使用mvvmlight for win8 让GridViewItem项 实现动态命令导航

前言：

该技术前提是 已经掌握一定程度的mvvmlight for win8 技巧

实现思路：

通过Messenger 机制 动态发送导航参数 到 需要导航的page 完成导航

导航参数：

public class NavigateParameter
{
private string pageType;

public string PageType
{
get { return pageType; }
set { pageType = value; }
}

private object parameter;

public object Parameter
{
get { return parameter; }
set { parameter = value; }
}
}

在 OnNavigated 到首页的地方 加入以下方法 注册 该处理通道

protected override void OnNavigatedTo(NavigationEventArgs e)
{
base.OnNavigatedTo(e);
this.prContent.IsIndeterminate = true;
this.ContentFrame.Navigate(typeof(MainPage));
this.TopFrame.Navigate(typeof(VideosPage));

#region Messengers  消息处理中心
Messenger.Default.Register<NavigateParameter>(this, "MenuNavigate", async s =>
{
var type = await Task.Run<Type>(() =>
{
var fullName = "IntTourism.View." + s.PageType;
return Type.GetType(fullName);
});
if (null != s.Parameter)
await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.High, () =>
this.ContentFrame.Navigate(type, s.Parameter));
else
await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.High, () =>
this.ContentFrame.Navigate(type));
});

Messenger.Default.Register<NavigateParameter>(this, "TopFrameNavigate", async s =>
{
var type = await Task.Run<Type>(() =>
{
var fullName = "IntTourism.View." + s.PageType;
return Type.GetType(fullName);
});
await this.Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.High, () =>
{
if (!TopFrame.CurrentSourcePageType.Equals(type))
if (null != s.Parameter)
this.TopFrame.Navigate(type, s.Parameter);
else
this.TopFrame.Navigate(type);
});
});

#endregion
}

Unloaded 注销

private void LayoutAwarePage_Unloaded(object sender, RoutedEventArgs e)
{
Messenger.Default.Unregister<NavigateParameter>(this, "MenuNavigate");
Messenger.Default.Unregister<LogBean>(this, "LogError");
Messenger.Default.Unregister<LogBean>(this, "TopBusy");
Messenger.Default.Unregister<LogBean>(this, "ContentBusy");
Messenger.Default.Unregister<LogBean>(this, "TopFrame");
this.btnCancel.PointerPressed -= SendError;
this.btnSend.PointerPressed -= SendError;
}

以下为xaml 里 gridview 菜单的binding方式

注意：ItemClick 此处通过eventTocommand 将事件与 viewmodel中相应的命令进行了binding处理 请结合我上一篇文章 对EventTocomand这一概念进行理解

<common:LayoutAwarePage x:Class="IntTourism.MainPage"
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:i="using:IntTourism.Com.Transvalue.Tools"
xmlns:ignore="http://www.ignore.com"
xmlns:common="using:IntTourism.Common"
xmlns:cmd="using:IntTourism"
mc:Ignorable="d ignore"
d:DesignHeight="1080"
d:DesignWidth="1080"
DataContext="{Binding Main, Source={StaticResource Locator}}"
NavigationCacheMode="Required">
<Viewbox>
<Grid Width="1080" Height="1080" x:Name="root">
<GridView HorizontalAlignment="Left"
VerticalAlignment="Top"
Width="1080"
Height="1080"
CanDragItems="false"
IsRightTapEnabled="False"
ScrollViewer.HorizontalScrollBarVisibility="Hidden"
IsSwipeEnabled="False"
x:Name="gv"
ItemsSource="{Binding MenuItems}"
SelectionMode="None"
>
<GridView.Transitions>
<TransitionCollection>
<EntranceThemeTransition/>
</TransitionCollection>
</GridView.Transitions>
<GridView.ItemContainerTransitions>
<TransitionCollection>
<EntranceThemeTransition/>
</TransitionCollection>
</GridView.ItemContainerTransitions>
<GridView.HeaderTransitions>
<TransitionCollection>
<EntranceThemeTransition/>
</TransitionCollection>
</GridView.HeaderTransitions>
<GridView.ItemTemplate>
<DataTemplate>
<GridViewItem>
<Image Height="280" Width="280" Source="{Binding IconUrl}"/>
<i:EventToCommandCollection.Items>
<i:EventToCommand Command="{Binding MenuCMD}"
CommandParameter="{Binding NavigateParameter}"
NavigateUrl="{Binding NavigateUrl}"
Event="ItemClick"/>
</i:EventToCommandCollection.Items>
</GridViewItem>
</DataTemplate>
</GridView.ItemTemplate>
<GridView.ItemsPanel>
<ItemsPanelTemplate>
<VariableSizedWrapGrid Orientation="Vertical" Margin="0,0,80,0"
ItemWidth="300" ItemHeight="300" MaximumRowsOrColumns="10"/>
</ItemsPanelTemplate>
</GridView.ItemsPanel>
</GridView>
</Grid>
</Viewbox>

</common:LayoutAwarePage>

下面这一段是ViewModel中对命令的处理，以及菜单的动态加载

using GalaSoft.MvvmLight;

using IntTourism.Com.Transvalue.Service;
using GalaSoft.MvvmLight.Command;
using System.Diagnostics;
using Windows.UI.Xaml.Controls;
using System.Collections;
using System.Collections.ObjectModel;
using IntTourism.Com.Transvalue.Model;
using GalaSoft.MvvmLight.Messaging;
using System;
using System.ComponentModel;
using System.Collections.Generic;
using IntTourism.Com.Transvalue.Bean;
using IntTourism.Com.Transvalue.Tools;
using IntTourism.Com.Transvalue.Const;
using System.Threading.Tasks;

namespace IntTourism.ViewModel
{
/// <summary>
/// This class contains properties that the main View can data bind to.
/// <para>
/// See http://www.galasoft.ch/mvvm /// </para>
/// </summary>
public class MainViewModel : ViewModelBase
{
private readonly IMainPageSerivce _dataService;

#region Command
private RelayCommand<ExCommandParameter> _menuCMD;

/// <summary>
/// Gets the MenuCMD.
/// </summary>
public RelayCommand<ExCommandParameter> MenuCMD
{
get
{
return _menuCMD ?? (_menuCMD = new RelayCommand<ExCommandParameter>(
ExecuteMenuCMD,
CanExecuteMenuCMD));
}
}

private async void ExecuteMenuCMD(ExCommandParameter url)
{
await Task.Run(() =>
{
var nav = new NavigateParameter();
nav.Parameter = url.Parameter;
nav.PageType = url.NavigateUrl;
if (null != url.NavigateUrl)
{
Messenger.Default.Send<bool>(true, "ContentBusy");
Messenger.Default.Send<NavigateParameter>(nav, "MenuNavigate");
}
});
}

private bool CanExecuteMenuCMD(ExCommandParameter url)
{
if (null != url && !"".Equals(url))
return true;
else return false;
}
#endregion

#region DataProperties

#region MenuItems
/// <summary>
/// The <see cref="MenuItems" /> property's name.
/// </summary>
public const string MenuItemsPropertyName = "MenuItems";

private ObservableCollection<MenuItem> _menuItems;

/// <summary>
/// Sets and gets the MenuItems property.
/// Changes to that property's value raise the PropertyChanged event.
/// This property's value is broadcasted by the MessengerInstance when it changes.
/// </summary>
public ObservableCollection<MenuItem> MenuItems
{
get
{
return _menuItems;
}

set
{
if (_menuItems == value)
{
return;
}

RaisePropertyChanging(() => MenuItems);
var oldValue = _menuItems;
_menuItems = value;
RaisePropertyChanged(() => MenuItems, oldValue, value, true);
}
}
#endregion

/// <summary>
/// The <see cref="WelcomeTitle" /> property's name.
/// </summary>
public const string WelcomeTitlePropertyName = "WelcomeTitle";

private string _welcomeTitle;

/// <summary>
/// Sets and gets the WelcomeTitle property.
/// Changes to that property's value raise the PropertyChanged event.
/// This property's value is broadcasted by the MessengerInstance when it changes.
/// </summary>
public string WelcomeTitle
{
get
{
return _welcomeTitle;
}

set
{
if (_welcomeTitle == value)
{
return;
}

RaisePropertyChanging(WelcomeTitlePropertyName);
var oldValue = _welcomeTitle;
_welcomeTitle = value;
RaisePropertyChanged(WelcomeTitlePropertyName, oldValue, value, true);
}
}
#endregion

/// <summary>
/// Initializes a new instance of the MainViewModel class.
/// </summary>
public MainViewModel(IMainPageSerivce dataService)
{
_dataService = dataService;
InitPropertyChanged();
_dataService.GetItemData(
async (items, error) =>
{
if (await Pollute.ReportError(error, "GetItemData", ErrorDesc._E01))
{
Messenger.Default.Send<bool>(false, "ContentBusy");
return;
}
var data = await items;
foreach (var item in data)
item.MenuCMD = MenuCMD;
MenuItems = data;
Messenger.Default.Send<bool>(false, "ContentBusy");
});
}

#region PropertyChangeMethods

/// <summary>
/// 初始化相关方法
/// </summary>
private void InitPropertyChanged()
{
PropertyChanging += PropertyChangingMethod;
PropertyChanged += PropertyChangedMethod;
}

//private static Dictionary<Predicate<string>, Action> PropertyChangingActions;
//private static Dictionary<Predicate<string>, Action> PropertyChangedActions;
private void PropertyChangedMethod(object sender, PropertyChangedEventArgs e)
{

}

private void PropertyChangingMethod(object sender, PropertyChangingEventArgs e)
{

}
#endregion

public override void Cleanup()
{
// Clean up if needed
base.Cleanup();
}

}
}

菜单实例数据：

using System;
using System.Collections.ObjectModel;
using System.Threading.Tasks;
using IntTourism.Com.Transvalue.Bean;
using IntTourism.Com.Transvalue.Model;
using IntTourism.Com.Transvalue.Service;

namespace IntTourism.Com.Transvalue.Service.Impl
{
public class MainPageService : IMainPageSerivce
{
public void GetData(Action<DataItem, Exception> callback)
{
var item = new DataItem("Welcome to MVVM Light");
callback(item, null);
}

public void GetItemData(Action<Task<ObservableCollection<MenuItem>>, Exception> callback)
{
var result = Task.Run(() =>
{
var items = new ObservableCollection<MenuItem>();
var menu1 = new MenuItem();
menu1.IconUrl = "../Assets/ICON/交通.png";
menu1.NavigateUrl = "IntMaps";
items.Add(menu1);
var menu2 = new MenuItem();
menu2.IconUrl = "../Assets/ICON/娱乐.png";
menu2.NavigateUrl = "IntMaps";
menu2.NavigateParameter = "Play";
items.Add(menu2);
var menu3 = new MenuItem();
menu3.IconUrl = "../Assets/ICON/景点.png";
menu3.NavigateUrl = "SceneViewGroup";
items.Add(menu3);
var menu4 = new MenuItem();
menu4.IconUrl = "../Assets/ICON/购物.png";
menu4.NavigateUrl = "IntMaps";
menu4.NavigateParameter = "Buy";
items.Add(menu4);
var menu5 = new MenuItem();
menu5.IconUrl = "../Assets/ICON/专题旅游.png";
menu5.NavigateUrl = "SceneViewGroup";
menu5.NavigateParameter = "Travel";
items.Add(menu5);
var menu6 = new MenuItem();
menu6.IconUrl = "../Assets/ICON/实用信息.png";
items.Add(menu6);
var menu7 = new MenuItem();
menu7.IconUrl = "../Assets/ICON/武汉之最.png";
items.Add(menu7);
var menu8 = new MenuItem();
menu8.IconUrl = "../Assets/ICON/住宿.png";
menu8.NavigateUrl = "IntMaps";
menu8.NavigateParameter = "Rest";
items.Add(menu8);
var menu9 = new MenuItem();
menu9.IconUrl = "../Assets/ICON/推荐线路.png";
items.Add(menu9);
//var menu10 = new MenuItem();
//menu10.IconUrl = "../Assets/ICON/武汉介绍.png";
//items.Add(menu10);
var menu11 = new MenuItem();
menu11.IconUrl = "../Assets/ICON/周边旅游.png";
menu11.NavigateUrl = "IntMaps";
menu11.NavigateParameter = "AllTravel";
items.Add(menu11);
var menu12 = new MenuItem();
menu12.IconUrl = "../Assets/ICON/旅游动态.png";
items.Add(menu12);
var menu13 = new MenuItem();
menu13.IconUrl = "../Assets/ICON/美图欣赏.png";
items.Add(menu13);
var menu14 = new MenuItem();
menu14.IconUrl = "../Assets/ICON/天气预报.png";
items.Add(menu14);
var menu15 = new MenuItem();
menu15.IconUrl = "../Assets/ICON/旅游咨询.png";
items.Add(menu15);
var menu16 = new MenuItem();
menu16.IconUrl = "../Assets/ICON/美食.png";
menu16.NavigateUrl = "IntMaps";
menu16.NavigateParameter = "Eat";
items.Add(menu16);
return items;
});
callback(result, null);
}
}
}

以上sample 数据 可以存入数据库中 进行动态配置，完成菜单的动态显示，降低了程序的耦合，增加了可配置性。