Android CoverFlow

It's been a while now and I've been pretty busy with life, work, and other things, but at last here's a new version of the coverflow widget that I released a while back. There's not really much new functionality here, but I have cut down the amount of code needed by a lot. Gone are the CoverAbsSpinner and the CoverAdapterView classes and now we are left with just the CoverFlow class weighing in at less than 200 lines of code. Of course, you still have to instantiate it and populate it using an ImageAdapter so I'll also include the activity class for doing those tasks as well.

Background

The basic idea is that the Coverflow widget works very much like the standard Android Gallery widget, but with the addition of the rotation of the images. For more background information on the Coverflow widget see my original post  here . 

How to use
In your Android project create a package called com.example.coverflow, and in this place the  CoverFlow  class. Now all you need is an activity to instantiate the Coverflow widget in this example the activity class is called  CoverflowExample .  CoverFlowExample  simply extends Activity and instantiates a Coverflow class in it's  onCreate  method. It also has an internal Class,  ImageAdapter  which we use as the adapter for the Coverflow widget, much as we would for a Gallery widget. It is also possible to use the Coverflow widget when it is specified in an XML layout file.

The  CoverFlow  and  CoverflowExample  classes are here:

/*
 * 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
 */
package com.example.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 {

    /**
     * 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 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);   
  }
  
    /**
     * 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);
                     
      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);          
      } 
      
      mCamera.rotateY(rotationAngle);
      mCamera.getMatrix(imageMatrix);               
      imageMatrix.preTranslate(-(imageWidth/2), -(imageHeight/2)); 
      imageMatrix.postTranslate((imageWidth/2), (imageHeight/2));
      mCamera.restore();
 }
}

Demo:

/*
 * 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
 */
package com.example.coverflow;

import java.io.FileInputStream;

import android.app.Activity;
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.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ImageView.ScaleType;

public class CoverFlowExample extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     
     CoverFlow coverFlow;
     coverFlow = new CoverFlow(this);
     
     coverFlow.setAdapter(new ImageAdapter(this));

     ImageAdapter coverImageAdapter =  new ImageAdapter(this);
     
     //coverImageAdapter.createReflectedImages();
     
     coverFlow.setAdapter(coverImageAdapter);
     
     coverFlow.setSpacing(-25);
     coverFlow.setSelection(4, true);
     coverFlow.setAnimationDuration(1000);
     
     
     setContentView(coverFlow);
    }
}

Adapter:

 public class ImageAdapter extends BaseAdapter {
     int mGalleryItemBackground;
     private Context mContext;

     private FileInputStream fis;
        
     private Integer[] mImageIds = {
       R.drawable.kasabian_kasabian,
             R.drawable.starssailor_silence_is_easy,
             R.drawable.killers_day_and_age,
             R.drawable.garbage_bleed_like_me,
             R.drawable.death_cub_for_cutie_the_photo_album,
             R.drawable.kasabian_kasabian,
             R.drawable.massive_attack_collected,
             R.drawable.muse_the_resistance,
             R.drawable.starssailor_silence_is_easy
     };

     private ImageView[] mImages;
     
     public ImageAdapter(Context c) {
      mContext = c;
      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(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 CoverFlow.LayoutParams(120, 180));
          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(130, 130));
         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))); 
      } 

 }

Code explanation

The  CoverflowExample  Code contains some extra code for creating reflections of the images, but apart from this is a standard activity class of the kind used with the Gallery widget.

The  CoverFlow  class extends the Gallery widget , but now we override a few methods to allow us to transform the images before they are displayed. The most important method that we override is the  getChildStaticTransformation  method. Here I have to say thank you to a user called Nerdrow on the Android developers group who first showed me an example of overriding this method.  By setting  setStaticTransformationsEnabled  in the constructors, we are telling the parent ViewGroup of the Coverflow class to invoke  getChildStaticTransformation  every time one of our images in drawn. In  getChildStaticTransformation  we simply calculate and apply a rotation and scale to the ImageView depending on it's position relative to the centre of the Coverflow widget. We also override the  onSizeChanged  method. This method is called every time the widget changes size e.g. when we change the orientation of the phone from portrait to landscape. In the  onSizeChanged  method we just get the centre position of the coverflow widget. There are also a few parameters that we can set,  mZoomMax  controls the maximum zoom of the central image and  mMaxRotationAngle  sets the maximum rotation angle of each image.

参考链接：

http://www.inter-fuser.com/2010/02/android-coverflow-widget-v2.html

http://www.eoeandroid.com/thread-29728-1-1.html

上述代码后半段的显示顺序有问题，需要重写Gallery的getChildDrawingOrder方法。

@Override
protected int getChildDrawingOrder(int childCount, int i)
{
	int mFirstPosition = getFirstVisiblePosition();
	int mSelectedPosition = getSelectedItemPosition();
	int selectedIndex = mSelectedPosition - mFirstPosition;

	if (i == 0)
	{
		lastPosition = 0;
	}

	int ret = 0;
	if (selectedIndex < 0)
	{
		return i;
	}

	if (i == childCount - 1)
	{
		ret = selectedIndex;
	}
	else if (i >= selectedIndex)
	{
		lastPosition++;
		ret = childCount - lastPosition;
	}
	else
	{
		ret = i;
	}

	return ret;
}