Data Binding doesn't update when TextBox is Empty
I am Binding a TextBox with a property which is of type float. Everything works fine, I change the value in TextBox and it gets updated in property. The problem occurs when I make the TextBox blank, my property doesn't get updated, it is still having old value. Now I need to use converter in my binding to update property with default value in case of blank value from TextBox. I want to know Why this behavior? Is there any other solution to开发者_如何学Python this?
Your property is not updating because it's not possible to convert empty string to float. There are two ways to solve this.
First way is to add a property which type is string, bind the TextBox with it and implement changing of float property. Like this:
public partial class Window1 : Window, INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public Window1()
{
InitializeComponent();
// don't use this as DataContext,
// it's just an example
DataContext = this;
}
private float _FloatProperty;
public float FloatProperty
{
get { return _FloatProperty; }
set
{
_FloatProperty = value;
OnPropertyCahnged("FloatProperty");
}
}
private string _StringProperty;
public string StringProperty
{
get { return _StringProperty; }
set
{
_StringProperty = value;
float newFloatValue;
// I think you want 0 when TextBox is empty, right?
FloatProperty = float.TryParse(_StringProperty, out newFloatValue) ? newFloatValue : 0;
OnPropertyCahnged("StringProperty");
}
}
protected void OnPropertyCahnged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs("StringProperty"));
}
}
}
Second way is to use a converter:
namespace WpfApplication3
{
public partial class Window1 : Window, INotifyPropertyChanged
{
public static readonly IValueConverter TextBoxConverter = new FloatConverter();
/* code from previous example without StringProperty */
}
public class FloatConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return value.ToString();
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
float f;
if (value is string && float.TryParse(value as string, out f))
{
return f;
}
return 0f;
}
}
}
XAML:
<Window x:Class="WpfApplication3.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:WpfApplication3="clr-namespace:WpfApplication3">
<Grid>
<TextBox Text="{Binding FloatProperty, Converter={x:Static WpfApplication3:Window1.TextBoxConverter}}" />
</Grid>
</Window>
There is an article about converters
I prefer the first way with MVVM pattern.
just change the Binding like this
<TextBlock Text={Binding Path=Name, TargetNullValue='',UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}/>
I think the problem would be to what the binding system match an empty TextBox. For you it might be zero but for someone else it might be Single.NegativeInfinity.
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