Xamarin.Forms 中可空的 TimePicker

Question

我用于TimePicker在我的应用程序中显示时间。当时间已设置时，它会正确显示，但当时间未设置时，则显示默认 12 : 00 AM 时间。所以我只想null在未设置时间时显示值。是否可以在 Xamarin Forms 中设置nullable值TimePicker？

Answer 1

我用这个

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/// <summary>\n/// DatePicker der null Werte erlaubt\n/// </summary>\npublic class CustomDatePicker : DatePicker\n{\n    /// <summary>\n    /// PropertyName f\xc3\xbcr die <c>NullableDate</c> Property\n    /// </summary>\n    public const string NullableDatePropertyName = "NullableDate";\n    /// <summary>\n    /// Die BinableProperty\n    /// </summary>\n    public static readonly BindableProperty NullableDateProperty = BindableProperty.Create<CustomDatePicker, DateTime?>(i => i.NullableDate, null, BindingMode.TwoWay, null, NullableDateChanged);\n    /// <summary>\n    /// Datumswert welches null Werte akzeptiert\n    /// </summary>\n    public DateTime? NullableDate\n    {\n        get\n        {\n            return (DateTime?)this.GetValue(NullableDateProperty);\n        }\n        set\n        {\n            this.SetValue(NullableDateProperty, value);\n        }\n    }\n    /// <summary>\n    /// Der Name der <c>NullText</c> Property\n    /// </summary>\n    public const string NullTextPropertyName = "NullText";\n    /// <summary>\n    /// Die BindableProperty\n    /// </summary>\n    public static readonly BindableProperty NullTextProperty = BindableProperty.Create<CustomDatePicker, string>(i => i.NullText, default(string), BindingMode.TwoWay);\n    /// <summary>\n    /// Der Text der angezeigt wird wenn <c>NullableDate</c> keinen Wert hat\n    /// </summary>\n    public string NullText\n    {\n        get\n        {\n            return (string)this.GetValue(NullTextProperty);\n        }\n        set\n        {\n            this.SetValue(NullTextProperty, value);\n        }\n    }\n    /// <summary>\n    /// Der Name der <c>DisplayBorder</c> Property\n    /// </summary>\n    public const string DisplayBorderPropertyName = "DisplayBorder";\n    /// <summary>\n    /// Die BindableProperty\n    /// </summary>\n    public static readonly BindableProperty DisplayBorderProperty = BindableProperty.Create<CustomDatePicker, bool>(i => i.DisplayBorder, default(bool), BindingMode.TwoWay);\n    /// <summary>\n    /// Gibt an ob eine Umrandung angezeigt werden soll oder nicht\n    /// </summary>\n    public bool DisplayBorder\n    {\n        get\n        {\n            return (bool)this.GetValue(DisplayBorderProperty);\n        }\n        set\n        {\n            this.SetValue(DisplayBorderProperty, value);\n        }\n    }\n\n    /// <summary>\n    /// Erstellt eine neue Instanz von <c>CustomDatePicker</c>\n    /// </summary>\n    public CustomDatePicker()\n    {\n        this.DateSelected += CustomDatePicker_DateSelected;\n\n        this.Format = "dd.MM.yyyy";\n    }\n    /// <summary>\n    /// Wird gefeuert wenn ein neues Datum selektiert wurde\n    /// </summary>\n    /// <param name="sender">Der Sender</param>\n    /// <param name="e">Event Argumente</param>\n    void CustomDatePicker_DateSelected(object sender, DateChangedEventArgs e)\n    {\n        this.NullableDate = new DateTime(\n            e.NewDate.Year, \n            e.NewDate.Month, \n            e.NewDate.Day, \n            this.NullableDate.HasValue ? this.NullableDate.Value.Hour : 0,\n            this.NullableDate.HasValue ? this.NullableDate.Value.Minute : 0,\n            this.NullableDate.HasValue ? this.NullableDate.Value.Second : 0);\n    }\n\n    /// <summary>\n    /// Gefeuert wenn sich <c>NullableDate</c> \xc3\xa4ndert\n    /// </summary>\n    /// <param name="obj">Der Sender</param>\n    /// <param name="oldValue">Der alte Wert</param>\n    /// <param name="newValue">Der neue Wert</param>\n    private static void NullableDateChanged(BindableObject obj, DateTime? oldValue, DateTime? newValue)\n    {\n        var customDatePicker = obj as CustomDatePicker;\n\n        if (customDatePicker != null)\n        {\n            if (newValue.HasValue)\n            {\n                customDatePicker.Date = newValue.Value;\n            }\n        }\n    }\n}\n

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