[英]WPF two way mode binding using INotifyPropertyChanged not working
所以我面临一个棘手的问题。 这是我的视图模型:
namespace Market.ViewModel
{
public class BillingViewModel : ViewModelBase
{
#region Private Members
private Customer _customer;
private Product _products;
private string _productId = "asd";
RelayCommand _numClickedCommand;
#endregion
public Customer Customer
{
get { return _customer; }
set
{
_customer = value;
NotifyPropertyChanged("Customer");
}
}
public Product Products
{
get { return _products; }
set
{
_products = value;
NotifyPropertyChanged("Products");
}
}
public bool CanClick
{
get { return true; }
}
public string ProductId
{
get { return _productId; }
set
{
_productId = value;
NotifyPropertyChanged("ProductId");
}
}
public ICommand NumClickedCommand
{
get
{
if (_numClickedCommand == null)
{
_numClickedCommand = new RelayCommand(param => this.NumClicked(param.ToString()),
param => this.CanClick);
}
return _numClickedCommand;
}
}
#region PrivateMethods
private void NumClicked(string numClicked)
{
ProductId = ProductId+numClicked;
}
#endregion
}
}
它继承了实现INotifyPropertyCanged的ViewModelBase。
public class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
我的看法是:
<Window x:Class="Billing.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:controls="clr-namespace:Billing"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:viewModel="clr-namespace:Market.ViewModel;assembly=Market.ViewModel"
xmlns:diag="clr-namespace:System.Diagnostics;assembly=WindowsBase"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<viewModel:BillingViewModel x:Key="ViewModel" />
</Window.Resources>
<Grid DataContext="{Binding Source={StaticResource ViewModel}}">
<controls:NumPad HorizontalAlignment="Left" Margin="265,205,0,-192" VerticalAlignment="Top" Height="307" Width="242"/>
<TextBox HorizontalAlignment="Left" Height="23" Margin="247,29,0,0" TextWrapping="Wrap" Text="{Binding ProductId, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" VerticalAlignment="Top" Width="120"/>
</Grid>
</Window>
在此xaml中使用了NumClickedCommand:
<UserControl x:Class="Billing.NumPad"
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:viewModel="clr-namespace:Market.ViewModel;assembly=Market.ViewModel"
mc:Ignorable="d" Height="109" Width="248">
<UserControl.Resources>
<viewModel:BillingViewModel x:Key="ViewModel"/>
</UserControl.Resources>
<Grid Height="109" VerticalAlignment="Top" DataContext="{Binding Source={StaticResource ViewModel}}">
<Button Content="1" HorizontalAlignment="Left" Margin="10,0,0,0" VerticalAlignment="Top" Width="75" CommandParameter="1" Command="{Binding NumClickedCommand}"/>
<Button Content="2" HorizontalAlignment="Left" Margin="90,0,0,0" VerticalAlignment="Top" Width="75" CommandParameter="2" Command="{Binding NumClickedCommand}"/>
<Button Content="3" HorizontalAlignment="Left" Margin="170,0,0,0" VerticalAlignment="Top" Width="75" CommandParameter="3" Command="{Binding NumClickedCommand}"/>
<Button Content="4" HorizontalAlignment="Left" Margin="10,27,0,0" VerticalAlignment="Top" Width="75" CommandParameter="4" Command="{Binding NumClickedCommand}"/>
<Button Content="5" HorizontalAlignment="Left" Margin="90,27,0,0" VerticalAlignment="Top" Width="75" CommandParameter="5" Command="{Binding NumClickedCommand}"/>
<Button Content="6" HorizontalAlignment="Left" Margin="170,27,0,0" VerticalAlignment="Top" Width="75" RenderTransformOrigin="1.034,2.171" CommandParameter="6" Command="{Binding NumClickedCommand}"/>
<Button Content="7" HorizontalAlignment="Left" Margin="10,54,0,0" VerticalAlignment="Top" Width="75" CommandParameter="7" Command="{Binding NumClickedCommand}"/>
<Button Content="8" HorizontalAlignment="Left" Margin="90,54,0,0" VerticalAlignment="Top" Width="75" CommandParameter="8" Command="{Binding NumClickedCommand}"/>
<Button Content="9" HorizontalAlignment="Left" Margin="170,54,0,0" VerticalAlignment="Top" Width="75" CommandParameter="9" Command="{Binding NumClickedCommand}"/>
<Button Content="0" HorizontalAlignment="Left" Margin="10,81,0,0" VerticalAlignment="Top" Width="75" CommandParameter="0" Command="{Binding NumClickedCommand}"/>
<Button Content="Submit" HorizontalAlignment="Left" Margin="90,81,0,0" VerticalAlignment="Top" Width="155" />
</Grid>
</UserControl>
问题在于,在视图模型中更新ProductId不会反映在视图中。 asd的初始值在应用程序启动时更新。 控件包含实现ICommand接口的按钮集,所有按钮都在viewmodel中调用NumClicked()。 在调试时,如果我单击按钮NumClicked()会被调用,然后ProductId将被更新,NotifyPropertyChanged()也将被调用,但是UI不会更新,它保持不变。 但是,如果我直接更新UI,即我在文本框中输入了一些值,则会发生相同的流程,则调用PropertyChanged(),然后再调用get来更新视图模型中的值。
我已经经历了许多这样的问题,但是无法获得阻止UI更新的确切原因。 感谢您提供任何帮助,并询问是否缺少任何内容。 谢谢。
Grid
和TextBox
DataContext
从Window资源绑定到视图模型实例。
NumPad
控件声明其自己的视图模型实例
NumClickedCommand
处理错误的数据,而不处理显示的对象
确保只有一个视图模型实例
NumPad
继承了DataContext
,不应创建新对象并更改DataContext
<UserControl x:Class="Billing.NumPad"
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:viewModel="clr-namespace:Market.ViewModel;assembly=Market.ViewModel"
mc:Ignorable="d" Height="109" Width="248">
<Grid Height="109" VerticalAlignment="Top">
<!--all Buttons here-->
</Grid>
您将相同的视图模型也作为DataContext传递到numpadUser控件和mainWindow中,因此将创建viewmodel的新实例,因此根据我,您还可以使用Minwindow的GridName在NumPad中使用mainwindow的DataContext,您必须像这样命名网格
<Grid DataContext="{Binding Source={StaticResource ViewModel}}" x:Name="grdNumPad">
这样您就可以在NumPad.XAML中访问该DataContext
<Button Content="1" HorizontalAlignment="Left" Margin="10,0,0,0" VerticalAlignment="Top" Width="75" CommandParameter="1" Command="{Binding DataContext.NumClickedCommand,ElementName=grdNumPad}"/>
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