A problem in Error providers

Question

3.00/5 (1 vote)

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C#

private void tbxWidthBackIamge_Validated(object sender, EventArgs e)
{
    this.errBackWidth.SetError(tbxWidthBackIamge, "Enter the Width");
    if (tbxBackImage.Text != "")
        this.errBackHeight.Dispose();
}

I use an errorProvider to validate a textbox. It appears when there occurred an error. But It didn't disappear after correct the error. Is any error in this code?

Posted 23-Aug-11 18:01pm

Jeremy Shin Woo

Updated 23-Aug-11 18:06pm

Simon Bang Terkildsen

v2

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Sergey Alexandrovich Kryukov 24-Aug-11 0:30am

Why disposing something on invalid case?
--SA

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Simon Bang Terkildsen · Accepted Answer · 2011-08-23T18:24:00

Solution 1

First of you should really use the Validating event. Second you don't validate anything you just set an error message and dispose something else.

So

Use the Validating event
Use SetError(..., "ErrorMessage") when the input is incorrect
Use SetError(..., string.Empty) when the input is correct

Posted 23-Aug-11 18:24pm

Simon Bang Terkildsen

Comments

Sergey Alexandrovich Kryukov 24-Aug-11 0:30am

Correct, my 5. I started to edit my answer at the same time; put some more detail, please see.
--SA

Jeremy Shin Woo 24-Aug-11 1:23am

Thanks Simon..

Sergey Alexandrovich Kryukov · Accepted Answer · 2011-08-23T18:27:00

You did not clear the error when the data is valid. You also call SetError with non-empty error message unconditionally. What's the criteria for validity? Non-empty value? Than call SetError depending on it:

C#

private void tbxWidthBackIamge_Validated(object sender, EventArgs e) {
    if (tbxBackImage.Text.Trim() == string.Empty)
       this.errBackWidth.SetError(tbxWidthBackIamge, "Enter the Width");
    else
       this.errBackWidth.SetError(tbxWidthBackIamge, string.Empty);
}

Pay attention, I use string.Empty instead of "" (never do it). I also suggest to add Trim assuming that a string containing only blank space characters is also invalid. If my assumption is wrong, simply remove Trim.

Better yet, use anonymous delegate:

C#

myControl.Validated += delegate(object sender, System.EventArgs eventArgs) {
    if (tbxBackImage.Text.Trim() == string.Empty)
       this.errBackWidth.SetError(tbxWidthBackIamge, "Enter the Width");
    else
       this.errBackWidth.SetError(tbxWidthBackIamge, string.Empty);
}

With C# v.3 or v.4 you could use the even better syntax with lambda form of the delegate:

C#

myControl.Validated += (sender, eventArgs) => {
    if (tbxBackImage.Text.Trim() == string.Empty)
       this.errBackWidth.SetError(tbxWidthBackIamge, "Enter the Width");
    else
       this.errBackWidth.SetError(tbxWidthBackIamge, string.Empty);
}

See the code sample on this MSDN help page: http://msdn.microsoft.com/en-us/library/system.windows.forms.errorprovider.aspx[^].

Does your code even compile? I mean, what is errBackHeight which you dispose. Does it implement IDisposable? Why disposing anything on error? Just checking.

—SA