allow only a single decimal point to be entered within textbox: c#, asp.net 2.x, visual studio 2008 pro, sql 2005 server, iis 6

allow only a single decimal point to be entered within textbox

how do you allow only a single decimal point to be entered within a textbox.

for example, when entering currency figures requiring a decimal point -- but obviously do not want multiple decimals points appearing.

attached is the javascript code I use for allowing just numbers to be entered within textbox field -- as a starting point.

function numeralsOnly(evt) {
    evt = (evt) ? evt : event;
    var charCode = (evt.charCode) ? evt.charCode : ((evt.keyCode) ? evt.keyCode : 
        ((evt.which) ? evt.which : 0));
    if (charCode > 31 && (charCode < 48 || charCode > 57)) {
    //alert("Enter numerals only in this field.");
        return false;
    }
    return true;
}

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Hello.

First of all, if you are unfamiliar with how to use the TextChanged event in C# to trigger an event when someone enters in the text box, see my solution here
http://www.experts-exchange.com/Microsoft/Development/.NET/Visual_CSharp/Q_23275773.html

Now, for the meat of it. Inside the text changed event handler method, you retrieve the contents of the text box like this (assuming its called textBox1)

string charCode = this.textBox1.Text;

once you have it, you can then check the most recent entry to see if it's a number or a decimal point. I can't remember if the least significant digit is in position 0 or in position (length - 1), so in the following code I'll use a 0 for the index, but if it checks the lead digit, just replace the 0 with (charCode.Length-1 I think that's a real option in C#).

if (charCode[0] > 31 && (charCode[0] < 48 || charCode[0] > 57))
{
MessageBox("Enter numerals only or decimal point in this field.");
//Some code to restore the value previously in the textbox (global variable, perhaps?)
}

You'll have to figure out the number for a decimal point in ASCII, I can't remember it now, and add it to the above code. I recommend creating a variable at the beginning of your code somewhere (outside your event handler) called something like this.decimalFlag as a boolean.

private bool decimalFlag = false;

Once you detect a decimal point, you set that flag to true. Every time through the event handler, have an "if" statement that checks to see if the decimal point exists. If it does, only allow one digit to the right of it. If they try to enter another digit, give them a message box saying they can't do that, and replace the text in the text box with what it was before they tried to enter the extra digit. Then put a

return;

and you;re out of the event handler function without any changes to the list box.

When I say replace the value in the text box with what it was before, I mean this: define at the beginning of your program

private string oldText;

Then, at the end of the event handler, put the following line

oldText = this.listBox1.Text;

This gives you something to revert to in case you need it.

If this isn't clear to you, I can get more in depth tomorrow with maybe some personalized code examples.

Luke

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allow only a single decimal point to be entered within textbox

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c#, asp.net 2.x, visual studio 2008 pro, sql 2005 server, iis 6

Microsoft Visual J#.Net

.NET Framework 2.x

Microsoft Visual C#.Net

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