C# &引用；a「；不包含“的定义”；b"；没有扩展方法'；b'；接受类型为的第一个参数

我有一个无法修复的错误：

Error 1 'System.Windows.Forms.Label' does not contain a definition for 'Copy' 
and no extension method 'Copy' accepting a first argument of     
type'System.Windows.Forms.Label' 
could be found (are you missing a using directive or an assembly reference?)
//path 156  22 FileWatcherEigen

那是我的错误。有人能帮我解释一下哪里出了问题吗

这是我的代码：

using System;
using System.IO;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{

public partial class Form1 : Form
{
    private bool pause = false;
    private bool cut1 = false;
    private bool copy1 = false;

    public Form1()

    {
        InitializeComponent();
    }



    // The lines with performed actions of a file
  private void fileSystemWatcher1_Created(object sender,System.IO.FileSystemEventArgs e)
    {
        if (!pause)
        {
            listBox1.Items.Add("File Created> " + e.FullPath + " -Date:" + DateTime.Now);
        }
    }

    private void fileSystemWatcher1_Changed(object sender, System.IO.FileSystemEventArgs e)
    {
        if (!pause)
        {
            listBox1.Items.Add("File Changed> " + e.FullPath + " -Date:" + DateTime.Now);
        }
    }
    private void fileSystemWatcher1_Deleted(object sender, System.IO.FileSystemEventArgs e)
    {
        if (!pause)
        {
            listBox1.Items.Add("File Deleted> " + e.FullPath + " -Date:" + DateTime.Now);
        }
    }

    private void fileSystemWatcher1_Renamed(object sender, System.IO.RenamedEventArgs e)
    {
        if (!pause)
        {
            listBox1.Items.Add("File Renamed> " + e.FullPath + " -Date:" + DateTime.Now);
        }
    }

    private void fileSystemWatcher2_Changed(object sender, System.IO.FileSystemEventArgs e)
    {
        if (!pause)
        {
            listBox1.Items.Add("File Changed> " + e.FullPath + " -Date:" + DateTime.Now);
        }
    }

    private void fileSystemWatcher2_Created(object sender, System.IO.FileSystemEventArgs e)
    {
        if (!pause)
        {
            listBox1.Items.Add("File Created> " + e.FullPath + " -Date:" + DateTime.Now);
        }
    }

    private void fileSystemWatcher2_Deleted(object sender, System.IO.FileSystemEventArgs e)
    {
        if (!pause)
        {
            listBox1.Items.Add("File Deleted> " + e.FullPath + " -Date:" + DateTime.Now);
        }
    }

    private void fileSystemWatcher2_Renamed(object sender, System.IO.RenamedEventArgs e)
    {
        if (!pause)
        {
            listBox1.Items.Add("File Renamed> " + e.FullPath + " -Date:" + DateTime.Now);
        }
    }

    //1st directory
    private void button2_Click(object sender, EventArgs e)
    {
        if (dlgOpenDir.ShowDialog() == DialogResult.OK)
        {
            fileSystemWatcher1.EnableRaisingEvents = false;  // Stop watching
            fileSystemWatcher1.IncludeSubdirectories = true;
            fileSystemWatcher1.Path = dlgOpenDir.SelectedPath;
            textBox1.Text = dlgOpenDir.SelectedPath;         // Text of textBox2 = Path of fileSystemWatcher2
            fileSystemWatcher1.EnableRaisingEvents = true;   // Begin watching
        }
    }
    //2nd directory
    private void button3_Click(object sender, EventArgs e)
    {
        if (dlgOpenDir.ShowDialog() == DialogResult.OK)
        {
            fileSystemWatcher2.EnableRaisingEvents = false;  // Stop watching
            fileSystemWatcher2.IncludeSubdirectories = true;
            fileSystemWatcher2.Path = dlgOpenDir.SelectedPath;
            textBox2.Text = dlgOpenDir.SelectedPath;         // Text of textBox2 = Path of fileSystemWatcher2
            fileSystemWatcher2.EnableRaisingEvents = true;   // Begin watching
        }
    }
    //log
    private void button1_Click(object sender, EventArgs e)
    {

        DialogResult resDialog = dlgSaveFile.ShowDialog();
        if (resDialog.ToString() == "OK")
        {
            FileInfo fi = new FileInfo(dlgSaveFile.FileName);
            StreamWriter sw = fi.CreateText();
            foreach (string sItem in listBox1.Items)
            {
                sw.WriteLine(sItem);
            }
            sw.Close();
        }
    }
    //pause watching
    private void pause_button_Click(object sender, EventArgs e)
    {
        if (!pause)
        {
            pause = true;
            pause_button.Text = "Unpause";
        }
        else
        {
            pause = false;
            pause_button.Text = "Pause Watching";
        }
    }
    //clear listbox
    private void clear_button_Click(object sender, EventArgs e)
    {
        listBox1.Items.Clear(); 
    }

    private void Transfer_Click(object sender, EventArgs e)
    {
        if (copy1)
        {
            File.Copy(FileBrowseBox.Text, Path.Combine(DestinationBox.Text, Path.ChangeExtension(FileNameBox.Text, Path.GetExtension(FileBrowseBox.Text))));
        }

        }

    private void Browse_file_Click(object sender, EventArgs e)
    {
        DialogResult resDialog = openFileDialog1.ShowDialog();
        if (resDialog == DialogResult.OK)
        {
            FileBrowseBox.Text = openFileDialog1.FileName;
        }
    }

    private void Browse_destination_Click(object sender, EventArgs e)
    {
        DialogResult resDialog = folderBrowserDialog1.ShowDialog();
        if (resDialog == DialogResult.OK)
        {
            DestinationBox.Text = folderBrowserDialog1.SelectedPath;
        }

    }

    private void CopyButton_CheckedChanged(object sender, EventArgs e)
    {
        copy1 = true;
    }

}
}

它说问题就在这一部分：

 File.Copy(FileBrowseBox.Text, Path.Combine(DestinationBox.Text, Path.ChangeExtension(FileNameBox.Text, Path.GetExtension(FileBrowseBox.Text))));

我试图在这个论坛上找到它，但我真的找不到答案或解决方案

它确实适用于以下代码：

using System;
using System.IO;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
    private bool cut = false;
    private bool copy = false;
    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
{
    File.Copy(FileBrowseBox.Text, Path.Combine(DestinationBox.Text, Path.ChangeExtension(FileBox.Text, Path.GetExtension(FileBrowseBox.Text))));
    label2.Text = "File Transfer Succeeded";
}

    private void button2_Click(object sender, EventArgs e)
    {
        DialogResult resDialog = openFileDialog1.ShowDialog();
        if (resDialog == DialogResult.OK)
        {
            FileBrowseBox.Text = openFileDialog1.FileName;
            label2.Text = "";
        }
    }

    private void button3_Click(object sender, EventArgs e)
    {
        DialogResult resDialog = folderBrowserDialog1.ShowDialog();
        if (resDialog == DialogResult.OK)
        {
            DestinationBox.Text = folderBrowserDialog1.SelectedPath;
            label2.Text = "";
        }
    }

    private void radioButton1_CheckedChanged(object sender, EventArgs e)
    {
        copy = true;
    }

    private void radioButton2_CheckedChanged(object sender, EventArgs e)
    {
        cut = true;
    }
}
}

---

出现此错误是因为表单上有一个名为

File

的标签被引用，而不是

System.IO.File

。您可以重命名

标签

，这是我的建议，或者您可以使用

System.IO.File.Copy

的完全限定路径。

显然，您有一个名为

File

的

标签。它对
System.IO.File
类进行阴影处理并导致错误。指定完整类名可以消除此问题：

System.IO.File.Copy(...

好的，我今天遇到了这个恼人的错误，“a”确实包含了“b”的定义

在VS2012中打开解决方案，然后在VS2010中打开解决方案后，我陷入了这种混乱

结果是删除受影响项目中的引用DLL，构建引用DLL项目，然后重新引用允许VS查看定义。
请注意。在我重命名了类中的属性之后，在调试时我遇到了类似的错误。检查了所有内容，甚至在所有解决方案中搜索了ctrl+shift+f5组合的旧属性名称。找不到任何东西

过了一段时间，我注意到旧属性的输出值中存在带有“When hit…”条件的断点。
还有一个简单的情况会发生这种情况。假设您在表单中添加了一个工具，如“按钮”。双击该工具后，（在Visual Studio中），将在Form1.cs中创建代码
private void按钮1\u click（对象发送者，事件参数e）{}
。代码
this.button1.Click+=newsystem.EventHandler（this.button1\u Click）也将在Form1.Designer.cs中创建。如果您删除了第一组代码（无论出于何种原因），那么您还需要删除第二位代码，否则将出现此错误。这可能是一种特定/简单的情况，但这是新程序员可能遇到的错误
 我得到了一个名为“文件”的标签，我更改了名称。但它不起作用。@loko同样的错误？您的行是否仍然显示
File.Copy
，还是更改为
myNewLabelName.Copy
？这就是为什么您应该坚持编码约定，即变量名称应始终以小写字母开头。@Michael Perrenoud您能告诉我如何添加剪切选项而不是复制选项吗？@Loko，这里的问题是，一个标签与您试图引用的类具有相同的名称。在这种情况下，我的约定通常是控件（例如lblFile）的类型缩写+用途。它确实避免了冲突，但也更容易理解我引用的内容。我的类字段都以u开头，也以小写开头。我是在VS 2013中发现这个问题的，所以我按照你的建议做了，删除了引用并重新添加了它。修正了这个问题。