[英]WPF two way mode binding using INotifyPropertyChanged not working
所以我面臨一個棘手的問題。 這是我的視圖模型:
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
}
}
它繼承了實現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>
問題在於,在視圖模型中更新ProductId不會反映在視圖中。 asd的初始值在應用程序啟動時更新。 控件包含實現ICommand接口的按鈕集,所有按鈕都在viewmodel中調用NumClicked()。 在調試時,如果我單擊按鈕NumClicked()會被調用,然后ProductId將被更新,NotifyPropertyChanged()也將被調用,但是UI不會更新,它保持不變。 但是,如果我直接更新UI,即我在文本框中輸入了一些值,則會發生相同的流程,則調用PropertyChanged(),然后再調用get來更新視圖模型中的值。
我已經經歷了許多這樣的問題,但是無法獲得阻止UI更新的確切原因。 感謝您提供任何幫助,並詢問是否缺少任何內容。 謝謝。
Grid
和TextBox
DataContext
從Window資源綁定到視圖模型實例。
NumPad
控件聲明其自己的視圖模型實例
NumClickedCommand
處理錯誤的數據,而不處理顯示的對象
確保只有一個視圖模型實例
NumPad
繼承了DataContext
,不應創建新對象並更改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>
您將相同的視圖模型也作為DataContext傳遞到numpadUser控件和mainWindow中,因此將創建viewmodel的新實例,因此根據我,您還可以使用Minwindow的GridName在NumPad中使用mainwindow的DataContext,您必須像這樣命名網格
<Grid DataContext="{Binding Source={StaticResource ViewModel}}" x:Name="grdNumPad">
這樣您就可以在NumPad.XAML中訪問該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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