Android 滑动效果进阶篇（六）—— 倒影效果

上篇介绍了使用Animation实现3D动画旋转翻页效果，现在介绍图片倒影实现，先看效果图

本示例主要通过自定义Gallery和ImageAdapter（继承自BaseAdapter）实现

1、倒影绘制

ImageAdapter继承自BaseAdapter，详细实现可见 Android 滑动效果入门篇（二）—— Gallery 这里重点介绍倒影原理及实现

倒影原理：

倒影效果是主要由原图+间距+倒影三部分组成，高度大约为原图的3/2（原图为1、倒影为1/2）

原图，就是我们看到了最开始的图片

间距，是原图与倒影之间的间隙，如：reflectionGap = 4;

倒影，是原图下半部分1/2高度，通过矩阵变换matrix.preScale(1, -1); 获取倒立图片，然后再加上线性遮罩和阴影实现

倒影实现：

/** 反射倒影 */
public boolean createReflectedImages() {
    final int reflectionGap = 4;
    int index = 0;
    for (Map<String, Object> map : list) {
        Integer id = (Integer) map.get("image");
        Bitmap originalImage = BitmapFactory.decodeResource(mContext.getResources(), id);   // 获取原始图片
        int width = originalImage.getWidth();
        int height = originalImage.getHeight();

        Matrix matrix = new Matrix();
        matrix.preScale(1, -1);         // 图片矩阵变换（从低部向顶部的倒影）
        Bitmap reflectionImage = Bitmap.createBitmap(originalImage, 0, height/2, width, height/2, matrix, false);   // 截取原图下半部分
        Bitmap bitmapWithReflection = Bitmap.createBitmap(width, (height + height / 2), Config.ARGB_8888);          // 创建倒影图片（高度为原图3/2）

        Canvas canvas = new Canvas(bitmapWithReflection);   // 绘制倒影图（原图 + 间距 + 倒影）
        canvas.drawBitmap(originalImage, 0, 0, null);       // 绘制原图
        Paint paint = new Paint();
        canvas.drawRect(0, height, width, height + reflectionGap, paint);       // 绘制原图与倒影的间距
        canvas.drawBitmap(reflectionImage, 0, height + reflectionGap, null);    // 绘制倒影图

        paint = new Paint();
        LinearGradient shader = new LinearGradient(0, originalImage.getHeight(), 0, bitmapWithReflection.getHeight() + reflectionGap, 0x70ffffff, 0x00ffffff, TileMode.CLAMP);
        paint.setShader(shader);    // 线性渐变效果
        paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN));     // 倒影遮罩效果
        canvas.drawRect(0, height, width, bitmapWithReflection.getHeight() + reflectionGap, paint);     // 绘制倒影的阴影效果

        ImageView imageView = new ImageView(mContext);
        imageView.setImageBitmap(bitmapWithReflection);     // 设置倒影图片
        imageView.setLayoutParams(new myGallery.LayoutParams(180, 240));
        imageView.setScaleType(ScaleType.MATRIX);
        mImages[index++] = imageView;
    }
    return true;
}

2、myGallery

自定义Gallery来实现倒影图片的浏览与选择

public class myGallery extends Gallery {

    private Camera mCamera = new Camera();
    private int mMaxRotationAngle = 60;     // 最大旋转角度 60
    private int mMaxZoom = -120;
    private int mCoveflowCenter;

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

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

    public myGallery(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 int getMaxZoom() {
        return mMaxZoom;
    }

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

    /** 获取Gallery的中心x */
    private int getCenterOfCoverflow() {
        return (getWidth() - getPaddingLeft() - getPaddingRight()) / 2 + getPaddingLeft();
    }

    /** 获取View的中心x */
    private static int getCenterOfView(View view) {
        return view.getLeft() + view.getWidth() / 2;
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        mCoveflowCenter = getCenterOfCoverflow();
        super.onSizeChanged(w, h, oldw, oldh);
    }

    @Override
    protected boolean getChildStaticTransformation(View child, Transformation trans) {
        final int childCenter = getCenterOfView(child);
        final int childWidth = child.getWidth();
        int rotationAngle = 0;

        trans.clear();
        trans.setTransformationType(Transformation.TYPE_BOTH);      // alpha 和 matrix 都变换

        if (childCenter == mCoveflowCenter) {   // 正中间的childView
            transformImageBitmap((ImageView) child, trans, 0);
        } else {        // 两侧的childView
            rotationAngle = (int) ( ( (float) (mCoveflowCenter - childCenter) / childWidth ) * mMaxRotationAngle );
            if (Math.abs(rotationAngle) > mMaxRotationAngle) {
                rotationAngle = (rotationAngle < 0) ? -mMaxRotationAngle : mMaxRotationAngle;
            }
            transformImageBitmap((ImageView) child, trans, rotationAngle);
        }

        return true;
    }

    private void transformImageBitmap(ImageView child, Transformation trans, int rotationAngle) {
        mCamera.save();

        final Matrix imageMatrix = trans.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);
        }

        mCamera.rotateY(rotationAngle);     // rotationAngle 为正，沿y轴向内旋转； 为负，沿y轴向外旋转

        mCamera.getMatrix(imageMatrix);
        imageMatrix.preTranslate(-(imageWidth / 2), -(imageHeight / 2));
        imageMatrix.postTranslate((imageWidth / 2), (imageHeight / 2));

        mCamera.restore();
    }
}

3、Activity

Activity中，主要实现自定义Gallery的图片填充ImageAdapter、myGallery选择事件监听、点击事件监听

private void initRes(){
    tvTitle = (TextView) findViewById(R.id.tvTitle);
    gallery = (myGallery) findViewById(R.id.mygallery);     // 获取自定义的myGallery控件

    adapter = new ImageAdapter(this);
    adapter.createReflectedImages();    // 创建倒影效果
    gallery.setAdapter(adapter);

    gallery.setOnItemSelectedListener(new OnItemSelectedListener() {    // 设置选择事件监听
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            tvTitle.setText(adapter.titles[position]);
        }

        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });

    gallery.setOnItemClickListener(new OnItemClickListener() {          // 设置点击事件监听
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            Toast.makeText(Main.this, "img " + (position+1) + " selected", Toast.LENGTH_SHORT).show();
        }
    });
}

main.xml布局文件中，通过实现自定义的myGallery，来显示图片集合

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
    <TextView
        android:id="@+id/tvTitle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:textSize="16sp" />

    <com.homer.reflect.myGallery
        android:id="@+id/mygallery"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/tvTitle"
        android:layout_marginTop="10dip" />
</RelativeLayout>