我正在使用TimePicker
在我的应用程序中显示时间。当时间已经设置然后它正确显示,但是如果没有设置时间,则它显示默认的上午12:00时间。所以我只想在没有设置时间时显示null
值。是否有可能在Xamarin Forms中将nullable
值设置为TimePicker
?
我用这个
/// <summary>
/// DatePicker der null Werte erlaubt
/// </summary>
public class CustomDatePicker : DatePicker
{
/// <summary>
/// PropertyName für die <c>NullableDate</c> Property
/// </summary>
public const string NullableDatePropertyName = "NullableDate";
/// <summary>
/// Die BinableProperty
/// </summary>
public static readonly BindableProperty NullableDateProperty = BindableProperty.Create<CustomDatePicker, DateTime?>(i => i.NullableDate, null, BindingMode.TwoWay, null, NullableDateChanged);
/// <summary>
/// Datumswert welches null Werte akzeptiert
/// </summary>
public DateTime? NullableDate
{
get
{
return (DateTime?)this.GetValue(NullableDateProperty);
}
set
{
this.SetValue(NullableDateProperty, value);
}
}
/// <summary>
/// Der Name der <c>NullText</c> Property
/// </summary>
public const string NullTextPropertyName = "NullText";
/// <summary>
/// Die BindableProperty
/// </summary>
public static readonly BindableProperty NullTextProperty = BindableProperty.Create<CustomDatePicker, string>(i => i.NullText, default(string), BindingMode.TwoWay);
/// <summary>
/// Der Text der angezeigt wird wenn <c>NullableDate</c> keinen Wert hat
/// </summary>
public string NullText
{
get
{
return (string)this.GetValue(NullTextProperty);
}
set
{
this.SetValue(NullTextProperty, value);
}
}
/// <summary>
/// Der Name der <c>DisplayBorder</c> Property
/// </summary>
public const string DisplayBorderPropertyName = "DisplayBorder";
/// <summary>
/// Die BindableProperty
/// </summary>
public static readonly BindableProperty DisplayBorderProperty = BindableProperty.Create<CustomDatePicker, bool>(i => i.DisplayBorder, default(bool), BindingMode.TwoWay);
/// <summary>
/// Gibt an ob eine Umrandung angezeigt werden soll oder nicht
/// </summary>
public bool DisplayBorder
{
get
{
return (bool)this.GetValue(DisplayBorderProperty);
}
set
{
this.SetValue(DisplayBorderProperty, value);
}
}
/// <summary>
/// Erstellt eine neue Instanz von <c>CustomDatePicker</c>
/// </summary>
public CustomDatePicker()
{
this.DateSelected += CustomDatePicker_DateSelected;
this.Format = "dd.MM.yyyy";
}
/// <summary>
/// Wird gefeuert wenn ein neues Datum selektiert wurde
/// </summary>
/// <param name="sender">Der Sender</param>
/// <param name="e">Event Argumente</param>
void CustomDatePicker_DateSelected(object sender, DateChangedEventArgs e)
{
this.NullableDate = new DateTime(
e.NewDate.Year,
e.NewDate.Month,
e.NewDate.Day,
this.NullableDate.HasValue ? this.NullableDate.Value.Hour : 0,
this.NullableDate.HasValue ? this.NullableDate.Value.Minute : 0,
this.NullableDate.HasValue ? this.NullableDate.Value.Second : 0);
}
/// <summary>
/// Gefeuert wenn sich <c>NullableDate</c> ändert
/// </summary>
/// <param name="obj">Der Sender</param>
/// <param name="oldValue">Der alte Wert</param>
/// <param name="newValue">Der neue Wert</param>
private static void NullableDateChanged(BindableObject obj, DateTime? oldValue, DateTime? newValue)
{
var customDatePicker = obj as CustomDatePicker;
if (customDatePicker != null)
{
if (newValue.HasValue)
{
customDatePicker.Date = newValue.Value;
}
}
}
}
您可以使用View
和TimePicker
创建一个自定义Label
。如果没有选择时间,则会出现“hh:mm”,否则时间将出现在标签上。为了显示timepicker对话框,有一个tapGestureRecognizer
,它会在点击标签时将焦点设置为timepicker。
public class NullableTimePicker : ContentView
{
private const string NullTimeLabel = "hh : mm";
private readonly TimePicker _timePicker;
private readonly Label _label;
public static readonly BindableProperty TimeProperty = BindableProperty.Create<NullableTimePicker, TimeSpan?>(t => t.Time, null, BindingMode.TwoWay, propertyChanged: OnTimeChanged);
public NullableTimePicker()
{
_label = new Label
{
Text = NullTimeLabel,
HorizontalOptions = LayoutOptions.FillAndExpand,
VerticalOptions = LayoutOptions.Fill,
HorizontalTextAlignment = TextAlignment.Start,
VerticalTextAlignment = TextAlignment.Center,
TextColor = Color.Black,
FontSize = Device.GetNamedSize(NamedSize.Medium, typeof(Label))
};
_timePicker = new TimePicker
{
IsVisible = false,
HorizontalOptions = LayoutOptions.FillAndExpand,
VerticalOptions = LayoutOptions.Fill
};
Content = new StackLayout
{
Children =
{
_label,
_timePicker
},
Padding = 0,
Spacing = 0,
Margin = 0
};
Padding = 0;
Margin = 0;
var tapGestureRecognizer = new TapGestureRecognizer();
tapGestureRecognizer.Tapped += TapGestureRecognizer_Tapped;
GestureRecognizers.Add(tapGestureRecognizer);
_timePicker.PropertyChanged += timePicker_PropertyChanged;
PropertyChanged += NullableTimePicker_PropertyChanged;
}
private void NullableTimePicker_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
if (_label != null && e.PropertyName == IsEnabledProperty.PropertyName)
{
_label.TextColor = IsEnabled ? Color.Black : Color.Gray;
}
}
private void timePicker_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == TimePicker.TimeProperty.PropertyName && _timePicker != null)
{
Time = _timePicker.Time;
}
}
private void TapGestureRecognizer_Tapped(object sender, EventArgs e)
{
if (IsEnabled == false)
{
return;
}
if (_timePicker.IsFocused)
{
_timePicker.Unfocus();
}
_timePicker.Focus();
}
private static void OnTimeChanged(BindableObject bindable, TimeSpan? oldvalue, TimeSpan? newvalue)
{
var nullableTimePicker = bindable as NullableTimePicker;
if (nullableTimePicker != null && oldvalue != newvalue)
{
nullableTimePicker.Time = newvalue;
}
}
public TimeSpan? Time
{
get
{
return GetValue(TimeProperty) as TimeSpan?;
}
set
{
SetValue(TimeProperty, value);
if (value.HasValue && _timePicker.Time != value)
{
_timePicker.Time = value.Value;
}
SetLabelText(value);
}
}
private void SetLabelText(TimeSpan? value)
{
_label.Text = value.HasValue ? ConvertTimeSpanToString(value.Value) : NullTimeLabel;
}
}