Bitmap和Drawable的关系、区别

淡淡的烟草味﹌ 2022-06-03 07:24 179阅读 0赞

**Bitmap**  
\- 称作位图，一般位图的文件格式后缀为bmp

**Drawable**  
\- 作为Android平下通用的图形对象，它可以装载常用格式的图像  
比如GIF、PNG、JPG，当然也支持BMP，当然还提供一些高级的可视化对象，比如渐变、图形等。

Bitmap是Drawable . Drawable不一定是Bitmap  
Drawable在内存占用和绘制速度这两个非常关键的点上胜过Bitmap

**1、Bitmap对象**  
Resources res = getResources();  
Bitmap bmp = BitmapFactory.decodeResource(res, R.drawable.icon);  
获取其宽高的方法：  
bmp.getHeight()  
bmp.getWidth()

**2、Drawable对象**  
Drawable drawable = getResources().getDrawable(R.drawable.icon);  
获取其宽高的方法：  
drawable.getIntrinsicWidth();  
drawable.getIntrinsicHeight();

**3、Bitmap转换成Drawable**

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

**4、Drawable转化为Bitmap**  
转化的方式是把Brawable通过画板画出来

\[java\] [view plain][] [copy][view plain]

1.  publicstatic 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. \}

**5、Bitmap → byte\[\]**

\[java\] [view plain][] [copy][view plain]

1.  publicbyte\[\] BitmapToByte(Bitmap bmp) \{ 
2.   ByteArrayOutputStream b = new ByteArrayOutputStream(); 
3.   bmp.compress(Bitmap.CompressFormat.PNG, 100, b); 
4.  return b.toByteArray(); 
5.  \}

**6、byte\[\] → Bitmap**

\[java\] [view plain][] [copy][view plain]

1.  public Bitmap Bytes2Bimap(byte\[\] b) \{ 
2.  if (b.length != 0) \{ 
3.  return BitmapFactory.decodeByteArray(b, 0, b.length); 
4.   \} else \{ 
5.  returnnull; 
6.   \} 
7.   \} 
8.

# Bitmap和Drawable的区别，为什么要用bitmap？ #

1. 注意看 Drawable 的注释:

>     * A Drawable is a general abstraction for "something that can be drawn."  Most
>     * often you will deal with Drawable as the type of resource retrieved for
>     * drawing things to the screen; the Drawable class provides a generic API for
>     * dealing with an underlying visual resource that may take a variety of forms.
>     * Unlike a {@link android.view.View}, a Drawable does not have any facility to
>     * receive events or otherwise interact with the user.

再看看其类定义:

public abstract class Drawable {
     ......
    }

也就是说 Drawable 只是一个抽象概念, 表示"something that can be drawn".

Drawable 的注释下面还有一段话:

>     Though usually not visible to the application, Drawables may take a variety of forms:
>     1. Bitmap: the simplest Drawable, a PNG or JPEG image.
>     2. Nine Patch: an extension to the PNG format allows it to specify information about how to stretch it and place things inside of it.
>     3. Shape: contains simple drawing commands instead of a raw bitmap, allowing it to resize better in some cases.
>     4. Layers: a compound drawable, which draws multiple underlying drawables on top of each other.
>     5. States: a compound drawable that selects one of a set of drawables based on its state.
>     6. Levels: a compound drawable that selects one of a set of drawables based on its level.
>     7. Scale : a compound drawable with a single child drawable, whose overall size is modified based on the current level.

那么形式就比较明朗了, Drawable 是一个抽象的概念, 而 Bitmap 是其存在的实体之一.

2. 我们来看 Bitmap 类的定义:

public final class Bitmap implements Parcelable {
    ......
    }

细心的同学会发现, Bitmap 并没有实现 Drawable,那么他们俩是如何联系起来的呢? 答案是 BitmapDrawable.:

public class BitmapDrawable extends Drawable {
    ......
    }

Drawable 类中有一个方法:

private static Drawable drawableFromBitmap(Resources res, Bitmap bm, byte[] np,
                Rect pad, Rect layoutBounds, String srcName) {
           
    
            if (np != null) {
           
                return new NinePatchDrawable(res, bm, np, pad, layoutBounds, srcName);
            }
    
            return new BitmapDrawable(res, bm);
        }

通过 BitmapDrawable 的构造函数,使得 Bitmap 可以转换为 Drawable.

同样, BitmapDrawable 的 getBitmap 方法也会返回 bitmap对象:

/**
         * Returns the bitmap used by this drawable to render. May be null.
         */
        public final Bitmap getBitmap() {
           
            return mBitmapState.mBitmap;
        }

[view plain]: http://blog.csdn.net/u014058109/article/details/45921497#