Silverlight：BitmapImage到WriteableBitmap

Question

我可以像这样成功加载下面的Bitmap，并在视图的Image控件中显示它。

var bitmapImage = new BitmapImage
                            {
                                UriSource = 
                                    new Uri("../Images/Test.JPG", UriKind.Relative)
                            };

但是，只要我添加此行以从位图创建WriteableBitmap，

    var w = new WriteableBitmap(bitmapImage);

我在上面的行中收到运行时错误：“对象引用未设置为对象的实例。”

似乎BitmapImage创建被延迟了，可能是吗？ 我该怎么解决这个问题？

更新：

我现在正在尝试这个，但openImage似乎永远不会被击中。 （即使没有试图让它同步，它仍然失败）这里有什么问题？

var image = new BitmapImage();
        image.ImageOpened += (sender, args) => resetEventBitmap.Set();
        image.ImageFailed += (o, eventArgs) =>
                                 {
                                     resetEventBitmap.Set();
                                     throw eventArgs.ErrorException;
                                 };
        image.CreateOptions = BitmapCreateOptions.IgnoreImageCache;
        image.UriSource = uri;

        resetEventBitmap.WaitOne();

谢谢，

Answer 1

参考： http ： //www.blog.ingenuitynow.net/Silverlight+Creating+A+WriteableBitmap+From+A+Uri+Source.aspx

基本上，位图图像具有依赖属性“CreateOptions”，默认情况下，它设置为“DelayCreation”。 这会导致位图延迟渲染，直到需要它为止。 因此，这会导致我们的“对象引用未设置为对象的实例”错误。 要解决这个问题，我们必须打破writeablebitmap构造函数中的位图创建，更改此选项，然后将其重新放入。在vb.net中，这看起来像：

    Dim tmpUri As New Uri(yourpath.ToString)
    Dim bmp As New BitmapImage
    bmp.CreateOptions = BitmapCreateOptions.None
    bmp.UriSource = tmpUri
    Dim wb As New WriteableBitmap(bmp)

Answer 2

    BitmapImage _classField;

    void LoadImageFunction()
    {
        _classField = new BitmapImage();
        _classField.ImageOpened += new EventHandler<RoutedEventArgs>(bi_ImageOpened);
        _classField.ImageFailed += new EventHandler<ExceptionRoutedEventArgs>(bi_ImageFailed);
        //sorry.. totally forgot about order :)
        _classField.UriSource = new Uri("../some/uri", UriKind.Relative);
    }

    void bi_ImageFailed(object sender, ExceptionRoutedEventArgs e)
    {
        //something has happend
        throw e.ErrorException;
    }

    void bi_ImageOpened(object sender, RoutedEventArgs e)
    {
        //image is loaded.. now we can work with it..
        var w = new WriteableBitmap(_classField);
    }

Answer 3

img1 = new BitmapImage(new Uri("/PrjName;component/Images/image01.jpg", UriKind.RelativeOrAbsolute));
        img2 = new BitmapImage(new Uri("/PrjName;component/Images/image02.jpg", UriKind.RelativeOrAbsolute));
        img1.CreateOptions = BitmapCreateOptions.None;
        img2.CreateOptions = BitmapCreateOptions.None;
        img1.ImageOpened += new EventHandler<RoutedEventArgs>(img1_ImageOpened);
        img2.ImageOpened += new EventHandler<RoutedEventArgs>(img2_ImageOpened);


    void img2_ImageOpened(object sender, RoutedEventArgs e)
    {
        load2 = true;
    }

    void img1_ImageOpened(object sender, RoutedEventArgs e)
    {
        load1 = true;
    }

    private void LayoutRoot_Loaded(object sender, RoutedEventArgs e)
    {
        while (!load1 && !load2)
        { }
        WriteableBitmap x = new WriteableBitmap(img1);
        WriteableBitmap y = new WriteableBitmap(img2);
    }

这应该工作。 它为我做了..！ 它使它变得很复杂，但这就是它的工作原理！