使用Android自带Gallery组件实现CoverFlow
源代码转载自国外Neil Davies，使用Apache2.0开源协议
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。
/* * Copyright (C) 2010 Neil Davies * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * 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))); } } }
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，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。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。
public class GalleryFlow extends Gallery { // Graphics Camera used for transforming the matrix of ImageViews private Camera mCamera = new Camera(); //The maximum angle the Child ImageView will be rotated by private int mMaxRotationAngle = 60; // The maximum zoom on the centre Child private int mMaxZoom = -120; // The Centre of the Coverflow */ private int mCoveflowCenter; public GalleryFlow(Context context) { super(context); this.setStaticTransformationsEnabled(true); } public GalleryFlow(Context context, AttributeSet attrs) { super(context, attrs); this.setStaticTransformationsEnabled(true); } public GalleryFlow(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); this.setStaticTransformationsEnabled(true); } /** * Get the max rotational angle of the image * @return the mMaxRotationAngle */ public int getMaxRotationAngle() { return mMaxRotationAngle; } /** * Set the max rotational angle of each image * @param maxRotationAngle the mMaxRotationAngle to set */ public void setMaxRotationAngle(int maxRotationAngle) { mMaxRotationAngle = maxRotationAngle; } /** * Get the Max zoom of the centre image @return the mMaxZoom */ public int getMaxZoom() { return mMaxZoom; } /** * Set the max zoom of the centre image @param maxZoom* the mMaxZoom to set */ public void setMaxZoom(int maxZoom) { mMaxZoom = maxZoom; } /** * Get the Centre of the Coverflow * * @return The centre of this Coverflow. */ private int getCenterOfCoverflow() { return (getWidth() - getPaddingLeft() - getPaddingRight()) / 2 + getPaddingLeft(); } /** * Get the Centre of the View @return The centre of the given view. */ private static int getCenterOfView(View view) { return view.getLeft() + view.getWidth() / 2; } /** * {@inheritDoc} @see #setStaticTransformationsEnabled(boolean) */ 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; } /** * This is called during layout when the size of this view has changed. If * you were just added to the view hierarchy, you're called with the old * values of 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); } /** * Transform the Image Bitmap by the Angle passed * @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); // 在Z轴上正向移动camera的视角，实际效果为放大图片。 // 如果在Y轴上移动，则图片上下移动；X轴上对应图片左右移动。 mCamera.translate(0.0f, 0.0f, 100.0f); // As the angle of the view gets less, zoom in if (rotation < mMaxRotationAngle) { float zoomAmount = (float) (mMaxZoom + (rotation * 1.5)); mCamera.translate(0.0f, 0.0f, zoomAmount); } // 在Y轴上旋转，对应图片竖向向里翻转。 // 如果在X轴上旋转，则对应图片横向向里翻转。 mCamera.rotateY(rotationAngle); mCamera.getMatrix(imageMatrix); imageMatrix.preTranslate(-(imageWidth / 2), -(imageHeight / 2)); imageMatrix.postTranslate((imageWidth / 2), (imageHeight / 2)); mCamera.restore(); } }
下面是调用的Activity示例：
public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.layout_gallery); Integer[] images = { R.drawable.img0001, R.drawable.img0030, R.drawable.img0100, R.drawable.img0130, R.drawable.img0200, R.drawable.img0230, R.drawable.img0300, R.drawable.img0330, R.drawable.img0354 }; ImageAdapter adapter = new ImageAdapter(this, images); adapter.createReflectedImages(); GalleryFlow galleryFlow = (GalleryFlow) findViewById(R.id.gallery_flow); galleryFlow.setAdapter(adapter); }
PS1:
可以看出来这样实现的gallery锯齿问题比较严重。可以在createReflectedImages()使用以下代码：
BitmapDrawable bd = new BitmapDrawable(bitmapWithReflection); bd.setAntiAlias(true);
然后用iv.setImageDrawable(bd);
代替iv.setImageBitmap(bitmapWithReflection);
即可基本消除锯齿。
PS2:
ImageAdapter有待确定的MemoryLeak问题，貌似的Bitmap的decode方法会造成ML，使用ImageAdapter时多次旋 转屏幕后会出现OOM。目前可以通过将使用完毕的bimap调用recycle()方法和设置null并及时调用system.gc()得到一些改善，但 是问题并不明显。