android 图像的位图子采样

Question

我在 SD 卡的列表视图中显示图像时遇到内存不足错误问题

我知道这是因为我需要对位图进行子采样，因为它们是 8mp 的大图片，如果我将它们缩小到 600 x 450，它们可以完美加载

我使用以下方式正常加载它们

  Bitmap bmp = BitmapFactory.decodeFile("/storage/emulated/0/Pictures/" + text7[i]);
  item_details.setImage(bmp);

正如我所说，如果我使用全尺寸图像，这会使应用程序崩溃

我有以下两种可能对位图进行子采样的方法

  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;

}

问题是我不知道如何调用它所以显示

这是我填充列表视图的方法

private ArrayList<ListItemDetails> GetSearchResults() {
    // TODO Auto-generated method stub
    ArrayList<ListItemDetails> results = new ArrayList<ListItemDetails>();
    ImageView imageview = (ImageView) findViewById(R.id.imageView1);
    DBAdapter db = new DBAdapter(this);
    db.open();
    Cursor c = db.getAsset3();
    String[] text1 = new String[c.getCount()];
    String[] text2 = new String[c.getCount()];
    String[] text3 = new String[c.getCount()];
    String[] text4 = new String[c.getCount()];
    String[] text5 = new String[c.getCount()];
    String[] text6 = new String[c.getCount()];
    String[] text7 = new String[c.getCount()];
    for(int i = 0; c.moveToNext(); ++i)
    {
        text1[i] = c.getString(0);
        text2[i] = c.getString(1);
        text3[i] = c.getString(2);
        text4[i] = c.getString(3);
        text5[i] = c.getString(4);
        text6[i] = c.getString(5);
        text7[i] = c.getString(6);
       }
     c.close();

    for(int i=0;i<text1.length;i++)
    {
        item_details= new ListItemDetails();
        item_details.setSR1("School: " + text1[i]);
        item_details.setSR2("Building: " + text2[i]);
        item_details.setSR3("Floor: " + text3[i]);
        item_details.setSR4("Room: " + text4[i]);
        item_details.setSR5("Drawing Ref: " + text5[i]);
        item_details.setSR6("Fault: " + text6[i]);
        item_details.setSR7("Picture Filename: " + text7[i]);
        String picFormat="Harris%d.jpg";
        String pic = String.format(picFormat, i+1);
 /////////////////////////////////////////////////////////////////           
 /// Load bitmap     

imageview.setImageBitmap(decodeSampledBitmapFromResource(getResources(), 
R.id.imageView1, 100, 100));

        results.add(item_details);
    }

    return results;
    }

它似乎在列表视图加载时工作，并且每个项目上的所有文本都在那里，但图像是空白的

我哪里出错了？

感谢任何帮助

马克

Answer 1

您没有将图像文件名传递给 decodeSampledBitmapFromResource，那么它如何知道要加载哪个文件？您传入的资源 ID 是您的 ImageView 的资源 ID，而不是图像资源的资源 ID。

如果您想从给定文件名而不是资源的文件中加载图像，您需要将 decodeSampledBitmapFromResource 更改为使用 BitmapFactory.decodeFile() instead of BitmapFactory.decodeResource 从文件中加载图像，如下所示：

public static Bitmap decodeSampledBitmapFromFile(String filename,
    int reqWidth, int reqHeight) {

    // First decode with inJustDecodeBounds=true to check dimensions
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeFile(filename, options);

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;
    return BitmapFactory.decodeFile(filename, options);
}

然后更改您的 ArrayList 代码以将文件名传递给它：

item_details.setImageBitmap(decodeSampledBitmapFromFile("/storage/emulated/0/Pictures/" + text7[i], 100, 100));

Answer 2

你可以用Picasso http://square.github.io/picasso/，它很简单，你会避免很多头痛。

android 图像的位图子采样

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