Decimal number validation in c# vb.net

Decimal number validation in c# vb.net
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private void textbox1_TextChanged(object sender, EventArgs e)
{
if (textbox1.Text != string.Empty)
{
string str = textbox1.Text.Trim();
double num;
bool isnum = double.TryParse(str, out num);
if (isnum)
{
}
else
{
textbox1.Text = string.Empty;
MessageBox.Show("Invalid Number");
}
}
}
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