使用Android自带Gallery组件实现CoverFlow首先声明，源代码转载自国外Neil Davies，使用Apache2.0开源协议，
使用Android自带Gallery组件实现CoverFlow
首先声明，源代码转载自国外Neil Davies，使用Apache2.0开源协议，请使用源代码的人自觉遵守协议内容。
本文为Kearnel原创，转载请注明出处。
http://www.eoeandroid.com/thread-39709-1-1.html
以下是正文：
使用过Android自带的gallery组件的人都知道，gallery实现的效果就是拖动浏览一组图片，相比iphone里也是用于拖动浏览图片的coverflow，显然逊色不少。实际上，可以通过扩展gallery，通过伪3D变换可以基本实现coverflow的效果。本文通过源代码解析这一功能的实现。具体代码作用可参照注释。
最终实现效果如下：
要使用gallery，我们必须首先给其指定一个adapter。在这里，我们实现了一个自定义的ImageAdapter，为图片制作倒影效果。
传入参数为context和程序内drawable中的图片ID数组。之后调用其中的createReflectedImages()方法分别创造每一个图像的倒影效果，生成对应的ImageView数组，最后在getView()中返回。
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* This code is base on the Android Gallery widget and was Created
* by Neil Davies neild001 'at' gmail dot com to be a Coverflow widget
*
* @author Neil Davies
*/
public class ImageAdapter extends BaseAdapter {
int mGalleryItemBackground;
private Context mContext;
private Integer[] mImageIds ;
private ImageView[] mImages;
public ImageAdapter(Context c, int[] ImageIds) {
mContext = c;
mImageIds = ImageIds;
mImages = new ImageView[mImageIds.length];
}
public boolean createReflectedImages() {
// The gap we want between the reflection and the original image
final int reflectionGap = 4;
int index = 0;
for (int imageId : mImageIds) {
Bitmap originalImage = BitmapFactory.decodeResource(
mContext.getResources(), imageId);
int width = originalImage.getWidth();
int height = originalImage.getHeight();
// This will not scale but will flip on the Y axis
Matrix matrix = new Matrix();
matrix.preScale(1, -1);
// Create a Bitmap with the flip matrix applied to it.
// We only want the bottom half of the image
Bitmap reflectionImage = Bitmap.createBitmap(originalImage, 0,
height / 2, width, height / 2, matrix, false);
// Create a new bitmap with same width but taller to fit
// reflection
Bitmap bitmapWithReflection = Bitmap.createBitmap(width,
(height + height / 2), Config.ARGB_8888);
// Create a new Canvas with the bitmap that's big enough for
// the image plus gap plus reflection
Canvas canvas = new Canvas(bitmapWithReflection);
// Draw in the original image
canvas.drawBitmap(originalImage, 0, 0, null);
// Draw in the gap
Paint deafaultPaint = new Paint();
canvas.drawRect(0, height, width, height + reflectionGap,
deafaultPaint);
// Draw in the reflection
canvas.drawBitmap(reflectionImage, 0, height + reflectionGap,
null);
// Create a shader that is a linear gradient that covers the
// reflection
Paint paint = new Paint();
LinearGradient shader = new LinearGradient(0,
originalImage.getHeight(), 0,
bitmapWithReflection.getHeight() + reflectionGap,
0x70ffffff, 0x00ffffff, TileMode.CLAMP);
// Set the paint to use this shader (linear gradient)
paint.setShader(shader);
// Set the Transfer mode to be porter duff and destination in
paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN));
// Draw a rectangle using the paint with our linear gradient
canvas.drawRect(0, height, width,
bitmapWithReflection.getHeight() + reflectionGap, paint);
ImageView imageView = new ImageView(mContext);
imageView.setImageBitmap(bitmapWithReflection);
imageView
.setLayoutParams(new GalleryFlow.LayoutParams(160, 240));
// imageView.setScaleType(ScaleType.MATRIX);
mImages[index++] = imageView;
}
return true;
}
public int getCount() {
return mImageIds.length;
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
// Use this code if you want to load from resources
/*
* ImageView i = new ImageView(mContext);
* i.setImageResource(mImageIds[position]); i.setLayoutParams(new
* CoverFlow.LayoutParams(350,350));
* i.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
*
* //Make sure we set anti-aliasing otherwise we get jaggies
* BitmapDrawable drawable = (BitmapDrawable) i.getDrawable();
* drawable.setAntiAlias(true); return i;
*/
return mImages[position];
}
/**
* Returns the size (0.0f to 1.0f) of the views depending on the
* 'offset' to the center.
*/
public float getScale(boolean focused, int offset) {
/* Formula: 1 / (2 ^ offset) */
return Math.max(0, 1.0f / (float) Math.pow(2, Math.abs(offset)));
}
}
}复制代码
仅仅实现了图片的倒影效果还不够，因为在coverflow中图片切换是有旋转和缩放效果的，而自带的gallery中并没有实现。因此，我们扩展自带的gallery，实现自己的galleryflow。在原gallery类中，提供了一个方法getChildStaticTransformation()以实现对图片的变换。我们通过覆写这个方法并在其中调用自定义的transformImageBitmap(“每个图片与gallery中心的距离”)方法，，即可实现每个图片做相应的旋转和缩放。其中使用了camera和matrix用于视图变换。具体可参考代码注释。
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1 楼 huxinli 2011-10-10 效果不错啊，多谢了啊。
