how to prevent negative number input from user in textbox

Eric L

13y9.7kVisual Basic .NET

This is what I have:

private void btnCompute_Click(object sender, EventArgs e)

{

double width = 0;

double length = 0;

double height = 0;

if (!double.TryParse(this.tbWidth.Text.Trim(), out width))

{

MessageBox.Show("The width is invalid.", "Notification", MessageBoxButtons.OK, MessageBoxIcon.Error);

return;

}

if (!double.TryParse(this.tbHeight.Text.Trim(), out height))

{

MessageBox.Show("The height is invalid.", "Notification", MessageBoxButtons.OK, MessageBoxIcon.Error);

return;

}

if (!double.TryParse(this.tbLength.Text.Trim(), out length))

{

MessageBox.Show("The length is invalid.", "Notification", MessageBoxButtons.OK, MessageBoxIcon.Error);

return;

}

It accepts negative numbers, but I want to able to show an error message when a negative number is entered for the width, height, or length.

Any help is greatly appreciated, Thanks!

2 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes13y ago
You could also combine the checks for negative numbers with the existing checks for invalidity.

One other thing you could do is to place the input focus back to the textbox where the problem lies:

private void btnCompute_Click(object sender, EventArgs e)
{

double width = 0;
double length = 0;
double height = 0;

if (!double.TryParse(this.tbWidth.Text.Trim(), out width) || width < 0)
{
MessageBox.Show("The width is invalid.", "Notification", MessageBoxButtons.OK, MessageBoxIcon.Error);
this.tbWidth.Focus();
return;
}

if (!double.TryParse(this.tbHeight.Text.Trim(), out height) || height < 0)
{
MessageBox.Show("The height is invalid.", "Notification", MessageBoxButtons.OK, MessageBoxIcon.Error);
this.tbHeight.Focus();
return;
}

if (!double.TryParse(this.tbLength.Text.Trim(), out length) || length < 0)
{
MessageBox.Show("The length is invalid.", "Notification", MessageBoxButtons.OK, MessageBoxIcon.Error);
this.tbLength.Focus();
return;
}
}
0

Faraz khan13y ago

you can use below statement for each of your value

if (_value < 0) 

{
        MessageBox.Show("The _value is                 invalid.", "Notification",MessageBoxButtons.OK, MessageBoxIcon.Error);
        return;
}