Suppose I have a object ListCollectionView and bind it to a datagrid. I bind the object's Name property to a TextBox(one of the datagrid's column)'s Text property and add my specific ValidationRule.
Now I want to the rule to check if the Name property is duplicated, I need to check other objects in the ListCollectionView, if there are objects' Name property equals to this Name, the validate result will be false.
My question is this check can apply only to the edited object, So only this object will become red when its Name is duplicated, but how can I also make check to other list objects, make the other objects which Name property equals to this edited one also become red? Thanks.
You are correct that the ValidationRule only has access to the data it is bound to. However you can write a custom ValidationRule - I've got a blog post detailing it here, and you can then add extra properties to it so you can inject the appropriate data that your bound value should be checked against.
However you will strike one tricky problem - the cells in the datagrid have no natural access to the DataContext of the datagrid because datagrid columns are not in the visual tree. To get around that problem you can use a static proxy object which contains (binds to) the ListCollectionView, this proxy object can then be bound to by the ValidationRule (example 1, example 2).
Related
In VS-2010, for a Datagrid whose columns employ ValidationRules, is there any way to give a ValidationRule a reference to the row's binded viewmodel? In certain situations, the validation logic will depend upon the current state of the viewmodel.
I have read about adding paramaters to ValidationRules using DependencyObjects. But the examples only show binding the validation parameters to StaticResources (such as max & min values). Since the ValidationRule is not part of the logical tree, I cannot figure how to create a parameter for the validation rule to reference the binded viewmodel of whichever DataGridRow is being edited.
The one workaround I know of is when ValidationStep is set to UpdatedValue - then the Value parameter of the Validate method becomes the BindingExpression, from which the viewmodel can be extracted. But I need to validate before updating the viewmodel, so this doesn't help me.
Well I managed a workaround but it is far from elegant. I did end up adding a DependencyProperty to the ValidationRule - but ValidationRule does not inherit from DependencyObject so you have to dump the parameters in a separate class that is a DependencyObject, then add an instance of that class to the ValidationRule.
In this case the "parameter" I'm creating for the ValidationRule is the DataGrid itself. I had to use a binding proxy in the window resources just to accomplish this, since ValidationRule is not part of the logical tree.
When the ValidationRule actually runs Validate, I use the DataGrid instance to find the editing row, get the binded viewmodel of that row, and now I can inspect the viewmodel to determine if the proposed value is acceptable.
I could probably add some code but in all honesty there has to be a better way than this. Already I can think of some possible bugs. Below is the example I found the most helpful.
Attached or dependecy Property for ValidationRule WPF
I have a BindingSource which I use to bind to a grid. The binding source itself binds to a custom class. For instance
MyGrid.DataSource = MyBindingSource
'Bind the Binding source to data
For each classInstance as myClass in MyCollection
MyBindingSource.List.Add(classInstance)
Next
A user may add or delete items to/from this List. My aim is to save this updated List to the database. I need to determine if my binding source's list has changed (i.e. has items added to it, or has items removed from it).
I am aware that I could implement the INotifyPropertyChanged on my custom class, and exploit the OnPropertyChanged event, but my classes' property would never change in my case. The other solution that I can think of is to use the BindingSource's ListChanged event, and maintain a collection of all the added and the deleted rows there. Although this approach may work for me, I reckon its a bit flaky.
Does the binding source or a Collection (such as the IList in my case) provide any other properties that can help me determine the above?
How is it possible to do multivalue binding in Silverlight?
I have to determine the Visibility of a Silverlight DataGrid column depending on the value present as part of Datacontext and other one from the QueryString.
I use MVVM Model of silverlight 5 and my plan is currently to define a property for querystring in code behind that can be binded to row visibility. But my problem clearly here is to pass multiple values for the IValueConverter implementation.
Can anyone provide a simple example to solve my problem?
Multi binding is not supported out of the box in Silverlight.
But with the introduction of customer markup extensions in Silverlight 5, this can be achieved.
There's a good example on code project: http://www.codeproject.com/Articles/286171/MultiBinding-in-Silverlight-5.
Alternatively, in this particular example you can have public boolean a property in your view model which uses the QueryString Value along with the other value you are concerned in DataContext and decides whether the column needs to be visible or not. You can then databind this property to your column's IsVisible property. (Along with a value converter which returns Visbility.Visble /Visibility.Collapsed depending on the value of the boolean property value)
I have a simple scenario and a issue with it which I just cant seem to resolve past few days.
OK, first of all I use MVVM to bind my View on a ViewModel. I have in my view several text boxes which binds to several properties (most strings) in ViewModel (binds actually to an Custom Object (type Person, name SelectedPerson) with strings properties , object which is a property of the viewmodel). This object implements INotifyPropertyChanged and IDataErrorInfo. It has also an int property named Age. I also have in my view a button which is bound to a command in my viewmodel, a command which inside CanExecute test the SelectedPerson's properties and return true if all are correct.
Now my issue is: if I put in my Age text box from my View something not int, a red tectagle will appear (is normal, because there is an exception to the conversion), but in that specific moment, to the object behind (SelectedPerson, type Person) there isn't sent the newValue (the setter to that property Age, or the IDataErrorInfo Members don't intercept the value .... I guess it is normal because there isn't any "new" value, because I put an incorrect format in the text box in the first place).
So, maybe I repeat myself, the issue is: if the new Age (new incorrect Age) isn't set, then the Object behind still hold last value, which if it was correct then the command itself it's correct (the can execute will return true) and the button is enabled
As you can imagine I want the submit button (it's a button which saves current person details in data storage module) to be disabled when current properties don't pass through conversions methods.
PS: I used a IValueConverter class , and on that text box binded to Age, I made use of my StringToIntConverter class....but on Convert Method I don't know how to pass the SelectedPerson binded object (I just pass the text value, and return the int value)
I guess one way to do it could be by using MultiBinding scenario , but I'm not sure.
If I could pass the SelectedPerson inside Convert method from that converter I could invalidate that command from the converter itself.
Sorry for my English, I know it's far from perfect :) and thanks in advance for your time.
I think the cleanest solution would be to bind the textbox to a string property instead, and update your view model so that your IDataErrorInfo implementation for that property name attempts a string to int conversion and returns the result of that. Your CanExecute test would also then include this conversion as part of the validation test.
So I have an ObservableCollection of items called "Class1" and
Class1 has a property named "ID".
I use a datagrid from the WPFToolkit and bind to this collection.
Within the datagrid is a combobox column and I bind it's ItemsSource to the ID property of the class.
At this point, all is good and everything populates as it should. What I want to do is modify the ObservableCollection to reflect the value selected in the ComboBox.
I have a ValueConverter bound to the SelectedItemBinding on the ComboBox as follows:
SelectedItemBinding="{Binding Path=ID, Converter={StaticResource IDConverter}}
What is the best (i.e: WPF approved method) of modifying the collection? When the IDConverter ConvertBack() method is called, I get the appropriate Class1 instance, but I can't access the Observable collection from within the ValueConverter and I also don't have access to the SelectedIndex value from the Datagrid.
I could create a class as a static resource with a pointer to my collection and pass that as a ConverterParameter, but that seems sort of hokey and I'm assuming there must be some slicker way of doing this with databinding.
For the record, a simple solution is to create a local resource with a reference to the collection you wish to modify as a dependency property. You can then pass this as a ConverterParameter and have access to it in the ConvertBack() interface method.
A caveat: You will most likely encounter a DeferRefresh exception when you make changes to the collection and then you lose focus.
An excellent fix is found here:
http://social.msdn.microsoft.com/Forums/en/wpf/thread/187b2b8f-d403-4bf3-97ad-7f93b4385cdf