c# - Xamarin Forms 最佳行为和验证

Question

我需要知道如何访问我的 View 模型这些行为的 IsValid 属性。

我宁愿你告诉我一个更健壮的行为，因为它们是从头开始制作的，我想用一些已经先进的 nuget 包进行更健壮的验证，尽管它是 Xamarin Forms 的新手。

这是我的行为，但我无法访问属性“IsValid”我的 View 模型:

  public class MesesTrabalhadosValidatorBehavior : Behavior<Entry>
        {
            private static readonly BindablePropertyKey IsValidPropertyKey = BindableProperty.CreateReadOnly("IsValid", typeof(bool), typeof(MesesTrabalhadosValidatorBehavior), false);

            public static readonly BindableProperty IsValidProperty = IsValidPropertyKey.BindableProperty;

            public bool IsValid
            {
                get { return (bool)base.GetValue(IsValidProperty); }
                private set { base.SetValue(IsValidPropertyKey, value); }
            }

            private void bindable_TextChanged(object sender, TextChangedEventArgs e)
            {
                double result;
                double.TryParse(e.NewTextValue, out result);
                IsValid = result > 0;

                ((Entry)sender).TextColor = IsValid ? Color.Green : Color.Red;
            }

            protected override void OnAttachedTo(Entry bindable)
            {
                bindable.TextChanged += bindable_TextChanged;
            }

            protected override void OnDetachingFrom(Entry bindable)
            {
                bindable.TextChanged -= bindable_TextChanged;
            }
        }

我的看法:

    <Entry Placeholder="Mêses trabalhados" Text="{Binding MesesTrabalhados}" Keyboard="Numeric">
          <Entry.Behaviors>
            <local:MesesTrabalhadosValidatorBehavior />
          </Entry.Behaviors>
        </Entry>

        <Entry Placeholder="Último salário" Text="{Binding Salario}" Keyboard="Numeric">
          <Entry.Behaviors>
            <local:SalarioValidatorBehavior />
          </Entry.Behaviors>
        </Entry>

    <ContentView Padding="0,20,0,0">
      <Button Text="Calcular" HorizontalOptions="Fill" IsEnabled="{Binding IsValid}" Command="{Binding CalcularFgtsCommand, Mode=TwoWay}"/>
    </ContentView>

Answer 1

需要加一个参数，我喜欢的是命令函数，这样达到一定条件就可以调用。例如

<local:SalarioValidatorBehavior Command="{Binding MyCommandInViewModel}" />

然后是行为中的可绑定(bind)属性。

    public static readonly BindableProperty CommandProperty = BindableProperty.Create(nameof(Command), typeof(ICommand), typeof(TextChangedBehavior), null);

    public ICommand Command
    {
        get { return (ICommand)GetValue(CommandProperty); }
        set { SetValue(CommandProperty, value); }
    }

    void OnEntryTextChanged(object sender, TextChangedEventArgs args)
    {
        if (Command != null)
            Command.Execute(null);
    }

或者您可以在 Behavior 中使用 IsValid 属性，然后将其绑定(bind)回 ViewModel 中的属性。

<local:SalarioValidatorBehavior IsValid="{Binding IsValid, Mode=TwoWay}" />