不单独贴出了。以下有完整的代码的。

public class ViewPagerWithTransformer extends ViewPager {// 左边的View
private View mLeftView;
// 右边的View
private View mRightView;
// 平移动画的梯度值
private float mTranslate;
// 缩放动画的梯度值
private float mScale;
// 最小缩放比例
private static final float MIN_SCALE = 0.6f;
// 保存ViewPager上View的对象
private Map<Integer, View> mViewCache = new HashMap<Integer, View>();/**
* 设置View的缓存
*
* @param position
* @param viewCache
*/
public void setViewCache(Integer position, View viewCache) {
mViewCache.put(position, viewCache);
}/**
* 从View的缓存集合中移除指定position的View
*
* @param position
*/
public void removeViewCache(Integer position) {
mViewCache.remove(position);
}public ViewPagerWithTransformer(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
}@Override
protected void onPageScrolled(int position, float offset, int offsetPixels) {
super.onPageScrolled(position, offset, offsetPixels);
mLeftView = mViewCache.get(position);
mRightView = mViewCache.get(position + 1);
animStack(mLeftView, mRightView, offset, offsetPixels);
}private void animStack(View left, View right, float offset, int offsetPixels) {
// TODO Auto-generated method stub
if (right != null) {
// 从第0页——》到第1页，offset:0~1。缩放比例mScale:0.6~1
mScale = (1 - MIN_SCALE) * offset + MIN_SCALE;
//平移的距离
mTranslate = -getWidth() - getPageMargin() + offsetPixels;//使用NineOldAndroids编写属性动画
ViewHelper.setScaleX(right, mScale);
ViewHelper.setScaleY(right, mScale);
ViewHelper.setTranslationX(right, mTranslate);
}
if (left != null) {
// 左边的页永远在最上面
left.bringToFront();
}
}
}

在布局文件里申明，activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" > <com.example.viewpagerwithtransformeranim.ViewPagerWithTransformer
android:id="@+id/viewpager"
android:layout_width="match_parent"
android:layout_height="match_parent" >
</com.example.viewpagerwithtransformeranim.ViewPagerWithTransformer></RelativeLayout>

在Activity中使用这个控件。MainActivity.java

public class MainActivity extends Activity {private int[] imgRes = new int[] { R.drawable.guide_image1, R.drawable.guide_image2, R.drawable.guide_image3 };
private List<ImageView> imgList = new ArrayList<ImageView>();
private ViewPagerWithTransformer mViewPager;@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.activity_main);
mViewPager = (ViewPagerWithTransformer) findViewById(R.id.viewpager);
mViewPager.setAdapter(new PagerAdapter() {@Override
public boolean isViewFromObject(View arg0, Object arg1) {
return arg0 == arg1;
}@Override
public int getCount() {
return imgRes.length;
}@Override
public Object instantiateItem(ViewGroup container, int position) {
ImageView mImageView = new ImageView(MainActivity.this);
mImageView.setBackgroundResource(imgRes[position]);
mImageView.setScaleType(ScaleType.CENTER_CROP);
imgList.add(mImageView);
//给ViewPager设置View缓存
mViewPager.setViewCache(position, mImageView);
container.addView(mImageView);
return mImageView;
}@Override
public void destroyItem(ViewGroup container, int position, Object object) {
//移除ViewPager的View缓存
mViewPager.removeViewCache(position);
container.removeView(imgList.get(position));
}
});
}
}

好，所有源代码在上面了，注意一下，在给ViewPager设置的适配器PagerAdapter里面重写instantiateItem方法时。一定要记得调用mViewPager.setViewCache(position, mImageView)方法，给ViewPager设置View缓存。然后在重写destroyItem方法中调用mViewPager.removeViewCache(position)方法移除View缓存。