I realize this thread is pretty old but I thought I'd post the solution I came up with.
The biggest problem with validation on WinForms is the validation is only executed when the control has "lost focus". So the user has to actually click inside a text box then click somewhere else for the validation routine to execute. This is fine if your only concerned about the data that is entered being correct. But this doesn't work well if you're trying to make sure a user didn't leave a textbox empty by skipping over it.
In my solution, when the user clicks the submit button for a form, I check each control on the form (or whatever container is specified) and use reflection to determine if a validating method is defined for the control. If it is, the validation method is executed. If any of the validations fail, the routine returns a failure and allows the process to stop. This solution works well especially if you have several forms to validate.
1) Just copy and paste this section of code to your project. We're using Reflection so you need to add System.Reflection to your using statements
class Validation
{
public static bool hasValidationErrors(System.Windows.Forms.Control.ControlCollection controls)
{
bool hasError = false;
// Now we need to loop through the controls and deterime if any of them have errors
foreach (Control control in controls)
{
// check the control and see what it returns
bool validControl = IsValid(control);
// If it's not valid then set the flag and keep going. We want to get through all
// the validators so they will display on the screen if errorProviders were used.
if (!validControl)
hasError = true;
// If its a container control then it may have children that need to be checked
if (control.HasChildren)
{
if (hasValidationErrors(control.Controls))
hasError = true;
}
}
return hasError;
}
// Here, let's determine if the control has a validating method attached to it
// and if it does, let's execute it and return the result
private static bool IsValid(object eventSource)
{
string name = "EventValidating";
Type targetType = eventSource.GetType();
do
{
FieldInfo[] fields = targetType.GetFields(
BindingFlags.Static |
BindingFlags.Instance |
BindingFlags.NonPublic);
foreach (FieldInfo field in fields)
{
if (field.Name == name)
{
EventHandlerList eventHandlers = ((EventHandlerList)(eventSource.GetType().GetProperty("Events",
(BindingFlags.FlattenHierarchy |
(BindingFlags.NonPublic | BindingFlags.Instance))).GetValue(eventSource, null)));
Delegate d = eventHandlers[field.GetValue(eventSource)];
if ((!(d == null)))
{
Delegate[] subscribers = d.GetInvocationList();
// ok we found the validation event, let's get the event method and call it
foreach (Delegate d1 in subscribers)
{
// create the parameters
object sender = eventSource;
CancelEventArgs eventArgs = new CancelEventArgs();
eventArgs.Cancel = false;
object[] parameters = new object[2];
parameters[0] = sender;
parameters[1] = eventArgs;
// call the method
d1.DynamicInvoke(parameters);
// if the validation failed we need to return that failure
if (eventArgs.Cancel)
return false;
else
return true;
}
}
}
}
targetType = targetType.BaseType;
} while (targetType != null);
return true;
}
}
2) Use the standard Validating event on any control you want to validate. Be Sure to use e.Cancel when the validation fails!
private void txtLastName_Validating(object sender, CancelEventArgs e)
{
if (txtLastName.Text.Trim() == String.Empty)
{
errorProvider1.SetError(txtLastName, "Last Name is Required");
e.Cancel = true;
}
else
errorProvider1.SetError(txtLastName, "");
}
3) Don't skip this step! Set the AutoValidate property on the form to EnableAllowFocusChange. This will allow tabbing to another control even when the validation fails.
4) Finally, in your Submit Button method, call the Validation method and specify what container you want to check. It can be the whole form, or just a container on the form like a Panel or a Group.
private void btnSubmit_Click(object sender, EventArgs e)
{
// the controls collection can be the whole form or just a panel or group
if (Validation.hasValidationErrors(frmMain.Controls))
return;
// if we get here the validation passed
this.close();
}
Happy Coding!
