我有一个 Windows Phone 8 应用程序，我有一个RelayCommand名为DiscoverExpansionModulesCommand. 我有一个Command属性绑定到的按钮DiscoverExpansionModulesCommand。当应用程序首次加载时，按钮会正确启用或禁用。但是，当在页面上并且我想更改命令是否可以执行时，该方法CanExecuteDiscoverExpansionModulesCommand()会正确触发并返回正确的 true 或 false 值，但按钮不会反映它。为什么按钮不更新它的 UI？我在这里找到了关于这个问题的另一篇文章http://social.msdn.microsoft.com/Forums/en-US/silverlightarchieve/thread/48a341e4-f512-4c33-befd-b614404b4920/
我的视图模型：
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Command;
using GalaSoft.MvvmLight.Messaging;
using MAL.Portable.Commands;
using MAL.Portable.Message;
using MAL.Portable.Model;
using System;
using System.Collections.Generic;
using System.Windows.Input;
namespace MAL.Portable.ViewModel
{
public class SettingsViewModel : ViewModelBase
{
// Define an observable collection property that controls can bind to.
private List<Setting> settings;
private String controllerUrl;
private String controllerPort;
private String temperature;
private Wifi wifi;
private Boolean connected;
private Boolean checkingConnection;
public SettingsViewModel()
{
DiscoverExpansionModulesCommand = new RelayCommand(OnDiscoverExpansionModules, CanExecuteDiscoverExpansionModulesCommand);
Messenger.Default.Register<RetrieveSettingsMessage>
(
this, (action) => RetrievedListsMessage(action)
);
Messenger.Default.Send<GetSettingsMessage>(new GetSettingsMessage());
}
public ICommand DiscoverExpansionModulesCommand
{
get;
private set;
}
public String ConnectionStatus
{
get
{
if (checkingConnection)
return "checking";
else
return connected ? "connected" : "not connnected";
}
}
private Boolean CanExecuteDiscoverExpansionModulesCommand()
{
return connected;
}
private void OnDiscoverExpansionModules()
{
}
private void CheckConnection()
{
wifi = null;
if (!String.IsNullOrWhiteSpace(ControllerUrl) && !String.IsNullOrWhiteSpace(ControllerPort) && !checkingConnection)
{
checkingConnection = true;
wifi = new ReefAngelWifi(controllerUrl, controllerPort);
wifi.TestConnectionComplete += wifi_TestConnectionComplete;
wifi.RequestFail += wifi_RequestFail;
wifi.BeginTestConnection();
}
}
private void wifi_RequestFail(object sender, RequestExceptionEventArgs e)
{
connected = false;
checkingConnection = false;
RaisePropertyChanged("ConnectionStatus");
}
private void wifi_TestConnectionComplete(object sender, TestConnectionEventArgs e)
{
connected = e.TestSuccessful;
checkingConnection = false;
DiscoverExpansionModulesCommand.CanExecute(null);
RaisePropertyChanged("ConnectionStatus");
RaisePropertyChanged("DiscoverExpansionModulesCommand");
}
private object RetrievedListsMessage(RetrieveSettingsMessage action)
{
settings = action.Settings;
CheckConnection();
return null;
}
private String GetStringValue(String key)
{
if (settings == null) return String.Empty;
var item = settings.Find(x => x.Key == key);
if (item == null) return String.Empty;
else return item.Value;
}
private Boolean GetBooleanValue(String key)
{
if (settings == null) return false;
var item = settings.Find(x => x.Key == key);
if (item == null) return false;
else return Boolean.Parse(item.Value);
}
}
}
和 XAML
<phone:PhoneApplicationPage
xmlns:ReefAngel="clr-namespace:MAL.WindowsPhone8"
xmlns:Controls="clr-namespace:Telerik.Windows.Controls;assembly=Telerik.Windows.Controls.Input"
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:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
xmlns:cmd="clr-namespace:GalaSoft.MvvmLight.Command;assembly=GalaSoft.MvvmLight.Platform.WP8"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:telerikPrimitives="clr-namespace:Telerik.Windows.Controls;assembly=Telerik.Windows.Controls.Primitives"
x:Class="MAL.WindowsPhone8.ReefAngel.SettingsPage"
xmlns:converter="clr-namespace:MAL.WindowsPhone8.Converters"
FontFamily="{StaticResource PhoneFontFamilyNormal}"
FontSize="{StaticResource PhoneFontSizeNormal}"
DataContext="{Binding Settings, Source={StaticResource Locator}}"
SupportedOrientations="Portrait" Orientation="Portrait"
mc:Ignorable="d"
shell:SystemTray.IsVisible="True">
<phone:PhoneApplicationPage.Resources>
<converter:BooleanToStringConverter x:Key="temperatureConverter" TrueString="Celsius" FalseString="Fahrenheit" />
<converter:BooleanToStringConverter x:Key="timeFormatConverter" TrueString="24 hour" FalseString="12 hour" />
<converter:BooleanToStringConverter x:Key="dateFormatConverter" TrueString="dd/mm/yyyy" FalseString="mm/dd/yyyy" />
</phone:PhoneApplicationPage.Resources>
<!--LayoutRoot is the root grid where all page content is placed-->
<Grid x:Name="LayoutRoot" >
<phone:Pivot Title="{Binding LocalizedResources.ApplicationTitle, Source={StaticResource LocalizedStrings}, StringFormat='\{0\} Settings'}">
<phone:PivotItem Header="connection">
<Grid>
<StackPanel Margin="12,0,0,0">
<TextBlock Margin="0,20,0,0" TextWrapping="Wrap" Text="Reef Angel Wifi Address"/>
<TextBox Height="72" TextWrapping="Wrap" Text="{Binding ControllerUrl, Mode=TwoWay}"/>
<TextBlock Margin="0,20,0,0" TextWrapping="Wrap" Text="Reef Angel Wifi Port"/>
<TextBox Height="72" TextWrapping="Wrap" Text="{Binding ControllerPort, Mode=TwoWay}"/>
<StackPanel Orientation="Horizontal">
<TextBlock Margin="0,20,0,0" TextWrapping="Wrap" Text="Reef Angel Wifi Status : "/>
<TextBlock Margin="0,20,0,0" TextWrapping="Wrap" Text="{Binding ConnectionStatus, Mode=OneWay}"/>
</StackPanel>
</StackPanel>
</Grid>
</phone:PivotItem>
<phone:PivotItem Header="expansion">
<Grid>
<Button Content="Discover Expansion Modules" x:Name="DiscoverButton" Command="{Binding DiscoverExpansionModulesCommand, Mode=OneWay}" />
</Grid>
</phone:PivotItem>
</phone:Pivot>
</Grid>
</phone:PhoneApplicationPage>
我正在使用 MVVM Light 便携式类库。