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c# custom credential provider

I am trying to develop a custom credential provider. Trying to learn the basics. I implemented ICredentialProvider and ICredentialProviderCredential.
I added a custom credential tile, edit text and command link to windows logon UI.
What i want to do is, when i click on CommandButton i try to read textbox value but i could not do that.
I want to open a custom windows form (e.g MFA form), how can i open a custom form?
I am using phaetto/windows-credentials-provider implementation as example
There is not much information about this topic.

1. Text field
You must collect and keep securely the value(s) of text box(ex) field(s) as far as it is updated and your tile implementation class is notified about the change of that value.
You will be notified about every single character user entered into the text field. Be ready for this.
As far as user type info input text box your provider's method ICredentialProviderCredential::SetStringValue will be called on every text box update.
2. Popup window (dialog)
If you want to open any window you must acquire a parent window handle from Logon UI / Cred UI. Handle acquisition method is ICredentialProviderCredentialEvents::OnCreatingWindow.
You can find more details in the answer and it's comments: https://stackoverflow.com/a/52089207/3868464 .

Dynamic validation in metro applications

Im developing an application for the windows store in c#, and wondering whats the best way to dynamically validate data in controls such as Textboxes, Dropdown boxes etc.
At the minute I usually check the validation when a buttons clicked, I would like to be able to notify the user in realtime.
An example of where i would like this to be used in when a user registers with an email address I would like to check the format of the string using a regex command.
Any assistance would be appreciated

you can use relay command
eg Relay Command and MVVM pattern

Best practice for visual validation of textbox control data

I think I want to show some kind of confirmation tick type thing by a textbox - (it's traditional windows forms stuff, not WPF) - but not sure if it's a bit naff. I would like some kind of slick way of showing that a value is incorrect or valid after some tests have been done i.e. a web service is valid with that name or SMTP server seems to running with that name etc.
Should there be even any visual stuff going on or should a simple message on a status strip at the bottom of the window be enough.....
Any ideas are most welcome.
PS - if the tick thing is a good idea what's the best way to implement this with a textbox control.
Example....

You could make a custom control which contains both a textbox and an imagebox. The custom control could raise a validation event which checks the text and then sets the imagebox graphic based on whether or not the validation passed (or sets it blank if there is not text in the textbox).
The .net centric way would probably be to implement validation providers and some type of custom error provider, like what Henrik is mentioning.

You can use ErrorProvider to show a little exclamation mark when the entered value is incorrect.

you can use the ErrorProviderComponent in order to show notifications. The naming of that component is slightly unfortunate in my mind but you can easily change the icon to show other things than the typical red error "X".

how to validate a textbox programmatically, that is at run time

i am creating textboxes when a button is clicked and again and again and so on
while accepting input i need to check if the boxes are all full,
i know how to do this using design view but how to do this using coding
that is add and validation control to the textbox when it created before initializing/adding it to the page.?
validation should be not null..

So as for validating the user input I would stay away from the ASP.Net Control Validators as hardly anyone in industry uses them. I would use the jQuery validator plugin which is included in a new Visual Studio project by default. You will still want Server side checking but it is much easier to call String.isNullOrEmpty(txtBox.Text) rather than using the Control Validators.

OnValidating Event in a custom control

When does the OnValidate event fire in the life-cycle of a control?
I'm creating a DateBox that will allow the user to enter a date in MM/DD/YYYY format (text) and need to verify that the date is in that format. It'll never be converted to a date (stored as string) but I would like to know the best time to validate that data (and provide feedback).
Note: It may seem a bit like re-inventing the wheel, but the app that I'm writing gets deployed to a tablet-pc and the winforms DateTimePicker is hell to edit with a stylus and my users just want to be able to write in the date.

MaskedTextBox Control might help you.

OnValidate happens after the Loading events (source)
You should validate on the client-side (javascript) AND server side either using the OnValidate or when handling the submission of the form (or both).