如何在关闭后销毁子窗口?

本人已提出以下申请:

正如您在父窗口中单击“设置”按钮时所看到的,会打开一个名为“设置”的新子窗口,但不幸的是,当关闭该子窗口时,该子窗口未关闭并保持隐藏状态。当再次打开子窗口时,它会创建另一个子窗口实例,依此类推。

问题是,当关闭父窗口时,它不会关闭并保持在 task manager -> processes 。

// Creates an instance of child window
void mainfrm::settings_btnOnButtonClick(wxCommandEvent & event) {
    this->settingWindow = new settingsfrm(this);
    settingWindow->ShowModal();
}

// When closing the child window
void settingsfrm::cancel_btnOnButtonClick(wxCommandEvent & event) {
    this->EndModal(0);
}

// When destroying the variable that contains the instance of child window
mainfrm::~mainfrm() {
    settingWindow = NULL;
    delete settingWindow;
}