WPF绑定与int类型的属性无法正常工作

Question

I am having a property of int type in my view model which is bound to a TextBox . Everything works properly, TwoWay binding works fine except in one case -

If I clear the value of TextBox , property setter doesn't gets called and although value is cleared in TextBox , property still holds the previous value.

has anyone faced similar issue? is there any workaround for this?

Here is the property -

public int MaxOccurrences
{
    get
    {
        return this.maxOccurrences;
    }
    set
    {
        if (this.maxOccurrences != value)
        {
            this.maxOccurrences = value;
            base.RaisePropertyChanged("MaxOccurrences");
        }
    }
}

Here is how I am binding the property in xaml -

<TextBox Text="{Binding Path=MaxOccurrences, Mode=TwoWay, 
    NotifyOnSourceUpdated=True, UpdateSourceTrigger=PropertyChanged}" 
    HorizontalAlignment="Center" Width="30" Margin="0,0,5,0"/>

Answer 1

I had the similar problem.

You just need to update the code as:

<TextBox Text="{Binding Path=MaxOccurrences, Mode=TwoWay, TargetNullValue={x:Static sys:String.Empty},
NotifyOnSourceUpdated=True,  UpdateSourceTrigger=PropertyChanged}"  
HorizontalAlignment="Center" Width="30" Margin="0,0,5,0"/> 

Answer 2

This is partially a guess (I haven't got VS handy right now to try it out), but I think it's because a cleared text box is an empty string ( "" ), which can't be implicitly converted to an int . You should probably implemented a type converter to provide the conversion for you. (you probably want to do something like convert "" to 0)

Answer 3

If you don't want to use a Nullable integer , you can use a converter that converts the empty string to 0, see the code below:

public class EmptyStringToZeroConverter : IValueConverter
{
    #region IValueConverter Members

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value == null || string.IsNullOrEmpty(value.ToString())
            ? 0
            : value;
    }

    #endregion
}

Answer 4

Akjoshi, I have a working solution!

You need to change your integer property to Naullable<int> (ie int? ), see the following snippet:

private int? _maxOccurrences;
public int? MaxOccurrences
{
    get { return _maxOccurrences; }
    set { _maxOccurrences = value; }
}

You also need to add a value converter to convert the empty string to null value, see the following code snippet:

public class EmptyStringToNullConverter : IValueConverter
{
    #region IValueConverter Members

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value == null || string.IsNullOrEmpty(value.ToString())
            ? null
            : value;
    }

    #endregion
}

The XAML code:

<Window x:Class="ProgGridSelection.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:System="clr-namespace:System;assembly=mscorlib" 
    xmlns:local="clr-namespace:ProgGridSelection"
    Title="MainWindow"
    Height="136" Width="525"
    Loaded="OnWindowLoaded">
<Window.Resources>
    <local:EmptyStringToNullConverter x:Key="EmptyStringToNullConverter"/>
</Window.Resources>
<StackPanel>
    <Button Content="Using Empty String to Null Converter"/>
    <TextBox Name="empNameTextBox"
             Text="{Binding Mode=TwoWay, Path=MaxOccurrences,
                RelativeSource={RelativeSource FindAncestor, AncestorType=Window},
                Converter={StaticResource EmptyStringToNullConverter}}"/>
</StackPanel>

[Note: this is just a proof of concept, and for the sake of simplicity I didn't use any patterns or best practices]

Answer 5

It's because an int value can't be null . It's best to use a string property that converts the value for you within your code to the required int property field.

That way you can perform a

if(string.IsNullOrEmpty(text))
{
  this.intValue = 0;
}

Answer 6

I have the same problem, but I need to handle and not numeric value to. I use the following converter for this:

public class StringFormatToIntConverter : IValueConverter
{            
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
          return value.ToString();
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
       if(value is string)
       {
           var inttext = 
            System.Text.RegularExpressions.Regex.Replace((string)value, "[^.0-9]", "");

           int number;
           return Int32.TryParse(inttext, out  number) ? number : 0;
       }
       else
       {
           return value;
       }
    }
}