I'm new to WPF, and I'm trying to do what I thought would be a simple task - display the value of a field in my business object as it changes during my program. I know how to "force" it to change by manually changing the TextBox.Text property in C#, but as I'm learning WPF I want to do it the "right" way, and that means databinding.
Question #1: As far as I understand it, my choice is to either use a DependencyProperty or implement INotifyPropertyChanged in my business object, right?
Question #2: Here is a generic version of my code in which I attempted to go the DependencyProperty route.
Markup:
Button x:Name="nextButton" Content="Click" Grid.Row="2" Click="nextButton_Click" />
TextBox x:Name="myTextBox" Grid.Row="1" Text="{Binding Source=myTest, Path=Name, UpdateSourceTrigger=PropertyChanged, NotifyOnSourceUpdated=True}"/>
Code-Behind:
namespace DependencyTest2
{
///
/// Interaction logic for MainWindow.xaml
///
public partial class MainWindow : Window
{
private int i;
private TestSphere myTest;
public MainWindow()
{
InitializeComponent();
i = 0;
myTest = new TestSphere();
}
private void nextButton_Click(object sender, RoutedEventArgs e)
{
switch (i)
{
case 0:
myTest.Name = "string1";
break;
case 1:
myTest.Name = "string2";
break;
case 2:
myTest.Name = "string3";
break;
}
i++;
}
}
class TestSphere : DependencyObject
{
public string Name
{
get { return (string)GetValue(NameProperty); }
set { SetValue(NameProperty, value); }
}
public static readonly DependencyProperty NameProperty =
DependencyProperty.Register("Name", typeof(string), typeof(TestSphere));
public TestSphere()
{
Name开发者_运维技巧 = "default";
}
}
}
When I run the program, nothing appears in text box, even though the bound property has a value - is there something else I need to do to alert the binding that the source value has changed? I thought that using a DependencyProperty as the source would take care of that, but then again, I'm a WPF rookie. Thanks!
- Steve
Ok, I tried to implement INotifyPropertyChanged using a wrapper class I found on codeproject as follows:
class TestSphere : NotifyProperyChangedBase
{
private string _Name;
public string Name
{
get { return _Name; }
set
{
this.CheckPropertyChanged("Name", ref _Name, ref value);
}
}
public TestSphere()
{
Name = "default";
}
}
public abstract class NotifyProperyChangedBase : INotifyPropertyChanged
{
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
#endregion
#region methods
protected bool CheckPropertyChanged(string propertyName, ref T oldValue, ref T newValue)
{
if (oldValue == null && newValue == null)
{
return false;
}
if ((oldValue == null && newValue != null) || !oldValue.Equals((T)newValue))
{
oldValue = newValue;
FirePropertyChanged(propertyName);
return true;
}
return false;
}
protected void FirePropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
{
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
#endregion
Here is my new Markup, too:
Grid Name="myGrid">
Grid.RowDefinitions>
RowDefinition Height="30"/>
RowDefinition Height="30"/>
RowDefinition Height="30"/>
RowDefinition Height="*"/>
/Grid.RowDefinitions>
Label x:Name="myLabel" Grid.Row="0" Foreground="Black" />
Button x:Name="nextButton" Content="Click" Grid.Row="2" Click="nextButton_Click" />
TextBox x:Name="myTextBox" Grid.Row="1" Text="{Binding Path=myTest.Name}"/>
/Grid>
I also added the line myGrid.DataContext = myTest;
to 'public MainWindow()' immediately after I instantiate myTest. When I step through the resulting program, the value of this.PropertyChanged
always evaluates to null
, so that the PropertyChanged even never fires. Sorry in advance for what must be a really noob question.
- Steve
You should only need to implement INotifyPropertyChanged
on the TestSphere class, not DependencyObject. As you update the value, call PropertyChanged(this, new PropertyChangedEventArgs("Name"))
.
Second, you need to set the DataContext for the window in your code-behind. Lets say you used this in your XAML for the root grid element:
<Grid Name="MainForm">
Then in your code-behind, you'd do this:
MainForm.DataContext = this;
Finally, change the myTest property to public
, and the binding in your XAML should then only need to be
Text="{Binding Path=myTest.Name}"
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