Android 开发中,一些小经验,如果没有及时总结记录,那么下次遇到了之后,又会同样的搜索思考测试,这就耽误了很多时间,效率不高,ImageView 是特别常用的一个控件,而图片加圆角、加水印、变灰也是特别常见的需求,其实代码就那么固定几行,下面看具体实现。

本文用到的示例原图:


下面就将这张图片处理成各种样式。

将彩色图片转化为灰图


/** 
 * 将彩色图转换为灰度图 
 * @param img 位图 
 * @return 返回转换好的位图 
 */ 
 public Bitmap convertGreyImg(Bitmap img) { 
   int width = img.getWidth(); //获取位图的宽 
   int height = img.getHeight(); //获取位图的高 
   int []pixels = new int[width * height]; //通过位图的大小创建像素点数组 
   img.getPixels(pixels, 0, width, 0, 0, width, height); 
   int alpha = 0xFF << 24;
     
   for(int i = 0; i < height; i++) { 
     for(int j = 0; j < width; j++) { 
       int grey = pixels[width * i + j]; 
       int red = ((grey & 0x00FF0000 ) >> 16); 
       int green = ((grey & 0x0000FF00) >> 8); 
       int blue = (grey & 0x000000FF); 
       grey = (int)((float) red * 0.3 + (float)green * 0.59 + (float)blue * 0.11); 
       grey = alpha | (grey << 16) | (grey << 8) | grey; 
       pixels[width * i + j] = grey; 
       }
     }
   Bitmap result = Bitmap.createBitmap(width, height, Config.RGB_565);
   result.setPixels(pixels, 0, width, 0, 0, width, height);
   
   return result;
 }

将图片转成圆角图


public static Bitmap getRoundedCornerBitmap(Bitmap bitmap, float roundPx) {


    Bitmap output = Bitmap.createBitmap(bitmap.getWidth(),
                                        bitmap.getHeight(), Config.ARGB_8888);
    Canvas canvas = new Canvas(output);


    final int color = 0xff424242;
    final Paint paint = new Paint();
    final Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());
    final RectF rectF = new RectF(rect);


    paint.setAntiAlias(true);
    canvas.drawARGB(0, 0, 0, 0);
    paint.setColor(color);
    canvas.drawRoundRect(rectF, roundPx, roundPx, paint);


    paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
    canvas.drawBitmap(bitmap, rect, rect, paint);


    return output;
}

图片添加倒影效果


/**
 * 获得带倒影的图片方法
 */
public static Bitmap createReflectionImageWithOrigin(Bitmap bitmap) {
    final int reflectionGap = 4;
    int width = bitmap.getWidth();
    int height = bitmap.getHeight();


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


    Bitmap reflectionImage = Bitmap.createBitmap(bitmap, 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(bitmap, 0, 0, null);
    Paint deafalutPaint = new Paint();
    canvas.drawRect(0, height, width, height + reflectionGap, deafalutPaint);


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


    Paint paint = new Paint();
    LinearGradient shader = new LinearGradient(0, bitmap.getHeight(), 0,
                                               bitmapWithReflection.getHeight() + reflectionGap, 0x70ffffff,
                                               0x00ffffff, TileMode.CLAMP);
    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);
    
    return bitmapWithReflection;
}

添加水印


/**
 * 
 * @param src
 *            要添加水印的图片
 * @param 水印
 * @return 添加了水印的图片
 */
private Bitmap createBitmap(Bitmap src, Bitmap watermark) {
    String tag = "createBitmap";
    Log.d(tag, "create a new bitmap");
    if (src == null) {
        return null;
    }


    int w = src.getWidth();
    int h = src.getHeight();
    int ww = watermark.getWidth();
    int wh = watermark.getHeight();
    // create the new blank bitmap
    Bitmap newb = Bitmap.createBitmap(w, h, Config.ARGB_8888);// 创建一个新的和SRC长度宽度一样的位图
    Canvas cv = new Canvas(newb);
    // draw src into
    cv.drawBitmap(src, 0, 0, null);// 在 0,0坐标开始画入src
    // draw watermark into
    cv.drawBitmap(watermark, w - ww + 5, h - wh + 5, null);// 在src的右下角画入水印
    // save all clip
    cv.save(Canvas.ALL_SAVE_FLAG);// 保存
    // store
    cv.restore();// 存储
    
    return newb;
}

生成图片:View 转成 Bitmap

/**
 * 把一个View的对象转换成bitmap
 */
static Bitmap getViewBitmap(View v) {


    v.clearFocus();
    v.setPressed(false);


    // 能画缓存就返回false
    boolean willNotCache = v.willNotCacheDrawing();
    v.setWillNotCacheDrawing(false);
    int color = v.getDrawingCacheBackgroundColor();
    v.setDrawingCacheBackgroundColor(0);
    if (color != 0) {
        v.destroyDrawingCache();
    }
    
    v.buildDrawingCache();
    Bitmap cacheBitmap = v.getDrawingCache();
    if (cacheBitmap == null) {
        Log.e(TAG, "failed getViewBitmap(" + v + ")",
              new RuntimeException());
        return null;
    }
    
    Bitmap bitmap = Bitmap.createBitmap(cacheBitmap);
    // Restore the view
    v.destroyDrawingCache();
    v.setWillNotCacheDrawing(willNotCache);
    v.setDrawingCacheBackgroundColor(color);
    
    return bitmap;
}

总结

这篇文章总结记录了关于 ImageView 的 5 个变换技巧,可以作为知识库使用,随着工作经验的积累,每个开发者都应该有自己的知识库,方便提高开发效率,总结经验。

我是一名安卓开发工程师,最近正在学习 Java 后端知识,每天保持学习,掌握一项技能其实用不了多长时间,加油!

本文文字及图片出自 InfoQ

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