How to use IDataErrorInfo.Error in a WPF program?

Question

I have an object like that:

public class Person : IDataErrorInfo
{
    public string PersonName{get;set;}
    public int Age{get;set;}

    string IDataErrorInfo.this[string propertyName]
    {
        get
        {
            if(propertyName=="PersonName")
            {
                if(PersonName.Length>30 || PersonName.Length<1)
                {
                    return "Name is required and less than 30 characters.";
                }
            }
            return null;
        }
    }

    string IDataErrorInfo.Error
    {
        get
        {
            if(PersonName=="Tom" && Age!=30)
            {
                return "Tom must be 30.";
            }
            return null;
        }
    }
}

Binding the PersonName and Age properties is easy:

<TextBox Text="{Binding PersonName, ValidatesOnDataErrors=True}" />
<TextBox Text="{Binding Age, ValidatesOnDataErrors=True}" />

However, how can I use the Error property and show it appropriately?

I finally found a workaround and I made a post [here](http://www.cnblogs.com/guogangj/archive/2013/01/03/2843495.html). — guogangj, Jan 03 '13 at 15:31
The Error property is not really used in WPF. You could even throw a NotImplementedException in there. IDataErrorInfo was used by WPF "because it was already there", but only for the this[] part. Not the prettiest corner of WPF, I think. — Robin, Apr 17 '15 at 14:03
@Robin, you could post an answer to this question. It's been like 3-4 years and there's no accepted answer ;) — Jeff B, Aug 11 '16 at 21:44

score 9 · Answer 1 · answered Dec 24 '12 at 16:29

You should modify the TextBox style so it shows what's wrong with the property. Here is a simple example that shows the error as tooltip:

<Style TargetType="TextBox">
        <Style.Triggers>
            <Trigger Property="Validation.HasError" Value="true">
                <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self},
                        Path=(Validation.Errors).CurrentItem.ErrorContent}" />
            </Trigger>
        </Style.Triggers>
</Style>

Just put it inside Application.Resources from your app.xaml file and it will be aplied for every textbox of your application:

<Application.Resources>
    <Style TargetType="TextBox">
            <Style.Triggers>
                <Trigger Property="Validation.HasError" Value="true">
                    <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self},
                            Path=(Validation.Errors).CurrentItem.ErrorContent}" />
                </Trigger>
            </Style.Triggers>
    </Style>
</Application.Resources>

score 7 · Answer 2 · edited May 23 '17 at 12:10

7

Here is an example, adapted from this question, that shows how to display the error in Tooltip:

<TextBox>
    <TextBox.Style>
        <Style TargetType="{x:Type TextBox}">
            <Style.Triggers>
                <Trigger Property="Validation.HasError" Value="true">
                    <Setter Property="ToolTip"
                Value="{Binding RelativeSource={RelativeSource Self}, 
                       Path=(Validation.Errors)[0].ErrorContent}"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    </TextBox.Style>
</TextBox>

edited May 23 '17 at 12:10

Community

1
1

answered Dec 24 '12 at 16:29

CodeNaked

40,753
6
122
148

Hi, I set a break point at IDataErrorInfo.Error.get, but It is never triggered. What's the matter? – guogangj Dec 25 '12 at 00:52
1

@jgg - The `Error` get probably won't get called in this case. The `IDataErrorInfo.this` get would, and would be passed `"PersonName"` and `"Age"`. So you would need to handle both properties, but right now you only handle the former. – CodeNaked Dec 26 '12 at 13:41

How to use IDataErrorInfo.Error in a WPF program?

2 Answers2

Linked