I want to set a user control property to the value of a property in a parent control. For example, let's say my main window control has some initial configuration data. Currently I use the following in XAML:
<Window x:Class="MyProject.MainWindow"
x:Name="TopWindow" ... >
...
<local:MyUserControl Config="{Binding ElementName=TopWindow,
Path=MyUserControlConfig, Mode=OneTime}" />
</Window>
But this appears to require two dependency properties, one in the MainWindow (MyUserControlConfig):
namespace MyProject
{
public partial class MainWindow: Window
{
public static readonly DependencyProperty MyUserControlConfigProperty=
DependencyProperty.Register("MyUserControlConfig",
typeof(UserControlConfig), typeof(MainWindow));
public UserControlConfig MyUserControlConfig
{
get { return (UserControlConfig)
GetValue(MyUserControlConfigProperty); }
set { SetValue(MyUserControlConfigProperty, value); }
}
}
}
and one in MyUserControl (Config):
namespace MyProject
{
public partial class MyUserControl: UserControl
{
public static readonly DependencyProperty ConfigProperty=
DependencyProperty.Register("Config",
typeof(UserControlConfig), typeof(MainWindow));
public UserControlConfig Config
{
get { return (UserControlConfig) GetValue(ConfigProperty); }
set { SetValue(ConfigProperty, value); }
}
}
}
I really don't need to observe any changes, just to pass data into my user control at the time of creation. Is this possible to do using simple properties for at least one of the two or must I use two dependency properties to perform this (one time) initialization?
Update: Jay's solution leaves us with just a CLR property in the MainWindow class:
namespace MyProject
{
public partial class MainWindow: Window
{
public UserControlConfig MyUserControlConfig {get; private set;}
...
}
}
Now if it was just possible to remove the dependency property from the MyUserControl class and replace it with a simple property that still gets initialized via XAML binding (or some other XAML mechanism, so I can pass in the data source via XAML).
I could be mistaken, but if you can bind to CLR properties on other classes, I'd expect you could bind to a CLR proprety on your MainWindow class.
Have you tried that?
Related
I am beginner to WPF and MVMM architecture. VI came across many links which explains about DataContext dependence property in WPF MVMM architecture,
i.e.
view.DataContext = new ViewModels.MainViewModel();
but they always made me confused. Although I have some basic idea about this DataContext like it is used to represent who's object we need in xaml file, but when blogs talks about tree structure inheritance of dataContext I gets confused. Can any one please help me with some very simple and clear example showing how this hierarchy of DataContext works?
Thanks in advanced.
The DataContext property specifies the default source for Data Binding. Consider the following example:
<TextBox Text="{Binding MyProperty}" />
What this Binding says: take the value of MyProperty from whatever object is inside the DataContext, convert it to a string and put it in the TextBox. So if we would set the DataContext of the TextBox to be an object of the following class:
public class Example {
int MyProperty { get { return 3; } }
}
Then, the Text of the TextBox would be set to 3.
What does it mean that the values Inherit? Consider a slightly more complex example:
<Window Name="MainWindow">
<StackPanel>
<TextBox Text="{Binding MyProperty}" />
...etc
If we would have 10 or more TextBox elements on our screen, it would be a lot of senseless work to assign the DataContext to each and every TextBox. To relieve this issue, the implementors of WPF decided that setting the DataContext on the MainWindow in our case would also apply it to everything inside that Window (all children, all nested elements) until the DataContext property is overwritten (i.e. we set the DataContext of the TextBox, then the TextBox and all its children would also receive this DataContext).
If you want to see this behavior in action, the same applies to the FontSize property, try setting the FontSize of your Window to 48 and see what happens to all the text in there!
The Datacontext property is the default source of all the binding of a View.
In MVVM, the Datacontext is used to link a ViewModel to a View.
As the Datacontext property is a dependence property, if you don't define it in a control, it will inherit from his father, etc.
Here is an exemple of MVVM implementation :
Parent of all ViewModel class (to implement INotifyPropertyChanged in all ViewModels) :
public abstract class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
{
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Note : INotifyPropertyChanged allow your ViewModel to notify the View of a change (used for bindings).
Let's say I want a MainWindows (View) to be linked to a ViewModel :
public MainWindow()
{
InitializeComponent();
MainViewModel mainViewModel = new MainViewModel(this);
this.DataContext = mainViewModel;
}
With for ViewModel :
class MainViewModel : ViewModelBase
{
#region fields
private MainWindow mainWindow;
private string message = "Hello world !";
#endregion
#region properties
public MainWindow MainWindow
{
get
{
return this.mainWindow;
}
}
public string Message
{
get
{
return message;
}
set
{
this.message = value; OnPropertyChanged("Message");
}
}
// ...
#endregion
public MainViewModel(MainWindow mainWindow)
{
this.mainWindow = mainWindow;
}
}
So now if I want to bind a property of MainViewModel in my View (mainwindow), i just have to have a public property in my ViewModel and to create a binding in my XAML. I won't have to specify the source as the DataContext is the default source.
So MainWindow.xaml I can add :
<TextBox Text="{Binding Message}" />
I have a template defined in a XAML file named 'MyTemplate.xaml'. This template is using a code-behind file named 'MyTemplate.cs'.
Mytemplate.xaml:
<ResourceDictionary x:Class="Project.Templates.MyTemplate">
<DataTemplate ... />
</ResourceDictionary>
MyTemplate.cs:
namespace Project.Templates
{
public partial class MyTemplate : ResourceDictionary
{
...
}
}
In the Visual Studio Solution Explorer, these two files are side by side. What I would like to do is to put these two files together, just like with a Control and its code-behind.
What I have:
What I would like to have:
What is the best way to do that? Thank you.
You need to edit the .csproj file. Find the <Compile> element for MyTemplate.cs, and add a <DependentUpon> element under it:
<Compile Include="MyTemplate.cs">
<DependentUpon>MyTemplate.xaml</DependentUpon>
</Compile>
See this blog post: make a project item a child item of another
This isn't an answer to your initial question, but to this:
In that case, please explain how to add an event handler to a template without using code-behind
You can do this with a ViewModel and an ICommand class.
First you need to create your ViewModel class, make this public and non static with a parameter-less constructor.
Then create another class which implements the ICommand interface:
public class Command : ICommand
{
public void Execute(object parameter)
{
//this is what happens when you respond to the event
}
public bool CanExecute(object parameter)
{
return true;
}
public event EventHandler CanExecuteChanged;
}
Add an instance of your command class to your ViewModel class, make this private and expose it through a read-only property:
public class ViewModel
{
private readonly ICommand _command = new Command();
public ICommand Command
{
get { return _command; }
}
}
Add your ViewModel as a static resource, in your App.xaml file:
<Application.Resources>
<wpfApplication1:ViewModel x:Key="ViewModel"/>
</Application.Resources>
Set your DataContext of your XAML file to your ViewModel:
<Window DataContext="{StaticResource ViewModel}">
Now respond to your event by binding to the Command class:
<Button Click="{Binding Command}"></Button>
Boom, no code-behind. Hope this helps.
Another way is to:
Add/Create a new XAML file/item
Copy and paste the old .xaml and xaml.cs content to the new equivalent files
delete the separate files
rename the new file
I have created a few Custom Controls (NOT UserControls) with bind-able "ClearCommand" ICommand dependency properties. This property will do exactly what it sounds: it will clear all the values from the control (textboxes, etc). I also bind (some) of those same properties to the VM I describe below.
Now I'm stuck trying to trigger the ClearCommand in those controls in the following MVVM scenario:
I've added a few such controls into my View. The View also includes a "Save" button that binds to my ViewModel's SaveCommand DelegateCommand property.
What I need to happen is that, upon a successful save, the VM should trigger the ClearCommand on those controls found in the View.
UPDATE
I've added code examples below. I have a few controls that resemble the ExampleCustomControl. Also, just to note, I am open to restructuring some of this if it's completely off.
Example Control snippet:
public class ExampleCustomControl : Control {
public string SearchTextBox { get; set; }
public IEnumerable<CustomObject> ResultList { get; set; }
public ExampleCustomControl() {
ClearCommand = new DelegateCommand(Clear);
}
/// <summary>
/// Dependency Property for Datagrid ItemSource.
/// </summary>
public static DependencyProperty SelectedItemProperty = DependencyProperty.Register("SelectedItem",
typeof(CustomObject), typeof(ExampleCustomControl), new PropertyMetadata(default(CustomObject)));
public CustomObject SelectedItem {
get { return (CustomObject)GetValue(SelectedCustomObjectProperty); }
set { SetValue(SelectedCustomObjectProperty, value); }
}
public static DependencyProperty ClearCommandProperty = DependencyProperty.Register("ClearCommand", typeof(ICommand),
typeof(ExampleCustomControl), new PropertyMetadata(default(ICommand)));
/// <summary>
/// Dependency Property for resetting the control
/// </summary>
[Description("The command that clears the control"), Category("Common Properties")]
public ICommand ClearCommand {
get { return (ICommand)GetValue(ClearCommandProperty); }
set { SetValue(ClearCommandProperty, value); }
}
public void Clear(object o) {
SearchTextBox = string.Empty;
SelectedItem = null;
ResultList = null;
}
}
Example View snippet:
<Grid HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
<Grid.RowDefinitions>
<RowDefinition Height="*" />
<RowDefinition Height="30"/>
</Grid.RowDefinitions>
<control:ExampleCustomControl Grid.Row="0"
SelectedItem="{Binding Selection, UpdateSourceTrigger=PropertyChanged}" />
<Button Grid.Row="1" x:Name="ResetButton" Command="{Binding SaveCommand}">
Save
</Button>
</Grid>
Example ViewModel:
public class TestViewModel : WorkspaceTask {
public TestViewModel() {
View = new TestView { Model = this };
SaveCommand = new DelegateCommand(Save);
}
private CustomObject _selection;
public CustomObject Selection {
get { return _selection; }
set {
_selection = value;
OnPropertyChanged("Selection");
}
}
public DelegateCommand SaveCommand { get; private set; }
private void Save(object o) {
// perform save
// clear controls
}
}
As others have said the VM shouldn't know about the view directly in MVVM so it doesn't make sense really that the VM triggers something on your custom control to clear everything.
I would have set the DataContext of the custom control to an object that has all the properties you want to clear, which are all each bound (two-way) to your textboxes etc. Then in the Save() method you can set a new object (which the custom control DataContext is bound to) and all the properties will be cleared for you (assuming you have implemented INotifyPropertyChanged on the object).
UPDATED:
As per my comment, see an example of the workaround for your current setup (untested btw):
public static DependencyProperty SelectedItemProperty = DependencyProperty.Register("SelectedItem",
typeof(CustomObject), typeof(ExampleCustomControl), new PropertyMetadata(default(CustomObject), OnSelectedItemChanged));
private static void OnSelectedItemChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
{
var cont = source as ExampleCustomControl;
//do all the clearing of txtboxes etc here....
cont.SearchTextBox = string.Empty;
}
But I would still try and move all this into the VM. i.e. have a clear command, like you do with the save command and bind the textbox text etc to a property in the VM and when the command is called it clears everything, which you can then easily call from the Save method in the VM too. But obviously I have no idea what you are trying to achieve in the long run or how selectedItem and the textboxes etc are related, so depends (as always) i guess.
It sounds like you are thinking about this the wrong way. In MVVM the ViewModel should never know anything about the custom controls (hence you are having a problem with this Clear functionality).
Your requirements are a bit vague, but have you considered:
1) If the properties are bound from the VM, can't the Control detect when these are changed?
2) If you really need to call Clear from the XAML layer and want to keep it pure MVVM, then consider something like the Expression Blend SDK's CallMethodAction.
As a followup to my comment. I suspect your command is targeting the View and clearing the TextBoxes directly. Instead, have your command target the ViewModel and clear the properties the View is bound to. Then you can have the command be a property on the ViewModel and call it whenever needed.
I'm not quite sure if I've got the right grasp on this or not, what I've read seems to agree with what I'm trying to do, however It doesn't seem to be working.
If I add an additional owner to a dependency property of a class, whenever the orig class dp changes, the change should get propagated to the additional owner, correct?
What I have is a custom control, which I want to set a property on, and then on certain objects that are within the custom control data template inherit this property value.
public class Class1: DependencyObject{
public static readonly DependencyProperty LongDayHeadersProperty;
public bool LongDayHeaders {
get { return (bool)GetValue(LongDayHeadersProperty); }
set { SetValue(LongDayHeadersProperty, value); }
}
static Class1(){
LongDayHeadersProperty = DependencyProperty.Register("LongDayHeaders", typeof(bool), typeof(Class1),
new FrameworkPropertyMetadata(true, FrameworkPropertyMetadataOptions.Inherits));
}
}
public class Class2: DependecyObject{
public static readonly DependencyProperty LongDayHeadersProperty;
public bool LongDayHeaders{
get{ return(bool)GetValue(LongDayHeadersProperty); }
set{ SetValue(LongDayHeadersProperty, value); }
}
static Class2(){
LongDayHeadersProperty = Class1.LongDayHeadersProperty.AddOwner(typeof(Class2));
}
}
But if I assign a DependencyPropertyDescriptor to both properties, it only fires for the Class1 and Class2 doesn't change.
Have I missed something in my understanding?
UPDATE
After some testing, I'm not even sure if my child control is considered a child control within the logical or visual tree. I think it is, but the lack of success leads me to believe otherwise.
There a many class2's which exist in an observable collection of class1. This, to me, makes them childs of class1? But even if I use RegisterAttach on class2, and set the property in class1, it doesn't seem to have any effect?
As MSDN states, the Inherits flag only works when you use RegisterAttached to create the property. You can still use the property syntax for the property.
Update
For clarity, here is how I would define the properties:
public class Class1 : FrameworkElement
{
public static readonly DependencyProperty LongDayHeadersProperty =
DependencyProperty.RegisterAttached("LongDayHeaders",
typeof(bool),
typeof(Class1),
new FrameworkPropertyMetadata(true, FrameworkPropertyMetadataOptions.Inherits));
public bool LongDayHeaders
{
get { return (bool)GetValue(LongDayHeadersProperty); }
set { SetValue(LongDayHeadersProperty, value); }
}
}
public class Class2: FrameworkElement
{
public static readonly DependencyProperty LongDayHeadersProperty =
Class1.LongDayHeadersProperty.AddOwner(typeof(Class2));
public bool LongDayHeaders
{
get{ return(bool)GetValue(LongDayHeadersProperty); }
set{ SetValue(LongDayHeadersProperty, value); }
}
}
If you want your children to be logical children of your control, you need to call the AddLogicalChild. Also, you should expose them through the LogicalChildren property. I must also point out that both classes must derive from FrameworkElement or FrameworkContentElement, as the logical tree is only defined for these elements.
Since you are using an ObservableCollection, you would handle the collection changed events and Add/Remove the children depending on the change. Also, the LogicalChildren property can just return your collection's enumerator.
You are confusing DependencyProperties with Attached (Dependency) Properties.
A DP is for when a class wants bindable, stylable etc properties on itself. Just like .NET properties, they are scoped within their classes. You can register for a property changed event on individual objects, but not globally. TextBox.Text is an example of this. Note that Label.Text is unrelated to TextBox.Text.
An AP is for when a class wants to decorate another object with additional properties. The class that declares the AP is able to listen for property changed events on ALL instances of other objects that have this AP set. Canvas.Left is an example of this. Note that you always have to qualify this setter: <Label Text="Hi" Canvas.Left="50"/>
I've got a WPF Control that exposes one of it's children (from it's ControlTemplate) through a read-only property. At the moment it's just a CLR property, but I don't think that makes any difference.
I want to be able to set one of the properties on the child control from the XAML where I'm instantiating the main control. (Actually, I would like to bind to it, but I think setting it would be a good first step.)
Here's some code:
public class ChartControl : Control
{
public IAxis XAxis { get; private set; }
public override void OnApplyTemplate()
{
base.OnApplyTemplate();
this.XAxis = GetTemplateChild("PART_XAxis") as IAxis;
}
}
public interface IAxis
{
// This is the property I want to set
double Maximum { get; set; }
}
public class Axis : FrameworkElement, IAxis
{
public static readonly DependencyProperty MaximumProperty = DependencyProperty.Register("Maximum", typeof(double), typeof(Axis), new FrameworkPropertyMetadata(20.0, FrameworkPropertyMetadataOptions.AffectsRender, OnAxisPropertyChanged));
public double Maximum
{
get { return (double)GetValue(MaximumProperty); }
set { SetValue(MaximumProperty, value); }
}
}
Here's the two ways I can think of setting the nested property in XAML (neither compile):
<!--
This doesn't work:
"The property 'XAxis.Maximum' does not exist in XML namespace 'http://schemas.microsoft.com/winfx/2006/xaml/presentation'."
"The attachable property 'Maximum' was not found in type 'XAxis'."
-->
<local:ChartControl XAxis.Maximum="{Binding Maximum}"/>
<!--
This doesn't work:
"Cannot set properties on property elements."
-->
<local:ChartControl>
<local:ChartControl.XAxis Maximum="{Binding Maximum}"/>
</local:ChartControl>
Is this even possible?
Without it I guess I'll just need to expose DP's on the main control that get bound through to the children (in the template). Not so bad, I guess, but I was just trying to avoid an explosion of properties on the main control.
Cheers.
You can't do it like this... you can access nested properties through its path in a binding, but not when you define the value of the property.
You have to do something like that :
<local:ChartControl>
<local:ChartControl.XAxis>
<local:Axis Maximum="{Binding Maximum}"/>
</local:ChartControl.XAxis>
</local:ChartControl>