模糊上的 xamarin.forms 条目绑定

Question

条目文本的默认绑定触发器似乎是 TextChanged 事件。我想推迟更新源，直到模糊事件。在 WPF 中有可以设置为修改绑定触发器的 UpdateSourceTrigger 参数，但我在 Xamarin.Form 中没有找到任何文档。

如何在 Xaramin.Forms 中通过 XAML 中的绑定来实现。由于显而易见的原因，我不想在后面的代码中手动处理它。

Answer 1

这个问题很老，但仍然很实际。特别是对于带小数点的字段... 使用 Xamarin 社区工具包EventToCommandBehavior（或类似实现，如 Prism）的第一个选项。然后可以将“Unfocused”事件绑定到某个命令：

    <Entry.Behaviors>
    <xct:EventToCommandBehavior
        EventName="Unfocused"
        Command="{Binding MyCustomCommand}" />
    </Entry.Behaviors>

添加处理此事件的自定义 Entry 组件的其他选项，此选项更适合我使用带小数点的数字输入（浮点、双精度、小数）。这是来自 MSDN 论坛Entry binding Decimal 的稍微修改的解决方案：

public class NumericEntry : Entry
    {
        #region Bindables

        public static readonly BindableProperty NumericValueProperty = BindableProperty.Create(
            "NumericValue",
            typeof(decimal?),
            typeof(NumericEntry),
            null,
            BindingMode.TwoWay,
            coerceValue: (_, value) => (decimal?)value,
            propertyChanged: (bindable, _, __) => SetDisplayFormat((NumericEntry)bindable)
        );

        public static readonly BindableProperty NumericValueFormatProperty = BindableProperty.Create(
            "NumericValueFormat",
            typeof(string),
            typeof(NumericEntry),
            "N0",
            BindingMode.TwoWay,
            propertyChanged: (bindable, _, __) => SetDisplayFormat((NumericEntry)bindable)
        );

        #endregion Bindables

        #region Constructor

        public NumericEntry()
        {
            Keyboard = Keyboard.Numeric;
            Focused += OnFocused;
            Unfocused += OnUnfocused;
        }

        #endregion Constructor

        #region Events

        private void OnFocused(object sender, FocusEventArgs e)
        {
            SetEditFormat(this);
        }

        private void OnUnfocused(object sender, FocusEventArgs e)
        {
            var numberFormant = CultureInfo.CurrentCulture.NumberFormat;
            var _text = Text.Replace(".", numberFormant.NumberDecimalSeparator);

            if (decimal.TryParse(_text, NumberStyles.Number, CultureInfo.CurrentCulture, out var numericValue))
            {
                var round = Convert.ToInt32(NumericValueFormat.Substring(1));
                NumericValue = Math.Round(numericValue, round);
            }
            else
            {
                NumericValue = null;
            }

            SetDisplayFormat(this);
        }

        #endregion Events

        #region Properties

        public decimal? NumericValue
        {
            get => (decimal?)GetValue(NumericValueProperty);
            set => SetValue(NumericValueProperty, value);
        }

        public string NumericValueFormat
        {
            get => (string)GetValue(NumericValueFormatProperty) ?? "N0";
            set
            {
                var _value = string.IsNullOrWhiteSpace(value) ? "N0" : value;
                SetValue(NumericValueFormatProperty, _value);
            }
        }

        #endregion Properties

        #region Methods

        private static void SetDisplayFormat(NumericEntry textBox)
        {
            if (textBox.NumericValue.HasValue)
            {
                textBox.Text = textBox.NumericValue.Value.ToString(textBox.NumericValueFormat, CultureInfo.DefaultThreadCurrentCulture);
            }
            else
            {
                textBox.Text = string.Empty;
            }
        }

        private static void SetEditFormat(NumericEntry textBox)
        {
            if (textBox.NumericValue.HasValue)
            {
                var numberFormant = CultureInfo.CurrentCulture.NumberFormat;
                textBox.Text = textBox.NumericValue.Value.ToString(textBox.NumericValueFormat, CultureInfo.CurrentCulture).Replace(numberFormant.NumberGroupSeparator, string.Empty);
            }
            else
            {
                textBox.Text = string.Empty;
            }
        }

        #endregion Methods
    }

并像这样使用它：

       // import our component
       xmlns:ex="clr-namespace:BoganPos.Extensions"
       //...
       <ex:NumericEntry NumericValue="{Binding DecimalValue}" NumericValueFormat="F2" Placeholder="Placeholder"/>