是否可以根据Silverlight 4中的可绑定属性动态选择要呈现的控件？ [英] Is it possible to dynamically choose which Control to render based on bindable attribute in Silverlight 4?
问题描述
我有一个带有ItemTemplate的ListBox，该列表可渲染具有两列的Grid。第一列是TextBlock，第二列是ComboBox。
I have a ListBox with an ItemTemplate which renders a Grid with two columns. The first column is a TextBlock and the second is a ComboBox.
这个想法是向用户呈现一个问题列表和一个Combo，用户可以从中选择一个回答。使用xaml可以正常工作：
The idea is to present to the user a list of questions and a Combo from which the user can choose an answer. This works ok with this xaml:
<ListBox x:Name="QAListBox" ScrollViewer.VerticalScrollBarVisibility="Auto" SelectedIndex="-1"
ItemsSource="{Binding Questions}" IsTabStop="True" TabIndex="5"
ScrollViewer.HorizontalScrollBarVisibility="Auto" Margin="10" BorderThickness="0">
<ListBox.ItemTemplate>
<DataTemplate>
<Grid d:DesignWidth="931" d:DesignHeight="61" d:IsLocked="True" Margin="0">
<Grid.ColumnDefinitions>
<ColumnDefinition Width=".80*" MinWidth="800"/>
<ColumnDefinition Width=".20*" MinWidth="200"/>
</Grid.ColumnDefinitions>
<TextBlock Text="{Binding Path=QuestionText}" Padding="10" FontSize="21.333" FontWeight="Bold" Margin="0" Grid.Column="0" d:IsLocked="True" />
<ComboBox ItemsSource="{Binding Path=AnswerAlternative}"
SelectedValue="{Binding Path=QuestionsAndAnswers}" SelectedValuePath="AnswerAlternativeId"
FontSize="21.333" FontWeight="Bold" Grid.Column="1" Margin="60,0,0,0" d:IsLocked="True" SelectionChanged="ComboBox_SelectionChanged">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBox Text="{Binding Path=AnswerText, Mode=TwoWay}" BorderThickness="0">
<TextBox.Background>
<SolidColorBrush />
</TextBox.Background>
</TextBox>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
将TextBox放在DataTemplate内的原因（而不是TextBlock），这是我除了允许用户从下拉菜单中进行选择之外，还允许用户输入自由文本的首次尝试。但是，TextBox在ComboBox内部。那不是我想要的。
The reason for putting a TextBox inside the DataTemplate (in stead of TextBlock), is my first attempt on allowing the user to enter free text in addition to choosing from the dropdown. It kind of work, however, the TextBox is inside the ComboBox. That is not what I want.
是否有可能基于某些可绑定属性而不是ComboBox呈现普通文本框？
Is it possible to have a "plain" TextBox render in stead of a ComboBox based upon some bindable attribute?
因此，如果属性InputType == FreeText，则视图将使用TextBox呈现；如果属性为Inputtype == Combo，则将其呈现为上方？
So that if an attribute InputType==FreeText the view is rendered with a TextBox and if the attribute is Inputtype==Combo it is rendered as above?
t。
推荐答案
针对您的特定问题的一种简单解决方案是同时包含这两者，并在其上使用值转换器可见性属性：-
A simplistic solution to your specific problem is to include both and use a value converter on the Visibility property:-
public class EqualityToValueConverter<T> : IValueConverter
{
public T FalseValue { get; set; }
public T TrueValue { get; set; }
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value == null)
return FalseValue;
else
return value.ToString().Equals(parameter) ? TrueValue : FalseValue;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return value != null && value.Equals(TrueValue) ? parameter : null;
}
}
public class EqualityToVisibilityConverter : EqualityToValueConverter<Visibility> { }
然后您的Xaml如下所示： b
Then your Xaml can look like:-
<ListBox x:Name="QAListBox" ScrollViewer.VerticalScrollBarVisibility="Auto" SelectedIndex="-1"
ItemsSource="{Binding Questions}" IsTabStop="True" TabIndex="5"
ScrollViewer.HorizontalScrollBarVisibility="Auto" Margin="10" BorderThickness="0">
<ListBox.Resources>
<local:EqualityToVisibilityConverter x:Key="converter"
TrueValue="Visible" FalseValue="Collapsed" />
</ListBox.Resources>
<ListBox.ItemTemplate>
<DataTemplate>
<Grid d:DesignWidth="931" d:DesignHeight="61" d:IsLocked="True" Margin="0">
<Grid.ColumnDefinitions>
<ColumnDefinition Width=".80*" MinWidth="800"/>
<ColumnDefinition Width=".20*" MinWidth="200"/>
</Grid.ColumnDefinitions>
<TextBlock Text="{Binding Path=QuestionText}" Padding="10" FontSize="21.333" FontWeight="Bold" Margin="0" Grid.Column="0" d:IsLocked="True" />
<ComboBox ItemsSource="{Binding Path=AnswerAlternative}"
SelectedValue="{Binding Path=QuestionsAndAnswers}" SelectedValuePath="AnswerAlternativeId"
FontSize="21.333" FontWeight="Bold" Grid.Column="1" Margin="60,0,0,0" d:IsLocked="True" SelectionChanged="ComboBox_SelectionChanged"
Visibility={Binding InputType, Converter={StaticResource converter}, ConverterParameter=Combo}">
<TextBox Text="{Binding Path=AnswerText, Mode=TwoWay}" Grid.Column="1" Margin="60,0,0,0"
Visibility={Binding InputType, Converter={StaticResource converter}, ConverterParameter=FreeText}">
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
更复杂的解决方案将使用 ListBox 和一个替代或 PrepareContainerForItemOverride 允许分配各种ItemTemplates。但是，我认为这对于解决这个问题可能是过大了。
More sophisticated solutions would use a sub-class of ListBox and an override or PrepareContainerForItemOverride to allow variety of ItemTemplates to be assigned. However I think that would be overkill for this problem.
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