C#回调机制

来源：互联网发布：apache storm 源码编辑：程序博客网时间：2024/05/17 20:09

在上述代码中有这样一条奇怪语句

CheckForIllegalCrossThreadCalls = false;//允许跨线程调用

在.net上执行的是托管代码，C#强制要求这些代码必须是线程安全的，不允许跨线程访问windows窗体控件。儿这条语句是将C#内置控件（Control）类的CheckForIllegalCrossThreadCalls属性为false，以屏蔽C#编译器对跨线程调用的检查。这种做法是不安全的。如何在遵守.net安全标准前提下从一个线程访问另一个线程创建的控件，就要使用到C#回调机制。
定义、声明回调

 private delegate void WriTextBox1Callback(char ch); private WriTextBox1Callback wriTextBox1Callback;//“回调”WriTextBox1Callback其实就是一个委托

初始化回调方法

wriTextBox1Callback = new WriTextBox1Callback(WriText1);//其实就是实例化委托，这里的WriText1称为“回调方法”

触发对象动作

textBox1.Invoke(wriTextBox1Callback,ch);//将委托wriTextBox1Callback作为参数传递给控件的Invoke方法

采用回调、线程和委托机制实现“文字抄写员”

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Windows.Forms;using System.Threading;namespace ThreadCallback{    public partial class Form1 : Form    {        //声明委托以实现回调机制        private delegate void WriteTextBox(char ch);//自定义委托        private WriteTextBox writeTextBox;        //操作文本1的回调        private delegate void WriTextBox1Callback(char ch);        private WriTextBox1Callback wriTextBox1Callback;        //操作文本2的回调        private delegate void WriTextBox2Callback(char ch);        private WriTextBox2Callback wriTextBox2Callback;        public Form1()        {            InitializeComponent();            //CheckForIllegalCrossThreadCalls = false;//允许跨线程调用            wriTextBox1Callback = new WriTextBox1Callback(WriText1);            wriTextBox2Callback = new WriTextBox2Callback(WriText2);                    }        private void button1_Click(object sender, EventArgs e)        {            if (checkBox1.Checked == true)            {                               textBox1.Clear();                textBox1.Refresh();                ThreadStart doTask1 = new ThreadStart(DoTask1);                Thread tsk1Thread = new Thread(doTask1);                tsk1Thread.Start();            }            if (checkBox2.Checked == true)            {                               textBox2.Clear();                textBox2.Refresh();                ThreadStart doTask2 = new ThreadStart(DoTask2);                Thread tsk2Thread = new Thread(doTask2);                tsk2Thread.Start();            }        }        private void DoTask1()        {            //使用回调            writeTextBox = new WriteTextBox(WriTextBox1);            WriText(writeTextBox);        }        private void DoTask2()        {            //使用回调            writeTextBox = new WriteTextBox(WriTextBox2);            WriText(writeTextBox);        }        private void WriText(WriteTextBox wMethod)        {            string str = textBox3.Text;            for (int i = 0; i < str.Length; i++)            {                wMethod(str[i]);                //延时                DateTime now = DateTime.Now;                while (now.AddSeconds(1)>DateTime.Now){}            }        }        private void WriTextBox1(char ch)        {             //使用回调语句            textBox1.Invoke(wriTextBox1Callback,ch);        }        private void WriTextBox2(char ch)        {            //使用回调语句            textBox2.Invoke(wriTextBox2Callback, ch);        }        private void WriText1(char ch)        {            textBox1.AppendText(ch + "\r");        }        private void WriText2(char ch)        {            textBox2.AppendText(ch +"\r");        }    }}

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