c# - C# : "An object reference is required for the non-static field, method, or property" 错误

Question

我在 WPF 中编写代码。首先，我编写了一个单独的项目来测试 COM port 的工作。设备，并且运行良好。接下来我决定将它集成到另一个项目中，但我得到了一个错误。我没有更改代码；我只是将它复制到一个新的代码文件中。

此代码运行良好:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.IO.Ports;
using System.Windows.Threading;

namespace WpfApplication2
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            serial.BaudRate = 9600;
            serial.Handshake = System.IO.Ports.Handshake.None;
            serial.Parity = Parity.None;
            serial.DataBits = 8;
            serial.StopBits = StopBits.One;
            serial.ReadTimeout = 200;
            serial.WriteTimeout = 500;
            serial.DataReceived += new System.IO.Ports.SerialDataReceivedEventHandler(Recieve);
        }

        SerialPort serial = new SerialPort();
        private string recieved_data;

        private delegate void UpdateUiTextDelegate(string text);

        private void Recieve(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
        {
            if (serial.IsOpen)
            {
                try
                {
                    recieved_data = serial.ReadLine();
                    Dispatcher.Invoke(DispatcherPriority.Send, new UpdateUiTextDelegate(DisplayText), recieved_data);
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.ToString());
                }
            }
        }

        private void DisplayText(string code)
        {
            textBox1.AppendText(string1);
        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            ListBoxItem lbi = new ListBoxItem();
            lbi = (ListBoxItem)listBox1.SelectedItem;
            serial.Close();
            serial.PortName = "COM" + (string)lbi.Content;
            try
            {
                serial.Open();
                textBox1.AppendText("Device opened at " + serial.PortName + '\n');
            }
            catch (Exception ex)
            {
                textBox1.AppendText(ex.Message + '\n');
            }
        }
    }
}

但是这个不想工作，我不明白为什么:

using System.IO.Ports;
using System.Windows.Threading;
using System;
using System.Windows;

namespace PresidentProtocol
{
    public class QRBarCode
    {
       // private SerialPort serial = new SerialPort();

        public QRBarCode(string com)
        {
            serial.BaudRate = 9600;
            serial.Handshake = System.IO.Ports.Handshake.None;
            serial.Parity = Parity.None;
            serial.DataBits = 8;
            serial.StopBits = StopBits.One;
            serial.ReadTimeout = 200;
            serial.WriteTimeout = 500;
            serial.DataReceived += new System.IO.Ports.SerialDataReceivedEventHandler(Recieve);
            serial.Close();
            serial.PortName = com;
            try
            {
                serial.Open();
            }
            catch (Exception)
            {
                MessageBox.Show("Error opening COM port.");
            }
        }

        SerialPort serial = new SerialPort();
        private string recieved_data;


        private delegate void UpdateUiTextDelegate(string text);

        private void Recieve(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
        {
            if (serial.IsOpen)
            {
                try
                {
                    recieved_data = serial.ReadLine();
                    Dispatcher.Invoke(DispatcherPriority.Send, new UpdateUiTextDelegate(DisplayText), recieved_data);
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.ToString());
                }
            }
        }

        private void DisplayText(string code)
        {
            MessageBox.Show(code);
        }
    }
}

错误:

An object reference is required for the non-static field, method, or property 'System.Windows.Threading.Dispatcher.Invoke(System.Windows.Threading.DispatcherPriority, System.Delegate, object)' E:\C#\PresidentProtocol\PresidentProtocol\classes\QRCodeReader.cs

在这行代码中:

Dispatcher.Invoke(DispatcherPriority.Send, new UpdateUiTextDelegate(DisplayText), recieved_data);

Answer 1

在第一段代码中，你在一个继承自 Window 的类中，所以你在范围内有一个 Dispatcher 属性，它返回一个 Dispatcher 的实例。在第二个代码中，您在 QRBarCode 类中，它没有 Dispatcher 属性；所以编译器假定您指的是 Dispatcher 类型，并尝试调用此类型的 Invoke，但由于它不是静态方法，因此无法调用直接在类型上。

你需要一个Dispatcher的实例来调用Invoke；您可以使用应用程序中的一个:

Application.Current.Dispatcher.Invoke(...);