ContentControl 与 ViewModel （二）

上文说到 可以使用DataTemplateSelector。

其实等于是用 DataTemplateSelector + 动态创建DataTemplate来实现。

using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Markup;

namespace ContentDemo
{
    class ContentDataTemplateSelector : DataTemplateSelector
    {
        //用来标示一下已经创建过的类型
        private readonly static Queue<Type> ViewModelQueue = new Queue<Type>();

        public override DataTemplate SelectTemplate(object item, DependencyObject container)
        {
            do
            {
                if (item == null
                    || item is UIElement)
                {
                    break;
                }

                // item 就是你的ViewModel的类型，在这主要就是找到ViewModel对应的View
                // 好多框架中会在启动时构建自己的Map，来对应ViewModel
                // 比如 Caliburn.Micro 框架中默认 是以名称对应的 XXXViewModel 和 XXXView,来构建Map的
                //      MvvmCross 框架中不仅提供了 名称，还提供了 Attribute的对应方式

                // 在这为了演示方便，我就直接反射对应名称的 View了。

                var viewModelType = item.GetType();

                if (ViewModelQueue.Contains(viewModelType))
                {
                    break;
                }

                var viewModelName = viewModelType.Name;

                string name = null;
                var index = viewModelName.LastIndexOf("ViewModel", StringComparison.OrdinalIgnoreCase);
                if (index > 0)
                {
                    name = viewModelName.Substring(0, index);
                }

                if (string.IsNullOrEmpty(name))
                {
                    break;
                }

                var viewName = string.Format("{0}.{1}{2}", viewModelType.Namespace, name, "View");

                var view = viewModelType.Assembly.GetType(viewName, false, true);

                if (view != null)
                {
                    var dataTemplate = CreateDataTemplate(view, viewModelType);

                    var dtkey = dataTemplate.DataTemplateKey;

                    if (dtkey != null)
                    {
                        Application.Current.Resources.Add(dtkey, dataTemplate);
                        ViewModelQueue.Enqueue(viewModelType);
                    }

                    return dataTemplate;
                }

            } while (false);

            return base.SelectTemplate(item, container);
        }

        /// <summary>
        /// 创建DataTemplate
        /// </summary>
        /// <param name="viewType"></param>
        /// <param name="viewModelType"></param>
        /// <returns></returns>
        private DataTemplate CreateDataTemplate(Type viewType, Type viewModelType)
        {
            const string xamlTemplate = "<DataTemplate DataType=\"{{x:Type vm:{0}}}\"><v:{1} /></DataTemplate>";
            var xaml = String.Format(xamlTemplate, viewModelType.Name, viewType.Name);

            var context = new ParserContext();

            context.XamlTypeMapper = new XamlTypeMapper(new string[0]);
            context.XamlTypeMapper.AddMappingProcessingInstruction("vm", viewModelType.Namespace, viewModelType.Assembly.FullName);
            context.XamlTypeMapper.AddMappingProcessingInstruction("v", viewType.Namespace, viewType.Assembly.FullName);

            context.XmlnsDictionary.Add("", "http://schemas.microsoft.com/winfx/2006/xaml/presentation");
            context.XmlnsDictionary.Add("x", "http://schemas.microsoft.com/winfx/2006/xaml");
            context.XmlnsDictionary.Add("vm", "vm");
            context.XmlnsDictionary.Add("v", "v");

            var template = (DataTemplate)XamlReader.Parse(xaml, context);
            return template;
        }
    }
}

WPF有一个好处就是他的DataType，所以 你也不一定非要在选择器中处理，你可以在任意你想要的时机时，把DataTemplate加到资源里就可以了。

但是WinRT中，的DataTemplate,就没有DataType，就得通过 选择器来，返回对应的DataTemplate.

还有 WinRT中 不支持 ParserContext，就只能拼字符串构造了。

Xaml:

<Window x:Class="ContentDemo.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:ContentDemo"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <local:MainViewModel x:Key="MainViewModel" />
        <!--<DataTemplate DataType="{x:Type local:FirstViewModel}">
            <local:FirstView />
        </DataTemplate>
        <DataTemplate DataType="{x:Type local:SecondViewModel}">
            <local:SecondView />
        </DataTemplate>-->

        <local:ContentDataTemplateSelector x:Key="ContentDataTemplateSelector" />
    </Window.Resources>
    <Grid DataContext="{StaticResource MainViewModel}">
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition />
        </Grid.ColumnDefinitions>
        <ContentControl Grid.ColumnSpan="2" Content="{Binding Path=ViewModel}" ContentTemplateSelector="{StaticResource ContentDataTemplateSelector}" />
        <Button Grid.Row="1" Grid.Column="0" Content="ViewModel  1" Command="{Binding Path=FirstCommand}"/>
        <Button Grid.Row="1" Grid.Column="1" Content="ViewModel  2" Command="{Binding Path=SecondCommand}"/>
    </Grid>
</Window>

其实要是，用了很多的 ContentControl ,每一个 都去绑定 Selector，还是很烦人的一件事。

这时候，我们可以加一个 ContentControl 的 默认样式，让他默认就使用这个Selector.

<Application x:Class="ContentDemo.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:ContentDemo"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <local:ContentDataTemplateSelector x:Key="ContentDataTemplateSelector" />

        <Style TargetType="{x:Type ContentControl}">
            <Setter Property="ContentTemplateSelector"
                    Value="{StaticResource ContentDataTemplateSelector}"/>
        </Style>
    </Application.Resources>
</Application>

<Window x:Class="ContentDemo.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:ContentDemo"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <local:MainViewModel x:Key="MainViewModel" />
        <!--<DataTemplate DataType="{x:Type local:FirstViewModel}">
            <local:FirstView />
        </DataTemplate>
        <DataTemplate DataType="{x:Type local:SecondViewModel}">
            <local:SecondView />
        </DataTemplate>-->

        <!--<local:ContentDataTemplateSelector x:Key="ContentDataTemplateSelector" />-->
    </Window.Resources>
    <Grid DataContext="{StaticResource MainViewModel}">
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition />
        </Grid.ColumnDefinitions>
        <ContentControl Grid.ColumnSpan="2" Content="{Binding Path=ViewModel}" />
        <Button Grid.Row="1" Grid.Column="0" Content="ViewModel  1" Command="{Binding Path=FirstCommand}"/>
        <Button Grid.Row="1" Grid.Column="1" Content="ViewModel  2" Command="{Binding Path=SecondCommand}"/>
    </Grid>
</Window>

源码：Code

转载请注明出处：http://www.cnblogs.com/gaoshang212/p/3961011.html