我正试图找出一种方法，使按钮点击页面上显示复选框。
默认情况下它是不可见的，因为我在自定义渲染器中设置了checkBox.Visibility = Android.Views.ViewStates.Invisible;。
我在页面内容中有一个按钮，模板中有一个复选框，位于页面资源中。
从我的ViewModel中，我可以在CheckBox控件中调用PropertyChanged，在那里我可以看到正确设置旧值和新值。
但我需要一种方法在ViewRenderer上设置它。我猜它需要处理类似于CheckedChanged的某种事件。
视图模型
CheckBox c = new CheckBox { IsCheckBoxVisible=true,IsVisible=true };
CheckBox control
public class CheckBox : View
{
/// <summary>
/// The checked state property.
/// </summary>
public static readonly BindableProperty CheckedProperty =
BindableProperty.Create<CheckBox, bool>(
p => p.Checked, false, BindingMode.TwoWay, propertyChanged: OnCheckedPropertyChanged);
**public static readonly BindableProperty IsCheckBoxVisibleProperty =
BindableProperty.Create<CheckBox, bool>(
p => p.IsCheckBoxVisible, false, BindingMode.OneWay, propertyChanged: OnVisibilityPropertyChanged);**
/// <summary>
/// The checked text property.
/// </summary>
public static readonly BindableProperty CheckedTextProperty =
BindableProperty.Create<CheckBox, string>(
p => p.CheckedText, string.Empty, BindingMode.TwoWay);
/// <summary>
/// The unchecked text property.
/// </summary>
public static readonly BindableProperty UncheckedTextProperty =
BindableProperty.Create<CheckBox, string>(
p => p.UncheckedText, string.Empty);
/// <summary>
/// The default text property.
/// </summary>
public static readonly BindableProperty DefaultTextProperty =
BindableProperty.Create<CheckBox, string>(
p => p.Text, string.Empty);
/// <summary>
/// Identifies the TextColor bindable property.
/// </summary>
///
/// <remarks/>
public static readonly BindableProperty TextColorProperty =
BindableProperty.Create<CheckBox, Color>(
p => p.TextColor, Color.Default);
/// <summary>
/// The font size property
/// </summary>
public static readonly BindableProperty FontSizeProperty =
BindableProperty.Create<CheckBox, double>(
p => p.FontSize, -1);
/// <summary>
/// The font name property.
/// </summary>
public static readonly BindableProperty FontNameProperty =
BindableProperty.Create<CheckBox, string>(
p => p.FontName, string.Empty);
/// <summary>
/// The checked changed event.
/// </summary>
public event EventHandler<EventArgs<bool>> CheckedChanged;
**public event EventHandler<EventArgs<bool>> VisibilityChanged;**
/// <summary>
/// Gets or sets a value indicating whether the control is checked.
/// </summary>
/// <value>The checked state.</value>
public bool Checked
{
get
{
return this.GetValue<bool>(CheckedProperty);
}
set
{
if (this.Checked != value)
{
this.SetValue(CheckedProperty, value);
this.CheckedChanged.Invoke(this, value);
}
}
}
**public bool IsCheckBoxVisible
{
get
{
return this.GetValue<bool>(IsCheckBoxVisibleProperty);
}
set
{
if (this.IsCheckBoxVisible != value)
{
this.SetValue(IsCheckBoxVisibleProperty, value);
this.VisibilityChanged.Invoke(this, value);
//OnPropertyChanged("IsCheckBoxVisible");
}
}
}**
/// <summary>
/// Gets or sets a value indicating the checked text.
/// </summary>
/// <value>The checked state.</value>
/// <remarks>
/// Overwrites the default text property if set when checkbox is checked.
/// </remarks>
public string CheckedText
{
get
{
return this.GetValue<string>(CheckedTextProperty);
}
set
{
this.SetValue(CheckedTextProperty, value);
}
}
/// <summary>
/// Gets or sets a value indicating whether the control is checked.
/// </summary>
/// <value>The checked state.</value>
/// <remarks>
/// Overwrites the default text property if set when checkbox is checked.
/// </remarks>
public string UncheckedText
{
get
{
return this.GetValue<string>(UncheckedTextProperty);
}
set
{
this.SetValue(UncheckedTextProperty, value);
}
}
/// <summary>
/// Gets or sets the text.
/// </summary>
public string DefaultText
{
get
{
return this.GetValue<string>(DefaultTextProperty);
}
set
{
this.SetValue(DefaultTextProperty, value);
}
}
/// <summary>
/// Gets or sets the color of the text.
/// </summary>
/// <value>The color of the text.</value>
public Color TextColor
{
get
{
return this.GetValue<Color>(TextColorProperty);
}
set
{
this.SetValue(TextColorProperty, value);
}
}
/// <summary>
/// Gets or sets the size of the font.
/// </summary>
/// <value>The size of the font.</value>
public double FontSize
{
get
{
return (double)GetValue(FontSizeProperty);
}
set
{
SetValue(FontSizeProperty, value);
}
}
/// <summary>
/// Gets or sets the name of the font.
/// </summary>
/// <value>The name of the font.</value>
public string FontName
{
get
{
return (string)GetValue(FontNameProperty);
}
set
{
SetValue(FontNameProperty, value);
}
}
/// <summary>
/// Gets the text.
/// </summary>
/// <value>The text.</value>
public string Text
{
get
{
return this.Checked
? (string.IsNullOrEmpty(this.CheckedText) ? this.DefaultText : this.CheckedText)
: (string.IsNullOrEmpty(this.UncheckedText) ? this.DefaultText : this.UncheckedText);
}
}
/// <summary>
/// Called when [checked property changed].
/// </summary>
/// <param name="bindable">The bindable.</param>
/// <param name="oldvalue">if set to <c>true</c> [oldvalue].</param>
/// <param name="newvalue">if set to <c>true</c> [newvalue].</param>
private static void OnCheckedPropertyChanged(BindableObject bindable, bool oldvalue, bool newvalue)
{
var checkBox = (CheckBox)bindable;
checkBox.Checked = newvalue;
}
**private static void OnVisibilityPropertyChanged(BindableObject bindable, bool oldvalue, bool newvalue)
{
var checkBox = (CheckBox)bindable;
checkBox.IsCheckBoxVisible = newvalue;
}**
}
CheckBoxRenderer
protected override void OnElementChanged(ElementChangedEventArgs e)
{
base.OnElementChanged(e);
if (this.Control == null)
{
var checkBox = new Android.Widget.CheckBox(this.Context);
checkBox.Visibility = Android.Views.ViewStates.Invisible;
checkBox.CheckedChange += CheckBoxCheckedChange;
defaultTextColor = checkBox.TextColors;
this.SetNativeControl(checkBox);
}
Control.Text = e.NewElement.Text;
Control.Checked = e.NewElement.Checked;
UpdateTextColor();
if (e.NewElement.FontSize > 0)
{
Control.TextSize = (float)e.NewElement.FontSize;
}
if (!string.IsNullOrEmpty(e.NewElement.FontName))
{
Control.Typeface = TrySetFont(e.NewElement.FontName);
}
}
protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
{
base.OnElementPropertyChanged(sender, e);
switch (e.PropertyName)
{
case "Checked":
Control.Text = Element.Text;
Control.Checked = Element.Checked;
break;
case "TextColor":
UpdateTextColor();
break;
case "FontName":
if (!string.IsNullOrEmpty(Element.FontName))
{
Control.Typeface = TrySetFont(Element.FontName);
}
break;
case "FontSize":
if (Element.FontSize > 0)
{
Control.TextSize = (float)Element.FontSize;
}
break;
case "CheckedText":
case "UncheckedText":
Control.Text = Element.Text;
break;
** case "IsCheckBoxVisible":
if(Element.IsCheckBoxVisible==true)
{
Control.Visibility = Android.Views.ViewStates.Visible;
}
else
{
Control.Visibility = Android.Views.ViewStates.Invisible;
}
break;**
default:
System.Diagnostics.Debug.WriteLine("Property change for {0} has not been implemented.", e.PropertyName);
break;
}
}
答案 0 :(得分：0)
所以这实际上应该非常简单。现在你有IsCheckBoxVisibleProperty，你可以一起摆脱它。 Xamarin.Forms.View已经有IsVisible属性，每个特定于平台的渲染器（VisualElementRenderer）都知道如何处理可见性。
因此，您可以毫无问题地执行此操作。
var checkbox = new Checkbox();
checkbox .SetBinding (Checkbox.IsVisibleProperty, "IsCheckboxVisible");
或者在您的XAML中
<controls:Checkbox IsVisible="{Binding IsCheckboxVisible}" />
当然这假设您有一个类似于。
的ViewModelpublic class MyViewModel : BaseViewModel
{
private bool _isCheckboxVisible;
public bool IsCheckboxVisible
{
get { return _isCheckboxVisible; }
set { SetField(ref _isCheckboxVisible, value); }
}
}