When a data binding is added to a control in WinForms:
Binding b =new Binding("Text", myDataRowView, "title");
TitleTextBox.DataBindings.Add(b);
the textbox displays the value at myDataRowView["title"].
If myDataRowView["title"] is then updated (directly, not via the form control) so that its value changes
myDataRowView["title"] = "foo";
is the textbox supposed to reflect the new value? Does Adding the binding to the textbox set up a listener to listen for changes to the column to which it has been bound?
Or does the control have to be rebound to the DataRowView whenever the DRV is changed in code, i.e. not as the result of user typing data into the form control?
When we say updation - there are two scenarios here.
Update the underlying datasource connected to the control (textbox in your case). For that look at the add overload - Add Method (String, Object, String, Boolean, DataSourceUpdateMode) The DataSourceUpdateMode property controls how the update happens.
OnValidation - If you have some validation rules for your control, underlying value won't be updated if validation fails.
OnPropertyChanged will update underlying source in any case.
Update the control when the datasource is updated.
The INotifyPropertyChanged interface is used to notify clients, typically binding clients, that a property value has changed. So for this you need to implement this interface.
Related
I have a combobox, and in the design view I have it databound to a bindingsource as follows:
this.itemTypeComboBox.DataBindings.Add(new System.Windows.Forms.Binding("SelectedValue", this.itemTypeContainerBindingSource, "ItemType", true));
this.itemTypeComboBox.DataBindings.Add(new System.Windows.Forms.Binding("Text", this.itemTypeContainerBindingSource, "ItemType", true));
In the code behind in the load event I have the following:
// bind the combobox to the enum
this.itemTypeComboBox.DataSource = Enum.GetValues(typeof(OpticalItemType));
// bind a custom object to the datasource
this.itemTypeContainerBindingSource.DataSource = customObjectContainer;
The "customObjectContainer" is a single object that contains a property "ItemType" that is bound to the combobox, and all properties of the object use change notification through "INotifyPropertyChanged".
In my code behind, if I programmatically change the custom object, the changes are reflected in the combobox. However, if I change the combobox through the UI, the bindingsource, and hence the custom object do not reflect the changes.
Any ideas what I am doing wrong?
As it is a singular object, it cannot be to do with using BindingList etc.
UPDATE 1:
Ok, whenever I change the combobox through the UI, it never changes the underlying object, the setter is never hit for the property in the custom object. However, I have just noticed that if I tab off of the control, it then fires the setter, and changes the underlying object. Why would this be?
PROBLEM SOLVED:
It appears, the issue was with my binding. I added "DataSourceUpdateMode.OnPropertyChanged" to the bindings, and it works now!!
The issue was with my binding. I added "DataSourceUpdateMode.OnPropertyChanged" to the bindings, and it works now!!
I have a WPF window that has a datagrid and a user control for a form for the fields in that datagrid. The user control and the WPF window have view models.
The user control's DataContext is bound to one of the window's view model's member field, whose value changes during the data grid's Selection Changed event.
I'm not sure if this is the right way to do it because I am unable to create references from the inner view model to the outer view model for some reason. Constructor injection won't work because I'm required to use default constructor only, and I can't seem to put a property injector in the right place (always getting null reference when I try to use it).
I am also unable to get my property change notification to work properly in the inner view model.
Is there a better way to wire my view models so that they automatically change the values in the user control when a new row is selected in the datagrid? I have a feeling that binding to the control's DataContext is not the way to go.
This doesn't seems a complex/nested scenario. Looks like pretty much a normal master details scenario. Suppose you want to edit Customer data, I would have an ObservableCollection instance bind to the DataGrid, and there will be a SelectedCustomer property in the VM also. In the DataGrid you can set SelectedItem twoway bind to the SelectedCustomer property which makes SelectedCustomer always updated with your selection. Since the usercontrol has the same instance of customer as in the DataGrid row, whenever you change anything in the UC those data will get reflected in the grid. Ofcourse all those properties should fire NotifypropertyChanged.
i've a contentcontrol in my Wpf-App (MVVM) which is bound to an object and displays the objects properties in textboxes, so the user can edit the values of the properties.
I want to implement undo/redo functionality with the command pattern of the GoF.
For this i need a point where i can create the command and set it into my undomanager.
My idea was to add a submitbutton. When the button is pressed, i update the sources of the textboxes (my properties) and create my command object to make the changes undoable (saving the old state of the object and the new state).
But:
- For using a submit button i need to set UpdateSourceTrigger of the textboxes to Explicit. If i want to update my sources i need to reference the controls in my view, which is bad as far as i've learned. How can i do that?
With MVVM i have to create a Command (WPF Command, not my undo redo command) for the SubmitButton but i don't see how to apply the changes to the properties from that command without referencing the textboxes (further hey are generated via datatemplates).
Thanks Walter
I assume your TextBox controls are bound to the properties in the ViewModel class. If you bind your submit button to a ViewModel Command which in turn can add appropriate command to you Command Pattern Collection and also changes some of ViewModel properties, the values in the Textbox controls will also be updated. Now, for a Textbox to update it's value when the value of a property it is bound to changes, the ViewModel class needs to implement INotifyPropertyChanged interface and raise the PropertyChanged event from the property setter with that's property's name as an argument.
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.
I have a "Login" button that I want to be disabled until 3 text boxes on the same WPF form are populated with text (user, password, server).
I have a backing object with a boolean property called IsLoginEnabled which returns True if and only if all 3 controls have data. However, when should I be checking this property? Should it be on the LostFocus event of each of the 3 dependent controls?
Thanks!
vg1890
I'd get the "backing object" to raise the IsLoginEnabled changed event when any of the 3 fields are updated. You can then bind the button to the IsLoginEnabled property and not have to keep checking it.
The pseudocode would look something like this:
Public Event IsLoginEnabledChanged As EventHandler
Public Property User() As String
Get.. ' snipped for brevity
Set(ByVal value As String)
mUser = value
RaiseEvent IsLoginEnabledChanged(Me, New EventArgs())
End Set
' do the same in the Set for Password() and Server() properties
The trick to this is naming the Event [PropertyName]Changed (i.e. IsLogonEnabledChanged) - because raising this event will automagically notify any bound controls :o)
Yes, I would say the easiest option would be to check it on the LostFocus or TextChanged event of each of those controls. However, if you want to do a little heavier lifting, you could implement the boolean as a dependency property that you could have bound to the button's Enable.
http://msdn.microsoft.com/en-us/library/ms750428.aspx
Can you just databind your IsLoginEnabled right to the Enabled property of the login button?
I think you could use RoutedCommands one of the most useful features of WPF. Basically add a CommandBinding, to use OnExecute and OnQueryCommandEnabled to manage button's enabled state.
Check out this wonderful explanation on using RoutedCommands in WPF