为什么这两种将图像从 SQL CE 加载到 WPF 图像的方法会产生不同的结果？

发布于 2024-10-13 11:10:59 字数 1185 浏览 4 评论 0原文

在 ValueConverter 中，我尝试将 System.Data.Linq.Binary（SQL CE 图像）转换为 BitmapImage。此方法有效（图像在表单上正确显示）：

public object Convert(object value, Type targetType, object parameter, 
                                                     CultureInfo culture) {
    Binary binary = value as Binary;
    if (binary != null) {
        BitmapImage bitmap = new BitmapImage();
        bitmap.BeginInit();
        bitmap.StreamSource = new MemoryStream(binary.ToArray());
        bitmap.EndInit();
        return bitmap;
    }
    return null;
}

此方法不有效（但奇怪的是没有抛出异常）：

public object Convert(object value, Type targetType, object parameter, 
                                                     CultureInfo culture) {
    Binary binary = value as Binary;
    if (binary != null) {
        using (var stream = new MemoryStream(binary.ToArray())) {
            BitmapImage bitmap = new BitmapImage();
            bitmap.BeginInit();
            bitmap.StreamSource = stream;
            bitmap.EndInit();
            return bitmap;
        }
    }
    return null;
}

良好的编程实践表明您应该处理您创建的任何流。所以我很困惑为什么第二种方法不起作用，但第一种方法可以。有什么见解吗？

原文

In a ValueConverter, I was trying to convert a System.Data.Linq.Binary (SQL CE image) to a BitmapImage. This method works (image is show correctly on the form):

public object Convert(object value, Type targetType, object parameter, 
                                                     CultureInfo culture) {
    Binary binary = value as Binary;
    if (binary != null) {
        BitmapImage bitmap = new BitmapImage();
        bitmap.BeginInit();
        bitmap.StreamSource = new MemoryStream(binary.ToArray());
        bitmap.EndInit();
        return bitmap;
    }
    return null;
}

This method does NOT work (but no exception is thrown, strangely):

public object Convert(object value, Type targetType, object parameter, 
                                                     CultureInfo culture) {
    Binary binary = value as Binary;
    if (binary != null) {
        using (var stream = new MemoryStream(binary.ToArray())) {
            BitmapImage bitmap = new BitmapImage();
            bitmap.BeginInit();
            bitmap.StreamSource = stream;
            bitmap.EndInit();
            return bitmap;
        }
    }
    return null;
}

Good programming practice states that you should dispose of any streams you create... so I'm confused why the second method doesn't work, but the first does. Any insights?

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﹉夏雨初晴づ 2024-10-20 11:10:59

请尝试这样做：

public object Convert(object value, Type targetType, object parameter, 
                                                     CultureInfo culture) {
    Binary binary = value as Binary;
    if (binary != null) {
        using (var stream = new MemoryStream(binary.ToArray())) {
            BitmapImage bitmap = new BitmapImage();
            bitmap.BeginInit();
            bitmap.CacheOption = BitmapCacheOption.OnLoad; 
            bitmap.StreamSource = stream;
            bitmap.EndInit();
            bitmap.Freeze(); 
            return bitmap;
        }
    }
    return null;
}

在您的非工作版本中，您的 using 块意味着在图像实际解码之前关闭流。

Try this instead:

public object Convert(object value, Type targetType, object parameter, 
                                                     CultureInfo culture) {
    Binary binary = value as Binary;
    if (binary != null) {
        using (var stream = new MemoryStream(binary.ToArray())) {
            BitmapImage bitmap = new BitmapImage();
            bitmap.BeginInit();
            bitmap.CacheOption = BitmapCacheOption.OnLoad; 
            bitmap.StreamSource = stream;
            bitmap.EndInit();
            bitmap.Freeze(); 
            return bitmap;
        }
    }
    return null;
}

In your non-working version, your using block means the stream is closed before the image is actually decoded.

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