Question

我正在尝试制作一个程序，将文件从一个文件夹复制到另一个文件夹，并且我还在使用进度条查看正在复制的文件。当我运行该程序时，在folderbrowserdialog1上收到错误消息。错误是System.NullReferenceException。当我运行程序时，我可以打开应用程序，但是当我选择按钮时，它给我一个错误。

Public Class Form1
    Dim my As System.Diagnostics.Process = System.Diagnostics.Process.GetCurrentProcess

    Dim directoryTargetLocation As String 'Selected file path
    Dim Destinydirectory As String 'Selected dest directory path

Private Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button1.Click
    Dim FolderBrowserDialog1 As Object = Nothing
    FolderBrowserDialog1.Description = "Select directory" **// Gettig error in this Line**
    With FolderBrowserDialog1
        If .ShowDialog() = DialogResult.OK Then
            directoryTargetLocation = .SelectedPath
            TextBox1.Text = directoryTargetLocation.ToString
            Button2.Enabled = True

        End If
    End With
End Sub

Private Sub Button2_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button2.Click
    FolderBrowserDialog2.Description = "Select destiny directory"
    With FolderBrowserDialog2
        If .ShowDialog() = DialogResult.OK Then
            Destinydirectory = .SelectedPath
            TextBox2.Text = Destinydirectory.ToString
            TextBox2.Text = TextBox2.Text.Remove(TextBox2.Text.Length - 1) & 
     TextBox1.Text.Substring(TextBox1.Text.LastIndexOf("\"))
            Button3.Enabled = True

        End If
    End With
End Sub

Answer 1

您尚未创建FolderBrowserDialog1对象。

修改

您接近了！

您需要的是：

Dim FolderBrowserDialog1 As New FolderBrowserDialog

这将创建一个新的FolderBrowserDialog对象。

您拥有的是：

Dim FolderBrowserDialog1 As Object = Nothing

哪个将创建新的通用对象名称FolderBrowserDialog1，并将其显式设置为“ nothing”

这意味着它不具有您所引用的任何属性或方法，因此会出现错误。

Answer 2

您已将FolderBrowserDialog1声明为对象。

您要做的是将其声明为FolderBrowserDialog。

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim FolderBrowserDialog1 As New FolderBrowserDialog
    FolderBrowserDialog1.Description = "Select directory"
    With FolderBrowserDialog1
        If .ShowDialog() = DialogResult.OK Then
            directoryTargetLocation = .SelectedPath
            TextBox1.Text = directoryTargetLocation.ToString
            Button2.Enabled = True

        End If
    End With
End Sub

VB.NET文件复制程序错误：FolderBrowserDialog1中的System.NullReferenceException

2 个答案: