Question

C＃.NET 4.0 WinForms

我开始从this tutorial实现MEF示例代码，该代码描述了为元数据创建自定义ExportAttribute属性。在我尝试在元数据中包含资源文件中的图像之前，一切都在顺利进行。目标是将每个插件DLL的标题，描述和图标提取为元数据，以便在主程序中构建插件菜单。

我现在得到编译错误：

“属性参数必须是常量表达式，typeof表达式或属性参数类型“
的数组创建表达式

所以现在我遇到了问题，需要弄明白：

1）如何在属性中包含图像？

或

2）如何在不使用属性的情况下在MEF中包含元数据？

以下是我正在使用的代码：

在合同类中：

// 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();
}

Plug-In 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，Plug-In 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);
    }
}

此行产生错误。

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

显然，ResourceFile不被视为常量，但是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” ）

感谢您提供任何帮助或建议！

Answer 1

找到解决方案：

好的，据我所知，你不能在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文件一样。然后可以使用.NET类型的内置静态方法读取图标：

Icon MyDLLIcon = Icon.ExtractAssociatedIcon(DLLFilePath);

我仍然不确定为什么你可以将资源文件中的字符串作为MEF元数据返回，而不是嵌入的图标或图像。

由于我一直试图拼凑一个功能性的示例程序，该程序现在提供带有图标的插件菜单几天，我想我会发布代码，以防它帮助其他任何人。

这是一个功能齐全的示例项目，具有以下功能：

旨在成为包含5个项目的单一解决方案（MainProgram，ContractInterfaces，PlugInA，PlugInB，PlugInC）
Post Build Events会自动将DLL从每个项目复制到一个常见的“Plug-Ins”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项目将实例化插件（利用Lazy实例化），然后启动它。
每个插件在启动时都会收到对主表单的引用，创建一个新的TextBox，并将其发布到主表单以证明它已运行并可以访问GUI。
< / LI>
所选插件的标题，说明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Icon（来自旧的Visual Studio 6 Common Graphics Misc文件夹）

Screenshot

从DLL插件中提取图标以创建ListView，并且一旦文件框启动（在双击ListView中的每个插件项之后），DLL就会创建文档框并将其发布到GUI。 / p>

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

由于某种原因，Code Sample解析器不喜欢Using语句，所以这里它们是作为要点：

使用System;
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ContractInterfaces;
（命名空间）MainProgram

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; }
}

现在将一个名为“listView1”的ListView控件添加到主窗体，并将其保存到窗体的右侧。插件中动态创建的TextBox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;
（namespace）ContractInterfaces

// 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System;
使用System.ComponentModel.Composition;
使用System.Windows.Forms;
使用ContractInterfaces;
（名称空间）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System;
使用System.ComponentModel.Composition;
使用System.Windows.Forms;
使用ContractInterfaces;
（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System;
使用System.ComponentModel.Composition;
使用System.Windows.Forms;
使用ContractInterfaces;
（名称空间）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：

Solution

右键单击解决方案，然后选择“项目依赖项...”。按如下方式设置依赖项：

MainProgram - 取决于 - ContractInterface
PlugInA - 取决于 - ContractInterface
PlugInB - 取决于 - ContractInterface
PlugInC - 取决于 - ContractInterface
ContractInterface - 取决于 - [没有]

右键单击解决方案，然后选择“项目构建订单...”。构建顺序应如下所示：

ContractInterface
PlugInA
PlugInB
PlugInC
MainProgram（主程序）

构建并运行该程序。您应该看到3个DLL文件被复制到与解决方案文件（* .sln）相同的目录级别的新“Plug-Ins”文件夹中。如果没有，请检查项目构建顺序，依赖项，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，则应在带有插件条目的表单中填充ListView。双击每个ListView条目以启动插件。

玩得开心，我希望这有助于某人......

如何在使用MEF的插件DLL的元数据中包含图像？

1 个答案: