FLTK Fl_Choice 获取选中项

Posted 2023-02-21

【中文标题】FLTK Fl_Choice 获取选中项

【英文标题】：FLTK Fl_Choice obtain selected item

【发布时间】：2014-05-22 05:38:12

【问题描述】：

我想获取选定的用户项，但此代码出错：

choice->value(); 

希望各位好心人能帮帮我。

    Fl_Choice*    choice;
    int    i   =   0;

    void but_cb(Fl_Button* obj, void*)
    
        i = choice->value();
        cout<<i;
    
    int main (int argc, char* argv[]) 
    Fl_Double_Window* win = new Fl_Double_Window(400,400,"Sample");
    win->begin();
    Fl_Choice* choice = new Fl_Choice(100,100,100,100,"Name");
    choice->add("Peter");
    choice->add("Tom");
    choice->add("Mary");
    Fl_Button* but = new Fl_Button(300,300,50,50,"Selected");
    but->callback((Fl_Callback*)but_cb);
    win->show();
    return (Fl::run());

【参考方案1】：

我没有花太多时间阅读代码，因此下面的修改和注释代码可能无法解决您的问题。我相信 choice 在 but_cb() 中为 NULL，因为您正在 main() 函数中重新定义选择，隐藏全局“选择”指针。

Fl_Choice* choice;
int i = 0;

void but_cb(Fl_Button* obj, void*) 
    i = choice->value(); // uses global `choice` pointer to Fl_Choice.
    cout << i;


int main (int argc, char* argv[]) 
    Fl_Double_Window* win = new Fl_Double_Window(400,400,"Sample");
    win->begin();
        /* You are redefining choice here! BAD, because but_cb uses the global one.
        Fl_Choice* choice = new Fl_Choice(100,100,100,100,"Name");
        */

        // Good, assigns to the global `choice`, so it won't be NULL when but_cb is called
        choice = new Fl_Choice(100,100,100,100,"Name"); 

        choice->add("Peter");
        choice->add("Tom");
        choice->add("Mary");
        Fl_Button* but = new Fl_Button(300,300,50,50,"Selected");
        but->callback((Fl_Callback*)but_cb);
    win->show();
    return (Fl::run());