Drawable概念及对子类的互相转换，实现圆角图片，图片缩放等

冷不防 2022-06-15 10:12 212阅读 0赞

### 一、Drawable相关概念 ###

1、Drawable就是一个可画的对象，其可能是一张位图（BitmapDrawable），也可能是一个图形（ShapeDrawable），还有可能是一个图层（LayerDrawable），我们根据画图的需求，创建相应的可画对象

2、Canvas画布，绘图的目的区域，用于绘图

3、Bitmap位图，用于图的处理

4、Matrix矩阵

Drawable的setBounds方法有四个参数，setBounds(int left, int top, int right, int bottom),这个四参数指的是drawable将在被绘制在canvas的哪个矩形区域内。 
        
         例如 
        
         @Override    protected void onDraw(Canvas canvas) {      
        
            drawable.setBounds(100, 100, 500, 500);     
        
             drawable.draw(canvas);  
        
            }
     
        
         上面的代码会将drawable绘制在canvas内部(100,100,500,500)表示的矩形区内（这个矩形区域的坐标是以canvas左上角为坐标原点的）

### 二、Bitmap ###

#### 1、从资源中获取Bitmap ####

Java代码 ![收藏代码][icon_star.png]

1.  Resources res = getResources();
2.  Bitmap bmp = BitmapFactory.decodeResource(res, R.drawable.icon);

#### 2、Bitmap → byte\[\] ####

Java代码 ![收藏代码][icon_star.png]

1.  public byte\[\] Bitmap2Bytes(Bitmap bm) \{
2.  ByteArrayOutputStream baos = new ByteArrayOutputStream();
3.  bm.compress(Bitmap.CompressFormat.PNG, 100, baos);
4.  return baos.toByteArray();
5.  \}

####  3、byte\[\] → Bitmap ####

Java代码 ![收藏代码][icon_star.png]

1.  public Bitmap Bytes2Bimap(byte\[\] b) \{
2.  if (b.length != 0) \{
3.  return BitmapFactory.decodeByteArray(b, 0, b.length);
4.  \} else \{
5.  return null;
6.  \}
7.  \}

#### 4、Bitmap缩放 ####

Java代码 ![收藏代码][icon_star.png]

1.  public static Bitmap zoomBitmap(Bitmap bitmap, int width, int height) \{
2.  int w = bitmap.getWidth();
3.  int h = bitmap.getHeight();
4.  Matrix matrix = new Matrix();
5.  float scaleWidth = ((float) width / w);
6.  float scaleHeight = ((float) height / h);
7.  matrix.postScale(scaleWidth, scaleHeight);
8.  Bitmap newbmp = Bitmap.createBitmap(bitmap, 0, 0, w, h, matrix, true);
9.  return newbmp;
10. \}

####  5、将Drawable转化为Bitmap ####

Java代码 ![收藏代码][icon_star.png]

1.  public static Bitmap drawableToBitmap(Drawable drawable) \{
2.  // 取 drawable 的长宽
3.  int w = drawable.getIntrinsicWidth();
4.  int h = drawable.getIntrinsicHeight();
5.  
6.  // 取 drawable 的颜色格式
7.  Bitmap.Config config = drawable.getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB\_8888
8.  : Bitmap.Config.RGB\_565;
9.  // 建立对应 bitmap
10. Bitmap bitmap = Bitmap.createBitmap(w, h, config);
11. // 建立对应 bitmap 的画布
12. Canvas canvas = new Canvas(bitmap);
13. drawable.setBounds(0, 0, w, h);
14. // 把 drawable 内容画到画布中
15. drawable.draw(canvas);
16. return bitmap;
17. \}

#### 6、获得圆角图片 ####

Java代码 ![收藏代码][icon_star.png]

1.  public static Bitmap getRoundedCornerBitmap(Bitmap bitmap, float roundPx) \{
2.  int w = bitmap.getWidth();
3.  int h = bitmap.getHeight();
4.  Bitmap output = Bitmap.createBitmap(w, h, Config.ARGB\_8888);
5.  Canvas canvas = new Canvas(output);
6.  final int color = 0xff424242;
7.  final Paint paint = new Paint();
8.  final Rect rect = new Rect(0, 0, w, h);
9.  final RectF rectF = new RectF(rect);
10. paint.setAntiAlias(true);
11. canvas.drawARGB(0, 0, 0, 0);
12. paint.setColor(color);
13. canvas.drawRoundRect(rectF, roundPx, roundPx, paint);
14. paint.setXfermode(new PorterDuffXfermode(Mode.SRC\_IN));
15. canvas.drawBitmap(bitmap, rect, rect, paint);
16. 
17. return output;
18. \}

####  7、获得带倒影的图片 ####

Java代码 ![收藏代码][icon_star.png]

1.  public static Bitmap createReflectionImageWithOrigin(Bitmap bitmap) \{
2.  final int reflectionGap = 4;
3.  int w = bitmap.getWidth();
4.  int h = bitmap.getHeight();
5.  
6.  Matrix matrix = new Matrix();
7.  matrix.preScale(1, -1);
8.  
9.  Bitmap reflectionImage = Bitmap.createBitmap(bitmap, 0, h / 2, w,
10. h / 2, matrix, false);
11. 
12. Bitmap bitmapWithReflection = Bitmap.createBitmap(w, (h + h / 2),
13. Config.ARGB\_8888);
14. 
15. Canvas canvas = new Canvas(bitmapWithReflection);
16. canvas.drawBitmap(bitmap, 0, 0, null);
17. Paint deafalutPaint = new Paint();
18. canvas.drawRect(0, h, w, h + reflectionGap, deafalutPaint);
19. 
20. canvas.drawBitmap(reflectionImage, 0, h + reflectionGap, null);
21. 
22. Paint paint = new Paint();
23. LinearGradient shader = new LinearGradient(0, bitmap.getHeight(), 0,
24. bitmapWithReflection.getHeight() + reflectionGap, 0x70ffffff,
25. 0x00ffffff, TileMode.CLAMP);
26. paint.setShader(shader);
27. // Set the Transfer mode to be porter duff and destination in
28. paint.setXfermode(new PorterDuffXfermode(Mode.DST\_IN));
29. // Draw a rectangle using the paint with our linear gradient
30. canvas.drawRect(0, h, w, bitmapWithReflection.getHeight()
31. \+ reflectionGap, paint);
32. 
33. return bitmapWithReflection;
34. \}

###  三、Drawable ###

#### 1、Bitmap转换成Drawable ####

Java代码 ![收藏代码][icon_star.png]

1.  Bitmap bm=xxx; //xxx根据你的情况获取
2.  BitmapDrawable bd= new BitmapDrawable(getResource(), bm);
3.  因为BtimapDrawable是Drawable的子类，最终直接使用bd对象即可。

#### 2、Drawable缩放 ####

Java代码 ![收藏代码][icon_star.png]

1.  public static Drawable zoomDrawable(Drawable drawable, int w, int h) \{
2.  int width = drawable.getIntrinsicWidth();
3.  int height = drawable.getIntrinsicHeight();
4.  // drawable转换成bitmap
5.  Bitmap oldbmp = drawableToBitmap(drawable);
6.  // 创建操作图片用的Matrix对象
7.  Matrix matrix = new Matrix();
8.  // 计算缩放比例
9.  float sx = ((float) w / width);
10. float sy = ((float) h / height);
11. // 设置缩放比例
12. matrix.postScale(sx, sy);
13. // 建立新的bitmap，其内容是对原bitmap的缩放后的图
14. Bitmap newbmp = Bitmap.createBitmap(oldbmp, 0, 0, width, height,
15. matrix, true);
16. return new BitmapDrawable(newbmp);
17. \}

[转载地址][Link 1]

[icon_star.png]: /images/20220615/2450b0b7611f40d59f480a7b848eb3dc.png
[Link 1]: http://blog.csdn.net/u010015108/article/details/52797165