Question

我是初学英语和vb.net 但是我想问一下，当我点击按钮进行数学计算时，如果文本框为空，我试图发出警告这是我的代码

Private Sub hitung_Click(ByVal eventSender As System.Object, ByVal eventArgs As System.EventArgs) Handles hitung.Click

    Dim z, iterasi, n1, n2, n3 As Single
    Dim fx0, fx1, fx2, x2, x0, x1 As Decimal

    If a.Text = Nothing Or
                  b.Text = Nothing Or
                  g.Text = Nothing Or
                  h.Text = Nothing Or
                  i.Text = Nothing Or
                  j.Text = Nothing Then
        MessageBox.Show("TextBox is empty", "No entry",
            MessageBoxButtons.OK, MessageBoxIcon.Error)
        With a
            .Focus()
            .SelectAll()
        End With
    End If



    x0 = (a.Text)
    x1 = (b.Text)
    n1 = (g.Text)
    n2 = (h.Text)
    n3 = (i.Text)
    iterasi = (j.Text)

但仍然有一个错误，上面写着“从字符串转换”“到'Decimal'类型无效。”如果我将文本框留空并按下按钮

所以我将x0更改为此

x0 = Decimal.Parse(a.Text)

但错误显示“输入字符串的格式不正确。”

如何解决错误？

Answer 1

Nothing和一个空字符串是不同的东西;您可以使用string.IsNullOrEmpty(a.Text)（等）代替a.Text = Nothing以获得更具弹性的方法

Answer 2

以下是代码：

  Public Class Form1

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
     If a.Text = "" Then
          MessageBox.Show("Empty TextBox", "No entry")
     End If
   End Sub
End Class

警告如果文本框空VB.NET

2 个答案: