我如何将一个文本框的数量与另一个文本框相加 VB.NET

Question

I have two text boxes TextBox1 and TextBox2 . I want to add the TextBox2 amount in TextBox1 . I have use the below but the answer is not correct.

Private Sub TextBox2_TextChanged(sender As System.Object, e As System.EventArgs) Handles TextBox2.TextChanged
    TextBox1.Text = Val(TextBox2.Text) + Val(TextBox1.Text)
    TextBox2.Text = (FormatNumber(TextBox2.Text))
End Sub

Answer 1

Your problem is where you put your code. It runs every time the text changes.

So, when you enter 2 in the TextBox2 it adds 2 to the 200 in TextBox1 . Now TextBox1 is 202.

You enter 0 in TextBox2 . TextBox2 is now 20. The code runs and 20 +202 = 222, the new value in TextBox1 .

Finally you enter 0. The value in TextBox1 is 222 + 200 = 422 .

You could see this happen if you set a break point in the code and stepped through line by line.

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim TB1Integer As Integer
    Dim TB2Integer As Integer
    If Integer.TryParse(TextBox1.Text, TB1Integer) AndAlso Integer.TryParse(TextBox2.Text, TB2Integer) Then
        TextBox1.Text = CStr(TB1Integer + TB2Integer)
    Else
        MessageBox.Show("Please enter a number in both boxes.")
    End If
End Sub

I used Integer.TryParse to validate the TextBox entries. It is much more reliable than the old Val from VB6. .TryParse returns a Boolean so can be used in a an If statement. It also fills the second parameter with the numeric value if successful.