android 图像的位图子采样

Question

在 SD 卡的列表视图中显示图像时，我遇到内存不足的问题

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 600x450，它们会完美加载

我使用以下方法正常加载它们

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

我有以下两种方法可以对位图进行子采样

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;
}

问题是我不知道怎么调用它所以显示

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

我哪里出错了？

Answer 1

您没有将图像文件名传递给

decodeSampledBitmapFromResource

，那么它怎么知道要加载哪个文件呢？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。

如果你想从给定文件名而不是资源的文件加载图像，你需要将

decodeSampledBitmapFromResource

更改为使用 BitmapFactory.decodeFile() 而不是 BitmapFactory.decodeResource 从文件加载，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));