在WPF列表视图中显示图像

Question

I want to show an image in my listview but i don't know how i should do this. My Guest class has the method GetGuestImage() it returns me a absolute path. When this file exists is should be loaded and when not a placeholder-image should be loaded.

How can i realize this?

<ListView x:Name="listview">
                    <ListView.View>
                        <GridView>
                            <GridViewColumn DisplayMemberBinding="{Binding GetGuestImage()}" Header="Image" />
                            <GridViewColumn DisplayMemberBinding="{Binding Vorname}" Header="Vorname" />
                            <GridViewColumn DisplayMemberBinding="{Binding Nachname}" Header="Nachname" />
                            <GridViewColumn DisplayMemberBinding="{Binding Postleitzahl}" Header="PLZ" />
                            <GridViewColumn DisplayMemberBinding="{Binding Ort}" Header="Ort" />
                            <GridViewColumn DisplayMemberBinding="{Binding Land}" Header="Land" />
                        </GridView>
                    </ListView.View>
                </ListView>

Answer 1

You could accomplish this with a CellTemplate and a value converter:

<ListView x:Name="listview" xmlns:local="clr-namespace:WpfApplication1">
    <ListView.Resources>
        <local:ImageConverter x:Key="ImageConverter" />
    </ListView.Resources>
    <ListView.View>
        <GridView>
            <GridViewColumn Header="Image">
                <GridViewColumn.CellTemplate>
                    <DataTemplate>
                        <Image Source="{Binding Path=., Converter={StaticResource ImageConverter}}" />
                    </DataTemplate>
                </GridViewColumn.CellTemplate>
            </GridViewColumn>
            <GridViewColumn DisplayMemberBinding="{Binding Vorname}" Header="Vorname" />
            <GridViewColumn DisplayMemberBinding="{Binding Nachname}" Header="Nachname" />
            <GridViewColumn DisplayMemberBinding="{Binding Postleitzahl}" Header="PLZ" />
            <GridViewColumn DisplayMemberBinding="{Binding Ort}" Header="Ort" />
            <GridViewColumn DisplayMemberBinding="{Binding Land}" Header="Land" />
        </GridView>
    </ListView.View>
</ListView>

---

namespace WpfApplication1
{
    public class ImageConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            dynamic dataObject = value;
            if (dataObject != null)
            {
                string path = dataObject.GetGuestImage();
                if(System.IO.File.Exists(path))
                    return new Uri(dataObject.GetGuestImage(), UriKind.RelativeOrAbsolute);
            }

            return new Uri(@"c:\yourplaceholderimage.png", UriKind.RelativeOrAbsolute);
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}

You can't bind directly to the GetGuestImage() method though. Another idea may be to expose the path through a Uri property of your data object class and bind to this one. Then you don't need a converter:

<GridViewColumn Header="Image">
    <GridViewColumn.CellTemplate>
        <DataTemplate>
            <Image Source="{Binding GuestImage}" />
        </DataTemplate>
    </GridViewColumn.CellTemplate>
</GridViewColumn>

---

public class YourDataClass
{
    public Uri GuestImage
    {
        get { return new Uri(@"c:\picture.png", UriKind.RelativeOrAbsolute); }
    }

    //+ the other properties...
}

Answer 2

Use a Converter for that.

public class NullGuestImageToPlaceholderConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value == null || !File.Exists(value as string))
            return placeholderImage;

        return GetImage(value);
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

XAML:

<ListView x:Name="listview">
    <ListView.View>
        <GridView>
            <GridViewColumn DisplayMemberBinding="{Binding GuestImage, Converter={StaticResource nullGuestImageConverter}}" Header="Image" />
            <!-- your other columns -->
        </GridView>
    </ListView.View>
</ListView>

I don't have the GetGuestImage implementation or your full XAML, so that's the most I can do for now.

nullGuestImageConverter should be the x:Key of the converter, defined in your XAML's resources (like <UserControl.Resources> ), and placeholderImage should be the implementation of how you retrieve said placeholder image (which I guess appears in GetGuestImage() ).

In fact, I guess you could simply replace the content of the Convert method by your GetGuestImage one, but I can't know for sure.

Answer 3

First you need to bind to a property not a method second the DisplayMemberBinding only supports basic binding you need to switch to CellTemplate

<ListView x:Name="listview">
    <ListView.View>
        <GridView>
            <GridViewColumn Header="Image" >
               <GridViewColumn.CellTemplate>
                   <DataTemplate>
                       <Image Source="{Binding GuestImageProperty}" />
                   </DataTemplate>
               </GridViewColumn.CellTemplate>
            </GridViewColumn>
            <GridViewColumn DisplayMemberBinding="{Binding Vorname}" Header="Vorname" />
            <GridViewColumn DisplayMemberBinding="{Binding Nachname}" Header="Nachname" />
            <GridViewColumn DisplayMemberBinding="{Binding Postleitzahl}" Header="PLZ" />
            <GridViewColumn DisplayMemberBinding="{Binding Ort}" Header="Ort" />
            <GridViewColumn DisplayMemberBinding="{Binding Land}" Header="Land" />
        </GridView>
    </ListView.View>
</ListView>

then you can use the binding's TargetNullValue and FallbackValue properties to handle missing values