从事件处理程序访问外部对象答案

【问题标题】：Access External Object From An Event Handler从事件处理程序访问外部对象
【发布时间】：2019-06-15 04:41:07
【问题描述】：

谁能告诉我如何从事件处理程序访问外部对象？

下面的代码提供了我正在尝试做的示例。事件处理程序中对 externalClass 的引用会生成以下错误消息“名称 'externalClass' 在当前上下文中不存在”。

我已将程序集输出类型设置为控制台应用程序，以便它打印到控制台。

谁能告诉我如何最好地从事件处理程序中访问 externalClass 对象？代码如下： XAML

<Window x:Class="AccessObjectFromEventHandler.MainWindow"
    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"
    xmlns:local="clr-namespace:AccessObjectFromEventHandler"
    mc:Ignorable="d"
    Title="MainWindow" Height="450" Width="800">
<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="10" />
        <RowDefinition Height="auto" />
        <RowDefinition Height="30" />
        <RowDefinition Height="Auto" />
        <RowDefinition Height="10" />
    </Grid.RowDefinitions>

    <Grid Grid.Row="1" ShowGridLines="True">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="20" />
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="auto" />
            <ColumnDefinition Width="20" />
        </Grid.ColumnDefinitions>
        <Button Grid.Row="1" Grid.Column="2"  Width="100" Height=" 30" Content="Click to Fire Event" Click="Button_Click"/>
    </Grid>
</Grid>

using System;
using System.Windows;
namespace AccessObjectFromEventHandler
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            ExternalClass externalClass = new ExternalClass();
        }
        private void Button_Click(object sender, RoutedEventArgs e)
        {
            Console.WriteLine($"Button Click Event Fired.");
            externalClass.Name = "Some Name";
            externalClass.ExternalClassMethod();
        }
    }
    public partial class ExternalClass
    {
        public string Name { get; set; }
        //  The access modifier is "public" to enable access from external types.
        public void ExternalClassMethod()
        {
            Console.WriteLine($"ExternalClassMethod executed.  Name = {Name}");
        }
     }
}

【问题讨论】：

externalClass 只存在于MainWindow 方法的范围内。将其移至MainWindow（类）作用域并仅在 MainWindow 方法中对其进行初始化。

标签： c# wpf event-handling

【解决方案1】：

试试这个：

using System;
using System.Windows;
namespace AccessObjectFromEventHandler
{
    public partial class MainWindow : Window
    {

        ExternalClass externalClass;

        public MainWindow()
        {
            InitializeComponent();
            externalClass = new ExternalClass();
        }
        private void Button_Click(object sender, RoutedEventArgs e)
        {
            Console.WriteLine($"Button Click Event Fired.");
            externalClass.Name = "Some Name";
            externalClass.ExternalClassMethod();
        }
    }
    public partial class ExternalClass
    {
        public string Name { get; set; }
        //  The access modifier is "public" to enable access from external types.
        public void ExternalClassMethod()
        {
            Console.WriteLine($"ExternalClassMethod executed.  Name = {Name}");
        }
     }
}

【讨论】：