如何在文件中声明小部件.cpp gtkmm

Question

我有一个简单的gtkmm程序：

文件main.cpp：

#include "mainwindow.h"
#include <gtkmm/application.h>

int main(int argc, char *argv[])
{
    auto app = Gtk::Application::create(argc, argv, "org.gtkmm.example");

    MainWindow window;
    //Shows the window and returns when it is closed.

    return app->run(window);
}

文件mainwindow.h：

#include <gtkmm/window.h>
#include <gtkmm.h>

class MainWindow : public Gtk::Window {

public:
    MainWindow();
    virtual ~MainWindow();

protected:

    Gtk::Label myLabel;
};

和文件mainwindow.cpp：

#include "mainwindow.h"
#include <iostream>
//using namespace gtk;

MainWindow ::MainWindow():myLabel("this is Label")
{
add(myLabel);
show_all_children();
}
MainWindow::~MainWindow() {}

此代码运行正常。但是现在我想在文件mainwindow.cpp中声明一个Label：

#include "mainwindow.h"
#include <iostream>

MainWindow ::MainWindow():myLabel("this is Label")
{
Gtk::Label myLabel2("this is label 2");
add(myLabel2);
show_all_children();
}
MainWindow::~MainWindow() {}

标签不显示我运行此代码时，有人能告诉我什么错误吗？谢谢你的帮助！

Answer 1

标签没有显示，因为它在范围的末尾被破坏（即在构造函数的末尾）。 为避免这种情况，您需要在堆上分配Label。但是，为避免内存泄漏，您应该使用Gtk :: manage函数，因此标签的内存将由容器[1]管理。

Gtk::Label* myLabel2 = Gtk::manage(new Gtk::Label("this is label 2"));
add(myLabel2);
show_all_children();

[1] https://developer.gnome.org/gtkmm-tutorial/stable/sec-memory-widgets.html.en#memory-managed-dynamic

Answer 2

You have two problems here. First myLabel2 goes out of scope have the end of your constructor and is destroyed. The second is Gtk::Window as a single item container and can only hold one widget.

The solution for myLabel2 going out of scope is to allocate it on the heap see @Marcin Kolny answer. Or construct it similar to how you have done with myLabel.

For the second issue a multi-item container needs to be added to your Gtk::Window, then you can add your other widgets to that. This container can be a Gtk::Box, Gtk::Grid, etc... It depends on your needs.

One of many possible solutions is:

mainwindow.h

#include <gtkmm.h>

class MainWindow : public Gtk::Window {
public:
    MainWindow();
    virtual ~MainWindow();
protected:
    Gtk::Box myBox;
    Gtk::Label myLabel;
    Gtk::Label myLabel2;
};

mainwindow.cpp

#include "mainwindow.h"

MainWindow::MainWindow():
  myLabel("this is Label"), myLabel2("this is label 2");
{
  add myBox;
  myBox.pack_start(myLabel);
  myBox.pack_start(myLabel2);
  show_all_children();
}
MainWindow::~MainWindow() {}