I have a WPF form with combobox and a text box (both are object bindings). Changing the input of a combobox or textbox updates the Object property and binds the data to zero and updates the user interface. The problem is that I implemented a way to undo a change that works, but twists the user interface upgrade. If I make a change from the drop-down list and cancel it, combobox will not return the selected value back to what it should be (bound by the value of the object). If I make this change from the text box and cancel it, the text box and the combo box will show the correct data, but then the focus will immediately be transferred to the combo box (when it should have remained in the text box, since this is the last place that I had it). I'm not quite surehow to do it in a general aspect, how it was connected with the processing of change events, and the change check was not canceled later (because then what is the data binding point?) ...
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Text;
namespace MyTesting
{
public class User : AbstractEntity
{
public User()
{
Rankings = new Dictionary<int,string>();
Rankings.Add(1, "Newbie");
Rankings.Add(10, "Novice");
Rankings.Add(25, "Adept User");
Rankings.Add(50, "Power User");
Rankings.Add(100, "Admin God");
}
public Dictionary<Int32, String> Rankings { get; set; }
private Int32 _rank;
public Int32 Rank
{
get
{
return _rank;
}
set
{
SetProperty<Int32>("Rank", ref _rank, value);
}
}
}
}
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Text;
namespace MyTesting
{
public abstract class AbstractEntity : INotifyPropertyChanging, INotifyPropertyChanged
{
protected void SetProperty<T>(String propertyName, ref T property, T value)
{
if (!Object.Equals(property, value))
{
if (OnPropertyChanging(propertyName, property, value))
{
T oldValue = (T)property;
property = value;
OnPropertyChanged(propertyName, property, value);
}
}
}
[field: NonSerialized]
public event PropertyChangingEventHandler PropertyChanging;
protected virtual Boolean OnPropertyChanging(String propertyName, Object oldValue = null, Object newValue = null)
{
CancellablePropertyChangingEventArgs e;
if ((oldValue != null) || (newValue != null))
e = new CancellablePropertyChangingEventArgs(propertyName, oldValue, newValue);
else
e = new CancellablePropertyChangingEventArgs(propertyName);
return OnPropertyChanging(e);
}
protected virtual Boolean OnPropertyChanging(CancellablePropertyChangingEventArgs e)
{
if (PropertyChanging != null)
PropertyChanging(this, e as PropertyChangingEventArgs);
return !e.IsCancelled;
}
[field: NonSerialized]
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(String propertyName, Object oldValue = null, Object newValue = null)
{
ExtendedPropertyChangedEventArgs e;
if ((oldValue != null) || (newValue != null))
e = new ExtendedPropertyChangedEventArgs(propertyName, oldValue, newValue);
else
e = new ExtendedPropertyChangedEventArgs(propertyName);
OnPropertyChanged(e);
}
protected virtual void OnPropertyChanged(ExtendedPropertyChangedEventArgs e)
{
if (PropertyChanged != null)
PropertyChanged(this, e as PropertyChangedEventArgs);
}
}
public class ExtendedPropertyChangedEventArgs : PropertyChangedEventArgs
{
public ExtendedPropertyChangedEventArgs(String propertyName)
: base(propertyName)
{
}
public ExtendedPropertyChangedEventArgs(String propertyName, Object oldValue, Object newValue)
: base(propertyName)
{
OldValue = oldValue;
NewValue = newValue;
}
public Object OldValue { get; private set; }
public Object NewValue { get; private set; }
}
public class CancellablePropertyChangingEventArgs : PropertyChangingEventArgs
{
public CancellablePropertyChangingEventArgs(String propertyName, Boolean cancel = false)
: base(propertyName)
{
IsCancelled = cancel;
}
public CancellablePropertyChangingEventArgs(String propertyName, Object oldValue, Object newValue, Boolean cancel = false)
: base(propertyName)
{
OldValue = oldValue;
NewValue = newValue;
IsCancelled = cancel;
}
public Object OldValue { get; private set; }
public Object NewValue { get; private set; }
public Boolean IsCancelled { get; set; }
}
}
<!-- MainWindow.xaml -->
<Window x:Class="ObservableDictionaryBinding.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:src="clr-namespace:MyTesting"
Title="MainWindow" Height="350" Width="525" Loaded="OnLoaded">
<Grid>
<ComboBox x:Name="RankList" Height="23" HorizontalAlignment="Stretch" VerticalAlignment="Top" Margin="12,12,12,0" />
<TextBlock Height="23" Width="40" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="13,100,0,0" Text="Rank:" />
<TextBox x:Name="RankBox" Height="23" HorizontalAlignment="Stretch" VerticalAlignment="Top" Margin="59,97,12,0" />
</Grid>
</Window>
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
namespace MyTesting
{
public partial class MainWindow : Window
{
public MainWindow()
{
MyUser = new User();
InitializeComponent();
MyUser.PropertyChanging += new PropertyChangingEventHandler(MyUser_PropertyChanging);
}
private User MyUser { get; set; }
private Binding RankListBinding { get; set; }
private Binding RankBinding { get; set; }
private Binding RankListRankBinding { get; set; }
private void OnLoaded(object sender, EventArgs e)
{
DataContext = MyUser;
RankListBinding = new Binding("Rankings");
RankListBinding.Source = MyUser;
RankList.SetBinding(ComboBox.ItemsSourceProperty, RankListBinding);
RankList.SelectedValuePath = "Key";
RankList.DisplayMemberPath = "Value";
RankBinding = new Binding("Rank");
RankBinding.Source = MyUser;
RankBox.SetBinding(TextBox.TextProperty, RankBinding);
RankListRankBinding = new Binding("Rank");
RankListRankBinding.Source = MyUser;
RankList.SetBinding(ComboBox.SelectedValueProperty, RankListRankBinding);
}
private void MyUser_PropertyChanging(Object sender, PropertyChangingEventArgs e)
{
CancellablePropertyChangingEventArgs ea = e as CancellablePropertyChangingEventArgs;
String text = String.Format("Would you like to change the property '{0}' from '{1}' to '{2}'?",
e.PropertyName,
(ea.OldValue == null) ? "<null>" : ea.OldValue.ToString(),
(ea.NewValue == null) ? "<null>" : ea.NewValue.ToString()
);
MessageBoxResult result = MessageBox.Show(this, text, "Property Changed",
MessageBoxButton.YesNo, MessageBoxImage.Question, MessageBoxResult.Yes);
if (result == MessageBoxResult.No)
ea.IsCancelled = true;
}
}
}
: , , combobox, , . , , . .
protected void SetProperty<T>(String propertyName, ref T property, T value)
{
if (!Object.Equals(property, value))
{
bool cancelled = OnPropertyChanging<T>(propertyName, property, value);
if (cancelled)
{
Application.Current.Dispatcher.BeginInvoke(
new Action(() =>
{
OnPropertyChanged<T>(propertyName);
}),
DispatcherPriority.ContextIdle,
null
);
return;
}
T originalValue = property;
property = value;
OnPropertyChanged(propertyName, originalValue, property);
}
}