我目前正在开发WPF(Surface 2.0)并在我的应用程序的大多数部分使用MVVM模式。不幸的是,我目前面临一个相当复杂的问题,我希望你们能帮助我:
我有一个View和一个属于它的ViewModel。 View包含对ViewModel中属性的双向绑定:
<pb:PivotBar ItemsSource="{Binding PivotBarEntries}"
SelectedItemIndex="{Binding SelectedPivotItemIndex, Mode=TwoWay}" />
(...)
<local:SomeOtherView />
首次加载View时,会调用SelectedPivotItemIndex的setter。这很好,除了在加载视图的其余部分之前调用setter。由于setter将消息(通过MVVMLight的Messenger)发送到稍后在视图中创建的其他视图模型,这是一个问题 - 这些消息永远不会到达目的地,因为到目前为止还没有为它们注册接收器。
public int SelectedPivotItemIndex
{
get
{
return this.selectedPivotItemIndex;
}
set
{
if (value != this.selectedPivotItemIndex)
{
this.selectedPivotItemIndex = value;
this.ReportPropertyChanged("SelectedPivotItemIndex");
(...)
ChangeSomeOtherViewModelProperty msg = new ChangeSomeOtherViewModelProperty { Property = newValueCalculatedBefore };
Messenger.Default.Send<ChangeSomeOtherViewModelProperty>(msg);
}
}
}
我现在能想到的唯一解决方案是在ViewModel中创建一个LoadedEventHandler并再次调用SelectedPivotItemIndex setter 。我不喜欢那样,但是:
有没有解决这个问题的方法比手动调用setter更好?
答案 0 :(得分:2)
我首先没有viewmodel的教程,但我确信那里有很多例子。首先是viewmodel,然后先让viewmodel实例,然后让wpf创建视图(通过datatemplate)。
假设您的主视图应显示您的PivotBarEntries视图。所以你现在要做的是在你的mainviewmodel(DI,MEF,new()中创建一个pivotbarviewmodel)。您的mainviewmodel将pivotvw公开为属性,并将其绑定到主视图中的ContentPresenter.Content。至少你必须为pivotvw DataType创建一个DataTemplate。
<DataTemplate DataType="{x:Type local:PivotViewModel>
<view:MyPivotView/>
</DataTemplate>
首先关于viewmodel,你不再依赖于视图上的加载事件,因为你的vm是先创建的。
当然,对于您的具体问题,您必须确保应该创建收听您的信使的所有组件(VM)
你的xaml
<ContentPresenter Content="{Binding MyPivotDataVM}" />
<ContentPresenter Content="{Binding MySomeOtherStuffVM}" />
而不是先查看
<pb:PivotBar ItemsSource="{Binding PivotBarEntries}"
SelectedItemIndex="{Binding SelectedPivotItemIndex, Mode=TwoWay}" />
(...)
<local:SomeOtherView />
编辑:首先是一个非常简单的viewmodel示例。 ps:我使用DI和MEF来创建我的对象路径。
的App.xaml
<Application x:Class="WpfViewModelFirst.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:WpfViewModelFirst="clr-namespace:WpfViewModelFirst">
<!--StartUp Uri is removed-->
<Application.Resources>
<!--comment these datatemplates and see what happens-->
<DataTemplate DataType="{x:Type WpfViewModelFirst:PivotViewModel}">
<WpfViewModelFirst:PivotView/>
</DataTemplate>
<DataTemplate DataType="{x:Type WpfViewModelFirst:OtherViewModel}">
<WpfViewModelFirst:OtherView/>
</DataTemplate>
<DataTemplate DataType="{x:Type WpfViewModelFirst:OtherChildViewModel}">
<WpfViewModelFirst:OtherChildView/>
</DataTemplate>
</Application.Resources>
</Application>
app.xaml.cs
public partial class App : Application
{
protected override void OnStartup(StartupEventArgs e)
{
//to be fair, sometimes i create the ApplicationRoot(JUST MainWindow with view first, and just the rest with viewmodel first.)
var mainvm = new MainViewModel();
var mainview = new MainWindow {DataContext = mainvm};
this.MainWindow = mainview;
this.MainWindow.Show();
}
}
mainview.xaml
<Window x:Class="WpfViewModelFirst.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="auto" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<TextBlock Text="{Binding MyProp}" Grid.ColumnSpan="2" Grid.Row="0"/>
<ContentPresenter Content="{Binding MyPivot}" Grid.Row="1" Grid.Column="0" />
<ContentPresenter Content="{Binding MyOther}" Grid.Row="1" Grid.Column="1" />
</Grid>
</Window>
mainviewmodel.cs
public class MainViewModel
{
public string MyProp { get; set; }
public PivotViewModel MyPivot { get; set; }
public OtherViewModel MyOther { get; set; }
public MainViewModel()
{
this.MyProp = "Main VM";
this.MyPivot = new PivotViewModel();
this.MyOther = new OtherViewModel();
}
}
PivotViewmodel
public class PivotViewModel
{
public string MyProp { get; set; }
public ObservableCollection<string> MyList { get; set; }
public PivotViewModel()//Dependency here with constructor injection
{
this.MyProp = "Test";
this.MyList = new ObservableCollection<string>(){"Test1", "Test2"};
}
}
OtherViewmodel
public class OtherViewModel
{
public string MyProp { get; set; }
public OtherChildViewModel MyChild { get; set; }
public OtherViewModel()
{
this.MyProp = "Other Viewmodel here";
this.MyChild = new OtherChildViewModel();
}
}
OtherChildViewmodel
public class OtherChildViewModel
{
public string MyProp { get; set; }
public OtherChildViewModel()//Dependency here with constructor injection
{
this.MyProp = "Other Child Viewmodel";
}
}
枢纽分析查看
<UserControl x:Class="WpfViewModelFirst.PivotView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="auto" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<TextBlock Text="{Binding MyProp}" Grid.Row="0"/>
<ListBox ItemsSource="{Binding MyList}" Grid.Row="1"/>
</Grid>
</UserControl>
奥瑟维尤
<UserControl x:Class="WpfViewModelFirst.OtherView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Grid>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<TextBlock Text="{Binding MyProp}" Grid.Row="0" />
<ContentPresenter Content="{Binding MyChild}" Grid.Row="1"/>
</Grid>
</UserControl>
OtherChildView
<UserControl x:Class="WpfViewModelFirst.OtherChildView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Grid>
<TextBlock Text="{Binding MyProp}" />
</Grid>
</UserControl>