I have the need to set a binding in code.
I can't seem to get it right tho.
This is what i have tried:
XAML:
<TextBox Name="txtText"></TextBox>
Code behind:
Binding myBinding = new Binding("SomeString");
myBinding.Source = ViewModel.SomeString;
myBinding.Mode = BindingMode.TwoWay;
myBinding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
BindingOperations.SetBinding(txtText, TextBox.TextProperty, myBinding);
ViewModel:
public string SomeString
{
get
{
return someString;
}
set
{
someString= value;
OnPropertyChanged("SomeString");
}
}
The property is not updating when i set it.
What am i doing wrong?
Replace:
myBinding.Source = ViewModel.SomeString;
with:
myBinding.Source = ViewModel;
Example:
Binding myBinding = new Binding();
myBinding.Source = ViewModel;
myBinding.Path = new PropertyPath("SomeString");
myBinding.Mode = BindingMode.TwoWay;
myBinding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
BindingOperations.SetBinding(txtText, TextBox.TextProperty, myBinding);
Your source should be just ViewModel, the .SomeString part is evaluated from the Path (the Path can be set by the constructor or by the Path property).
You need to change source to viewmodel object:
myBinding.Source = viewModelObject;
In addition to the answer of Dyppl, I think it would be nice to place this inside the OnDataContextChanged event:
private void OnDataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
{
// Unforunately we cannot bind from the viewmodel to the code behind so easily, the dependency property is not available in XAML. (for some reason).
// To work around this, we create the binding once we get the viewmodel through the datacontext.
var newViewModel = e.NewValue as MyViewModel;
var executablePathBinding = new Binding
{
Source = newViewModel,
Path = new PropertyPath(nameof(newViewModel.ExecutablePath))
};
BindingOperations.SetBinding(LayoutRoot, ExecutablePathProperty, executablePathBinding);
}
We have also had cases were we just saved the DataContext to a local property and used that to access viewmodel properties. The choice is of course yours, I like this approach because it is more consistent with the rest. You can also add some validation, like null checks. If you actually change your DataContext around, I think it would be nice to also call:
BindingOperations.ClearBinding(myText, TextBlock.TextProperty);
to clear the binding of the old viewmodel (e.oldValue in the event handler).
Example:
DataContext:
class ViewModel
{
public string SomeString
{
get => someString;
set
{
someString = value;
OnPropertyChanged(nameof(SomeString));
}
}
}
Create Binding:
new Binding("SomeString")
{
Mode = BindingMode.TwoWay,
UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged
};
Related
I'm making a small application, it's a form that reads from a data source, I want to use it for editing and adding new records.
so the default binding mode for the textboxes in the form is TwoWay mode, so the user can edit an existing record, but I want to add a Checkbox that when checked, it marks the data in the textboxes as new, and then adding them to the data source, so I need to change the binding mode to OneWay,
to my knowledge, to do this in code I need to create a new Binding object, that I will have to set properties like Source that doesn't change:
Binding myBinding = new Binding();
myBinding.Source = ViewModel;
myBinding.Path = new PropertyPath("SomeString");
myBinding.Mode = BindingMode.TwoWay;
myBinding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
So is there a way to change only the Binding mode in code?
EDIT
some further explanation of the application:
In the form there's a combobox that is bound to a List<Book>, there are 3 TextBoxs, their Text properties bound to the DataContext object of their container which itself set to the SelectedItem of the Combobox.
When I added the ReadOnly property as described in the answer, when I check the checkbox I can't change the text in the textboxes.
..
Thanks!
Don't change Mode of binding. Just correct your view-model logic.
public class ViewModel : INotifyPropertyChanged
{
private string _text;
private bool _readOnly;
public string Text
{
get { return _text; }
set
{
if (ReadOnly || value == _text)
return;
_text = value;
OnPropertyChanged(nameof(Text));
}
}
public string ReadOnly
{
get { return _readOnly; }
set
{
if (value == _readOnly)
return;
_readOnly = value;
OnPropertyChanged(nameof(ReadOnly));
}
}
}
In XAML bind IsChecked property of your CheckBox to ReadOnly property.
The answer to this is "Yes, but". The Mode property of Binding has a setter. So it appears that you can set the mode of an existing binding like so...
BindingExpression be = textBox.GetBindingExpression(TextBox.TextProperty);
Binding b = be?.ParentBinding as Binding;
if (b != null)
{
b.Mode = BindingMode.OneWay;
}
However if you do this you will get in every case the exception...
System.InvalidOperationException occurred
HResult=0x80131509
Message=Binding cannot be changed after it has been used.
So the only way to accomplish what you want is to create a new binding based on the old binding while changing the mode. Then replace the old binding.
BindingExpression be = textBox.GetBindingExpression(TextBox.TextProperty);
Binding b = be?.ParentBinding as Binding;
if (b != null)
{
Binding b2 = new Binding();
b2.Path = b.Path;
b2.Mode = BindingMode.OneWay;
textBox.SetBinding(TextBox.TextProperty, b2);
}
This is less than ideal because for completeness you would need to copy the converter, the converter parameter and so on, but this is the best you can do.
I have a ObservableCollection<List<MessageView>> (MessageView is a custom class) I instantiate it that way
public ObservableCollection<List<MessageView>> _messagesView;
public ObservableCollection<List<MessageView>> messagesView {
get {
if (_messagesView == null) {
_messagesView = new ObservableCollection<List<MessageView>>();
}
return _messagesView;
}
set {
if (_messagesView != value) {
_messagesView = value;
PropertyChanged(this, new PropertyChangedEventArgs(nameof(messagesView)));
}
}
}
This property is set on a Singleton
I want to bind one of the item collection to a datagrid it would look that way in xaml:
<xmlns:module="clr-namespace:Myproject.MyNameSpace;assembly=Myproject">
<DataGrid
Name="DataGrid_messages"
...
ItemsSource="{Binding messagesView[2], Source={x:Static module:Singleton.Instance}}"
>
This is working well that way but this is not what I want to do. I want to have the control of my index. So I have to do the binding in c# with my controller but I never found an example to bind with a special index.
Binding myBinding = new Binding("messagesView");
myBinding.Source = Singleton.Instance;
myBinding.Path = ??
DataGrid_messages.SetBinding(DataGrid.ItemsSourceProperty, myBinding);
Share your thought about this, is it possible? Or a better way to do it?
UPDATE
Additional change to do with Clemens Answer:
The binding is set with the internal list so it's it which should be ObservableCollection type:
public List<ObservableCollection<MessageView>> messagesView;
Provided that the index is fixed, creating the binding path in code behind could look like this:
myBinding.Path = new PropertyPath(string.Format("messagesView[{0}]", index));
I'm trying to create a label at runtime and connect it's Content property to another TextBox control which is in my UserControl called MyLabelSettings.
This is what I got so far:
Label currCtrl = new Label();
MyLabelSettings currCtrlProperties = new MyLabelSettings();
// Bindings to properties
Binding binding = new Binding();
binding.Source = currCtrlProperties.textBox_Text.Text;
binding.Path = new PropertyPath(Label.VisibilityProperty);
BindingOperations.SetBinding(currCtrl.Content, Label.ContentProperty, binding);
The last row shows an error which I did not figure out how to solve:
The best overloaded method match for 'System.Windows.Data.BindingOperations. SetBinding(System.Windows.DependencyObject, System.Windows.DependencyProperty, System.Windows.Data.BindingBase)' has some invalid arguments
I have in MyLabelSettings the implementation of INotifyPropertyChanged
which has the following code when the TexBox.Text changes
private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
{
InvokePropertyChanged(new PropertyChangedEventArgs("TextChanged"));
}
Is there a better way to bind these 2? Or am I doing something wrong in this one?
Thanks!
The problem is simpler than you realize:
This:
binding.Source = currCtrlProperties.textBox_Text.Text;
binding.Path = new PropertyPath(Label.VisibilityProperty);
BindingOperations.SetBinding(currCtrl.Content, Label.ContentProperty, binding);
Should be this:
//The source must be an object, NOT a property
binding.Source = currCtrlProperties;
//Since the binding source is not a DependencyObject, we using string to find it's property
binding.Path = new PropertyPath("TextToBind");
BindingOperations.SetBinding(currCtrl, Label.ContentProperty, binding);
Before, you were attempting to bind the value to an object's property via a property. Now, you're binding the value to an object's property via an object (:
Notes:
You are attempting to bind the text of a control that exists in an instance of a class you just made.
MyLabelSettings currCtrlProperties = new MyLabelSettings();
I base this assumption off this line:
currCtrlProperties.textBox_Text.Text;
Which appears to contain a text control of some sort. Rather, you want bind the text of a property that exists in an instance of a class you make, not a control.
I'm trying to create a custom control which inherits from a TextBox control. in the constructor of my custom control I need to have the text property bound. this the code I'm using by now.
var binding = new Binding("Name");
binding.Mode = BindingMode.TwoWay;
binding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
binding.ValidatesOnDataErrors = true;
SetValue(TextProperty, binding);
I haven't set a source for binding because I want it be the DataContext of the form on which my custom control will be placed however I suppose I'm doing it in a wrong way because when I added on the form I face the error message in xaml which says: "System.Windows.Data.Binding is not a valid value for property text.
Its not good to do in code-behind, hope this answers your question
Binding binding = new Binding();
binding.Path = new PropertyPath("yourPropertyTobeBinded");
binding.Source = sourceObject;
BindingOperations.SetBinding(youTextBox, TextBox.TextProperty, binding);
Here is the combobox in my UserControl:
<Combobox ItemsSource="{Binding ComboItemsProperty}" />
I have tried:
Binding bind = new Binding();
bind.Mode = BindingMode.OneWay;
bind.Source = this;
bind.Path = new PropertyPath("ComboItemsProperty");
this.SetBinding(ComboBox.ItemsSourceProperty, bind);
However, this doesn't work. I think I am doing the bind.Source wrong, but I'm not sure what to set the Source to. This code is inside my UserControl.xaml.cs.
You can try (Replace this)
Binding bind = new Binding();
bind.Mode = BindingMode.OneWay;
bind.Source = yourCollectionSourceOrClass; //<--Replace with your collection
bind.Path = new PropertyPath("ComboItemsProperty");
this.SetBinding(ComboBox.ItemsSourceProperty, bind);
You need to the set context of the instance containing your property ComboItemsProperty. So instead of 'this' u should set it to 'this.DataContext' or other class object instance containing the ItemSource property you have defined..
Try this,
Binding bind = new Binding();
bind.Mode = BindingMode.OneWay;
bind.Source = this.DataContext;
bind.Path = new PropertyPath("ComboItemsProperty");
this.SetBinding( ComboBox. ItemsSource Property, bind);
(posting frm mobile)
I have tried a lot of ways to do this, however, nothing seems to work.
I am instead going to serialize the binding when the .xaml file gets saved out. This seems to be working perfectly. Binding will no longer have to be set in code.