我有以下设置:
XAML:
<ListBox x:Name="MyList" ItemsSource="{Binding MyItems}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<Image Height="20" Width="20" Visibility="{Binding HasInformation, Converter={StaticResource VC}, ConverterParameter=True}" Source="/path/to/information.png" />
<TextBlock Text="{Binding Name}" VerticalAlignment="Center" Padding="5,0" />
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
注意:传入的ConverterParameter只是控制可见性是“折叠”(False
)还是“隐藏”(True
),所以在这种情况下,我想要可见性为Hidden
。
ViewModel代码段
private ObservableCollection<IItem> _MyItems;
public ObservableCollection<IItem> MyItems
{
get
{
return _MyItems;
}
set
{
NotifyPropertyChanged(ref _MyItems, value, "MyItems");
}
}
private IItem _SelectedItem;
public IItem SelectedItem
{
get
{
return _SelectedItem;
}
set
{
NotifyPropertyChanged(ref _SelectedItem, value, "SelectedItem");
}
}
的iItem:
public interface IItem
{
string Name { get; }
bool HasInformation { get; set; }
}
我将数据库中IItem
列表的实现填充到列表中,如果HasInformation
为真,则信息图标会正确显示。一切正常。
但是,如果我手动设置HasInformation
,则视图不会更新。我试过了:
在ViewModel中:
OnPropertyChanged("MyItems");
MyItems[MyItems.IndexOf(SelectedItem)].HasInformation = true;
// Note that "SelectedItem" is persisted correctly, and always
// points to the selected item that we want to update.
在背后的代码中:
MyList.GetBindingExpression(ItemsControl.ItemsSourceProperty).UpdateTarget();
所有这些都会触发MyItems
属性的getter,但视图永远不会更新,图标也不会显示。我已确保项目的HasInformation
属性事实上,我更新的确是true
。我已经附加了PropertyChanged
事件,以确保它为"MyItems"
触发属性更改(它也会触发getter),我甚至确保它正在调用值转换器HasInformation
属性的正确值(它是!),所以我错过了什么?图像显示/隐藏或可见性值转换是否有些奇怪我无法正确处理?
答案 0 :(得分:4)
ObservableCollection仅通知集合更改而不是每个项目中的更改。为了实现您的目标,其中一个选项是将IItem从接口更改为实现INotifyPropertyChanged接口的类(或在IItem具体类型中实现它),并将其与ViewModel的PropertyChanged委托挂钩(记得取消订阅)它)。请参阅下面的一些代码。
<强>视图模型强>
public class MyViewModel: INotifyPropertyChanged
{
private ObservableCollection<Item> _MyItems;
public ObservableCollection<Item> MyItems
{
get
{
return _MyItems;
}
set
{
if (_MyItems != null)
{
foreach (var item in _MyItems)
{
item.PropertyChanged -= PropertyChanged;
}
}
if (value != null)
{
foreach (var item in value)
{
item.PropertyChanged += PropertyChanged;
}
}
OnPropertyChanged();
}
}
private Item _SelectedItem;
public Item SelectedItem
{
get
{
return _SelectedItem;
}
set
{
_SelectedItem = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}
<强>物品强>
public class Item : INotifyPropertyChanged
{
private string _name;
private bool _hasInformation;
public string Name
{
get { return _name; }
set
{
_name = value;
OnPropertyChanged();
}
}
public bool HasInformation
{
get { return _hasInformation; }
set
{
_hasInformation = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
var handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}