C ++ MFC附加文字以编辑控件会使程序崩溃

Question

Class in test.h:

class CHelixV3Dlg : public CDialogEx
{
   DECLARE_DYNAMIC(CHelixV3Dlg);
friend class CHelixV3DlgAutoProxy;

// Construction
public:
   CHelixV3Dlg(CWnd* pParent = NULL);   // standard constructor

// Dialog Data
   enum { IDD = IDD_HELIXV3_DIALOG };


// Implementation
protected:
   CHelixV3DlgAutoProxy* m_pAutoProxy;
   HICON m_hIcon;
public:
   DWORD WINAPI loop(LPVOID); //thread identifier
   void AppendText(CEdit &edit, LPCTSTR pszText);
};

I have a method defined like so, which is supposed to print a string to editbox, which normally works (in test.cpp):

void TestDlg::AppendText(CEdit &edit, LPCWSTR pszText)
{
   // get the initial text length
   int nLength = edit.GetWindowTextLength();
   // put the selection at the end of text
   edit.SetSel(nLength, nLength);
   // replace the selection
   edit.ReplaceSel(pszText);
 }

Then here is my thread, which listens for key presses(test.cpp)

 DWORD WINAPI TestDlg::KeyThread(LPVOID PARAMS)
 {
    TestDlg* Testdlg;
    while (1)
    {
       Sleep(1);
       if (GetAsyncKeyState(VK_F1) & 1)
       {
           Enabled = !Enabled;
           if (Enabled) {
            CEdit* log = (CEdit*)GetDlgItem(IDC_EDIT1);
            log->AppendText(*log, "test"); //causes a crash
       }
    }
   return 0;
  }

Dialog initialization, where the "loop" thread is created:

BOOL CHelixV3Dlg::OnInitDialog()
{
TestDlg* Testdlg;
CDialogEx::OnInitDialog();

//creates the thread->
CreateThread(NULL, NULL, &Testdlg->KeyThread, NULL, NULL, NULL);

/* IGNORE THIS */
CMenu* pSysMenu = GetSystemMenu(FALSE);
if (pSysMenu != NULL)
{
    BOOL bNameValid;
    CString strAboutMenu;
    bNameValid = strAboutMenu.LoadString(IDS_ABOUTBOX);
    ASSERT(bNameValid);
    if (!strAboutMenu.IsEmpty())
    {
        pSysMenu->AppendMenu(MF_SEPARATOR);
        pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
    }
}

// Set the icon for this dialog.  The framework does this automatically
//  when the application's main window is not a dialog
SetIcon(m_hIcon, TRUE);         // Set big icon
SetIcon(m_hIcon, FALSE);        // Set small icon

// TODO: Add extra initialization here

return TRUE;  // return TRUE  unless you set the focus to a control
}

So, the program compiles, but when it's running and i press F1, it crashes.

Answer 1

You have multiple problems in your code. The uninitialized Testdlg pointer has been already pointed by others.

Here is another one:

log->AppendText(*log, "test");

I'm sure you want to say:

Testdlg->AppendText(*log, "test");

However, that won't work, because this is on a worker thread. What you have to do is post/send a message from the worker thread to the queue of the main thread (that created your test dialog window). In the handler for the message, you can actually call your AppendText method.

Here is how you do that ( notice that I've typed all this in the browser so it may contain errors ):

In the header (TestDlg.h) declare a handler:

LRESULT OnMessageFromWorker(WPARAM wParam, LPARAM lPARAM);

In the source file (TestDlg.cpp):

Define your message:

#define MY_WORKER_THREAD_MSG   WM_APP + 123

Add an entry for the message in the message map

ON_MESSAGE(MY_WORKER_THREAD_MSG, &TestDlg::OnMessageFromWorker)

Send the message from the worker thread:

 DWORD WINAPI TestDlg::KeyThread(LPVOID PARAMS)
 {
    HWND dlgWnd = (HWND)PARAMS;
    while (1)
    {
       Sleep(1);
       if (GetAsyncKeyState(VK_F1) & 1)
       {
           Enabled = !Enabled;
           if (Enabled) 
           {
               CString* msg = new CString("test");
               PostMessage(dlgWnd, 0, reinterpret_cast<LPARAM>(msg));
           }
       }
    }
   return 0;
  }

Notice that in this example you need to pass the HWND of the dialog window, not the this pointer to the thread function. In other words:

CreateThread(nullptr, nullptr, &Testdlg->KeyThread, this->GetSafeHwnd(), nullptr, nullptr);

Handle the message:

LRESULT TestDlg::OnMessageFromWorker(WPARAM wParam, LPARAM lPARAM)
{
   CString* msg = reinterpret_cast<CString*>(lPARAM);
   CEdit* log = (CEdit*)TestDlg->GetDlgItem(IDC_EDIT1);
   AppendText(*log, *msg);
   delete msg; // you must delete the object

   return 0;
}

Answer 2

First you should define TestDlg::Thread as a static member function. When you call CreateThread, the fourth argument should be 'this'.

In your header file (TestDlg.h or whatever):

static DWORD WINAPI TestDlg::KeyThread(LPVOID PARAMS);

In OnInitDialog:

//creates the thread->

CreateThread(NULL, NULL, &Testdlg->KeyThread, this, NULL, NULL);


DWORD WINAPI TestDlg::KeyThread(LPVOID PARAMS)
 {
    TestDlg* Testdlg = (TestDlg*) PARAMS;
    while (1)
    {
       Sleep(1);
       if (GetAsyncKeyState(VK_F1) & 1)
       {
           Enabled = !Enabled;
           if (Enabled) {
            CEdit* log = (CEdit*)TestDlg->GetDlgItem(IDC_EDIT1);
            log->AppendText(*log, "test"); //causes a crash
       }
    }
   return 0;
  }

It still may not work because the CWnd pointers may only be valid in the main thread. YMMV