WPF命令未执行

Question

我的主窗口目前通过DataTemplated YearViewModel在内容控件中显示YearView。当我单击YearView上的月份按钮时，我希望主窗口显示的是MonthView。MainViewModel(未显示的主窗口的视图模型)从'_navigationStorage '中检索要显示的视图模型。CurrentViewModel'，如NavigateMonthCommand.Execute()中所示。但是当我点击月份按钮时，NavigateMonthCommand.Execute()永远不会被调用。

月份按钮绑定不工作吗?在YearView。我是否应该以不同的方式指定数据上下文?

MainWindow.xaml

<Window x:Class="Calandar.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:viewmodels="clr-namespace:Calandar.ViewModels"
xmlns:views="clr-namespace:Calandar.Views"
xmlns:local="clr-namespace:Calandar"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Grid Background="LightSlateGray">

<ContentControl Content="{Binding CurrentViewModel}">
<ContentControl.Resources>
<DataTemplate DataType="{x:Type viewmodels:YearViewModel}">
<views:YearView/>
</DataTemplate>
<DataTemplate DataType="{x:Type viewmodels:MonthViewModel}">
<views:MonthView/>
</DataTemplate>
</ContentControl.Resources>
</ContentControl>
</Grid>
</Window>

YearView.xaml

<UserControl x:Class="Calandar.Views.YearView"
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:local="clr-namespace:Calandar.Views"
xmlns:viewmodels="clr-namespace:Calandar.ViewModels"
mc:Ignorable="d" 
d:DesignHeight="450" d:DesignWidth="800">
<Grid Background="White" DataContext="viewmodels:YearViewModel">
<StackPanel>
<TextBlock Text="Year" FontSize="55"/>
<Button Content="Month" Command="{Binding NavigateMonthCommand}"/>
</StackPanel>
</Grid>
</UserControl>

YearViewModel.cs

public class YearViewModel : ViewModelBase
{
public ICommand NavigateMonthCommand { get; }
public YearViewModel(NavigationStorage navigationStorage)
{
NavigateMonthCommand = new NavigateMonthCommand(navigationStorage);
}
}

NavigateMonthCommand.cs

public class NavigateMonthCommand : CommandBase
{
private readonly NavigationStorage _navigationStorage;
public NavigateMonthCommand(NavigationStorage navigationStorage)
{
_navigationStorage = navigationStorage;
}
public override void Execute(object parameter)
{
;
_navigationStorage.CurrentViewModel = new MonthViewModel();
}
}

CommandBase.cs

public abstract class CommandBase : ICommand
{
public event EventHandler CanExecuteChanged;
public bool CanExecute(object parameter) => true;
public abstract void Execute(object parameter);
public void OnCanExecuteChanged()
{
CanExecuteChanged?.Invoke(this, new EventArgs());
}
}

Answer 1

看这个

没有iNotifyPropertyChanged, Viewmodel无法从视图接口获取数据。你必须正确连接。你应该从INotifyPropertyChanged推导出ViewModelBase。

我想你已经创建了你的BaseViewModel，你可以在那里创建方法。

public event PropertyChangedEventHandler PropertyChanged;         
public void OnPropertyChanged(string PropertyName)         
{             
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(PropertyName));
}

需要在指定的YearViewModel中执行属性设置操作时调用它。示例:

private string surName;
public string SurName
{
get { return surName; }
set { surName = value; OnPropertyChanged(nameof(SurName)); }
}

好运