c# - 用C#动态改变元素的样式

Question

我有一个包含 4x LineSeries 的图表。我定义了两种不同的样式来表示线条，我希望能够动态更改应用于特定 LineSeries 的样式(例如，基于用户点击按钮等)。

我似乎不知道如何从 C# 更新样式。任何帮助表示赞赏!

我试过:

lineChartMood.PolylineStyle = this.Resources.PolylineStyle2 as Style;

但这会返回 Null 异常。

这是页面的 XAML，包括样式定义:

    <phone:PhoneApplicationPage 
    x:Class="Bhutaan.ChartingTest"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
    xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:charting="clr-namespace:System.Windows.Controls.DataVisualization.Charting;assembly=System.Windows.Controls.DataVisualization.Toolkit"
    xmlns:local="clr-namespace:Bhutaan"
    FontFamily="{StaticResource PhoneFontFamilyNormal}"
    FontSize="{StaticResource PhoneFontSizeNormal}"
    Foreground="{StaticResource PhoneForegroundBrush}"
    SupportedOrientations="Portrait" Orientation="Portrait"
    mc:Ignorable="d" d:DesignHeight="768" d:DesignWidth="480"
    shell:SystemTray.IsVisible="True">

    <phone:PhoneApplicationPage.Resources>
        <Style x:Key="PolylineStyle" TargetType="Polyline">
            <Setter Property="StrokeThickness" Value="5"/>
        </Style>
        <Style x:Key="PolylineStyle2" TargetType="Polyline">
            <Setter Property="StrokeThickness" Value="1"/>
        </Style>
    </phone:PhoneApplicationPage.Resources>


    <!--LayoutRoot is the root grid where all page content is placed-->
    <Grid x:Name="LayoutRoot" Background="Transparent">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>

        <!--TitlePanel contains the name of the application and page title-->
        <StackPanel x:Name="TitlePanel" Grid.Row="0" Margin="12,17,0,28">
            <TextBlock x:Name="ApplicationTitle" Text="TEST" Style="{StaticResource PhoneTextNormalStyle}"/>
            <TextBlock x:Name="PageTitle" Text="added" Margin="9,-7,0,0" Style="{StaticResource PhoneTextTitle1Style}"/>
        </StackPanel>

        <!--ContentPanel - place additional content here-->
        <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,-0,12,0">
            <ScrollViewer>
                <StackPanel>
                    <TextBlock Text="Great! That's been saved." FontSize="30" Margin="0,0,0,0"/>
                    <!-- Chart  -->
                    <charting:Chart
                        x:Name="myChart"
                        Margin="0,20,0,0"
                        Height="350"
                        Style="{StaticResource PhoneChartStyle}"
                        Template="{StaticResource PhoneChartPortraitTemplate}">

                        <!-- Series -->
                        <charting:LineSeries
                            x:Name="lineChartMood"
                            Title="Mood"
                            ItemsSource="{Binding}"
                            DependentValuePath="MoodValue"
                            IndependentValuePath="Timestamp"
                            PolylineStyle="{StaticResource PolylineStyle}" >

                            <charting:LineSeries.LegendItemStyle>
                                <Style TargetType="charting:LegendItem">
                                    <Setter Property="Margin" Value="5 0 5 0"/>
                                </Style>
                            </charting:LineSeries.LegendItemStyle>
                        </charting:LineSeries>
                        <!-- Series -->
                        <charting:LineSeries
                            Title="Energy"
                            ItemsSource="{Binding}"
                            DependentValuePath="EnergyValue"
                            IndependentValuePath="Timestamp">
                            <charting:LineSeries.LegendItemStyle>
                                <Style TargetType="charting:LegendItem">
                                    <Setter Property="Margin" Value="5 0 5 0"/>
                                </Style>
                            </charting:LineSeries.LegendItemStyle>
                        </charting:LineSeries>
                        <!-- Series -->
                        <charting:LineSeries
                            Title="Mental"
                            ItemsSource="{Binding}"
                            DependentValuePath="MentalValue"
                            IndependentValuePath="Timestamp">
                            <charting:LineSeries.LegendItemStyle>
                                <Style TargetType="charting:LegendItem">
                                    <Setter Property="Margin" Value="5 0 5 0"/>
                                </Style>
                            </charting:LineSeries.LegendItemStyle>
                        </charting:LineSeries>
                        <!-- Series -->
                        <charting:LineSeries
                            Title="Hunger"
                            ItemsSource="{Binding}"
                            DependentValuePath="HungerValue"
                            IndependentValuePath="Timestamp">
                            <charting:LineSeries.LegendItemStyle>
                                <Style TargetType="charting:LegendItem">
                                    <Setter Property="Margin" Value="5 0 5 0"/>
                                </Style>
                            </charting:LineSeries.LegendItemStyle>
                        </charting:LineSeries>
                    </charting:Chart>

                </StackPanel>
            </ScrollViewer>
        </Grid>
    </Grid>


</phone:PhoneApplicationPage>

Answer 1

我测试了你的代码，找到了问题的原因。

您收到 NullReferenceException 是因为应用程序出于某些未知原因未设置字段 this.lineChartMood。

您必须自己获取此线系列对象。有两种可能的获取方式:

var lineSeriesWay1 = this.FindName("lineChartMood");
var lineSeriesWay2 = myChart.Series.OfType<LineSeries>().First(ls => ls.Name == "lineChartMood");

但我建议在构造函数中显式设置字段 this.lineSeriesMood，如下所示:

public partial class MainPage : PhoneApplicationPage
{
    // Constructor
    public MainPage()
    {
        InitializeComponent();
        // because the code 'this.FindName("lineChartMood")' doesn't work in the constructor, I'll use the following line:
        this.lineChartMood = this.myChart.Series.OfType<LineSeries>().First(ls => ls.Name == "lineChartMood");

        // other code
    }


    private void Button_Click(object sender, RoutedEventArgs e)
    {
        this.lineChartMood.PolylineStyle = (Style)this.Resources["PolylineStyle2"];
        this.lineChartMood.Refresh(); // you should call this method so that the style is applied
    }
}

然后您将能够毫无异常(exception)地引用您的系列。