C# 印德里，看一看。。thanksI补充了另一个问题，在我看来，这是正确的方法，我没有测试它，所以你可能需要修复或调整它，我希望它能让你继续。我使用了这个答案，仍然不起作用。。。没有错误，我在转换器中插入断点，并且正在调用断点。。但是，我不知道为什么它不起作用
C# 印德里，看一看。。thanksI补充了另一个问题，在我看来，这是正确的方法，我没有测试它，所以你可能需要修复或调整它，我希望它能让你继续。我使用了这个答案，仍然不起作用。。。没有错误，我在转换器中插入断点，并且正在调用断点。。但是，我不知道为什么它不起作用,c#,.net,xamarin,xamarin.forms,C#,.net,Xamarin,Xamarin.forms,印德里，看一看。。thanksI补充了另一个问题，在我看来，这是正确的方法，我没有测试它，所以你可能需要修复或调整它，我希望它能让你继续。我使用了这个答案，仍然不起作用。。。没有错误，我在转换器中插入断点，并且正在调用断点。。但是，我不知道为什么它不起作用；）。。我添加了上面的代码，看一看，可能我遗漏了什么..启动应用程序时按钮是否已启用？是的，它已启用。。我可以导航到另一个页面，而无需从picker中选择任何项目。我编辑了我的答案，请注意，在视图模型中创建命令时，我添加了（x）=>false作
印德里，看一看。。thanksI补充了另一个问题，在我看来，这是正确的方法，我没有测试它，所以你可能需要修复或调整它，我希望它能让你继续。我使用了这个答案，仍然不起作用。。。没有错误，我在转换器中插入断点，并且正在调用断点。。但是，我不知道为什么它不起作用；）。。我添加了上面的代码，看一看，可能我遗漏了什么..启动应用程序时按钮是否已启用？是的，它已启用。。我可以导航到另一个页面，而无需从picker中选择任何项目。我编辑了我的答案，请注意，在视图模型中创建命令时，我添加了（x）=>false作为第二个参数，这将解决问题。
<Picker x:Name="picker_provider"
Title="Select a Provider">
<Picker.ItemsSource>
<x:Array Type="{x:Type x:String}">
<x:String>Provider 1</x:String>
<x:String>Provider 2</x:String>
</x:Array>
</Picker.ItemsSource>
</Picker>
<Button
Text="Next"
Command="{Binding NextPageCommand}"/>
public async Task NextPage(RegisterViewModel nextpage) => await NavigationService.NavigateToAsync(nextpage, null, NavigationType.Modal);
#region Bindable Command
public ICommand NextPageCommand => new Command<RegisterViewModel>(async (nextpage) =>
{
await NextPage(nextpage);
});
#endregion
public bool IsNextButtonEnabled => SelectedItem!=null;
public string SelectedItem
{
get=>_selectedItem;
set { _selectedItem = value; OnPropertyChanged("SelectedItem");}
}
private string _selectedItem;
<Picker x:Name="picker_provider"
Title="Select a Provider"
SelectedItem="{Binding SelectedItem}>
<Picker.ItemsSource>
<x:Array Type="{x:Type x:String}">
<x:String>Provider 1</x:String>
<x:String>Provider 2</x:String>
</x:Array>
</Picker.ItemsSource>
public ICommand NextPageCommand => new Command<RegisterViewModel>(async (nextpage) =>
{
if(_selectedItem == "Provider 1") await ThisPage();
else await OtherPage();
});
<ContentPage.Resources>
<ResourceDictionary>
<local:MultiTriggerConverter x:Key="dataHasBeenEntered" />
</ResourceDictionary>
</ContentPage.Resources>
<StackLayout>
<Picker x:Name="picker_provider"
Title="Select a Provider" SelectedItem="{Binding xxx}">
<Picker.ItemsSource>
<x:Array Type="{x:Type x:String}">
<x:String>Provider 1</x:String>
<x:String>Provider 2</x:String>
</x:Array>
</Picker.ItemsSource>
</Picker>
<Button Text="Next" IsEnabled="False" Command="{}">
<Button.Triggers>
<DataTrigger
TargetType="Button"
Binding="{Binding Source={x:Reference picker_provider}, Path = SelectedIndex ,
Converter={StaticResource dataHasBeenEntered}}" Value="true">
<Setter Property="IsEnabled" Value="True" />
</DataTrigger>
</Button.Triggers>
</Button>
</StackLayout>
public class MultiTriggerConverter : IValueConverter
{
public object Convert(object value, Type targetType,
object parameter, CultureInfo culture)
{
if ((int)value >= 0) // length > 0 ?
return true; // some data has been entered
else
return false; // input is empty
}
public object ConvertBack(object value, Type targetType,
object parameter, CultureInfo culture)
{
throw new NotSupportedException();
}
}
public ICommand NextPageCommand => new Command<RegisterViewModel>(async (nextpage) =>
{
// here you could get the value of `Picker.SelectedItem`.
});
private bool _canNavigate;
public bool CanNavigate
{
get { return _canNavigate; }
set { this.RaiseAndSetIfChanged(ref _canNavigate, value) }
}
<Button
Text="Next"
IsEnabled="{Binding CanNavigate}"
Command="{Binding NextPageCommand}"/>
private string _selectedItem;
public string SelectedItem {
get { return _selectedItem; }
set
{
if (!string.IsNullOrWhiteSpace(value))
{
this.RaiseAndSetIfChanged(ref _selectedItem, value) }
}
}
}
<Picker x:Name="picker_provider"
Title="Select a Provider" SelectedItem="{Binding SelectedItem}">
<Picker.ItemsSource>
<x:Array Type="{x:Type x:String}">
<x:String>Provider 1</x:String>
<x:String>Provider 2</x:String>
</x:Array>
</Picker.ItemsSource>
</Picker>
namespace Osma.Mobile.App.Converters
{
public class StringNullOrEmptyValueBoolConverter: IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value is string str && !string.IsNullOrEmpty(str))
{
// String is not null or empty
return false;
}
// String is null or empty
return true;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
}
public class ProviderViewModel : ABaseViewModel
{
public ProviderViewModel(
IUserDialogs userDialogs,
INavigationService navigationService
) : base(
nameof(ProviderViewModel),
userDialogs,
navigationService)
{
}
public override async Task InitializeAsync(object navigationData)
{
await base.InitializeAsync(navigationData);
}
private string _selectedProvider;
public string SelectedProvider {
get { return _selectedProvider; }
set
{
this.RaiseAndSetIfChanged(ref _selectedProvider, value) }
}
}
private string _selectedCountry;
public string SelectedCountry {
get { return _selectedCountry; }
set
{
this.RaiseAndSetIfChanged(ref _selectedCountry, value) }
}
}
public async Task RegistrationPage(RegisterViewModel registration) => await NavigationService.NavigateToAsync(registration, null, NavigationType.Modal);
public ICommand RegistrationPageCommand => new Command<RegisterViewModel>(async (registration) =>
{
await RegistrationPage(registration);
}, (x) => false);
}
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:converters="clr-namespace:Osma.Mobile.App.Converters"
x:Class="Osma.Mobile.App.Views.ProviderPage"
NavigationPage.HasNavigationBar="False"
BackgroundColor="#004B86">
<ContentPage.Resources>
<ResourceDictionary>
<converters:StringNullOrEmptyValueBoolConverter x:Key="stringNullOrEmptyValueBoolConverter" />
</ResourceDictionary>
</ContentPage.Resources>
<ContentPage.Content>
<StackLayout
Spacing="30">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="70" />
<RowDefinition Height="70" />
</Grid.RowDefinitions>
<Grid Grid.Row="0">
<Picker
x:Name="picker_country"
Title="Select a Country"
TextColor="Silver"
TitleColor="Silver"
HorizontalOptions="Start"
WidthRequest = "200"
VerticalOptions="Start"
Margin="130,0,0,0"
SelectedItem="{Binding SelectedCountry}">
<Picker.ItemsSource>
<x:Array Type="{x:Type x:String}">
<x:String>Sweden</x:String>
</x:Array>
</Picker.ItemsSource>
</Picker>
</Grid>
<Grid Grid.Row="1">
<Picker
x:Name="picker_provider"
Title="Select a Provider"
TextColor="Silver"
TitleColor="Silver"
HorizontalOptions="Start"
WidthRequest = "200"
VerticalOptions="Start"
Margin="130,0,0,0"
SelectedItem="{Binding SelectedProvider}">
<Picker.ItemsSource>
<x:Array Type="{x:Type x:String}">
<x:String>Provider 1</x:String>
</x:Array>
</Picker.ItemsSource>
</Picker>
</Grid>
</Grid>
<Button
BackgroundColor="#2194EF"
TextColor="White"
Text="Next"
HeightRequest="60"
MinimumHeightRequest="60"
IsEnabled="False"
Command="{Binding RegistrationPageCommand}">
<Button.Triggers>
<MultiTrigger TargetType="Button">
<MultiTrigger.Conditions>
<BindingCondition Binding="{Binding SelectedCountry,
Converter={StaticResource stringNullOrEmptyValueBoolConverter }}" Value="false" />
<BindingCondition Binding="{Binding SelectedProvider,
Converter={StaticResource stringNullOrEmptyValueBoolConverter }}" Value="false" />
</MultiTrigger.Conditions>
<Setter Property="IsEnabled" Value="True" />
</MultiTrigger>
</Button.Triggers>
</Button>
</StackLayout>
</ContentPage.Content>
</ContentPage>