无法在表单的文本框中更新(或连续写入)计数器

can't update (or write continuously) counter in ther form's textbox

本文关键字：连续计数器更新表单文本更新时间：2023-10-16

我是中级 c++ 程序员。但是Visual Studio GUI编程的新手。请相信我，我确实搜索了其他用户也得到的以前的错误，但真的无法继续下去。非常感谢您的进一步帮助。

我只想在小屏幕上看到一个连续的计数器。当我按下"开始"按钮时，计数器必须启动，直到按下"停止"按钮。

我调试表单项目时显示窗口，但是当我按"开始"按钮时，出现错误：

An unhandled exception of type 'System.InvalidOperationException' occurred in System.Windows.Forms.dll
Additional information: Cross-thread operation not valid: Control 'textBox1' accessed from a thread other than the thread it was created on.

我也尝试了在/* */中选择代码部分，但我再次无法做我想做的事。

#include <windows.h>
using namespace System;
using namespace System::Threading;
int formcounter, xx;
#pragma once
namespace denemeform {
    using namespace System;
    using namespace System::ComponentModel;
    using namespace System::Collections;
    using namespace System::Windows::Forms;
    using namespace System::Data;
    using namespace System::Drawing;
    public ref class Form1 : public System::Windows::Forms::Form
    {
    public:
        Form1(void)
        {
            InitializeComponent();
            formcounter=0;
        }
    protected:
        ~Form1()
        {
            if (components)
            {
                delete components;
            }
        }
    private: System::Windows::Forms::Button^  button1;
    protected: 
    private: System::Windows::Forms::Button^  button2;
    private: System::Windows::Forms::TextBox^  textBox1;
    private:
        System::ComponentModel::Container ^components;
#pragma region Windows Form Designer generated code
        void InitializeComponent(void)
        {
            this->button1 = (gcnew System::Windows::Forms::Button());
            this->button2 = (gcnew System::Windows::Forms::Button());
            this->textBox1 = (gcnew System::Windows::Forms::TextBox());
            this->SuspendLayout();
            this->button1->Location = System::Drawing::Point(27, 24);
            this->button1->Name = L"button1";
            this->button1->Size = System::Drawing::Size(75, 23);
            this->button1->TabIndex = 0;
            this->button1->Text = L"&Start";
            this->button1->UseVisualStyleBackColor = true;
            this->button1->Click += gcnew System::EventHandler(this, &Form1::button1_Click);
            this->button2->Location = System::Drawing::Point(166, 24);
            this->button2->Name = L"button2";
            this->button2->Size = System::Drawing::Size(75, 23);
            this->button2->TabIndex = 1;
            this->button2->Text = L"Sto&p";
            this->button2->UseVisualStyleBackColor = true;
            this->button2->Click += gcnew System::EventHandler(this, &Form1::button2_Click);
            this->textBox1->Location = System::Drawing::Point(82, 71);
            this->textBox1->Name = L"textBox1";
            this->textBox1->Size = System::Drawing::Size(100, 20);
            this->textBox1->TabIndex = 2;
            this->AutoScaleDimensions = System::Drawing::SizeF(6, 13);
            this->AutoScaleMode = System::Windows::Forms::AutoScaleMode::Font;
            this->ClientSize = System::Drawing::Size(269, 139);
            this->Controls->Add(this->textBox1);
            this->Controls->Add(this->button2);
            this->Controls->Add(this->button1);
            this->Name = L"Form1";
            this->Text = L"Form1";
            this->ResumeLayout(false);
            this->PerformLayout();
        }
#pragma endregion
        void Test() //test code:: when "Start" is pushed, this code is what executes
        {
            int formcounter=0; //test variable
            while(xx) 
            {
                formcounter++;
                this->textBox1->Text = formcounter.ToString(); //sets first textbox to 'a'
                Sleep(100); //pause for 1 second before continuing
            }
                /*formcounter++;
                if (this->InvokeRequired)
                this->Invoke(gcnew MethodInvoker(this, &Form1::Test));
            else
                this->textBox1->Text = formcounter.ToString();
                Sleep(1000);*/
        }
    private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) 
    {
        xx=1;
        /*Thread^ oThread = gcnew Thread( gcnew ThreadStart( this, &Form1::Test ) );
        oThread->Start();*/
        Thread^ tThread = gcnew Thread(gcnew ThreadStart(this, &Form1::Test));
        tThread->Start();
    }
    private: System::Void button2_Click(System::Object^  sender, System::EventArgs^  e) 
    {
        xx=0;
    }
};
}

代码现在可以正确执行。

void SetTextBoxOnce()
{
    this->textBox1->Text = formcounter.ToString(); 
}
void Test()  
{
    formcounter=0; //test variable
    while(xx) 
    {
        formcounter++;
    this->Invoke(gcnew MethodInvoker(this, &Form1::SetTextBoxOnce));
        Sleep(100);  
        }
    }
private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) 
{
    xx=1;
    Thread^ tThread = gcnew Thread(gcnew ThreadStart(this, &Form1::Test));
    tThread->Start();
}
private: System::Void button2_Click(System::Object^  sender, System::EventArgs^  e) 
{
    xx=0;
}

代码现在可以正确执行。

你没有说当你使用注释掉的代码时会发生什么，但我相信我看到了发生了什么。

你确实需要使用InvokeRequired和this->Invoke，但是你把错误的东西传递给了this->Invoke。您正在传递一个包含循环的方法（Form1：：Test），并且它没有返回。您应该传递一个只设置文本框一次的委托。

尝试将formcounter移动到类字段而不是局部变量，并执行以下操作：

bool xx;
int formcounter;
void SetTextBoxOnce()
{
    this->textBox1->Text = formcounter->ToString();
}
void TestThread()
{
    this->formcounter = 0;
    while(xx)
    {
        this->formcounter++;
        // We're running on a newly created thread, we know that we ALWAYS need to Invoke.
        this->Invoke(gcnew MethodInvoker(this, &Form1::SetTextBoxOnce));
        Thread::Sleep(1000);
    }
}