c# - 如何使用 MEF 在插件 DLL 的元数据中包含图像？

Question

C# .NET 4.0 WinForms

我从 this tutorial 开始实现 MEF 示例代码它描述了为元数据创建自定义 ExportAttribute 属性。一切都在顺利进行，直到我尝试在元数据中包含来自资源文件的图像。目标是提取每个插件 DLL 的标题、描述和图标作为元数据，用于在主程序中构建插件菜单。

我现在得到编译错误:

"An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type"

所以现在我有一个问题，需要弄清楚:

1)如何在属性中包含图像？

或者

2) 如何在不使用属性的情况下在 MEF 中包含元数据？

这是我正在使用的代码:

在合约类中:

// Metadata contract interface
public interface IPlugInMetadata
{
    string PlugInTitle { get; }
    string PlugInDescription { get; }
    Image PlugInIcon { get; }
}

// Plug-In contract interface
public interface IPlugIn
{
    void StartPlugIn(object systemObject);
    void StopPlugin();
}

插件 DLL 中的自定义属性:

[MetadataAttribute]
[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
public class PluginMetadataAttribute : ExportAttribute
{
    public string title { get; set; }
    public string description { get; set; }
    public Image icon { get; set; }

    public PluginMetadataAttribute(string plugInTitle, string plugInDescription, Image plugInIcon) 
        : base(typeof(IPlugInMetadata))
    {
        title = plugInTitle;
        description = plugInDescription;
        icon = plugInIcon;
    }
}

最后，插件 DLL 中的 Program 类:

[Export(typeof(IPlugIn))]
[PluginMetadata(ResourceFile.PlugInTitle, ResourceFile.PlugInDescription, ResourceFile.PlugInIcon24)]
public class Program : IPlugIn
{
    public void StartPlugIn(object systemObject)
    {
        Console.WriteLine("Start Plug-In: " + ResourceFile.PlugInTitle);
    }

    public void StopPlugin()
    {
        Console.WriteLine("Stop Plug-In: " + ResourceFile.PlugInTitle);
    }
}

这条线正在产生错误。

[PluginMetadata(ResourceFile.PlugInTitle, ResourceFile.PlugInDescription, ResourceFile.PlugInIcon24)]

显然 ResourceFile 不被视为常量，但是我如何将图像用作元数据，或者这是不可能的？ (请注意，图像设置为“嵌入 .resx”)

感谢您的任何帮助或建议!

Answer 1

找到了解决办法:

好吧，据我所知，您不能在 MEF 元数据中使用图像或图标。但是，您可以为 DLL 文件指定一个图标，就像为 EXE 文件所做的那样。然后可以使用内置于 .NET 图标类型中的静态方法读取图标:

Icon MyDLLIcon = Icon.ExtractAssociatedIcon(DLLFilePath);

我仍然不确定为什么可以从资源文件中返回字符串作为 MEF 元数据，而不是嵌入的图标或图像。

由于几天来我一直在尝试拼凑一个功能强大的示例程序，该程序提供带有图标的插件菜单，因此我想我会发布代码以帮助其他人。

这是一个功能齐全的示例项目，具有以下功能:

旨在成为具有 5 个项目( MainProgram、ContractInterfaces、PlugInA、PlugInB、PlugInC)的单一解决方案

Post Build Events 会自动将每个项目中的 DLL 复制到一个公共(public)的“插件”文件夹

MainProgram (WinForm) 项目将构建可用 DLL 插件的目录，并使用每个插件的图标和元数据标题填充 ListView

双击 ListView 项将实例化插件(利用延迟实例化)，并启动它。

每个 Plug-In 在启动时都会收到对主 Form 的引用，创建一个新的 TextBox，并将其发布到主 Form 以证明它可以运行并可以访问 GUI。

所选插件的标题、描述和版本元数据值将打印到控制台窗口

我为每个 DLL 分配了一个不同的图标(来自旧的 Visual Studio 6 Common Graphics Misc 文件夹)



从 DLL 插件中提取图标以创建 ListView，并且文本框由 DLL 创建并在它们启动后发布到 GUI(在双击 ListView 中的每个插件项之后)。

将以下代码添加到名为“MainProgram”的全新 C# WinForm 项目(我使用 VS 2010):

出于某种原因，代码示例解析器不喜欢 Using 语句，所以这里将它们作为要点:

使用系统；

使用 System.Collections.Generic;

使用 System.ComponentModel.Composition;

使用 System.ComponentModel.Composition.Hosting;

使用 System.Drawing；

使用 System.IO；

使用 System.Windows.Forms;

使用合约接口(interface)；

(命名空间)主程序

public partial class Form1 : Form
{
    // Prerequisites to run:
    //      1)  Project, Add Reference, Projects, ContractInterface
    //      2)  Project, Add Reference, .NET, System.ComponentModel.Composition

    [ImportMany(typeof(IPlugIn))]
    private IEnumerable<Lazy<IPlugIn, IPlugInMetadata>> LoadedPlugIns;

    List<PlugInInfo> AvailablePlugIns = null;


    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        // Get a list of the available Plug-Ins
        AvailablePlugIns = GetPlugInList();

        // Prepare an ImageList to hold the DLL icons
        ImageList ImgList = new ImageList();
        ImgList.ColorDepth = ColorDepth.Depth32Bit;
        ImgList.ImageSize = new Size(32, 32);

        // Populate ImageList with Plug-In Icons
        foreach (var item in AvailablePlugIns)
        {
            ImgList.Images.Add(item.PlugInIcon.ToBitmap());
        }

        // Assign the ImageList to the ListView
        listView1.LargeImageList = ImgList;

        int imageIndex = 0;

        // Create the ListView items
        foreach (var item in AvailablePlugIns)
        {
            listView1.Items.Add(item.PlugInTitle, imageIndex);
            imageIndex++;
        }

        listView1.MouseDoubleClick += new MouseEventHandler(listView1_MouseDoubleClick);
    }

    void listView1_MouseDoubleClick(object sender, MouseEventArgs e)
    {
        // Get the Plug-In index number 
        int plugInNum = listView1.SelectedItems[0].Index;

        PlugInInfo selectedPlugIn = AvailablePlugIns[plugInNum];

        // Call the StartPlugIn method in the selected Plug-In.
        // Lazy Instantiation will fully load the Assembly here
        selectedPlugIn.PlugIn.StartPlugIn(this);

        Console.WriteLine("Plug-In Title:          {0}", selectedPlugIn.PlugInTitle);
        Console.WriteLine("Plug-In Description:    {0}", selectedPlugIn.PlugInDescription);
        Console.WriteLine("Plug-In Version:        {0}", selectedPlugIn.PlugInVersion);
        Console.WriteLine();
    }



    private List<PlugInInfo> GetPlugInList()
    {
        // Create a List to hold the info for each plug-in
        List<PlugInInfo> plugInList = new List<PlugInInfo>();

        // Set Plug-In folder path to same directory level as Solution
        string plugInFolderPath = System.IO.Path.Combine(Application.StartupPath, @"..\..\..\Plug-Ins");

        // Test if the Plug-In folder exists
        if (!Directory.Exists(plugInFolderPath))
        {
            // Plug-In Folder is missing, so try to create it
            try
            { Directory.CreateDirectory(plugInFolderPath); }
            catch
            { MessageBox.Show("Failed to create Plug-In folder", "Folder Creation Error:", MessageBoxButtons.OK, MessageBoxIcon.Exclamation); }
        }

        try
        {
            // Create a catalog of plug-ins
            var catalog = new DirectoryCatalog(plugInFolderPath, "*.dll");
            AggregateCatalog plugInCatalog = new AggregateCatalog();
            plugInCatalog.Catalogs.Add(catalog);
            CompositionContainer container = new CompositionContainer(plugInCatalog);

            // This line will fetch the metadata from each plug-in and populate LoadedPlugIns
            container.ComposeParts(this);

            // Save each Plug-Ins metadata
            foreach (var plugin in LoadedPlugIns)
            {
                PlugInInfo info = new PlugInInfo();

                info.PlugInTitle = plugin.Metadata.PlugInTitle;
                info.PlugInDescription = plugin.Metadata.PlugInDescription;
                info.PlugInVersion = plugin.Metadata.PlugInVersion;
                info.PlugIn = plugin.Value;

                plugInList.Add(info);
            }

            int index = 0;

            // Extract icons from each Plug-In DLL and store in Plug-In list
            foreach (var filePath in catalog.LoadedFiles)
            {
                plugInList[index].PlugInIcon = Icon.ExtractAssociatedIcon(filePath);
                index++;
            }
        }
        catch (FileNotFoundException fex)
        {
            Console.WriteLine("File not found exception : " + fex.Message);
        }
        catch (CompositionException cex)
        {
            Console.WriteLine("Composition exception : " + cex.Message);
        }
        catch (DirectoryNotFoundException dex)
        {
            Console.WriteLine("Directory not found exception : " + dex.Message);
        }

        return plugInList;
    }
}


public class PlugInInfo
{
    public string PlugInTitle { get; set; }
    public string PlugInDescription { get; set; }
    public string PlugInVersion { get; set; }
    public Icon PlugInIcon { get; set; }
    public IPlugIn PlugIn { get; set; }
}

现在向主窗体添加一个名为“listView1”的 ListView 控件，并将其保留在窗体的右侧。从插件动态创建的文本框将显示在左侧。

接下来添加一个名为“ContractInterfaces”的类项目，然后包含以下代码:

使用 System.Windows.Forms;

(命名空间)契约(Contract)接口(interface)

// Prerequisites to run:
//      1)  Project, Add Reference, .NET, "System.Windows.Forms"

public interface IPlugIn
{
    void StartPlugIn(Form mainForm);
}

public interface IPlugInMetadata
{
    string PlugInTitle { get; }
    string PlugInDescription { get; }
    string PlugInVersion { get; }
}

接下来添加一个名为“PlugInA”的类项目，然后包含以下代码:

使用系统；

使用 System.ComponentModel.Composition;

使用 System.Windows.Forms;

使用合约接口(interface)；

(命名空间) PlugInA

    // Prerequisites to run:
//      1)  Project, Add Reference, Projects, "ContractInterface"
//      2)  Project, Add Reference, .NET, "System.Windows.Forms"
//      3)  Project, Add Reference, .NET, "System.ComponentModel.Composition"
//      4)  Project, Properties, Build Events, Post-Build event command line:
//          xcopy "$(ProjectDir)$(OutDir)$(TargetFileName)"  "$(SolutionDir)Plug-Ins\" /Y
//      5)  Project, Properties, Build Events, Run the post-build event:, Always
//      6)  Project, Properties, Application, Icon and manifest, [Select an icon]

[Export(typeof(IPlugIn))]
[PluginMetadata]
public class Program : IPlugIn
{
    private Form MainForm;

    public void StartPlugIn(Form mainForm)
    {
        MainForm = mainForm;

        // Place a TextBox on the Main Form
        TextBox textBox = new TextBox();
        textBox.Text = "PlugInA";
        MainForm.Controls.Add(textBox);
        textBox.Width = 65;
        textBox.Height = 20;
        textBox.Top = 0;
        textBox.Left = 0;
    }
}

// Create a custom strong-typed Metadata Attribute for MEF
[MetadataAttribute]
[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
public class PluginMetadataAttribute : ExportAttribute
{
    public string PlugInTitle { get; set; }
    public string PlugInDescription { get; set; }
    public object PlugInVersion { get; set; }

    public PluginMetadataAttribute()
        : base(typeof(IPlugInMetadata))
    {
        PlugInTitle = "Plug-In A";
        PlugInDescription = "This is Plug-In A";
        PlugInVersion = "1.0.0.0";
    }
}

接下来添加一个名为“PlugInB”的类项目，然后包含以下代码:

使用系统；

使用 System.ComponentModel.Composition;

使用 System.Windows.Forms;

使用合约接口(interface)；

(命名空间) PlugInB

// Prerequisites to run:
//      1)  Project, Add Reference, Projects, "ContractInterface"
//      2)  Project, Add Reference, .NET, "System.Windows.Forms"
//      3)  Project, Add Reference, .NET, "System.ComponentModel.Composition"
//      4)  Project, Properties, Build Events, Post-Build event command line:
//          xcopy "$(ProjectDir)$(OutDir)$(TargetFileName)"  "$(SolutionDir)Plug-Ins\" /Y
//      5)  Project, Properties, Build Events, Run the post-build event:, Always
//      6)  Project, Properties, Application, Icon and manifest, [Select an icon]

[Export(typeof(IPlugIn))]
[PluginMetadata]
public class Program : IPlugIn
{
    private Form MainForm;

    public void StartPlugIn(Form mainForm)
    {
        MainForm = mainForm;

        // Place a TextBox on the Main Form
        TextBox textBox = new TextBox();
        textBox.Text = "PlugInB";
        MainForm.Controls.Add(textBox);
        textBox.Width = 65;
        textBox.Height = 20;
        textBox.Top = 30;
        textBox.Left = 0;
    }
}

// Create a custom strong-typed Metadata Attribute for MEF
[MetadataAttribute]
[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
public class PluginMetadataAttribute : ExportAttribute
{
    public string PlugInTitle { get; set; }
    public string PlugInDescription { get; set; }
    public object PlugInVersion { get; set; }

    public PluginMetadataAttribute()
        : base(typeof(IPlugInMetadata))
    {
        PlugInTitle = "Plug-In B";
        PlugInDescription = "This is Plug-In B";
        PlugInVersion = "1.0.0.1";
    }
}

接下来添加一个名为“PlugInC”的类项目，然后包含以下代码:

使用系统；

使用 System.ComponentModel.Composition;

使用 System.Windows.Forms;

使用合约接口(interface)；

(命名空间) PlugInC

// Prerequisites to run:
//      1)  Project, Add Reference, Projects, "ContractInterface"
//      2)  Project, Add Reference, .NET, "System.Windows.Forms"
//      3)  Project, Add Reference, .NET, "System.ComponentModel.Composition"
//      4)  Project, Properties, Build Events, Post-Build event command line:
//          xcopy "$(ProjectDir)$(OutDir)$(TargetFileName)"  "$(SolutionDir)Plug-Ins\" /Y
//      5)  Project, Properties, Build Events, Run the post-build event:, Always
//      6)  Project, Properties, Application, Icon and manifest, [Select an icon]

[Export(typeof(IPlugIn))]
[PluginMetadata]
public class Program : IPlugIn
{
    private Form MainForm;

    public void StartPlugIn(Form mainForm)
    {
        MainForm = mainForm;

        // Place a TextBox on the Main Form
        TextBox textBox = new TextBox();
        textBox.Text = "PlugInC";
        MainForm.Controls.Add(textBox);
        textBox.Width = 65;
        textBox.Height = 20;
        textBox.Top = 60;
        textBox.Left = 0;
    }
}

// Create a custom strong-typed Metadata Attribute for MEF
[MetadataAttribute]
[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
public class PluginMetadataAttribute : ExportAttribute
{
    public string PlugInTitle { get; set; }
    public string PlugInDescription { get; set; }
    public object PlugInVersion { get; set; }

    public PluginMetadataAttribute()
        : base(typeof(IPlugInMetadata))
    {
        PlugInTitle = "Plug-In C";
        PlugInDescription = "This is Plug-In C";
        PlugInVersion = "1.0.0.2";
    }
}

解决方案应如下所示:



右键单击解决方案，然后选择“项目依赖项...”。设置依赖项如下:

MainProgram - 取决于 - ContractInterface

PlugInA - 取决于 - ContractInterface

PlugInB - 取决于 - ContractInterface

PlugInC - 取决于 - ContractInterface

ContractInterface - 取决于 - [nothing]

右键单击解决方案，然后选择“项目构建顺序...”。构建顺序应如下所示:

契约(Contract)界面

插件

插件B

PlugInC

主程序

构建并运行程序。您应该会看到 3 个 DLL 文件复制到与解决方案文件 (*.sln) 相同目录级别的新“插件”文件夹中。如果没有，请检查项目构建顺序、依赖关系，以及您是否根据上面插件代码中的注释输入了构建后事件。如果文件在那里，那么 ListView 应该用插件条目填充到表单中。双击每个 ListView 条目以启动插件。

玩得开心，我希望这对某人有帮助....