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。

效果图：
[img]
[img]http://dl.iteye.com/upload/attachment/0066/8103/02103f1e-93f5-3418-83fa-7876fa314876.jpg[/img]
[/img]

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。

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。

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。

工程结构图：
[img]
[img]http://dl.iteye.com/upload/attachment/0066/8105/3dd03163-ba37-3772-9966-6966e6d31966.jpg[/img]
[/img]


CoverFlow：

package com.coverflow;

import android.content.Context;
import android.graphics.Camera;
import android.graphics.Matrix;
import android.util.AttributeSet;
import android.view.View;
import android.view.animation.Transformation;
import android.widget.Gallery;
import android.widget.ImageView;

public class CoverFlow extends Gallery {

	private Camera mCamera = new Camera();
	private int mMaxRotationAngle = 50;//60;
	private int mMaxZoom = -380;//-120;
	private int mCoveflowCenter;
	private boolean mAlphaMode = true;
	private boolean mCircleMode = false;

	public CoverFlow(Context context) {
		super(context);
		this.setStaticTransformationsEnabled(true);
	}

	public CoverFlow(Context context, AttributeSet attrs) {
		super(context, attrs);
		this.setStaticTransformationsEnabled(true);
	}

	public CoverFlow(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);
		this.setStaticTransformationsEnabled(true);
	}

	public int getMaxRotationAngle() {
		return mMaxRotationAngle;
	}

	public void setMaxRotationAngle(int maxRotationAngle) {
		mMaxRotationAngle = maxRotationAngle;
	}

	public boolean getCircleMode() {
		return mCircleMode;
	}

	public void setCircleMode(boolean isCircle) {
		mCircleMode = isCircle;
	}

	public boolean getAlphaMode() {
		return mAlphaMode;
	}

	public void setAlphaMode(boolean isAlpha) {
		mAlphaMode = isAlpha;
	}

	public int getMaxZoom() {
		return mMaxZoom;
	}

	public void setMaxZoom(int maxZoom) {
		mMaxZoom = maxZoom;
	}

	private int getCenterOfCoverflow() {
		return (getWidth() - getPaddingLeft() - getPaddingRight()) / 2
				+ getPaddingLeft();
	}

	private static int getCenterOfView(View view) {
		return view.getLeft() + view.getWidth() / 2;
	}

	protected boolean getChildStaticTransformation(View child, Transformation t) {
		final int childCenter = getCenterOfView(child);
		final int childWidth = child.getWidth();
		int rotationAngle = 0;
		t.clear();
		t.setTransformationType(Transformation.TYPE_MATRIX);
		if (childCenter == mCoveflowCenter) {
			transformImageBitmap((ImageView) child, t, 0);
		} else {
			rotationAngle = (int) (((float) (mCoveflowCenter - childCenter) / childWidth) * mMaxRotationAngle);
			if (Math.abs(rotationAngle) > mMaxRotationAngle) {
				rotationAngle = (rotationAngle < 0) ? -mMaxRotationAngle
						: mMaxRotationAngle;
			}
			transformImageBitmap((ImageView) child, t, rotationAngle);
		}
		return true;
	}

	/**
	 * 这就是所谓的在大小的布局时,这一观点已经发生了改变。如果 你只是添加到视图层次,有人叫你旧的观念 价值观为0。
	 * 
	 * @param w
	 *            Current width of this view.
	 * @param h
	 *            Current height of this view.
	 * @param oldw
	 *            Old width of this view.
	 * @param oldh
	 *            Old height of this view.
	 */
	protected void onSizeChanged(int w, int h, int oldw, int oldh) {
		mCoveflowCenter = getCenterOfCoverflow();
		super.onSizeChanged(w, h, oldw, oldh);
	}

	/**
	 * 把图像位图的角度通过
	 * 
	 * @param imageView
	 *            ImageView the ImageView whose bitmap we want to rotate
	 * @param t
	 *            transformation
	 * @param rotationAngle
	 *            the Angle by which to rotate the Bitmap
	 */
	private void transformImageBitmap(ImageView child, Transformation t,
			int rotationAngle) {
		mCamera.save();
		final Matrix imageMatrix = t.getMatrix();
		final int imageHeight = child.getLayoutParams().height;
		final int imageWidth = child.getLayoutParams().width;
		final int rotation = Math.abs(rotationAngle);
		mCamera.translate(0.0f, 0.0f, 100.0f);

		// 如视图的角度更少,放大
		if (rotation <= mMaxRotationAngle) {
			float zoomAmount = (float) (mMaxZoom + (rotation * 1.5));
			mCamera.translate(0.0f, 0.0f, zoomAmount);
			if (mCircleMode) {
				if (rotation < 40)
					mCamera.translate(0.0f, 155, 0.0f);
				else
					mCamera.translate(0.0f, (255 - rotation * 2.5f), 0.0f);
			}
			if (mAlphaMode) {
				((ImageView) (child)).setAlpha((int) (255 - rotation * 2.5));
			}
		}
		mCamera.rotateY(rotationAngle);
		mCamera.getMatrix(imageMatrix);
		imageMatrix.preTranslate(-(imageWidth / 2), -(imageHeight / 2));
		imageMatrix.postTranslate((imageWidth / 2), (imageHeight / 2));
		mCamera.restore();
	}
}

ImageAdapter：

package com.coverflow;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.LinearGradient;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.PorterDuffXfermode;
import android.graphics.Bitmap.Config;
import android.graphics.PorterDuff.Mode;
import android.graphics.Shader.TileMode;
import android.graphics.drawable.BitmapDrawable;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;

public class ImageAdapter extends BaseAdapter {
	int mGalleryItemBackground;
	private Context mContext;
	private Integer[] mImageIds = { 
			R.drawable.a1,
			R.drawable.a2, 
			R.drawable.a3,
			R.drawable.a4, 
			R.drawable.a5 };

	public ImageAdapter(Context c) {
		mContext = c;
	}

	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) {

		ImageView i = createReflectedImages(mContext,mImageIds[position]);

		i.setLayoutParams(new CoverFlow.LayoutParams(120, 100));//120 100
		i.setScaleType(ImageView.ScaleType.CENTER_INSIDE);

		// 设置的抗锯齿
		BitmapDrawable drawable = (BitmapDrawable) i.getDrawable();
		drawable.setAntiAlias(true);
		return i;
	}

	public float getScale(boolean focused, int offset) {
		return Math.max(0, 1.0f / (float) Math.pow(2, Math.abs(offset)));
	}

	public ImageView createReflectedImages(Context mContext,int imageId) {

		Bitmap originalImage = BitmapFactory.decodeResource(mContext.getResources(), imageId);

		final int reflectionGap = 4;

		int width = originalImage.getWidth();
		int height = originalImage.getHeight();

		Matrix matrix = new Matrix();
		matrix.preScale(1, -1);

		Bitmap reflectionImage = Bitmap.createBitmap(originalImage, 0,
				height / 2, width, height / 2, matrix, false);

		Bitmap bitmapWithReflection = Bitmap.createBitmap(width,
				(height + height / 2), Config.ARGB_8888);

		Canvas canvas = new Canvas(bitmapWithReflection);

		canvas.drawBitmap(originalImage, 0, 0, null);

		Paint deafaultPaint = new Paint();
		canvas.drawRect(0, height, width, height + reflectionGap, deafaultPaint);

		canvas.drawBitmap(reflectionImage, 0, height + reflectionGap, null);

		Paint paint = new Paint();
		LinearGradient shader = new LinearGradient(0, originalImage
				.getHeight(), 0, bitmapWithReflection.getHeight()
				+ reflectionGap, 0x70ffffff, 0x00ffffff, TileMode.MIRROR);

		paint.setShader(shader);

		paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN));

		canvas.drawRect(0, height, width, bitmapWithReflection.getHeight()
				+ reflectionGap, paint);

		ImageView imageView = new ImageView(mContext);
		imageView.setImageBitmap(bitmapWithReflection);

		return imageView;
	}

}

HelloAndroid：

package com.coverflow;

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;

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

		CoverFlow cf = new CoverFlow(this);
		// cf.setBackgroundResource(R.drawable.shape);
		cf.setBackgroundColor(Color.BLACK);
		cf.setAdapter(new ImageAdapter(this));
		ImageAdapter imageAdapter = new ImageAdapter(this);
		cf.setAdapter(imageAdapter);
		// cf.setAlphaMode(false);
		// cf.setCircleMode(false);
		cf.setSelection(2, true);
		cf.setAnimationDuration(1000);
		setContentView(cf);
	}

}