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[英]MVVMLight Toolkit changes not reflected when property is changed
[英]MVVMLight - UI not updating when property has changed
我正在使用C#和MVVMLight开发小型数据驱动的应用程序,尝试添加/编辑新项目时遇到问题。
基本上,我可以将SelectedMember属性设置为构造函数中数据库中已经存在的Member对象,而不会出现问题:
public MemberDetailViewModel()
{
_context = new DatabaseEntities();
GetMembers(); // This just loads the Member objects into an ObservableCollection.
SelectedMember = _members.FirstOrDefault(); // UI updates as expected.
}
SelectedMember的实现如下:
public Member SelectedMember
{
get { return _selectedMember; }
set { Set(ref _selectedMember, value); }
}
现在这很好,因为当我编辑对象时,所有数据验证都有效。
但是,当我使用以下代码添加新对象时:
private void NewMember()
{
var member = new Member();
SelectedMember = member; // UI doesn't update, is still on previous object.
}
UI不会更新,并且似乎SelectedMember中的Member对象与构造函数中加载的成员对象相同。
此外,当我从构造函数将空对象加载到SelectedMember属性中时,应用程序似乎不知道该对象存在,并且在编辑控件中的值时不会触发任何数据验证例程:
public MemberDetailViewModel()
{
_context = new DatabaseEntities();
SelectedMember = new Member(); // Binding appears to fail, data validation code not firing when control values changed.
}
我究竟做错了什么?
编辑:当视图模型实际被加载时,我只是看了输出,而我已经看到了。
System.Windows.Data Error: 40 : BindingExpression path error: 'Centres' property not found on 'object' ''Member_B31A44ECE333F4E7E07BE25FA5BDC79874BAE6C64589F9765ACA373D89BBBD6B' (HashCode=45485186)'. BindingExpression:Path=Centres; DataItem='Member_B31A44ECE333F4E7E07BE25FA5BDC79874BAE6C64589F9765ACA373D89BBBD6B' (HashCode=45485186); target element is 'ComboBox' (Name=''); target property is 'ItemsSource' (type 'IEnumerable')
System.Windows.Data Warning: 40 : BindingExpression path error: 'SelectedMember' property not found on 'object' ''Member_B31A44ECE333F4E7E07BE25FA5BDC79874BAE6C64589F9765ACA373D89BBBD6B' (HashCode=45485186)'. BindingExpression:Path=SelectedMember.LocalCentre; DataItem='Member_B31A44ECE333F4E7E07BE25FA5BDC79874BAE6C64589F9765ACA373D89BBBD6B' (HashCode=45485186); target element is 'ComboBox' (Name=''); target property is 'SelectedValue' (type 'Object')
我觉得自己做了一些愚蠢的事……但是呢?
编辑2:上述错误已得到解决,但是即使对SelectedMember进行了更改,即使显式调用RaisePropertyChanged,UI也不会更新。
Edit3:希望这是您需要的XAML:
<UserControl x:Class="Project.Views.MemberDetailView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:models="clr-namespace:Project.Client.Models"
mc:Ignorable="d"
d:DesignHeight="600" d:DesignWidth="800">
<UserControl.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/Assets/ResourceDictionaries/DataEntryScreens.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</UserControl.Resources>
<WrapPanel>
<Expander Header="Personal Information">
<StackPanel Orientation="Vertical">
<StackPanel Orientation="Vertical">
<TextBlock Text="Forename:" />
<TextBox Text="{Binding SelectedMember.Forename, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}"/>
</StackPanel>
<!-- Other controls omitted. -->
</Expander>
</WrapPanel>
</UserControl>
<!--MemberDetailView.xaml.cs-->
public partial class MemberDetailView : UserControl
{
public MemberDetailView()
{
InitializeComponent();
this.DataContext = new MemberDetailViewModel();
}
}
我已经解决了这个...
我不确定我做了什么,但是显然在视图的构造函数中设置了ViewModel设法使所有事情搞砸了。
所以从这开始:
public MemberDetailView()
{
InitializeComponent();
this.DataContext = new MemberDetailViewModel() { Header = "Members" };
}
对此:
public MemberDetailView()
{
InitializeComponent();
//this.DataContext = new MemberDetailViewModel() { Header = "Members" };
}
解决了问题。
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