c# - 如何在 Windows Phone 8 中释放图像缓存/内存？

Question

在我的 Windows Phone 8 应用程序中，我有一个包含 LongListSelector 的页面，该页面绑定(bind)到一个包含 1000 个对象的列表，该对象具有用于图像的 base64string 属性。现在为了显示图像，我编写了这个转换器来将 bas64string 转换为 stream。

public object Convert(object value, Type targetType, object parameter,  System.Globalization.CultureInfo culture)
{
    if (!value.ToString().Contains("http://"))
    {
        string str = value.ToString();
        byte[] bytes = Converter.FromBase64String(str);

        using (MemoryStream stream = new MemoryStream(bytes))
        {
            stream.Seek(0, SeekOrigin.Begin);

            BitmapImage image = new BitmapImage();
            image.SetSource(stream); 
            bytes = null;
            var memoryusage = string.Format("Memory: {0} bytes", 
            DeviceExtendedProperties.GetValue("ApplicationCurrentMemoryUsage"));
            Debug.WriteLine(memoryusage);
            return image;
        }
    }
    else
    { 
        return null;
    }
}

这是内存使用情况:

    Memory: 92549120 bytes
    Memory: 92946432 bytes
    Memory: 92946432 bytes
    Memory: 92946432 bytes
    Memory: 92946432 bytes
    Memory: 93192192 bytes
    Memory: 93192192 bytes
    Memory: 96079872 bytes
    Memory: 100700160 bytes
    Memory: 100700160 bytes
    Memory: 109568000 bytes
    Memory: 111734784 bytes
    Memory: 142852096 bytes
    Memory: 143056896 bytes
    Memory: 143056896 bytes
    Memory: 143261696 bytes
    Memory: 140791808 bytes
    Memory: 141103104 bytes
    Memory: 141529088 bytes
    Memory: 142151680 bytes
    Memory: 146784256 bytes
    Memory: 146784256 bytes
    Memory: 155066368 bytes
    Memory: 156368896 bytes

At memory equals to or maybe some bytes greater than this 156368896 bytes, the application crashes with the EngineExecutionException. Once I got "OutOfMemoryException for this:

image.SetSource(stream);

显然这是内存问题。我需要清除图像缓存内存，但如何？我在这个答案中看到了链接 https://stackoverflow.com/a/12267163/1949475 ，但我无法使用它。

注意:并非所有图像都同时显示，应用程序在我返回并再次返回页面更改要在 LongListSelector 中显示的数据后占用这么多内存。

Answer 1

在你的转换器类中设置很重要

BitmapImage image = new BitmapImage(); 
image.DecodePixelType = DecodePixelType.Logical; 
image.CreateOptions = BitmapCreateOptions.BackgroundCreation; 
image.CreateOptions = BitmapCreateOptions.DelayCreation; 
image.DecodePixelWidth = 56; 
image.DecodePixelHeight = 100;