Is it possible to get/set the value of CaretIndex property of a TextBox control in viewmodel in wpf via Binding defined in view?
Thanks
You can not bind the property CaretIndex since it is not a DependencyProperty. It is a CLR
property that does not accept binding.
The issue here is how to get the CaretIndex of the TextBox control via the view model.
If you intent to get it directly by binding to the view model its impossible. As I posted in the previous answer its a CLR property and not a dependency property.
What can we do?
The best solution for that is to follow the steps:
Define attached property on the control via separate class.
Define a property in the view model and bind the attached property to the one in the view-model
Update the control property in the callback of the attached property changed event according to the new value received.
In this case, we still separate the view from the model.
I hope my answer helps you!
Related
I have a main window coupled with a view model.This main window uses a usercontrol which also has its own viewmodel.
What I would like to achieve is setting a binding in the main window's xaml between one of its viewmodel's custom property and one of the usercontrol's viewmodel's custom property.
How would one go about doing that?
Could you instead use the ViewModels as projections of a Model?
That is, could you have a class that holds the state (or actions) that both the VMs need to expose and have both the VMs reference this class?
If for some reason you have to couple views to something outside their own DataContext I believe you can only go up the visual tree by using RelativeSource FindAncestor in the binding. I don't think you can traverse down (e.g. Window -> Control).
If you really want to Bind them together you could make your ViewModel's properties Dependency Properties and your ViewModel derive from DependencyObject - then you could do..
var binding = new Binding("Something");
binding.Source = myViewModel1;
binding.Mode = BindingMode.TwoWay;
BindingOperations.SetBinding(viewModel2,ViewModelType.SomethingProperty,binding);
If this is a good design having your viewmodels derive from DependencyObject is another question..
You could also try looking at this library that allows binding to and from POCOs.
I ended up not using a modelview for my usercontrol, not as neat but at least it works and is less complicated datacontext wise.
Thanks to all.
let say there is a textbox and i want to control the visibility of this control using MVVM, is there a sample on how to do this? First create a dependency property then get it hooked up in the ViewModel. Thanks.
Typically, you wouldn't need to use a dependency property in this case. Dependency properties really only need to be implemented for things like controls themselves, not for determining behavior. Behavior, such as the visibility of an element, can be handled directly via data binding.
Your ViewModel would just have some property, and you'd bind the TextBox.Visibility property directly to the ViewModel property.
The one "sticky point" is that you often will want to have some type of IValueConverter that will convert from your property type to a Visibility enum.
In WPF some properties of controls are dependency properties, others are normal properties.
Eg TextBox.SelectedText is a normal property and not a dependency property. I use MVVM and it happens often to me that I want to bind to some property, but I cant, because it is a normal property.
Can someone explain to me, what logic stands behind the decision whether a property is normal or a dependency property.
Also, can I work around this and somehow bind to the normal properties as if they were dependency properties?
Go through these links
When to use a WPF Dependency Property versus INotifyPropertyChanged
http://social.msdn.microsoft.com/forums/en-US/wpf/thread/65bf126f-e706-4d3e-8cc3-e0130a0ee6de
http://joshsmithonwpf.wordpress.com/2007/06/22/overview-of-dependency-properties-in-wpf/
WPF: What distinguishes a Dependency Property from a regular CLR Property?
How to set bindings on CLR Properties using DataResource
You will get better idea about what you are looking to find out
You can bind to normal properties, but if your property changes, your binding will not get notified. However, you can implement INotifyPropertyChanged in your classes and the binding will update your control automatically.
I have a business object that comes from the core of the application. That object does not inherit from INotifyPropertyChanged. It contains some property that my XAML code bind to it.
I only want to update the properties not the UI dynamically (OneWayToSource style).
By example, if I change the text of a text box, the source item does not get updated.
It is a limitation of silverlight that if the object does not implement INotifyPropertyChanged or use DepencyProperties that the source of the binding cannot be updated?
The source property does not need to be a dependency property nor does the class that exposes it need to implement INotifyPropertyChanged.
If you have the binding on the TextBox set to use the TwoWay mode editing the text box should update the bound property even if it is a plain "vanila" property. Note by default the focus has to leave the TextBox in order for the binding to update.
If your business object has a set method on the property you want to update, then the value should be updated, provided the value you enter doesn't trigger an exception.
Not implementing INotifyPropertyChanged hinders just visual feedback.
I am deriving from combobox (WinForms) and am providing a new implementation for the Selectedvalue property.
It works fine as is, but any change to the selectedvalue property is not updating other controls bound to the same "binding context" to change their values accordingly.
I did try adding the BindableAttribute(true) to the property, but still it does nottrigger the change in value to the other linked controls.
The control's DataBindings.add(...) is all set up. And other controls are also bound to the same data filed on the same datasource.
Any ideas what i am doing wrong.
Have you called your base class' implementation of overridden methods? It's possible that failing to call the base class implementation is accidentally circumventing the code that fires various event plumbing.