How do i extend an existing control (ComboBox in my case) to include a new property which i can bind to a property on my view model??
I have a Dependancy Property on the control's class as follows:
public class MyComboBox : ComboBox
{
public static readonly DependencyProperty MyTextProperty =
DependencyProperty.Register("MyText", typeof(string), typeof(MyComboBox));
public string MyText
{
get
{
return GetValue(MyComboBox.MyTextProperty).ToString();
}
set
{
SetValue(MyComboBox.MyTextProperty, value);
}
}
And want to bind to it declaratively from XAML like this:
<MyComboBox MyText="{Binding MyTextOnViewModel,
UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"/>
The Binding just won't work, any ideas why??
Thanks.
Your getter and setter reference TestTextProperty while the property is declared as MyTextProperty.
Your getter should also be casting instead of calling .ToString()
return (string)GetValue(MyTextProperty);
See this page for more complete instructions.
Related
I cannot properly bind to a UserControl property placed in a Page.
I have this UserControl :
<UserControl x:Class="xxxx.NumericBox" (...)>
<TextBox Name="TextBoxValue" Text="{Binding RelativeSource {RelativeSource AncestorType=UserControl}, Path=Value, Mode=TwoWay}" (...)
With this behind code :
public partial class NumericBox : UserControl
{
public NumericBox()
{
InitializeComponent();
}
public uint? Value
{
get => (uint?)GetValue(ValueProperty);
set => SetValue(ValueProperty, value);
}
public static readonly DependencyProperty ValueProperty = DependencyProperty.Register("Value", typeof(uint?), typeof(NumericBox), new PropertyMetadata(null));
The UserControl contains others controls witch interract with Value property (+/-) and it works fine.
But I create the DependencyProperty to also bind the value in parent page.
A exemple of code in a page where I inject the UserControl :
var binding = new Binding("Line.Quantity");
binding.Mode = BindingMode.TwoWay;
var numeric = new NumericBox();
numeric.SetBinding(ValueProperty, binding);
The binding works on startup but not update Line.Quantity when I modify the Textbox...
The Line class implements INotifyPropertyChanged and notify change on Quantity.
What is the correct way to do that ?
I have seen this question but but I have not been able to correct my code :
Binding on DependencyProperty of custom User Control not updating on change
I am using WPF and I have a custom datagrid. What I would like to do is add a property (CustomGridCommands) to that grid which I can set in xaml from any view.
What I have at the moment is as follows (I have changed the code a bit to simplify it):
Custom grid C# code:
public class CustomWPFDataGrid : DataGrid, INotifyPropertyChanged
{
public static readonly DependencyProperty CustomContextMenuCommandsProperty =
DependencyProperty.Register("CustomContextMenuCommands",
typeof (ObservableCollection<WPFBaseCommand>),
typeof (CustomWPFDataGrid));
[Bindable(true)]
public ObservableCollection<WPFBaseCommand> CustomContextMenuCommands
{
get { return (ObservableCollection<WPFBaseCommand>) GetValue(CustomContextMenuCommandsProperty); }
set { SetValue(CustomContextMenuCommandsProperty, value); }
}
...
...
}
XAML code:
<common:CustomWPFDataGrid
ItemsSource="{Binding Path=ItemList}"
CustomContextMenuCommands="{Binding Path=CustomGridCommands, Mode=TwoWay}">
....
</common:CustomWPFDataGrid >
The object I have bound to the view that contains the grid is as follows:
public class TestViewModel
{
public ObservableCollection<TestDisplayViewModel> ItemList { get; set; }
public ObservableCollection<WPFBaseCommand> CustomGridCommands;
public TestViewModel()
{
... population of objects here
}
When I run this, and check the value of the property (CustomContextMenuCommands) in the datagrid, it is always null.
Any ideas what I am doing wrong?
EDIT
The setter of the "CustomContextMenuCommands" is never hit.
CustomGridCommands in your ViewModel is a field, View cannot use it. If you make it a public property, then it will become accessible. More details on what can be used as binding source can be found on MSDN - Binding Sources.
If using WPF 4.5, static properties can also be used for binding, as described in release notes.
Just wondering if this is a good practice or if it could cause any troubles in the long run. To be honest, I'm surprised it even works - it does the job, but I'm not sure if it's risky.
Basically we created a NumericTextBox that derives from TextBox, and we overrode the Text property with the new keyword to remove commas from the text:
public class NumericTextBox : TextBox
{
public new string Text
{
get
{
return base.Text.Replace(",", String.Empty);
}
set
{
base.Text = value;
}
}
}
What I don't like about it is that I know Text is a dependency property and we're overriding it, but surprisingly we can still bind to it in XAML:
<this:NumericTextBox x:Name="textBox"
Text="{Binding RelativeSource={RelativeSource AncestorType={x:Type Window}}, Path=SomeText, Converter={StaticResource debugConverter}}" />
Then in C# when we call textBox.Text we do get the values without commas.
What do you guys think?
Perhaps you should add your class as an owner of the dependency property and override the getter and setter there:
public class NumericTextBox : TextBox
{
public NumericTextBox() { }
public static readonly DependencyProperty NumericTextProperty = TextBox.TextProperty.AddOwner(typeof(NumericTextBox), new PropertyMetadata(null));
public new string Text
{
get { return ((string)this.GetValue(NumericTextProperty )).Replace(",", String.Empty); }
set { this.SetValue(NumericTextProperty , value); }
}
}
You also have the possibility of overriding the metadata of the dependency property to hook in a custom validation callback method.
You approach doesn't work, because WPF doesn't actually use the class properties to change the value, but the dependency property system. It simply calls the SetValue method as you do in your property setter. You can try it out by setting a breakpoint in the setter, and changing the bound property in the gui. The setter breakpoint will never be hit. But you can hook into the events provided by the dependency property metadata.
I am creating a ToggleSwitchItem user control, which contains a ToggleSwitch and a TextBlock. I have defined a dependency property called IsChecked which I just want to use to expose the IsChecked property of the private ToggleSwitch child.
But the data binding doesn't work... It just stays at the default value when loaded.
What am I missing?
Code:
public static readonly DependencyProperty IsCheckedProperty =
DependencyProperty.Register(
"IsChecked",
typeof(bool),
typeof(ToggleSwitchItem),
new PropertyMetadata(new PropertyChangedCallback
(OnIsCheckedChanged)));
public bool IsChecked
{
get
{
return (bool)GetValue(IsCheckedProperty);
}
set
{
SetValue(IsCheckedProperty, value);
}
}
private static void OnIsCheckedChanged(DependencyObject d,
DependencyPropertyChangedEventArgs e)
{
ToggleSwitchItem item = (ToggleSwitchItem)d;
bool newValue = (bool)e.NewValue;
item.m_switch.IsChecked = newValue;
}
for the data binding, I'm using to following:
<phone:PhoneApplicationPage.Resources>
<myApp:SharedPreferences x:Key="appSettings"/>
</phone:PhoneApplicationPage.Resources>
IsChecked="{Binding Source={StaticResource appSettings},
Path=SomeProperty, Mode=TwoWay}"
The SharedPreferences class is working fine, as it works without issue when bound to a plain vanilla ToggleSwitch's IsChecked property exactly as per above.
Thanks!
SOLUTION (with help from Anthony):
I bind my child toggle switch to my user control in the user control's constructor like so:
Binding binding = new Binding();
binding.Source = this;
binding.Path = new PropertyPath("IsChecked");
binding.Mode = BindingMode.TwoWay;
m_switch.SetBinding(ToggleSwitch.IsCheckedProperty, binding);
And I remove the callback as I no longer need it:
public static readonly DependencyProperty IsCheckedProperty =
DependencyProperty.Register(
"IsChecked",
typeof(bool),
typeof(ToggleSwitchItem),
null);
public bool IsChecked
{
get
{
return (bool)GetValue(IsCheckedProperty);
}
set
{
SetValue(IsCheckedProperty, value);
}
}
I can't quite see what is actually wrong with the code you've show so far, except that you haven't show how the user toggling the switch would actually cause the IsChecked property to change.
Have you try using binding inside the UserControl:
<ToggleButton IsChecked="{Binding Parent.IsChecked, ElementName=LayoutRoot, Mode=TwoWay}" />
You do not need the OnPropertyChanged callback with this approach.
Check the DataContext of your control.Which means 2 things : All instances of your control must have right DataContext to work -ok-, and also you should not 'break' this DataContext when you define the control (at the Class level). If, when you define your control, you set the DataContext to 'this' / Me in code or to 'Self' in xaml, it nows refer only to itself and forget about the DataContext in which it is when you instanciate it in your application -- Binding fails.
If you have to refer to your control's properties within your control Xaml, use a binding with findAncestor / AncestorType = ToggleSwitchItem Or name your control in Xaml and bind with its ElementName.
Maybe this could help
public bool IsChecked
{
get { return GetValue(IsCheckedProperty) is bool ? (bool) GetValue(IsCheckedProperty) : false; }
set
{
SetValue(IsCheckedProperty, value);
}
}
I am looking for a way to create an UserControl in silverlight 4 and expose a dependency property, which can accept any type. What I mean by that is, for example, if you look at standard silverlight control like AutoCompleteBox, it is capable of handling any type of collections. So you can bind AutoCompleteBox with IEnumerable<Human> or IENumerable<Animal> etc. And when any item is selected AutoCompleteBox returns the selected value either Human instance or Animal instance via SelectedItem dependency property.
I want to achieve similar flexibility with my usercontrol. I wouild like to expose 2 dependency properties SuggestedItems and SelectedItem. Which ever collection is set to SuggestedItems via consumers of this usercontrol thru Binding, lets take as an example IEnumerable<Car>, the I want SelectedItem property to send instance of Car type back to consumer thru Binding. If I used IEnumerable<Boat>, then I need Boat to be returned with SelectedItem.
I was trying to achieve it by using below example using MVVM, but its not working. I am looking for some clues as to how it should be designed, Am I even on a correct path or I have to completely alter my design?
I created an UserControl called VehicleSelectorUserControl which has its own dedicated ViewModel called VehicleSelectorViewModel with two proerties SuggestedItems, SelectedItem.
And usercontrol has corresponding Dependency properties in its codebehind to expose them to consumers of usercontrol. UserControl XAML has a ListBox which is bound to SuggestedItems property of VehicleSelectorViewModel. When user makes a selection, VehicleSelectorViewModel SelectedItem is set, which them invokes a delegate called ItemSelected to notify VehicleSelectorUserControl codebehind, which then sets the SelectedItem Dependency property to make it available to consumer.
Below is code from the VehicleSelectorUserControl.xaml.cs code behind.
private VehicleSelectorViewModel _TheViewModel;
public UserNameControl()
{
InitializeComponent();
_TheViewModel = Resources["TheViewModel"] as VehicleSelectorViewModel;
_TheViewModel.ItemSelected = OnItemSelected;
}
public IEnumerable<object> SuggestedItems
{
get { return (IEnumerable<object>)GetValue(SuggestedItemsProperty); }
set { SetValue(SuggestedItemsProperty, value); }
}
public static readonly DependencyProperty SuggestedItemsProperty =
DependencyProperty.Register("SuggestedItems", typeof(IEnumerable<object>), typeof(VehicleSelectorControl), new PropertyMetadata(OnSuggestedItemsSet));
private static void OnSuggestedItemsSet(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
_TheViewModel.SuggestedItems = e.NewValue;
}
public object SelectedItem
{
get { return (String) GetValue(SelectedItemProperty); }
set { SetValue(SelectedItemProperty, value); }
}
public static readonly DependencyProperty SelectedItemProperty =
DependencyProperty.Register("SelectedItem", typeof(object), typeof(VehicleSelectorControl), null);
private void OnItemSelected()
{
SelectedItem = _TheViewModel.SelectedItem;
}
Its ViewModel VehicleSelectorViewModel code
public Action ItemSelected { get; set; }
private dynamic _SelectedItem;
public dynamic SelectedItem
{
get { return _SelectedItem; }
set
{
if (value != _SelectedItem)
{
_SelectedItem = value;
NotifyPropertyChanged("SelectedItem");
if(ItemSelected != null) ItemSelected.Invoke();
}
}
}
private dynamic _SuggestedItems;
public dynamic SuggestedItems
{
get { return _SuggestedItems; }
set
{
if (value != _SuggestedItems)
{
_SuggestedItems = value;
NotifyPropertyChanged("SuggestedItems");
}
}
}
The XAML of consumer will look like (Consumer has its own ViewModel, which responsible for supplying SuggestedCars [IEnumerable<Car>], SuggestedBoats [IEnumerable<Boat>].
<my:VehicleSelectorControl x:Name="MyCarSelectorControl"
SuggestedItems="{Binding SuggestedCars, Mode=TwoWay}"
SelectedItem="{Binding UserSelectedCar, Mode=TwoWay}" />
<my:VehicleSelectorControl x:Name="MyBoatSelectorControl"
SuggestedItems="{Binding SuggestedBoats, Mode=TwoWay}"
SelectedItem="{Binding UserSelectedBoat, Mode=TwoWay}" />