I've just started to follow the EntLib hands on labs for the validation integration with WPF.
http://www.microsoft.com/downloads/details.aspx?FamilyID=4f8cd377-5522-4f45-a024-44a6ca5111ec&displaylang=en
What I have found is that my textbox's databinding is firing fine when my validators pass.
I have a string property with the following validators;
Required validator
StringLengthValidator (with a max length set)
Like I say, the binding fires fine when the validators pass. However, if I then delete the textbox text, for example, (making my textbox again invalid) the binding is not fired and my view model object remains as it was the last time it was valid.
Why is this? Can anyone please show me where I'm going wrong? I would be very grateful.
Thanks.
I have just started reading about the WPF features of VAB.
I came across this information http://msdn.microsoft.com/en-us/library/ff664451(PandP.50).aspx which possibly goes towards answering you question.
The paragraph starts - "If the value of the validated control that carries the Required validation attribute is empty to begin with"
Related
I've got a combobox that is triggering an accessibility error from the Accessibility for Insights tool (https://accessibilityinsights.io/en/downloads/). The combobox can be seen in the mobile phone field with the country flag selector here - https://configure.awardsplatform.com
This is the error message I get from Accessibility for Insights:
Wai-aria 1.1 guidelines say the textbox is necessary - https://www.w3.org/TR/wai-aria-1.1/#combobox
However, I'm confused because Wai-aria 1.2 guidelines (still in development apparently) don't have it as a requirement - https://www.w3.org/TR/wai-aria-1.2/#combobox
And this example combobox also doesn't include the textbox - https://w3c.github.io/aria-practices/examples/combobox/combobox-select-only.html
There's conflicting information here so I'm unsure whether it's required or not. Does anyone know?
Short Answer to "Does a combobox require a child element with the role of textbox?"
Under current (aria-1.1) standards: yes.
Longer Answer
The standards will change soon(ish), you are looking at future guidance that has not yet been finalised. Under current guidance your country selection is using the incorrect role.
Why are you getting an error?
We are still working with aria-1.1 standards.
The definition of a combobox in the aria 1.1 standards is:
A composite widget containing a single-line textbox and another element, such as a listbox or grid, that can dynamically pop up to help the user set the value of the textbox.
As for the example combobox you gave, you may have been looking at an example intended for aria-1.2 (although I still don't believe it would be valid then as it should still set the value of some kind of input, but we will see when everything gets officially released as I think the 1.2 definition of an "input" still needs to be better defined)
For now a combobox is an <input> (or equivalent) with a related list that can be used to set the value of the <input>. A key feature is that you should still be able to manually enter a value.
What should you use instead?
For your example a <select> (or equivalent such as role="listbox") would be far more appropriate as a user cannot manually enter a country.
Even when new guidance comes out a listbox will probably still be a better choice from the definition currently in place.
I have a following requirement for a very complex UI. (Complex here means there are lot of controls in the form [approximately 100]). I am using MVVM (if my problem requires it to slightly go away from MVVM I am ok with it)
My question is for Editable ComboBox and TextBox. But I would say I like to hear a common algorithm which will fit all controls.
Requirement 1 : The user edits the content and goes to next control, the color of the control/text should become red.
Requirement 2 : When the user comes back to the previously edited control and enters the value which was initially present, the color of the control/text should become back to black.
I know the requirement is tough and I have been breaking my head to design a generic algorithm using which I can store the previous value and call a function to change the color of control.
To just give you all an idea, --> I tried storing 2 properties for every TextBox like Default_Text and Text. But since the number of properties are huge, the memory footprint is very huge. Also maintaining so many properties is very tough.
--> I tried adding a Dictionary to every ViewModel to store what values have got changed. But here the problem I faced was giving unique keys to all the controls in my application, which is not very helpful
--> I had even thought and tried about subclassing controls like TextBox, ComboBox and overriding some methods to suit my requirement, but sadly I failed miserabley when I started adding validations and all.
So here I am stuck with designing a generic WPF property system/algorithm to handle all undo redo functionality, changing styles of controls,etc!!!
It will be really great if you experts can guide me in right direction and also help me in developing such an algorithm/system. A sample illustration will be nice though!!!
I found an answer to the above problem. I used attached behavior for this. More details on this link Function call from XAML from StackOverFlow.
When I databind, I store the initial value of the DataBound variable in the Tag property by using Binding=OneWay. Then I have written a attached behaviour for LostFocus event. Whenever the user enters a control and then goes to other control, it fires LostFocus event and calls my attached behaviour. In this, I check whether the value is equal to the value in Tag. If it is same, I display in black else I display in red.
Attached Behaviour rocks in WPF. I can achieve anything from that cleanly without code cluttering!!!!
Another alternative is to use some "dirty" tracking in your models (or viewmodels) and bind to a properties isdirty (and convert it to a color).
I'm trying figure out the best way to validate user input and I've been looking at ValidationRule and IDataErrorInfo. I have a VM and a model and I want to ensure a user does not enter alpha char's into multiple textbox's bound to doubles (or ints).
I'm running into 3 issues
1) When I use the ValidationRule the method returns a 'ValidationResult' but where does that go? Is it stored as property some where?
2) If I user IDataErrorInfo and enter some alpha char's it is never called (it is if numbers are entered) Is that expected? *
*(I thought maybe a value converter might help here but I feel like I'm mixing together two separate concepts)
3) Really what I want to do is do a validation at the end when a user clicks 'Save' and check all the values. So maybe using these two methods aren't what i need as per 1838300. Is that correct, these really are only for 'on the fly' validation?
My thought on point 3 was if the result of the ValidationRule was store somewhere I could check that for each control or where ever it is stored. Or if IDataErrorInfo was called I could manually store some Boolean for each control and check those.
Any thoughts or ideas?
Thanks!
There are a couple of things, you need to know:
When the type of the dependencyproperty is not the same as the underlying value - an automatic conversion is tried if no valueconverter is present.
This is all part of the normal binding engine. So, since your textbox input doesn't convert well to ints/doubles with alpha chars, an exception is thrown and will be continually thrown until you correct the value of the dependency property (here the TextBox's Text property) - the property setter of the underlying dataobject is never reached now.
You can verify this behaviour if you look in your output window for exceptions when you alter the text in the textbox. See this article to see how to properly implement Validation and IDataErrorInfo: link.
You might be interested in the BookLibrary sample application of the WPF Application Framework (WAF). It shows how to use validation in WPF and how to control the Save button when validation errors exists.
I am creating a WPF app using MVVM. The app manages tagged documents, called Notes, similar to blog posts. A Note has a Title, Text and a Tags collection. I want to validate a Note at the time it is submitted for two validation rules:
The Title can't be empty; and
The Note must have at least one Tag.
If validation fails, then the Note submission is canceled, the offending control in the UI should get the familair red outline, and a tool tip should explain the error. This all seems pretty straightforward if one wants to validate at the time a WPF control updates its binding source. Just create a custom ValidationRule and add it to the <Binding.ValidationRules> collection.
My problem is that I want to validate when the Note is submitted, not when controls update their binding sources. I know I can create a custom error message and display it in a MessageBox, but I would much rather use the red outline-tooltip approach--it's less intrusive. I figure there must be some simple way of doing this.
My question is pretty simple: What is the best way of performing on-submission validation in WPF/MVVM? How does my code instruct the UI to show the red error outline when validation fails? Thanks for your help.
One option is to use IDataErrorInfo in conjunction with WPF.
This would make it fairly easy to handle this scenario. You can just setup the IDataErrorInfo information at submission time, which would then cause the "red outline" (or other error theming) to appear.
I'm looking at developing a simple validation framework for WPF (the IDataErrorInfo method doesn't provide enough info for my needs), and am wondering if there is a way to be notified when a Property is going to validate? Please note that I need to know any time it is going to attempt validation rather than only when there is an error (so NotifyOnValidationError doesn't cut it)
Alternatively, my ultimate goal is simply to package more information than just an error string into my validations (How critical is the error, links for more info, etc.) while still allowing the validation to be driven by the data object (IDataErrorInfo style). If anyone can point me to a method for doing that then I'll be perfectly happy as well. :)
The problem you are going to run into is that WPF databinding and validation are tied to the IDataErrorInfo interface. The bindings check for validation based on the UpdateSourceTrigger property of the binding. So if your binding has "UpdateSourceTrigger=PropertyChanged" then everytime the property changes it calls the item["MyProperty"] which is where you would return information as to whether of not your property is valid. If it's set to "LostFocus" then it checks whenever the control loses focus. The binding also requires the "ValidatesOnDataErrors=True" in order for it to force validation on your bound entity.
I think your best bet would be to create a class that implements IDataErrorInfo and then supply more detailed information based on the severity of the error.
You need to look into inheriting from ValidationRule and then adding the new rule to all you binding objects.