Android Bitmap开发之旅--基本操作

1 Bitmap加载方式

在介绍Bitmap--OOM 异常时，首先介绍一下Bitmap有哪几种加载方式。通常Bitmap的加载方式有Resource资源加载、本地（SDcard）加载、网络加载等加载方式。

1.1 Resource资源加载

1. Assets资源加载方式：
   

   AssetManager am = getAssets();
   InputStream is = am.open("high_pixel_img.jpg");
   Bitmap bitmap = BitmapFactory.decodeStream(is);

2.  Res资源加载方式：
   

   Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.high_pixel_img);

1.2 本地（SDcard）加载

String file_name = Environment.getExternalStorageDirectory().toString()+"/"+"high_pixel_img.jpg";
nbsp;Bitmap bitmap = BitmapFactory.decodeFile(file_name);

文件描述符

1.3 网络加载

注意：网络加载图片的时候必须在非主线成中操作

String website = "http://www.baidu.com/img/baidu_sylogo1.gif";
URL image_url = new URL(website);
HttpURLConnection conn = (HttpURLConnection) image_url.openConnection();
conn.connect();
InputStream is = conn.getInputStream();
bitmap = BitmapFactory.decodeStream(is);

2 Bitmap | Drawable | InputStream | Byte[ ] 之间进行转换

2.1 Drawable转化成Bitmap

Drawable drawable = getResources().getDrawable(R.drawable.ic_launcher);
Bitmap bitmap = Bitmap.createBitmap(
                               drawable.getIntrinsicWidth(),
                               drawable.getIntrinsicHeight(),
                               drawable.getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB_8888
                                               : Bitmap.Config.RGB_565);
Canvas canvas = new Canvas(bitmap);
//canvas.setBitmap(bitmap);
drawable.setBounds(0, 0, drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight());
drawable.draw(canvas);

2. 2 Bitmap转换成Drawable

Drawable drawable = new BitmapDrawable(bitmap);

2.3 Bitmap转换成byte[]

Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.high_pixel_img);
ByteArrayOutputStream baos = new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.PNG, 100, baos);
byte[] info = baos.toByteArray();

2.4 byte[]转换成Bitmap

Bitmap bitmap = BitmapFactory.decodeByteArray(byte, 0, b.length);

2.5 InputStream转换成Bitmap

InputStream is  = getResources().openRawResource(id);
Bitmap bitmap = BitmaoFactory.decodeStream(is);

2.6 InputStream转换成byte[]

InputStream is = getResources().openRawResource(id);//也可以通过其他方式接收一个InputStream对象
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] b = new byte[1024*2];
int len = 0;
while ((len = is.read(b, 0, b.length)) != -1)
{
   baos.write(b, 0, len);
   baos.flush();
}
byte[] bytes = baos.toByteArray();

3 转换Bitmap大小

Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.high_pixel_img);
Bitmap target = Bitmap.createBitmap(width,height,Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(tartget);
canvas.scale(scale,scale);
Paint paint = new Pain(Paint.FILTER_BITMAP_FLAG | Paint.DITHER_FLAG);
canvas.drawBitmap(bitmap,0,0,paint);
bitmap.recycle();

4 将Bitmap保存为本地文件

String filename = "save.jpg";
File file = new File(Environmnet.getExternalStorageDirectory,filename);
try{
    OutputStream os  =  new FileOutputString(file);
    bitmap.compress(CompressFormat.JPEG,100,os);
}catch(FileNotFoundException e){
   e.printStackTrace();
}

以上是关于Bitmap的相关操作，如果大家在阅读中发现有什么问题，请在评论中留言。