createBitmap（）返回未绘制的位图

Question

    Bitmap imageBitmap;
    imageBitmap = weiboView.getDrawingCache();
    Log.d("cosmo", "bitmap generated: "+imageBitmap.getWidth()+" * "+imageBitmap.getHeight());

    //Init and configure and load the image view
    ImageView imageView = new ImageView(this);
    imageView.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT));
    imageView.setScaleType(ScaleType.FIT_CENTER);
    containerLayout.addView(imageView);

    //create a scaled bitmap to assign to the image view
    Bitmap scaledImageBitmap = MyBitmapUtils.getBitmapScaledToFitWidth(getWindowManager().getDefaultDisplay().getWidth(), imageBitmap);
    Log.d("cosmo", "scaled: "+scaledImageBitmap.getWidth()+" * "+scaledImageBitmap.getHeight());
    //Here if I set imageBitmap as the image of imageView it works well
    imageView.setImageBitmap(scaledImageBitmap);

以下是MyBitmapUtils.GetBitmapScaledToFitWidth：

public static Bitmap getBitmapScaledToFitWidth(int targetWidth, Bitmap bitmap) {
    float ratio = (float)targetWidth/(float)bitmap.getWidth();
    Log.d("cosmo", "ratio is "+ratio);
    //ratio = 0.5f;
    Matrix matrix = new Matrix();
    matrix.postScale(ratio, ratio);
    Bitmap target = Bitmap.createBitmap(bitmap,0,0,bitmap.getWidth(),bitmap.getHeight(),matrix,false);
    return target;
}

我知道这是怎么发生的。这是因为图像的高度大于2048，而在Android系统中创建一个大于2048*2048的位图会导致OOM（奇怪的是，我的logcat没有报告这个错误）

Answer 1

为什么不直接使用createScaledBitmap？

Bitmap scaledBitmap = Bitmap.createScaledBitmap(bitmap, targetWidth, targetHeight, true);

您可以直接提供targetWidth和targetHeight，这应该比使用矩阵自己缩放位图更可靠。

如果只向方法提供targetWidth,则必须计算targetHeight,它看起来如下所示：

float ratio = (float)targetWidth/(float)bitmap.getWidth();
int targetHeight = (int)((float)bitmap.getHeight * ratio);

public static Bitmap getBitmapScaledToFitWidth(double targetWidth, Bitmap bitmap) {
    double bitmapWidth = bitmap.getWidth();
    double bitmapHeight = bitmap.getHeight();

    double widthRatio = targetWidth / bitmapWidth;
    double targetHeight = widthRatio * bitmapHeight;

    Bitmap target = Bitmap.createScaledBitmap(bitmap, (int)targetWidth, (int)targetHeight, true);
    return target;
}

public static Bitmap getBitmapScaledToFitWidth(double targetWidth, Bitmap bitmap) {
    double bitmapWidth = bitmap.getWidth();
    double bitmapHeight = bitmap.getHeight();

    double widthRatio = targetWidth / bitmapWidth;
    double targetHeight = widthRatio * bitmapHeight;

    Bitmap target = Bitmap.createScaledBitmap(bitmap, (int)targetWidth, (int)targetHeight, true);

    // Recycle old bitmap to free up memory.
    bitmap.recycle();

    return target;
}