Silverlight Slider 控件“未将对象引用设置到对象的实例”错误解决方案
当在xaml文件中设置Value值之后,编译解决方案后，会报错“未将对象引用设置到对象的实例”
sColour.xaml文件代码
代码
<
UserControl
x:Class
="sample.sColour"
xmlns
="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x
="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d
="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc
="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable
="d"
d:DesignHeight
="300"
d:DesignWidth
="400"
>
<
Grid
x:Name
="LayoutRoot"
Background
="White"
>
<
Grid.RowDefinitions
>
<
RowDefinition
Height
="120"
/>
<
RowDefinition
Height
="120"
/>
</
Grid.RowDefinitions
>
<
Grid.ColumnDefinitions
>
<
ColumnDefinition
Width
="200"
/>
<
ColumnDefinition
Width
="*"
/>
</
Grid.ColumnDefinitions
>
<
Rectangle
Grid.Row
="0"
Grid.Column
="1"
x:Name
="PreviewColour"
Fill
="#FFFF6600"
Margin
="15"
></
Rectangle
>
<
StackPanel
Grid.Row
="1"
Grid.Column
="1"
>
<
TextBlock
FontSize
="12"
>
Color
</
TextBlock
>
<
TextBox
x:Name
="HexColour"
Text
="#FFFF6600"
Height
="30"
Width
="160"
Margin
="5"
HorizontalAlignment
="Left"
FontSize
="11"
></
TextBox
>
</
StackPanel
>
<
StackPanel
Grid.Row
="0"
Grid.Column
="0"
Grid.RowSpan
="2"
VerticalAlignment
="Center"
>
<
TextBlock
Text
="Alpha"
FontSize
="11"
Margin
="10,15,0,0"
/>
<
Slider
x:Name
="SliderAlpha"
Margin
="20,0,10,0"
Maximum
="255"
Value
="255"
ValueChanged
="Slider_ValueChanged"
/>
<
TextBlock
Text
="Red"
FontSize
="11"
Margin
="10,15,0,0"
/>
<
Slider
x:Name
="SliderRed"
Margin
="20,0,10,0"
Maximum
="255"
Value
="255"
ValueChanged
="Slider_ValueChanged"
/>
<
TextBlock
Text
="Green"
FontSize
="11"
Margin
="10,15,0,0"
/>
<
Slider
x:Name
="SliderGreen"
Margin
="20,0,10,0"
Maximum
="255"
Value
="102"
ValueChanged
="Slider_ValueChanged"
/>
<
TextBlock
Text
="Blue"
FontSize
="11"
Margin
="10,15,0,0"
/>
<
Slider
x:Name
="SliderBlue"
Margin
="20,0,10,0"
Maximum
="255"
Value
="0"
ValueChanged
="Slider_ValueChanged"
/>
</
StackPanel
>
</
Grid
>
</
UserControl
>
sColour.xaml.cs文件代码
代码
1
using
System.Windows.Documents;
2
using
System.Windows.Input;
3
using
System.Windows.Media;
4
using
System.Windows.Media.Animation;
5
using
System.Windows.Shapes;
6
namespace
sample
7
{
8
public
partial
class
sColour : UserControl
9
{
10
public
sColour()
11
{
12
InitializeComponent();
13
}
14
private
void
Slider_ValueChanged(
object
sender, RoutedPropertyChangedEventArgs
<
double
>
e)
15
{
16
Color myColor
=
Color.FromArgb((
byte
)SliderAlpha.Value, (
byte
)SliderRed.Value, (
byte
)SliderGreen.Value, (
byte
)SliderBlue.Value);
17
PreviewColour.Fill
=
new
SolidColorBrush(myColor);
18
HexColour.Text
=
myColor.ToString();
19
}
20
}
21
}
仔细查看代码，貌似没有什么错误，但是总是会提示“未将对象引用设置到对象的实例”。后来经过查看资料，这可能是silverlight的一个bug，如果定义了ValueChanged，似乎不能给Slider的value属性在Xaml中赋初值。我们可以在sColour的构造函数中赋值：
1
public
sColour()
2
{
3
InitializeComponent();
4
this
.SliderAlpha.Value
=
255
;
5
this
.SliderRed.Value
=
255
;
6
this
.SliderGreen.Value
=
102
;
7
this
.SliderBlue.Value
=
0
;
8
}
运行界面，一个简易的取色器
