在WPF中动态加载图像

Question

我对WPF有一个奇怪的问题,我在运行时从磁盘加载图像并将它们添加到StackView容器中.但是,图像未显示.经过一些调试我找到了诀窍,但它确实没有任何意义.我制作了一个小型演示应用程序来识别问题:

创建一个新的WPF项目,并粘贴代码如下:

XAML:

<Window x:Class="wpfBug.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300" Loaded="Window_Loaded">
    <StackPanel Name="sp">
    </StackPanel>
</Window>

xaml.cs,粘贴在默认值下面:

namespace wpfBug
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            Image i = new Image();
            BitmapImage src = new BitmapImage();
            src.BeginInit();
            src.UriSource = new Uri("picture.jpg", UriKind.Relative);
            src.EndInit();
            i.Source = src;
            i.Stretch = Stretch.Uniform;
            //int q = src.PixelHeight;        // Image loads here
            sp.Children.Add(i);
        }
    }
}

将图像复制到bin/Debug文件夹并将其命名为"picture.jpg"

除非注释行被取消注释,否则此程序不显示任何内容.

任何人都可以解释我做错了什么,或者为什么会这样？如果删除图像并运行程序,它会在'int q = ...'行生成异常.如果该行被注释,即使没有图像存在,程序也会无异常地运行.只有当nesseary有意义时加载图像,但是当我将Image控件添加到StackPanel时,应该加载图像.

任何想法？

编辑:顺便说一句,如果您将图像添加为资源,则不需要'int q = ..'行.

Answer 1

这是因为创造被推迟了.如果您希望立即加载图片,只需将此代码添加到init阶段即可.

src.CacheOption = BitmapCacheOption.OnLoad;

像这样:

src.BeginInit();
src.UriSource = new Uri("picture.jpg", UriKind.Relative);
src.CacheOption = BitmapCacheOption.OnLoad;
src.EndInit();

Answer 2

在代码中加载执行程序集中的资源,其中我的图像'Freq.png'位于文件夹"Icons"中并定义为"Resource".

        this.Icon = new BitmapImage(new Uri(@"pack://application:,,,/" 
             + Assembly.GetExecutingAssembly().GetName().Name 
             + ";component/" 
             + "Icons/Freq.png", UriKind.Absolute)); 

如果有人愿意,我也做了一个功能......

/// <summary>
/// Load a resource WPF-BitmapImage (png, bmp, ...) from embedded resource defined as 'Resource' not as 'Embedded resource'.
/// </summary>
/// <param name="pathInApplication">Path without starting slash</param>
/// <param name="assembly">Usually 'Assembly.GetExecutingAssembly()'. If not mentionned, I will use the calling assembly</param>
/// <returns></returns>
public static BitmapImage LoadBitmapFromResource(string pathInApplication, Assembly assembly = null)
{
    if (assembly == null)
    {
        assembly = Assembly.GetCallingAssembly();
    }

    if (pathInApplication[0] == '/')
    {
        pathInApplication = pathInApplication.Substring(1);
    }
    return new BitmapImage(new Uri(@"pack://application:,,,/" + assembly.GetName().Name + ";component/" + pathInApplication, UriKind.Absolute)); 
}

用法:

        this.Icon = ResourceHelper.LoadBitmapFromResource("Icons/Freq.png");

Answer 3

这是一种奇怪的行为,虽然我无法说明为什么会这样,但我可以推荐一些选项.

首先,观察.如果将图像作为内容包含在VS中并将其复制到输出目录,则代码可以正常工作.如果图像在VS中标记为"无"并将其复制,则不起作用.

解决方案1:FileStream

BitmapImage对象接受UriSource或StreamSource作为参数.我们改用StreamSource.

        FileStream stream = new FileStream("picture.png", FileMode.Open, FileAccess.Read);
        Image i = new Image();
        BitmapImage src = new BitmapImage();
        src.BeginInit();
        src.StreamSource = stream;
        src.EndInit();
        i.Source = src;
        i.Stretch = Stretch.Uniform;
        panel.Children.Add(i);

问题:流保持打开状态.如果在此方法结束时关闭它,图像将不会显示.这意味着该文件在系统上保持写锁定状态.

解决方案2:MemoryStream

这基本上是解决方案1,但是您将文件读入内存流并将该内存流作为参数传递.

        MemoryStream ms = new MemoryStream();
        FileStream stream = new FileStream("picture.png", FileMode.Open, FileAccess.Read);
        ms.SetLength(stream.Length);
        stream.Read(ms.GetBuffer(), 0, (int)stream.Length);

        ms.Flush();
        stream.Close();

        Image i = new Image();
        BitmapImage src = new BitmapImage();
        src.BeginInit();
        src.StreamSource = ms;
        src.EndInit();
        i.Source = src;
        i.Stretch = Stretch.Uniform;
        panel.Children.Add(i);

现在,您可以修改系统上的文件,如果这是您需要的.