I am working on a WPF app using MVVM. On the main windows is a combo box of customer names. When a customer is selected I want to show the addresses for it.
So I created an Address user control and in the control's code behind I added a DP:
public static DependencyProperty CustomerIdProperty =
DependencyProperty.Register("CustomerId", typeof(int), typeof(AddressView));
public int CustomerId
{
get { return (int)GetValue(CustomerIdProperty); }
set { SetValue(CustomerIdProperty, value); }
}
Next, in the main window I bound the combo to the user control's CustomerId DP:
<vw:AddressView Grid.Row="1"
Grid.Column="0"
x:Name="AddressList"
CustomerId="{Binding ElementName=CustomersList, Path=SelectedCustomer.Id, Mode=TwoWay}"/>
I now have a problem and a question:
Problem: When I run this and select a customer, the setter on the DP never fires. The SelectedCustomer property in the Main Window fires, but not the DP in the user control.
Question: How does the ViewModel for the control know about the CustomerId in the DP?
I have created a small sample app here to demonstrate what I'm doing:
http://sdrv.ms/17OZv1x
I would appreciate any help on this.
Thanks
instead of using dependency properties you can go an easy way when your customer object also has the address property
<AdressView>
<TextBlock Text="{Binding Path=MyAddress.Name}" />
<TextBlock Text="{Binding Path=MyAddress.Street}" />
mainwindow
<ComboBox X:Name=cbo .../>
<local:AddressView DataContext="{Binding ElementName=cbo, Path=SelectedItem}"/>
customer.cs
public Address MyAddress {get;set;}
if you want your dependency property stuff to work, you have to post the code for your addressview, so that we can check the bindings to the dependency properties and you have to give some information how you wanna get the address with your customerid.
CustomerList is of type ComboBox and a ComboBox has no property SelectedCustomer. The property you need for your binding is SelectedItem. You should get binding errors during your debug session in Visual Studio. See Output Window.
To get it work you need to update the binding of the CustomerId-Property to the following.
CustomerId="{Binding ElementName=CustomersList, Path=SelectedItem.Id}"
The TwoWay-Binding is only relevant if you want to change the Id from your AddressView. And I think that you don´t want it. So it can be removed.
Related
OK this is an interesting one.
I have a wpf application with tabs. What I want to do is have a DB setting that turns off the ability to edit all textboxs. What I was thinking was to bring in the value, if the value is true then I would turn all the text boxes to read only.
I have seen this example:
private void DisableControls(Control con)
{
foreach (Control c in controls)
{
DisableControls(c);
}
con.Enabled = false;
}
However I get red squiggly line under controls and again under Enabled. I will preface this by saying I am new to WPF.
Does anyone have a solution to this (or even a better way) any pointing in the right way would help.
Create a view model that wraps your database models
public class MyViewModel : INotifyPropertyChanged
{
public bool MakeReadOnly {get;set;}
}
Reference your view model in the View
<Window x:Class="Example.MainWindow"
...
xmlns:local="clr-namespace:Example"
...>
<Window.Resources>
<local:MyViewModel x:Key="ViewModel"/>
</Window.Resources>
...
</Window>
Bind the boolean value to your textboxes IsReadOnly property
<TextBox x:Name="FirstName" IsReadOnly="{Binding MakeReadOnly">
The user may not modify the contents of this TextBox if marked as readonly
</TextBox>
<TextBox x:Name="LastName" IsReadOnly="{Binding MakeReadOnly">
The user may not modify the contents of this TextBox if marked as readonly
</TextBox>
More on View Models here
Hope this helps!
How can I bind a Text property for my TextBox that read from a source but it will store its value to a different target?
Let's say
I have a textbox which is bond to a path in a CollectionViewSource
<Window>
<Window.Resources>
<CollectionViewSource Source="{Binding Source={StaticResource ProgramView}, Path='FK_LevelList_ProgramList'}" x:Key="LevelLookupView" />
</Window.Resources>
<TextBox Name="FeePerTermTextbox" Text="{Binding Source={StaticResource LevelLookupView}, Path='FeePerTerm', Mode=OneWay, StringFormat=c2}"/>
</Window>
When perform save, the value of the TextBox will store to another model that is different from the CollectionViewSource
Thanks
I consider this flawed. What happens if the source gets updated? Should the textbox be overwritten?
The reason for this design is imho, that the UI should reflect the "traits" of the element set as DataContext, therefore i expect it to contain the value i give in the model or in the ui. Now there is of course nothing stopping you from not writing the value in your viewmodel to your model, when receiving the set value from the textbox.
public class Redirecter
{
public string FileName
{
get{return mModel.FileName;}
set{mProxy.FileName = value;}
}
}
But this of course won't work well together with INotifyPropertyChanged. I would use a different approach. Use a model that reflects your ui more. If you open the view fill in this ui model with your settings from model A. If you now save this, save each property into Model B.
I searched the forum and did everything as advised to create dependancy property and bind it to checkbox, but for some reason it doesn't bind.
<CheckBox IsChecked="{Binding ElementName=MainWindow, Path=isLoop}" Content="" Height="22" HorizontalAlignment="Left" Margin="250,208,0,0" x:Name="checkBox1" VerticalAlignment="Top" Width="22" />
C#
public bool isLoop
{
get { return (bool)GetValue(isLoopProperty); }
set { SetValue(isLoopProperty, value); }
}
public static readonly DependencyProperty isLoopProperty =
DependencyProperty.Register("isLoop", typeof(bool), typeof(MainWindow), new UIPropertyMetadata(true));
You've made some key mistakes in your sample.
First, you are not binding to an object that supports your "isLoop" property (unless "MainWindow" is a custom control that has that property). Somewhere in that CheckBox's hierarchy, you need to set the DataContext to an object that supports it, or bind to an element that has that property.
Second, you should rarely, if ever, create a dependency property in your business object. For business objects, follow the INotifyPropertyChanged pattern. Typically, you should create dependency properties in visual UI elements, such as custom controls in order to be able to bind data to them (a target, not the source).
So, to fix your problem, you should probably create an object that implements INotifyPropertyChanged, create an IsLoop property that throws the NotifyPropertyChanged event in the setter, and set this object as the DataContext to the CheckBox's parent container (or further up the hierarchy if appropriate).
HTH
You are binding to the Window itself. Do you mean to do that? Unless your code example is in the code behind then the binding will not work.
Since you're using an ElementName binding, I am guessing you are binding to a UI element. The problem is, none of the default UI elements come with a property called isLoop, so your binding is invalid.
There are a few things you can try.
If your isLoop property is part of the object named MainWindow's DataContext, change your binding to DataContext.isLoop
<CheckBox IsChecked="{Binding ElementName=MainWindow, Path=DataContext.isLoop}" ... />
If isLoop is actually a property on a custom class called MainWindow, such as your dependency property implies, verify that the object named MainWindow is actually of type MainWindow
<local:MainWindow x:Name="MainWindow" />
And if neither of those work, post your full XAML (particularly the part named MainWindow), the code for the class MainWindow, and the code that ties the MainWindow class object with the XAML UI.
The isLoop won't trigger when the checkbox is clicked. That is simply for accessing the depency property in code. You should add a PropertyCallback function and register that in the metadata.
I'm using EntityFramework, WPF and MVVM in my application and got some problems with updating the databinding of relationships between EntityObjects. I was able to downsize my problem to only a few lines of XAML and I hope someone can help me as I'm still not very confident with EF and MVVM.
Anyway, here we go with the simplified XAML:
<DatePicker Grid.Row="2" Grid.Column="1"
SelectedDate="{Binding Path=File.SentDate,
StringFormat={}{0:dd/MM/yyyy}, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
VerticalAlignment="Center" IsEnabled="{Binding Path=IsEnabled}"/>
<ComboBox Grid.Row="3" Grid.Column="1" ItemsSource="{Binding Contacts}" DisplayMemberPath="Name"
SelectedItem="{Binding Path=File.Sender, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" IsEditable="True"
VerticalAlignment="Center">
</ComboBox>
<Label Content="{Binding Path=File.SenderId}" Grid.Row="4"/>
<Label Content="{Binding Path=File.Sender.Name}" Grid.Row="5"/>
<Label Content="{Binding Path=File.SentDate}" Grid.Row="6"/>
I'm using the last 3 Labels to test my databinding. Changing the File.SentDate using the DatePicker updates the databinding to the last Label without problem.
Now File is of type EntityObject and has a SenderId property of type GUID. It also has a relationship to my Contacts through the Sender property. Obvisouly, SenderId is the GUID of the corresponding Contact EntityObject which is related to File through the Sender relationship. A File can have only 1 single Sender of type Contact.
Anyway, what happens is that when I select another sender using the combobox, the Label displaying the File.SenderId property get properly updated. However, the one with the File.Sender.Name property i.e. the one using the reléationship does not get updated.
So I'm guessing that there is something special about updating the databinding of relationships in EF.
Can someone please suggest a solution to this?
Unfortunately, the Entity Framework doesn’t notify when an association property changes. That’s the reason why your Binding didn’t work.
The issue is reported to Microsoft: http://connect.microsoft.com/VisualStudio/feedback/details/532257/entity-framework-navigation-properties-don-t-raise-the-propertychanged-event
Another workaround is shown by the BookLibrary sample application of the WPF Application Framework (WAF). The Book class listens to the AssociationChanged event and raises the appropriate PropertyChanged event.
public Book()
{
…
LendToReference.AssociationChanged += LendToReferenceAssociationChanged;
}
private void LendToReferenceAssociationChanged(object sender,
CollectionChangeEventArgs e)
{
// The navigation property LendTo doesn't support the PropertyChanged event.
// We have to raise it ourselves.
OnPropertyChanged("LendTo");
}
Looks like I've found a solution, though to me its more like a workaround. It's not the solution I
would have expected but it works.
The XAML is still the same as above, except for one thing. Instead of binding to File.Sender.Name, I bind to File.SenderName like this:
<Label Content="{Binding Path=File.SenderName}" Grid.Row="4"/>
SenderName in this case is a property of the object File which I added in a partial class like this:
public partial class File
{
public string SenderName
{
get
{
if (this.Sender != null)
{
return this.Sender.Name;
}
return string.Empty;
}
}
protected override void OnPropertyChanged(string property)
{
if (property == "SenderId")
{
OnPropertyChanged("SenderName");
}
base.OnPropertyChanged(property);
}
}
So what happens here is that if the SenderId property is changed, I tell the framework to also update the SenderName property. That's it. Works like a charm. Although I'm still not convinced that this is the way it is supposed to work.
Another workaround if you simply want a name is to overide ToString() for the Sender and bind directly to sender. This workaround is good because most of the time when we are databinding to Property of a Property we do it in order to get a "name" of object set as property value. Also this method works for Database First approach too if you edit tt files to add partial to all class definitions.
So you add a file to contain ToString extensions of your Entites and in it you add something like this:
public partial Contacts
{
public override string ToString()
{
return Name;
}
}
so you can databind
<Label Content="{Binding Path=File.Sender}" Grid.Row="5"/>
Now the databinding will detect if the Sender changes, and when it does it will call ToString to determine what to display.
On the other hand if you need to bind to another non standard property you might have problems. I do remember having success with using DataContext and templates to get around it. You bind to Sender and use DataTemplate to determine what to display.
I understand that Silverlight 3.0 has binding but just want a simple example on how to use this to read a property from a class.
I have a class called Appointment which as a String property called Location:
Public Property Location() As String
Get
Return _Location
End Get
Set(ByVal Value As String)
_Location = Value
End Set
End Property
With a Private Declaration for the _Location as String of course.
I want a XAML element to bind to this property to display this in a TextElement, but it must be in XAML and not code, for example I want something like this:
<TextBlock Text="{Binding Appointment.Location}"/>
What do I need to do to get this to work?
It has to be a Silverlight 3.0 solution as some WPF features are not present such as DynamicResource which is what I'm used to using.
Just to add that my XAML is being loaded in from a seperate XAML File, this may be a factor in why the binding examples don't seem to work, as there are different XAML files the same Appointment.Location data needs to be applied.
You have two options.
If the "Appointment" class can be used as the DataContext for the control or Window, you can do:
<TextBlock Text="{Binding Location}" />
If, however, "Appointment" is a property of your current DataContext, you need a more complex path for the binding:
<TextBlock Text="{Binding Path=Appointment.Location}" />
Full details are documented in MSDN under the Binding Declarations page. If neither of these are working, make sure you have the DataContext set correctly.
You need something in code, unless you want to declare an instance of Appointment in a resource and bind to that but I doubt thats what you want.
You need to bind the Text property to the Property Path "Location" then assign the DataContext of the containing XAML to an instance of the Appointment:-
<Grid x:Name="LayoutRoot" Background="White">
<TextBlock Text="{Binding Location}" />
</Grid>
Then in the control's load event:-
void Page_Loaded(object sender, RoutedEventArgs e)
{
this.DataContext = new Appointment() { Location = "SomePlace" };
}
Note in this case I'm using the default Page control.
If I'm reading correctly, you need to create an instance of Appointment, set the DataContext of the control to that instance and modify your binding to just say: Text="{Binding Location}"
Also, consider implementing INotifyPropertyChanged on your Appointment class to allow the data classes to notify the UI of property value changes.