根據 C# 中的條件隱藏/取消隱藏按鈕

Question

我在 Xamarin.Forms 工作。 在 CredentialPage.xml 頁面中，有一個按鈕，我想根據 CredentialViewMode.cs 頁面中的憑據狀態隱藏和取消隱藏。

CredentialPage.xml

<Button x:Name="Button_Round"
WidthRequest="40"
HeightRequest="40"
CornerRadius="20"
BorderWidth="2"
TextColor="White"
BorderColor="Teal"
BackgroundColor="Teal"
Text="Accept Offer"
Command="{Binding ProcessOffer}" />

CredentialViewModel.cs

#region Bindable Command
[Obsolete]
public ICommand ProcessOffer => new Command(async () =>
{
    var RegisteredPIN = await SecureStorage.GetAsync("RegisteredPIN");
    string PIN = await App.Current.MainPage.DisplayPromptAsync("Enter PIN", null, "Ok", "Cancel", null, 6, Keyboard.Numeric);
    if (PIN == RegisteredPIN)
    {
        try
        {
            //await _poolConfigurator.ConfigurePoolsAsync();
            var agentContext = await _agentContextProvider.GetContextAsync();
            var credentialRecord = await _credentialService.GetAsync(agentContext, _credential.Id);
            var connectionId = credentialRecord.ConnectionId;
            var connectionRecord = await _connectionService.GetAsync(agentContext, connectionId);
            (var request, _) = await _credentialService.CreateRequestAsync(agentContext, _credential.Id);
            await _messageService.SendAsync(agentContext.Wallet, request, connectionRecord);
            await DialogService.AlertAsync("Request has been sent to the issuer.", "Success", "Ok");
        }
        catch (Exception e)
        {
            await DialogService.AlertAsync(e.Message, "Error", "Ok");
        }
    }
    else if (PIN != RegisteredPIN && PIN != null)
    {
        DialogService.Alert("Provided PIN is not correct");
    }
});

#endregion

我想隱藏/取消隱藏按鈕的條件

if(_credentialStatus == "Offered")
{
    // Button should be Visible
}
else
{
    // Hide the Button
}

Answer 1

使用 IsVisible 屬性：

<Button x:Name="Button_Round"
WidthRequest="40"
HeightRequest="40"
CornerRadius="20"
BorderWidth="2"
TextColor="White"
BorderColor="Teal"
BackgroundColor="Teal"
Text="Accept Offer"
Command="{Binding ProcessOffer}" 
IsVisible="{Binding IsOfferButtonVisible}"
/>

然后在你的代碼后面

if(_credentialStatus == "Offered")
{
    IsOfferButtonVisible  = true;
}
else
{
    // Hide the Button
    IsOfferButtonVisible = false;
}

Answer 2

向您的 ViewModel 添加一個 bool 屬性，例如：

private bool _credentialVisible;
public bool CredentialVisible
{
    get 
    {
        return _credentialVisible;
    }
    set
    {
       if (_credentialVisible != value)
       {
           _credentialVisible = value;
           NotifyPropertyChanged();
       }
    }
}

您的視圖 model 應該實現接口INotifyPropertyChanged ：

public event PropertyChangedEventHandler PropertyChanged;

protected void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
{
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}

然后在您的視圖中綁定到IsVisible屬性：

<Button x:Name="Button_Round"
IsVisible={Binding CredentialVisible}
WidthRequest="40"
HeightRequest="40"
CornerRadius="20"
BorderWidth="2"
TextColor="White"
BorderColor="Teal"
BackgroundColor="Teal"
Text="Accept Offer"
Command="{Binding ProcessOffer}" />

您沒有指定何時需要檢查按鈕是否應該可見，但我想您在加載頁面時需要它，在這種情況下，您需要一種行為來在頁面出現時觸發命令，而不是自己編寫您可以使用以下 NuGet： https://www.nuget.org/packages/Behaviors.Forms/

安裝后，將命名空間添加到您的ContentPage ：

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:behaviors="clr-namespace:Behaviors;assembly=Behaviors"

然后你可以按如下方式使用它：

<ContentPage.Behaviors>
    <behaviors:EventHandlerBehavior EventName="Appearing">
        <behaviors:InvokeCommandAction Command="{Binding AppearingCommand}" />
    </behaviors:EventHandlerBehavior>
</ContentPage.Behaviors>

這將在頁面出現時調用AppearingCommand方法，您可以在那里設置按鈕的可見性：

public ICommand AppearingCommand => new Command(() =>
{
    if(_credentialStatus == "Offered")
    {
        CredentialsVisible = true;
    }
});