C# 在Xamarin Forms Framework中导致空引用异常的自定义控件
我构建了一个自定义SVG按钮,这样我就可以拥有一个带有文本和SVG图像的Xamarin表单按钮。我已经让它运行良好,然后我将我的项目迁移到.NET标准2.0 现在,当更改控件上的文本时,我在ListDictionaryInternal上的Xamarin Forms框架的StackLayout的LayoutChildIntoBoundingRegion方法中得到一个空引用异常 这是控制按钮。这很简单C# 在Xamarin Forms Framework中导致空引用异常的自定义控件,c#,svg,xamarin.forms,custom-controls,nullreferenceexception,C#,Svg,Xamarin.forms,Custom Controls,Nullreferenceexception,我构建了一个自定义SVG按钮,这样我就可以拥有一个带有文本和SVG图像的Xamarin表单按钮。我已经让它运行良好,然后我将我的项目迁移到.NET标准2.0 现在,当更改控件上的文本时,我在ListDictionaryInternal上的Xamarin Forms框架的StackLayout的LayoutChildIntoBoundingRegion方法中得到一个空引用异常 这是控制按钮。这很简单 using System.Windows.Input; using FFImageLoading.
using System.Windows.Input;
using FFImageLoading.Svg.Forms;
using Core.Interfaceses;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;
namespace CustomControls
{
[XamlCompilation(XamlCompilationOptions.Compile)]
public class SVGImageButton : ContentView
{
#region Member Variables
private readonly Button _button;
private readonly SvgCachedImage _svgImage;
#endregion
#region Bindible Properties
public static BindableProperty ButtonPressedCommandProperty = BindableProperty.Create(nameof(ButtonPressedCommand), typeof(ICommand), typeof(SVGImageButton));
public ICommand ButtonPressedCommand
{
get
{
return (ICommand)GetValue(ButtonPressedCommandProperty);
}
set
{
SetValue(ButtonPressedCommandProperty, value);
}
}
public static BindableProperty CommandParameterProperty = BindableProperty.Create(nameof(CommandParameter), typeof(object), typeof(SVGImageButton));
public object CommandParameter
{
get { return GetValue(CommandParameterProperty); }
set { SetValue(CommandParameterProperty, value); }
}
public static BindableProperty ButtonTextProperty = BindableProperty.Create(nameof(ButtonText), typeof(string), typeof(SVGImageButton), string.Empty, BindingMode.TwoWay, propertyChanged: (bindable, oldValue, newValue) =>
{
if (newValue == null) return;
var control = (SVGImageButton)bindable;
control.ButtonText = newValue.ToString();
});
public string ButtonText
{
get
{
return _button.Text;
}
set
{
_button.Text = value;
}
}
public static BindableProperty ButtonBackgroundColorProperty = BindableProperty.Create(nameof(ButtonBackgroundColor), typeof(Color), typeof(View), Color.Fuchsia, BindingMode.OneWay, propertyChanged: (bindable, oldValue, newValue) =>
{
if (newValue == null) return;
var control = (SVGImageButton)bindable;
control.ButtonBackgroundColor = (Color)newValue;
});
public Color ButtonBackgroundColor
{
get
{
return _button.BackgroundColor;
}
set
{
_button.BackgroundColor = value;
}
}
public static BindableProperty ButtonTextColorProperty = BindableProperty.Create(nameof(ButtonTextColor), typeof(Color), typeof(View), Color.Fuchsia, BindingMode.OneWay, propertyChanged: (bindable, oldValue, newValue) =>
{
if (newValue == null) return;
var control = (SVGImageButton)bindable;
control.ButtonTextColor = (Color)newValue;
});
public Color ButtonTextColor
{
get
{
return _button.TextColor;
}
set
{
_button.TextColor = value;
}
}
public static BindableProperty ButtonStyleProperty = BindableProperty.Create(nameof(ButtonBackgroundColor), typeof(Style), typeof(View), null, BindingMode.OneWay, propertyChanged: (bindable, oldValue, newValue) =>
{
if (newValue == null) return;
var control = (SVGImageButton)bindable;
control.ButtonStyle = (Style)newValue;
});
public Style ButtonStyle
{
get
{
return _button.Style;
}
set
{
_button.Style = value;
}
}
public static BindableProperty ButtonBorderWidthProperty = BindableProperty.Create(nameof(ButtonBorderWidth), typeof(double), typeof(View), 0.0, BindingMode.OneWay, propertyChanged: (bindable, oldValue, newValue) =>
{
if (newValue == null) return;
var control = (SVGImageButton)bindable;
control.ButtonBorderWidth = (double)newValue;
});
public double ButtonBorderWidth
{
get
{
return _button.BorderWidth;
}
set
{
_button.BorderWidth = value;
}
}
public static BindableProperty ButtonBorderColorProperty = BindableProperty.Create(nameof(ButtonBorderColor), typeof(Color), typeof(View), Color.Fuchsia, BindingMode.OneWay, propertyChanged: (bindable, oldValue, newValue) =>
{
if (newValue == null) return;
var control = (SVGImageButton)bindable;
control.ButtonBorderColor = (Color)newValue;
});
public Color ButtonBorderColor
{
get
{
return _button.BorderColor;
}
set
{
_button.BorderColor = value;
}
}
#endregion
#region Properties
public string SVGImageName { get; set; }
#endregion
#region Life Cycle
protected override void OnParentSet()
{
base.OnParentSet();
_button.Text = ButtonText;
_svgImage.Source = SvgImageSource.FromResource(SVGImageName);
}
protected override SizeRequest OnMeasure(double widthConstraint, double heightConstraint)
{
_button.HorizontalOptions = (Parent as View).HorizontalOptions;
_button.VerticalOptions = (Parent as View).VerticalOptions;
if (_button.Text != null)
{
var size = DependencyService.Get<ITextMeter>().MeasureTextSize(_button.Text.TrimEnd(), 200, _button.FontSize);
WidthRequest = size.Width + 60 + _button.Height;
}
return base.OnMeasure(widthConstraint, heightConstraint);
}
public SVGImageButton()
{
var content = new RelativeLayout();
_button = new Button { BackgroundColor = Color.Gray, TextColor = Color.Black };
_svgImage = new SvgCachedImage { IsEnabled = false };
content.Children.Add(_button,
Constraint.RelativeToParent((parent) =>
{
return parent.X;
}),
Constraint.RelativeToParent((parent) =>
{
return parent.Y;
}),
Constraint.RelativeToParent((parent) =>
{
return parent.Width;
}),
Constraint.RelativeToParent((parent) =>
{
return parent.Height;
}));
content.Children.Add(_svgImage,
Constraint.RelativeToParent((parent) =>
{
return parent.Width - (parent.Height / 2) - (parent.Height / 4);
}),
Constraint.RelativeToParent((parent) =>
{
return parent.Height - (parent.Height / 2) - (parent.Height / 4);
}),
Constraint.RelativeToParent((parent) =>
{
return parent.Height / 2;
}),
Constraint.RelativeToParent((parent) =>
{
return parent.Height / 2;
}));
Content = content;
_button.Clicked += (sender, e) =>
{
ButtonPressedCommand?.Execute(CommandParameter);
};
}
#endregion
}
}
使用System.Windows.Input;
使用ffimageload.Svg.Forms;
使用核心接口;
使用Xamarin.Forms;
使用Xamarin.Forms.Xaml;
命名空间自定义控件
{
[XamlCompilation(XamlCompilationOptions.Compile)]
公共类SVGImageButton:ContentView
{
#区域成员变量
专用只读按钮_按钮;
私有只读SvgCachedImage _svgImage;
#端区
#区域可结合性质
public static BindableProperty ButtonPressedCommandProperty=BindableProperty.Create(nameof(ButtonPressedCommand)、typeof(ICommand)、typeof(SVGImageButton));
公用图标命令按钮按下命令
{
得到
{
返回(ICommand)GetValue(按钮PressedCommand属性);
}
设置
{
SetValue(按钮PressedCommand属性,值);
}
}
public static BindableProperty CommandParameterProperty=BindableProperty.Create(nameof(CommandParameter)、typeof(object)、typeof(SVGImageButton));
公共对象命令参数
{
获取{return GetValue(CommandParameterProperty);}
set{SetValue(CommandParameterProperty,value);}
}
public static BindableProperty buttonextproperty=BindableProperty.Create(nameof(buttonext)、typeof(string)、typeof(SVGImageButton)、string.Empty、BindingMode.TwoWay、propertyChanged:(bindable、oldValue、newValue)=>
{
if(newValue==null)返回;
var control=(SVGImageButton)可绑定;
control.ButtonText=newValue.ToString();
});
公共字符串按钮文本
{
得到
{
返回_button.Text;
}
设置
{
_文本=值;
}
}
公共静态BindableProperty ButtonBackgroundColorProperty=BindableProperty.Create(名称)(ButtonBackgroundColor)、类型(颜色)、类型(视图)、颜色.Fuchsia、BindingMode.OneWay、属性更改:(bindable、oldValue、newValue)=>
{
if(newValue==null)返回;
var control=(SVGImageButton)可绑定;
control.ButtonBackgroundColor=(Color)newValue;
});
公共颜色按钮背景颜色
{
得到
{
返回按钮。背景颜色;
}
设置
{
_button.BackgroundColor=值;
}
}
公共静态BindableProperty ButtonExtColorProperty=BindableProperty.Create(名称)(ButtonExtColor)、typeof(颜色)、typeof(视图)、Color.Fuchsia、BindingMode.OneWay、propertyChanged:(bindable、oldValue、newValue)=>
{
if(newValue==null)返回;
var control=(SVGImageButton)可绑定;
control.buttonextcolor=(Color)newValue;
});
公共颜色按钮ExtColor
{
得到
{
返回_button.TextColor;
}
设置
{
_button.TextColor=值;
}
}
public static BindableProperty ButtonStyleProperty=BindableProperty.Create(nameof(ButtonBackgroundColor)、typeof(Style)、typeof(View)、null、BindingMode.OneWay、propertyChanged:(bindable、oldValue、newValue)=>
{
if(newValue==null)返回;
var control=(SVGImageButton)可绑定;
control.ButtonStyle=(Style)newValue;
});
公共样式按钮样式
{
得到
{
返回按钮样式;
}
设置
{
_样式=值;
}
}
公共静态BindableProperty ButtonOrderWidthProperty=BindableProperty.Create(nameof(ButtonOrderWidth)、typeof(double)、typeof(View)、0.0、BindingMode.OneWay、propertyChanged:(bindable、oldValue、newValue)=>
{
if(newValue==null)返回;
var control=(SVGImageButton)可绑定;
control.ButtonOrderWidth=(双精度)newValue;
});
公共双按钮宽度
{
得到
{
返回按钮。边框宽度;
}
设置
{
_button.BorderWidth=值;
}
}
公共静态BindableProperty ButtonOrderColorProperty=BindableProperty.Create(nameof(ButtonOrderColor)、typeof(Color)、typeof(View)、Color.Fuchsia、BindingMode.OneWay、propertyChanged:(bindable、oldValue、newValue)=>
{
if(newValue==null)返回;
var control=(SVGImageButton)可绑定;
control.ButtonOrderColor=(颜色)newValue;
});
公共颜色按钮顺序颜色
{
得到
{
返回按钮。边框颜色;
}
设置
{
_button.BorderColor=值;
}
}
#端区
#区域属性
公共字符串SVGImageName{get;set;}
#端区
#区域生命周期
受保护的覆盖无效OnParentSet()
{
base.OnParentSet();
_button.Text=ButtonText;
_svgImage.Source=SvgImageSource.FromResource(SVGImageName);
}
测量时受保护的覆盖尺寸请求(双宽度约束、双高度约束)
<customcontrols:SVGImageButton
x:Name="TypeSelectionButton"
HorizontalOptions="Start"
VerticalOptions="Center"
ButtonPressedCommand="{Binding TypeButtonClickedCommand}"
SVGImageName="SVGImages.ic_triangle_down.svg"
CommandParameter="{x:Reference TypeSelectionButton}"
ButtonText="{Binding SearchTypeButtonText}"
ButtonBackgroundColor="{Binding ButtonBackgroundColor}"/>
protected override SizeRequest OnMeasure(double widthConstraint, double heightConstraint)
{
_button.HorizontalOptions = (Parent as View).HorizontalOptions;
_button.VerticalOptions = (Parent as View).VerticalOptions;
var width = 0d;
if (_button.Text != null)
{
var size = DependencyService.Get<ITextMeter>().MeasureTextSize(_button.Text.TrimEnd(), 200, _button.FontSize);
width = size.Width + 40 + _button.Height;
}
return base.OnMeasure(width, heightConstraint);
}