将 ContentControl 绑定到视图模型的视图
本文关键字:视图 模型 ContentControl 绑定 | 更新日期: 2023-09-27 17:56:33
我在Windows Phone 8应用程序中使用MVVM。我想在我的外壳视图模型中从一个视图模型移动到另一个视图模型。我似乎无法让 ContentControl 绑定到视图模型上的用户控件/电话应用程序页面模板。
我错过了什么?
我试图避免像 MVVM 光这样的东西。(我希望我的应用程序尽可能小的下载量)这应该是可以做到的。
附言我对WPF/WP8还很陌生
这是我到目前为止拥有的示例,请原谅愚蠢的功能:)
/**外壳视图 **/
<phone:PhoneApplicationPage
x:Class="PhoneAppWithDataContext.Navigation.ViewModelNavigation"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
FontFamily="{StaticResource PhoneFontFamilyNormal}"
FontSize="{StaticResource PhoneFontSizeNormal}"
Foreground="{StaticResource PhoneForegroundBrush}"
SupportedOrientations="Portrait" Orientation="Portrait"
mc:Ignorable="d"
shell:SystemTray.IsVisible="True"
xmlns:vm="clr-namespace:PhoneAppWithDataContext.Navigation">
<phone:PhoneApplicationPage.DataContext>
<vm:AppViewModel/>
</phone:PhoneApplicationPage.DataContext>
<phone:PhoneApplicationPage.Resources>
<DataTemplate x:Key="MonthViewModel">
<vm:MonthViewControl/>
</DataTemplate>
</phone:PhoneApplicationPage.Resources>
<!--LayoutRoot is the root grid where all page content is placed-->
<Grid x:Name="LayoutRoot" Background="Transparent">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<!--TitlePanel contains the name of the application and page title-->
<StackPanel Grid.Row="0" Margin="12,17,0,28">
<TextBlock Text="MY APPLICATION" Style="{StaticResource PhoneTextNormalStyle}"/>
<TextBlock Text="page name" Margin="9,-7,0,0" Style="{StaticResource PhoneTextTitle1Style}"/>
</StackPanel>
<!--ContentPanel - place additional content here-->
<Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
<ContentControl Content="{Binding CurrentViewModel}"
ContentTemplate="{Binding ContentTemplate}"
HorizontalContentAlignment="Stretch"
VerticalContentAlignment="Stretch"/>
</Grid>
<Button Content="Change VM" Command="{Binding ChangeViewModelCommand}"/>
</Grid>
</phone:PhoneApplicationPage>
/** 外壳/应用程序视图模型 **/
public class AppViewModel : ViewModelBase
{
private ViewModelBase _currentViewModel;
private List<ViewModelBase> _viewModels = new List<ViewModelBase>();
private byte _month = 1;
public ViewModelBase CurrentViewModel
{
get
{
return _currentViewModel;
}
set
{
if (_currentViewModel == value)
return;
_currentViewModel = value;
NotifyPropertyChanged("CurrentViewModel");
}
}
public DataTemplate SelectedTemplate
{
get
{
if (_currentViewModel == null)
return null;
return DataTemplateSelector.GetTemplate(_currentViewModel);
}
}
public List<ViewModelBase> ViewModels
{
get
{
return _viewModels;
}
}
public AppViewModel()
{
ViewModels.Add(new MonthViewModel(_month));
CurrentViewModel = ViewModels.FirstOrDefault();
}
private ICommand _changeViewModelCommand;
public ICommand ChangeViewModelCommand
{
get
{
return _changeViewModelCommand ?? (_changeViewModelCommand = new GenericCommand(() =>
{
_month++;
var newVM = new MonthViewModel(_month);
ViewModels.Add(newVM);
CurrentViewModel = newVM;
}, true));
}
}
private void ChangeViewModel(ViewModelBase viewModel)
{
if (!ViewModels.Contains(viewModel))
ViewModels.Add(viewModel);
CurrentViewModel = ViewModels.FirstOrDefault(vm => vm == viewModel);
}
}
/** 数据模板选择器 **/
public static class DataTemplateSelector
{
public static DataTemplate GetTemplate(ViewModelBase param)
{
Type t = param.GetType();
return App.Current.Resources[t.Name] as DataTemplate;
}
}
/** 用户控制 **/
<UserControl x:Class="PhoneAppWithDataContext.Navigation.MonthViewControl"
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"
mc:Ignorable="d"
FontFamily="{StaticResource PhoneFontFamilyNormal}"
FontSize="{StaticResource PhoneFontSizeNormal}"
Foreground="{StaticResource PhoneForegroundBrush}"
d:DesignHeight="480" d:DesignWidth="480"
xmlns:vm="clr-namespace:PhoneAppWithDataContext.Navigation">
<UserControl.DataContext>
<vm:MonthViewModel/>
</UserControl.DataContext>
<Grid x:Name="LayoutRoot" Background="{StaticResource PhoneChromeBrush}">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="100"/>
<ColumnDefinition Width="Auto"/>
</Grid.ColumnDefinitions>
<TextBlock Text="Id" Width="100" VerticalAlignment="Center" Grid.Row="0" Grid.Column="0" />
<TextBlock Text="{Binding Id}" Width="100" VerticalAlignment="Center" Grid.Row="0" Grid.Column="1" />
<TextBlock Text="Name" Width="100" VerticalAlignment="Center" Grid.Row="1" Grid.Column="0" />
<TextBlock Text="{Binding Name}" Width="100" VerticalAlignment="Center" Grid.Row="1" Grid.Column="1" />
</Grid>
</UserControl>
/** 视图模型库 **/
public abstract class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void NotifyPropertyChanged(String propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
/** 用户控件应绑定到的视图模型 **/
public sealed class MonthViewModel : ViewModelBase
{
private byte _id;
private string _name;
public MonthViewModel()
{
}
public MonthViewModel(byte id)
{
_id = id;
_name = "Month " + id.ToString() + " of the year";
}
public override string ToString()
{
return _name;
}
public byte Id
{
get
{
return _id;
}
}
public string Name
{
get
{
return _name;
}
}
}
这里的问题是:
<UserControl.DataContext>
<vm:MonthViewModel/>
</UserControl.DataContext>
当您的Content
从一个MonthViewModel
更改为下一个时,返回的数据模板的数据上下文将设置为绑定到Content
的对象。 好吧,一旦设置了 DataContext,您应该就可以开始了,但是一旦加载了 UserControl,它就会将 DataContext 重置为空 MonthViewModel (vm:MonthViewModel
) 的新 instace。 摆脱显式的 DataContext 声明 - 换句话说,删除我上面发布的代码。
这样,当您首次调用 CurrentViewModel 并引发 INPC 时,它不会重置 DataContext。 当您在 MonthViewModel 类型的 CurrentViewModel 之间切换时,您的 UserControl 不会再次调用 InitializeComponent,而是 DataContext 将更改。
编辑
此外,如果您仍然没有看到变化,那么我会指出SelectedTemplate
属性。 只需将 null 传递给GetTemplate
,而不是属性中的 null 检查。 在 GetTemplate
内部,检查 null 并在那里返回 null,如果它是 null。