What I have?
I have Frame in XAML, (binding works properly).
<Frame Name="frmMainContent"
DataContext="MyPageInformation"
Source="{Binding ElementName=thisPage, Path=MyPageInformation.UserControlPath}"
NavigationUIVisibility="Hidden"></Frame>
In the code behind I have a DependencyProperty of my class, PageInformation
public static DependencyProperty PageInformationProperty = DependencyProperty.Register("MyPageInformation", typeof(PageInformation), typeof(Administration));
public PageInformation MyPageInformation
{
get { retur n (PageInformation)GetValue(PageInformationProperty); }
set{ SetValue(PageInformationProperty, value); }
}
What I want?
The Frame should update its binding whenever value of MyPageInformation changes.
Can somebody tell me how I can achieve this?
Thanks in advance!
You don't have to make the PageInformationProperty a dependency property just for this binding. Implement INotifyPropertyChanged in the code behind.
Also since you are actually binding to "UserControlPath", make sure that this property actually sends change notifications.
Well, the first thing I'll tell you is that all binding errors appear on the Output window. So you need to look at it and find out if you have any errors.
The next thing.. for bindings to update automatically, you either need to make the property it is "binded" to, either a dependency property, or implement INotifyPropertyChanged for other classes.
Be sure that the property that you exactly bind to, is either one of these cases.
Related
I'm making app with using Xamarin.forms.
I already asked question here.
How to set child of class' property with using xaml? (Xamarin.forms)
But I couldn't get right answer for this, or there may be no solution for that.
What I want to do is setting my class's view's property from ContentPage's XAML.
my class has some view like Image and else.
I searched and found that there is 'ControlTemplete'. But I'm not sure it's what I'm looking for.
And I also don't think putting BindableProperty and OnPropertyChangedDelegate codes for every property that I want to set is a best way.
Is there another better solution?
Thanks.
You can map XAML that is inside your control to a property using ContentProperty attribute.
[ContentProperty("MyContent")]
public class MyControl : ContentView
{
public View MyContent { get; set; }
}
And in XAML somthing like this
<local:MyControl>
<Grid></Grid>
</local:MyControl>
this limits you to only one property but should work with any types.
I got a binding source not being updated when the targeted DependencyProperty of a custom UserControl changes.
The source is a ViewModel loaded with MEF into the DataContext of my custom UserControl.
My binding looks like this in the root XAML of MyUserControl
// MyUserControl.xaml
<MyUserControlBase x:Class="MyUserControl" MyDependencyProperty="{Binding ViewModelProperty}">
If i use the MyDependencyProperty with a FrameworkPropertyMetadata and use the callback function when the property changes i can do the following which works fine
// MyUserControlBase.cs
private static void MyDependencyProperty_Changed(DependencyObject depObj, DependencyPropertyChangedEventArgs args)
{
var filter = (UserControl )depObj;
var vm = (ViewModel)filter.DataContext;
vm.ViewModelProperty= (VMPropType)args.NewValue;
}
Registration of the DependencyProperty in MyUserControlBase which inherit UserControl.
// MyUserControlBase.cs
public static readonly DependencyProperty MyDependencyPropertyProperty = DependencyProperty.Register("MyDependencyProperty",
typeof(VMPropType),
typeof(MyUserControlBase),
new FrameworkPropertyMetadata(null, MyDependencyProperty_Changed));
But why can't i get the simple two way binding to work when done in the XAML?
Output window show no binding failurs. I can see the ViewModel.ViewModelProperty getter is being called. Just not the setter once MyDependencyProperty changes.
It don't appear to be a problem with the ordering of events. The ViewModel is created long before DependencyProperty is changed for the first time.
I've also looked at Setting up binding to a custom DependencyProperty inside a WPF user control
But his problem seems slightly different since i actualy inherit from my own Base class which holds the DependencyProperty.
Thank you for any help.
Edit: with link to example solution.
Solution zip here
Sorry for the scary looking link, I don't know alot of quick fileshareing sites. If its bad post comment and I will remove it asap, but it seems ok.
Answer updated / irrelevant info deleted
After looking at the code in your sample I saw what the problem is. You have this "selector" control. In the BindDependencies method you set a binding on the MyControlBase.MyDependencyProperty. But at the same time you also bind this property to your control's datacontext (in MyUserControl.xaml). Effectively this means that in the BindDependencies method you are overwriting the binding to your viewmodel thus it is not active after that method - you can see this yourself by breaking into before and after the SetBinding call and calling BindingOperations.GetBindingExpression(control, MyUserControlBase.MyPropertyDependencyProperty) - the bindings are different. This is why your code does not work. I guess you will have to find another way of transferring the value there :)
Some additional info
In WPF a property can be a target of only one binding. This is actually very logical - if a property is bound to two sources - which one should it use? The fact that the binding is marked as OneWayToSource does not really matter in this situation as it still counts as a binding that targets the control's property.
One way you can investigate and see if it works for you is the MultiBinding - it does allow to bind the control's property to several sources by implementing your own IMultiValueConverter. You can find more info on this on MSDN in the link provided.
Do you expose the ViewModelProperty as a regular property..
Usually you do the following....
public static readonly DependencyProperty ViewModelPropertyProperty = DependencyProperty.Register("ViewModelProperty",
typeof(VMPropType),
typeof(MyUserControlBase),
new FrameworkPropertyMetadata(null, ViewModelProperty_Changed));
public VMPropType ViewModelProperty {
get { return (VMPropType)GetValue(ViewModelPropertyProperty); }
set { SetValue(ViewModelPropertyProperty,value); }
}
EDIT -- After comment.
When are you checking that the property has changed? By default WPF bindings only update the values when they lose focus, you change change the UpdateSourceTrigger property of the binding to alter this behaviour.
Is it possible to change property value from xaml?
Imagine we have a usercontrol which have a property that is initialized already
public class MyUserControl : UserControl
{
...
public SomeClass MainWindow
{
get
{
return _someClass ?? (_someClass = new SomeClass();)
}
}
}
Now is it possible to change property of SomeClass without initializing it from xaml, and without animation?
Why xaml doesn't allow syntax to write <UserControl.MainWindow.Property>?
Add a setter to the property and allow the XAML to create its own SomeClass according to its need - that's now it is usually done.
XAML is declarative language, it doesn't try to be Turing complete or something like that, it merely describes creation of objects.
Of course, there is one extreme solution. But please, don't do it. For your sake, and everyone else's :)
EDIT:
Another solution could be to create a new property in the UserControl, and synchronize this property with property of SomeClass ( set{ this._someClass.someProperty = value; }). If you set this property in XAML declaration of the UserControl, the change will be propagated to the _someClass member.
Of course the wrapper property will have to be a dependency property, if you want to bind to the wrapped property.
One, you need to have a set to change the value. Two, just bind to it TwoWay in in the XAML.
I'm having one hell of a time trying to get my databinding to work correctly. I have reason to believe that what I'm trying to accomplish can't be done, but we'll see what answers I get.
I've got a UserControl. This UserControl contains nothing more than a button. Now within the code behind, I've got a property name IsBookmarked. When IsBookmarked is set, code is run that animates the look of the button. The idea is that you click the button and it visually changes. We'll call this UserControl a Bookmark control.
Now I have another control, which we'll call the FormControl. My FormControl contains a child Bookmark control. I've tried to do databinding on my Bookmark control, but it's not working. Here's some code to help you out.
This is the XAML and Loaded event handler of my control. As you can see it contains a child element that is a custom control (bookmark). So once this control loads, it's DataContext is set to an new instance of an Employee object. Silverlight also sets the DataContext property of my child bookmark control to the same instance. I've verified this by debugging. If my parent has a valid DataContext set then why can't my child control (bookmark) property databind to it?
<UserControl ......>
<q:Bookmark x:Name="BookMarkControl1" IsBookmarked="{Binding IsSiteBookmarked}" />
</UserControl>
public void Control_Loaded(object sender, EventArgs e)
{
DataContext = new Employee { IsSiteBookmarked = True };
}
This is my custom control below. Obviously it contains more than this, but for readability I've trimmed it down to the property I'm trying to databind to.
//this is the bookmark control. I've included this control within another control, and I'm trying to databind to properties within my parents DataContext
public partial class Bookmark : UserControl
{
bool _IsBookmarked= false;
public bool IsBookmarked
{
get {return _IsBookmarked;}
set {
_IsBookmarked= value;
SwitchMode(value);
}
}
}
UPDATE
Got some javascript errors that I should mention. Firebug reports a AG_E_PARSER_BAD_PROPERTY_VALUE exception. It doesn't seem like my databinding is even working yet.
Make your IsBookmarked property on the Bookmark control a dependency property.
I presume Control_Loaded is a part of your FormControl, in which case I'm not sure you are using DataContext properly. Best double check that.
UPDATE: Yes, you are using the DataContext properly. AG_E_PARSER_BAD_PROPERTY_VALUE indicates you need to make the IsBookmarked property a dependency property, like so:
Public Property IsBookmarked() As Boolean
Get
Return Me.GetValue(IsBookmarkedProperty)
End Get
Set(ByVal value As Boolean)
Me.SetValue(IsBookmarkedProperty, value)
End Set
End Property
Public Shared ReadOnly IsBookmarkedProperty As DependencyProperty = DependencyProperty.Register("IsBookmarked", GetType(Boolean), GetType(Bookmark), New PropertyMetadata(New PropertyChangedCallback(AddressOf OnIsBookmarkedPropertyChanged)))
Private Shared Sub OnIsBookmarkedPropertyChanged(ByVal d As DependencyObject, ByVal e As DependencyPropertyChangedEventArgs)
Dim cntrl As Bookmark = TryCast(d, Bookmark)
cntrl.SetIsBookmarked(e.NewValue)
End Sub
If you only need to store the value for later use, then you don't need to do anything in the OnIsBookmarkedPropertyChanged procedure, But I put some code there as an example anyway.
Good Luck!
I don't recall the exact order in which databinding is evaluated (and I'm too lazy to go look it up), but as I recall, it initially happens BEFORE the form's Loaded event fires, and without making the IsBookmarked property a dependency property, or at least using INotifyPropertyChanged, it may have trouble establishing the datacontext appropriately. I'd recommend either implementing INotifyPropertyChanged or making IsBookmarked a dependency property. DataBinding is tough enough to get right in the best of circumstances (see my long, bad-tempered rant about it here), and you'll just be making it more difficult on yourself if you aren't setting up your properties in the way that it expects.
The control exposes a IsSiteBookmarked property(which I believe should be a DependencyProperty) but the control is binding to a IsBookmarked which is not shown. Is this intentional? Have you checked your Visual Studio output window for binding errors?
Addition 1:
Since you have fixed the typo in your question and added that there is an error being reported.
Start by clearing up the AG_E_PARSER_BAD_PROPERTY_VALUE problem. Is there a line number and start position in the error message? Start looking there. One strategy is to start taking out XAML until there is no longer an error. This will narrow down the offending code.
Running in debug, mode check for binding errors in the output window.
You might want to also post the Employee class code, especially the IsSiteBookmarked property.
Typically when doing databinding to an object you will want to leverage the INotifyPropertyChanged interface and implement that so that the control can properly invalidate it's property value. Unless you use INotifyPropertyChanged with Mode=TwoWay then any code that changes your DataContext's IsSiteBookmarked will have no effect.
Let's say I have a Class called ModelBase
public class ModelBase
{
public string Name
{
get { return "one"; }
}
}
and I have a property named Model of type ModelBase.
Now to the question how do I Bind to the Name property? The c# code would be this.Model.Name.
I've been trying to get this to work a long time, can some one enlighten me?
Not sure why you are having trouble with this.
You should be able to set the object that the Model property is on as the DataContext for your control, then simply bind using {Binding Model.Name}...
What have you tried to do so far?
(You can definitely bind to properties in Silverlight BTW)
You need to assign Model to the datacontext property before you can do any data binding, an example would be:
this.DataContext = Model;
In xaml, setup binding in this way:
<TextBlock Text={Binding Name}/>
Note: The way you declare the Name property only allows one time binding, to allow OneWay/TwoWay binding, look at dependencyproperty or INotifyPropertyChanged interface.
You can definitely databind to properties.
If you want more, you can use dependency properties of silverlight.
Check this URL.
Silverlight doesn't allow binding to properties. You'll need to expose a property on your viewmodel that returns the value of the models properties to bind correctly.