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;
}
Related
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.
I saw this example - Binding.UpdateSourceTrigger Property
in the example the UpdateSourceTrigger set to Explicit and then in the view code he call to UpdateSource of the TextBox name.
But if i use the MVVM dp i dont want to have names to my controls and source properties are in the VM and not in the view so what is the right way to bind controls to VM properties and set the UpdateSourceTrigger to explicit?
I want to do this because in my case its ShowDialog window and I want that the source will update only if the user click "ok"
Thanks in advance!
If you are using MVVM truely then your OK button click must be handled by some Command. This command must be coming from your ViewModel. The Expliticly bound properties must be coming from your ViewModel again. So whats stopping you.
Do not use Explicit binding but use OneWay binding.
In you button, bind a command and bind a command parameter to the OneWay bound Dependency property.
In your Command's Execute handler (which must be some method from your ViewModel), change the ViewModel's property with the parameter coming.
Raise the NotifyPropertyChanged for that property from your ViewModel.
E.g.
Assume I need to update a TextBox's Text back into my model on OK button click.
So for that I have a EmployeeViewModel class that has EmployeeName property in it. The property is has a getter and a setter. The setter raises property changed notification. The view model also has another property of type ICommand named SaveNameCommand that return a command for me to execute.
EmployeeViewModel is the data context type of my view. Myview has a TextBox (named as x:Name="EmployeeNameTxBx") OneWay bound to the EmployeeName and a Button as OK. I bind Button.Command property to EmployeeViewModel.SaveNameCommand property and Button.CommandParameter is bound to EmployeeNameTxBx.Text property.
<StackPanel>
<TextBox x:Name="EmployeeNameTxBx"
Text="{Binding EmployeeName, Mode=OneWay}" />
<Button Content="OK"
Command="{Binding SaveNameCommand}"
CommandParameter="{Bidning Text, ElementName=EmployeeNameTxBx}" />
</StackPanel>
Inside my EmployeeViewModel I have OnSaveNameCommandExecute(object param) method to execute my SaveNameCommand.
In this perform this code...
var text = (string)param;
this.EmployeeName = text;
This way ONLY OK button click, updates the TextBox's text back into EmployeeName property of the model.
EDIT
Looking at your comments below, I see that you are trying to implement Validation on a UI. Now this changes things a little bit.
IDataErrorInfo and related validation works ONLY IF your input controls (such as TextBoxes) are TwoWay bound. Yes thats how it is intended. So now you may ask "Does this mean the whole concept of NOT ALLOWING invalid data to pass to model is futile in MVVM if we use IDataErrorInfo"?
Not actually!
See MVVM does not enforce a rule that ONLY valid data should come back. It accept invalid data and that is how IDataErrorInfo works and raises error notfications. The point is ViewModel is a mere softcopy of your View so it can be dirty. What it should make sure is that this dirtiness is not committed to your external interfaces such as services or data base.
Such invalid data flow should be restricted by the ViewModel by testing the invalid data. And that data will come if we have TwoWay binding enabled. So considering that you are implementing IDataErrorInfo then you need to have TwoWay bindings which is perfectly allowed in MVVM.
Approach 1:
What if I wan to explicitly validate certain items on the UI on button click?
For this use a delayed validation trick. In your ViewModel have a flag called isValidating. Set it false by default.
In your IDataErrorInfo.this property skip the validation by checking isValidating flag...
string IDataErrorInfo.this[string columnName]
{
get
{
if (!isValidating) return string.Empty;
string result = string.Empty;
bool value = false;
if (columnName == "EmployeeName")
{
if (string.IsNullOrEmpty(AccountType))
{
result = "EmployeeName cannot be empty!";
value = true;
}
}
return result;
}
}
Then in your OK command executed handler, check employee name and then raise property change notification events for the same property ...
private void OnSaveNameCommandExecute(object param)
{
isValidating = true;
this.NotifyPropertyChanged("EmployeeName");
isValidating = false;
}
This triggers the validation ONLY when you click OK. Remember that EmployeeName will HAVE to contain invalid data for the validation to work.
Approach 2:
What if I want to explicitly update bindings without TwoWay mode in MVVM?
Then you will have to use Attached Behavior. The behavior will attach to the OK button and will accept list of all items that need their bindings refreshed.
<Button Content="OK">
<local:SpecialBindingBehavior.DependentControls>
<MultiBinding Converter="{StaticResource ListMaker}">
<Binding ElementName="EmployeeNameTxBx" />
<Binding ElementName="EmployeeSalaryTxBx" />
....
<MultiBinding>
</local:SpecialBindingBehavior.DependentControls>
</Button>
The ListMaker is a IMultiValueConverter that simply converts values into a list...
Convert(object[] values, ...)
{
return values.ToList();
}
In your SpecialBindingBehavior have a DependentControls property changed handler...
private static void OnDependentControlsChanged(
DependencyObject depObj,
DependencyPropertyChangedEventArgs e)
{
var button = sender as Button;
if (button != null && e.NewValue is IList)
{
button.Click
+= new RoutedEventHandler(
(object s, RoutedEventArgs args) =>
{
foreach(var element in (IList)e.NewValue)
{
var bndExp
= ((TextBox)element).GetBindingExpression(
((TextBox)element).Textproperty);
bndExp.UpdateSource();
}
});
}
}
But I will still suggest you use my previous pure MVVM based **Approach 1.
This is an old question but still I want to provide an alternative approach for other users who stumble upon this question...
In my viewmodels, I do not expose the model properties directly in the get/set Property methods. I use internal variables for all the properties. Then I bind all the properties two-way. So I can do all the validation as "usual" because only the internal variables are changed. In the view model constructor, I have the model object as parameter and I set the internal variables to the values of my model. Now when I click on the "Save" Button (-> Save Command fires in my view model fires) and there are no errors, I set all the properties of my model to the values of the correspondng internal variable. If I click on the "Canel/Undo"-Button (-> Cancel-Command in my view model fires), I set the internal variables to the values of my untouched model (using the setters of the view model properties so that NotifyPropertyChanged is called and the view shows the changes=old values).
Yet another approach would be to implement Memento-Support in the model, so before you start editing you call a function in the model to save the current values, and if you cancel editing you call a function to restore those values...that way you would have the undo/cancel support everywhere an not just in one view model...
I've implemented both methods in different projects and both work fine, it depends on the requirements of the project...
I have a custom control (an Adorner) that wraps another control (a textbox).
public class MyCustomAdorner : Decorator
{
...
public MyCustomAdorner()
{
Child = new TextBox();
}
}
I want to be able to override the VisibilityChanged so that the MyCustomAdorner's event is only fired if the Child's visiblity changes, not the actual decorator. How would I go about this?
On a first approach I would try to bind the Adorner's Visibility to the TextBox's Visibility (not sure if this one works). This way, if the textbox changes visibility, the adorner will follow. If you bind them two way, then it will work the other way around too. So if you don't want it to work both ways, make sure you don't set the Adorner's Visibility.
If binding the Visibilities together doesn't work, you can try to declare a new property (for example a bool), that manages the visibilities, and bind the two Visibilities to that bool through a Converter. And when you want to change something around the Visibilities, you set this bool to a new value.
Overriding the VisibilityChange event doesn't sound good to me, also I'm not sure if you can even do that...
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.
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