Silverlight MVVM. I have a RadCombobox, and for each selection I'm adding a new row in another datagrid. I add necessaries codes in my ViewModel class and this part is working. What I’d like to perform is:
Keep the comboBox open while the control has the focus in order to allow the user repeating selection (I bind IsDropDownOpen to a method and setting in SelectedItem property to true but still it closes after selection )
Unselect the Item selected to allow duplication selection. I added the event SelectionChanged and add code in MainPage.xaml.cs but looking for a solution within my ViewModel.
Lets say,
IsDropDownOpen = {Binding IsDropDownFromViewModel}
Also, assuming that the getter of IsDropDownFromViewModel is encompassing all your conditions for the drop down to be open, and will always return the correct drop down state.
Now all that you will need to do is fire the PropertyChanged event for this property wherever/whenver you think the drop down should have been open, but is closed, or vice versa.
Unfortunately I didn't get your exact scenario, but lets assume this is the case (You should be use a similar approach to fix whatever problem you have).
Example Scenario:
The drop down closes when you select an item, it is intended to stay open
In the above case, one the user selects an item, the setter for the selectedItem's corresponding binding property should be invoked, so that is where we write the notification code
public SelectedItemType SelectedItemInViewModel {
get{
return _selectedItemVM;
},
set{
_selectedItemVM=value;
NotifyPropertyChanged("IsDropDownFromViewModel");
}
}
What this does is, it will tell the radComboBox's IsDropDownOpen property to reevaluate it's binding expression on the RHS and get its new value
Hope you get the gist of the approach, if not leave a comment.
Related
Looking through the standard WPF commands, such as copy/paste, they seem to all work using one button and act on a textbox.
My question: how do I use commands when I have one button, but I need data to be set in two separate controls(a textbox and a combobox). If the user has written text in textbox, but not selected a combobox value, then CanExecute should fail. This applies if combobox has been set, but not the textbox.
In my case specifically, all these controls are wrapped in a tabitem. As well, I have another tab with only a textbox and a button. I want it to have the same functionality as the first tab, except, instead of checking for the combobox value, it should detect that there is no combobox and pass in a default 'null object' value instead.
The Execute method should call a method in my viewmodel and pass in values from the combobox and textbox. As well, each tab should pass in another unique static value; i think i can handle this using commandparameter though.
How do I make this work? Do I make the parent tab that commandtarget and directly reference its children controls in the can/execute methods?
You need to implement CanExecute method that checks both TextBox databinding value and ComboBox.SelectedItem databinding value.
Take example from your question.
Your TextBox.Text should be databinding to your ViewModel
And as well as your ComboBox.
So your ViewModel should have two Properties:
public string TextBoxCurrentText {get { ...}set {...}}
public string ComboBoxCurrentSelected {get { ...}set {...}}
Then in both Setter, you would do your YourCommmand.RaiseCanExecuteChanged();
So it will execute your CanExecute code piece to determines can your Button be click.
Which can be:
bool YourCommandCanExecute()
{
//Just example
if (!string.IsNullOrEmpty(TextBoxCurrentText) && !string.IsNullOrEmpty(ComboBoxCurrentSelected))
return true;
return false;
}
I have a ListBox bound to an ObservableCollection of type T - each ListBoxItem is a checkbox with IsChecked bound to a bool property in T. I want to validate the checked items in the ListBox so that at least one checkbox must be ticked - if none of the check boxes are ticked I want to show a red border (standard validation notification) around the ListBox.
How do I go about doing that? Can I use ValidatesOnDataErrors?
Implement IDataErrorInfo in the class that exposes the ObservableCollection<T> property and make the indexer return an error for that property's name if all of the objects in the collection have a value of false in their boolean property. Then use the DataErrorValidationRule in your binding's ValidationRules.
Your goal is to validate selected items of a ListBox: at least one selected item is required. First, there are different ways to handle the selection itself:
a) You can use the ListBox selection mechanism via ListBox.SelectedItem.
I guess, you can specifiy the binding as SelectedItem="{Binding SelectedThing, ValidatesOnNotifyDataErrors=True}" and WPF's regular validation works. Not sure, if this works well with multi-selection.
b) You can use ListBox.SelectedItems. Binding is not possible and needs to be faked via code behind event handler. Thus, WPF's validation cannot trigger here.
c) You use your own IsSelected property (or similar) per item, either explicitely bound to your viewmodel via CheckBox or implicitely via ListBoxItem.IsSelected (via ListBox.ItemContainerStyle).
From here you could create a bool IsValidSelection property in your viewmodel that updates whenever the selection changed. Or you can run validation rules on any of the resulting properties of your viewmodel (e.g. SelectedItems). However, you don't validate the bound ListBox.ItemSource itself! Therefore WPF's standard mechanisms don't work (the list box doesn't get a red border or whatever).
Workarounds
You can explicitely create error notifications by showing an otherwise invisible Label and binding its visibility to the above-mentioned bool IsValidSelection property. This is a very explicit way, not using WPF validation at all.
You can modify your INotifyDataErrorInfo (or similar) implementation to trigger errors on a different property name. This is not possible, if you use a generic ValidatableViewModel<T> (like me). I guess this was the intention of the other answer.
Building my first SL MVVM application (Silverlight4 RC) and have some issues i don't understand.
Having a WPF background i don't know what is going on here:
ViewModel has several properties, in which one is called SelectedRecord. This is a get only property and is defined like this:
public Culture SelectedRecord {
get { return culturesView.View.CurrentItem as Culture; } }
As you can see it is gets the current value of a CollectionViewSource (called culturesView). So if i select a Culture, the SelectedRecord (gets a value directly from within the CollectionViewSource) as expected. (Actually there is a datagrid control bound to the CollectionViewSource, hence it is possible to change the selected item)
OK. Now to the View . There are several views which access this ViewModel and in particular there is one which shows the values of the aforementioned property SelectedRecord (let's call it the EditView). To show this EditView there is a button (which has its Command property bound to an ICommand in the ViewModel) which functions (the first time) as expected.
This means:
1st try : i select a record, switch to EditView, outcome: selected record values are shown (as expected!!).
2nd try: switch back to datagrid, select another record, switch to EditView, outcome: the values of the previous shown record are shown again!!! WHY??
First i thought that the SelectedRecord has not the correct value set, but i was mistaken: it HAS the correct value! So it should be shown!?
What am i missing? In WPF this would work!!
Thanks in advance
When CurrentItem value changes, your ViewModel that has SelectedRecord must call RaisePropertyChanged("SelectedRecord") so whatever View is bound to it is notified about the change.
In my WPF application I have a CheckBox whose IsChecked value is bound to a property in my viewmodel. Notice that I have commented out the actual line which sets the value in my viewmodel. It's the standard pattern:
View.xaml
<CheckBox IsChecked="{Binding Path=SomeProperty}" />
ViewModel.cs
public bool SomeProperty
{
get { return this.mSomeProperty; }
set
{
if (value != this.mSomeProperty)
{
//this.mSomeProperty = value;
NotifyPropertyChanged(new PropertyChangedEventArgs("SomeProperty"));
}
}
}
When I click the CheckBox I expect nothing to happen, since the value of this.mSomeProperty does not get set. However the observed behavior is that the CheckBox is being checked and unchecked regardless of the value of this.mSomeProperty.
What is going on? Why isn't my binding forcing the CheckBox to show what the underlying data model is set to?
Because WPF does not automatically reload from the binding source after updating the source. This is probably partly for performance reasons, but mostly to handle binding failures. For example, consider a TextBox bound to an integer property. Suppose the user types 123A. WPF wants to continue showing what the user typed so that they can correct it, rather than suddenly resetting the TextBox contents to the old value of the property.
So when you click the CheckBox, WPF assumes that it should continue to display the control state, not to re-check the bound property.
The only way I've found around this, which is not very elegant, is to raise PropertyChanged after WPF has returned from calling the property setter. This can be done using Dispatcher.BeginInvoke:
set
{
// ...actual real setter logic...
Action notify = () => NotifyPropertyChanged(...);
Dispatcher.CurrentDispatcher.BeginInvoke(DispatcherPriority.ApplicationIdle, notify);
}
This could be made a bit less horrible by consolidating it into the NotifyPropertyChanged implementation so that you wouldn't have to pollute individual properties with this implementation concern. You might also be able to use NotifyOnSourceUpdated and the SourceUpdated attached event, but I haven't explored this possibility.
I have a "Login" button that I want to be disabled until 3 text boxes on the same WPF form are populated with text (user, password, server).
I have a backing object with a boolean property called IsLoginEnabled which returns True if and only if all 3 controls have data. However, when should I be checking this property? Should it be on the LostFocus event of each of the 3 dependent controls?
Thanks!
vg1890
I'd get the "backing object" to raise the IsLoginEnabled changed event when any of the 3 fields are updated. You can then bind the button to the IsLoginEnabled property and not have to keep checking it.
The pseudocode would look something like this:
Public Event IsLoginEnabledChanged As EventHandler
Public Property User() As String
Get.. ' snipped for brevity
Set(ByVal value As String)
mUser = value
RaiseEvent IsLoginEnabledChanged(Me, New EventArgs())
End Set
' do the same in the Set for Password() and Server() properties
The trick to this is naming the Event [PropertyName]Changed (i.e. IsLogonEnabledChanged) - because raising this event will automagically notify any bound controls :o)
Yes, I would say the easiest option would be to check it on the LostFocus or TextChanged event of each of those controls. However, if you want to do a little heavier lifting, you could implement the boolean as a dependency property that you could have bound to the button's Enable.
http://msdn.microsoft.com/en-us/library/ms750428.aspx
Can you just databind your IsLoginEnabled right to the Enabled property of the login button?
I think you could use RoutedCommands one of the most useful features of WPF. Basically add a CommandBinding, to use OnExecute and OnQueryCommandEnabled to manage button's enabled state.
Check out this wonderful explanation on using RoutedCommands in WPF