OutOfMemoryError与Android中的图像选择。如何在将图像解码为位图之前调整图像大小？

虽然加载大的位图文件，BitmapFactory类提供了几种解码方法（decodeByteArray（），decodeFile（），decodeResource（），等等）。

STEP 1

的inJustDecodeBounds属性设置为true，而解码避免了内存分配，为位图对象返回空但设置outWidth，outHeight和outMimeType。该技术允许您在构建位图之前读取图像数据的尺寸和类型（以及内存分配）。

BitmapFactory.Options options = new BitmapFactory.Options(); 
options.inJustDecodeBounds = true; 
BitmapFactory.decodeResource(getResources(), R.id.myimage, options); 
int imageHeight = options.outHeight; 
int imageWidth = options.outWidth; 
String imageType = options.outMimeType; 

要避免java.lang.OutOfMemory异常，请在解码之前检查位图的维数。

STEP 2

告诉解码器子样本图像，加载一个较小的版本到内存中，设置inSampleSize为true你BitmapFactory.Options对象。

例如，分辨率为2048x1536且用inSampleSize为4解码的图像会生成大约512x384的位图。将其加载到内存中时，整个图像使用0.75MB而不是12MB。

这里的计算样本大小值是两个基于目标宽度和高度的功率的方法：

public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId, 
    int reqWidth, int reqHeight) { 
// First decode with inJustDecodeBounds=true to check dimensions 
final BitmapFactory.Options options = new BitmapFactory.Options(); 
options.inJustDecodeBounds = true; 
BitmapFactory.decodeResource(res, resId, options); 
// Calculate inSampleSize 
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight); 
// Decode bitmap with inSampleSize set 
options.inJustDecodeBounds = false; 
return BitmapFactory.decodeResource(res, resId, options); 
} 
public static int calculateInSampleSize(
     BitmapFactory.Options options, int reqWidth, int reqHeight) { 
// Raw height and width of image 
final int height = options.outHeight; 
final int width = options.outWidth; 
int inSampleSize = 1; 
if (height > reqHeight || width > reqWidth) { 
    final int halfHeight = height/2; 
    final int halfWidth = width/2; 
    // Calculate the largest inSampleSize value that is a power of 2 and keeps both 
    // height and width larger than the requested height and width. 
    while ((halfHeight/inSampleSize) > reqHeight 
      && (halfWidth/inSampleSize) > reqWidth) { 
     inSampleSize *= 2; 
    } 
} 
return inSampleSize; 
} 

请仔细阅读本链接了解详情。 http://developer.android.com/training/displaying-bitmaps/load-bitmap.html

避免这种错误，清单中使用该AQUIRE一大堆：

android:largeHeap="true" 

然后根据你的需要

试试这个我曾经用它解码位图，再大小。它为我工作。

private Bitmap getBitmap(String path) { 
    Uri uri = getImageUri(path); 
    InputStream in = null; 
    try { 
     final int IMAGE_MAX_SIZE = 1200000; // 1.2MP 
     in = mContentResolver.openInputStream(uri); 
     // Decode image size 
     BitmapFactory.Options o = new BitmapFactory.Options(); 
     o.inJustDecodeBounds = true; 
     BitmapFactory.decodeStream(in, null, o); 
     in.close(); 
     int scale = 1; 
     while ((o.outWidth * o.outHeight) * (1/Math.pow(scale, 2)) > 
       IMAGE_MAX_SIZE) { 
      scale++; 
     } 
     Log.d(TAG, "scale = " + scale + ", orig-width: " + o.outWidth + ", 
      orig-height: " + o.outHeight); 
     Bitmap b = null; 
     in = mContentResolver.openInputStream(uri); 
     if (scale > 1) { 
      scale--; 
      // scale to max possible inSampleSize that still yields an image 
      // larger than target 
      o = new BitmapFactory.Options(); 
      o.inSampleSize = scale; 
      b = BitmapFactory.decodeStream(in, null, o); 
      // resize to desired dimensions 
      int height = b.getHeight(); 
      int width = b.getWidth(); 
      Log.d(TAG, "1th scale operation dimenions - width: " + width + ", 
       height: " + height); 
      double y = Math.sqrt(IMAGE_MAX_SIZE 
        /(((double) width)/height)); 
      double x = (y/height) * width; 
      Bitmap scaledBitmap = Bitmap.createScaledBitmap(b, (int) x, 
       (int) y, true); 
      b.recycle(); 
      b = scaledBitmap; 
      System.gc(); 
     } else { 
      b = BitmapFactory.decodeStream(in); 
     } 
     in.close(); 
     Log.d(TAG, "bitmap size - width: " +b.getWidth() + ", height: " + 
      b.getHeight()); 
     return b; 
    } catch (IOException e) { 
     Log.e(TAG, e.getMessage(),e); 
     return null; 
    } 

基本上，您应该使用BitmapFactory.decodeFile(path, options)传递Bitmap.Options.inSampleSize来解码原始位图的子采样版本。

您的代码将是这个样子：

public Bitmap decodeBitmap(String path, int maxWidth, int maxHeight) { 
    BitmapFactory.Options options = new BitmapFactory.Options(); 
    options.inJustDecodeBounds = true; 
    BitmapFactory.decodeFile(path, options); 
    options.inJustDecodeBounds = false; 
    options.inSampleSize = calculateInSampleSize(maxWidth, maxHeight, options.outWidth, options.outHeight); 
    return BitmapFactory.decodeFile(path, options); 
} 

而且calculateInSampleSize代码：

private int calculateInSampleSize(int maxWidth, int maxHeight, int width, int height) { 
    double widthRatio = (double) width/maxWidth; 
    double heightRatio = (double) height/maxHeight; 
    double ratio = Math.min(widthRatio, heightRatio); 
    float n = 1.0f; 
     while ((n * 2) <= ratio) { 
      n *= 2; 
     } 
     return (int) n; 
    } 

您可以使用图像采集其加载较小尺寸的图像，而无需加载大。你可以用Options参数传递给BitmapFactory。设置Options.inJustDecodeBoundstrue并且BitmapFactory会将Options.outWidth和Options.outHeight字段设置为图像的原始大小。请注意，将inJustDecodeBounds设置为true时，返回的位图为空。还可以使用Options.inSampleSize解码采样图像。样本大小显示结果图像缩小的程度。