我正在尝试创建自定义Tag Cloud控件。它应该工作的方式是用户可以在itemsSource中为它提供一组字符串,转换后的字符串将显示在UI中。问题是当我尝试将控件放入应用程序时,我收到以下错误:“无法创建TagCloudControl类型的实例”。有人可以帮忙吗?
代码
public class TagCloudControl : ListBox
{
static TagCloudControl()
{
DefaultStyleKeyProperty.OverrideMetadata(typeof(TagCloudControl), new FrameworkPropertyMetadata
(typeof(TagCloudControl)));
}
//tags dependency property
public static DependencyProperty TagsProperty = DependencyProperty.Register("Tags",
typeof(IEnumerable<Tag>),
typeof(TagCloudControl));
public CollectionView GroupedTagsView { get; set; }
public TagCloudControl()
{
ItemsSource = Tags;
//group my tags by "name" property
GroupedTagsView = (ListCollectionView)CollectionViewSource.GetDefaultView(Tags);
GroupedTagsView.GroupDescriptions.Add(new PropertyGroupDescription("Name"));
}
public IEnumerable<Tag> Tags
{
get { return (IEnumerable<Tag>)GetValue(TagsProperty); }
set { SetValue(TagsProperty, value); }
}
}
XAML
<Window x:Class="TagCloudDemo.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:src="clr-namespace:TagCloudControlLibrary;assembly=TagCloudControlLibrary"
Title="Window1" Height="300" Width="300">
<Grid>
<src:TagCloudControl HorizontalAlignment="Center" VerticalAlignment="Center" Name="firstTag"/>
</Grid>
</Window>
TagControl xaml
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:TagCloudControlLibrary">
<local:CountToBrushConverter x:Key="CountToBrushConverter"/>
<local:CountToFontSizeConverter x:Key="CountToFontSizeConverter"/>
<Style TargetType="{x:Type local:TagCloudControl}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type local:TagCloudControl}">
<Grid>
<WrapPanel Orientation="Horizontal"
Margin="2"
IsItemsHost="True">
</WrapPanel>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<DataTemplate x:Key="TagsTemplate">
<WrapPanel>
<TextBlock Text="{Binding Name}"
FontSize="{Binding ItemCount, Converter={StaticResource CountToBrushConverter}}"
Foreground="{Binding ItemCount, Converter={StaticResource CountToFontSizeConverter}}"/>
</WrapPanel>
</DataTemplate>
</ResourceDictionary>
标记类
public class Tag
{
public Tag(string name)
{
Name = name;
}
public string Name { get; set;}
}
答案 0 :(得分:0)
您是否需要实例化标签?
我猜它是一个空引用异常,你在构造函数中将你的项目源设置为标签,但你还没有实例化标签。
public TagCloudControl()
{
Tags = new ObservableCollection<Tags>();
ItemsSource = Tags;
...
}
编辑:
在玩代码之后......我认为标签可能不需要是DependencyProperty。看来你想将ItemsSource绑定到Tags ...但是你可以只使Tags成为一个简单的属性,并在其中将ItemsSource设置为传入的值:
public TagCloudControl()
{
//this is now empty.
}
public IEnumerable<Tag> Tags
{
get { return (this.ItemsSource as IEnumerable<Tag>); }
set { this.ItemsSource = value; }
}
另外我认为你的风格可能想要更像这样:
<Style TargetType="{x:Type local:TagCloudControl}">
<Setter Property="ItemTemplate">
<Setter.Value>
<DataTemplate DataType="{x:Type local:Tag}">
<TextBlock Text="{Binding Name}"
FontSize="{Binding ItemCount, Converter={StaticResource CountToBrushConverter}}"
Foreground="{Binding ItemCount, Converter={StaticResource CountToFontSizeConverter}}">
</DataTemplate>
</Setter.Value>
</Setter>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type local:TagCloudControl}">
<Grid>
<WrapPanel Orientation="Horizontal" Margin="2" IsItemsHost="True">
</WrapPanel>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
最后,我认为您可能在“标签”类中缺少ItemCount。