调整对象不是小部件类型GtkBuilder

Question

我无法使用glade文件中的Gtk::Adjustment小部件。程序构建和运行时出现以下错误：

(test-glade-spinbutton:227780): gtkmm-CRITICAL **: 13:38:45.769: gtkmm: object `adjustment_width' (type=`gtkmm__GtkAdjustment') (in GtkBuilder file) is not a widget type.
(test-glade-spinbutton:227780): gtkmm-CRITICAL **: 13:38:45.769: gtkmm: Gtk::Builder: widget `adjustment_width' was not found in the GtkBuilder file, or the specified part of it.
** (test-glade-spinbutton:227780): CRITICAL **: 13:38:45.769: Gtk::Builder::get_widget(): dynamic_cast<> failed.

然而，在这篇文章中，我删除了与Gtk::Adjustment的交互，这样程序就可以实际运行了。如果我试图读取调整小部件的当前值，程序就会崩溃。

下面是C++代码：

#include <gtkmm.h>
using Gtk::Adjustment;
using Gtk::Application;
using Gtk::Builder;
using Gtk::Grid;
using Gtk::SpinButton;
using Gtk::Window;
class MyWindow : public Window
{
Grid       *main_content;
Adjustment *adjustment_width;
SpinButton *width;
public:
MyWindow()
{
auto builder = Builder::create_from_file("test-spinbutton.glade");
builder->get_widget("main_content"    , main_content);
builder->get_widget("adjustment_width", adjustment_width);
builder->get_widget("width"           , width);
add(*main_content);
present();
}
};
int main()
{
auto app = Application::create("domain.reverse.test-spinbutton");
MyWindow hello;
return app->run(hello);
}

和glade文件：

<?xml version="1.0" encoding="UTF-8"?>
<!-- Generated with glade 3.22.2 -->
<interface>
<requires lib="gtk+" version="3.20"/>
<object class="GtkAdjustment" id="adjustment_height">
<property name="lower">1</property>
<property name="upper">2147483647</property>
<property name="value">1</property>
<property name="step_increment">1</property>
<property name="page_increment">10</property>
</object>
<object class="GtkAdjustment" id="adjustment_width">
<property name="lower">1</property>
<property name="upper">2147483647</property>
<property name="value">1</property>
<property name="step_increment">1</property>
<property name="page_increment">10</property>
</object>
<object class="GtkGrid" id="main_content">
<property name="visible">True</property>
<property name="can_focus">False</property>
<child>
<object class="GtkLabel">
<property name="visible">True</property>
<property name="can_focus">False</property>
<property name="margin_left">24</property>
<property name="margin_top">6</property>
<property name="label" translatable="yes">Width</property>
</object>
<packing>
<property name="left_attach">0</property>
<property name="top_attach">1</property>
</packing>
</child>
<child>
<object class="GtkLabel">
<property name="visible">True</property>
<property name="can_focus">False</property>
<property name="margin_left">24</property>
<property name="margin_top">6</property>
<property name="label" translatable="yes">Height</property>
</object>
<packing>
<property name="left_attach">0</property>
<property name="top_attach">2</property>
</packing>
</child>
<child>
<object class="GtkSpinButton" id="width">
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="margin_left">6</property>
<property name="margin_top">6</property>
<property name="hexpand">True</property>
<property name="adjustment">adjustment_width</property>
</object>
<packing>
<property name="left_attach">1</property>
<property name="top_attach">1</property>
</packing>
</child>
<child>
<object class="GtkSpinButton" id="height">
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="margin_left">6</property>
<property name="margin_top">6</property>
<property name="hexpand">True</property>
<property name="adjustment">adjustment_height</property>
</object>
<packing>
<property name="left_attach">1</property>
<property name="top_attach">2</property>
</packing>
</child>
<child>
<object class="GtkLabel">
<property name="visible">True</property>
<property name="can_focus">False</property>
<property name="label" translatable="yes">Image Size</property>
<attributes>
<attribute name="weight" value="bold"/>
</attributes>
</object>
<packing>
<property name="left_attach">0</property>
<property name="top_attach">0</property>
</packing>
</child>
<child>
<object class="GtkToggleButton" id="toggle_ratio_wh">
<property name="label">gtk-execute</property>
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="receives_default">True</property>
<property name="margin_left">6</property>
<property name="margin_top">6</property>
<property name="use_stock">True</property>
<property name="always_show_image">True</property>
</object>
<packing>
<property name="left_attach">2</property>
<property name="top_attach">1</property>
<property name="height">2</property>
</packing>
</child>
<child>
<placeholder/>
</child>
<child>
<placeholder/>
</child>
<style>
<class name="dialog-main-content"/>
</style>
</object>
</interface>

Answer 1

错误表明adjustment_width不是一个小部件，就像它的继承树所建议的那样(不像网格或旋转按钮(，所以get_widget无法工作。您需要使用get_object。例如：

#include <iostream>
#include <gtkmm.h>
using Gtk::Adjustment;
using Gtk::Application;
using Gtk::Builder;
using Gtk::Grid;
using Gtk::SpinButton;
using Gtk::Window;
class MyWindow : public Window
{
Grid       *main_content;
SpinButton *width;

Glib::RefPtr<Adjustment> adjustment_width;
public:
MyWindow()
{
auto builder = Builder::create_from_file("test-spinbutton.glade");
// Widgets:
builder->get_widget("main_content"    , main_content);
builder->get_widget("width"           , width);
// Other objects (non widgets):
// 1. Get the object from the object three:
Glib::RefPtr<Glib::Object> adjustmentObject = builder->get_object("adjustment_width");
// 2. At this point, it is a Glib::Object (which is Adjustment's base type), so we need
//    to cast:
adjustment_width = Glib::RefPtr<Adjustment>::cast_dynamic(adjustmentObject);
// 3. Then we can access it normally:
std::cout << "The adjustment value is : " << adjustment_width->get_value() << std::endl;
add(*main_content);
present();
}
};
int main()
{
auto app = Application::create("domain.reverse.test-spinbutton");
MyWindow hello;
return app->run(hello);
}