Qt提供了一个Designer界面，使得我们可以自由拖动控件对ui进行布局，但所有的控件都是固定的，如果我们想要自定义一个自己设计的控件，添加到Designer中，可供设计者自由设计。那么可以进行如下操作。
首先新建一个项目，选择其他项目，点击Qt4设计师自定义控件。
然后确定，控件类随便添加一个即可。
创建好后如下图所示：
为了扩展多个控件，我们将lqcfcjx.h和lqcfcjx.cpp文件删除，在其他项目中单独设计，然后并在lqcfcjx.pri中扩展其他项目，Switch是一个单独的项目如下：
//lqcfcjx.priinclude(Switch/Switch.pri)
对于lqcfcjxplugin.h中创建一个自定义控件接口，如下：
#ifndef LQCFCJXPLUGIN_H#define LQCFCJXPLUGIN_H//插件子项目的头文件#include"switch.h"#include <QDesignerCustomWidgetInterface>class CustomWidgetInterface: public QObject,public QDesignerCustomWidgetInterface{Q_OBJECTQ_INTERFACES( QDesignerCustomWidgetInterface )public:CustomWidgetInterface( QObject *parent );virtual bool isContainer() const;virtual bool isInitialized() const;virtual QIcon icon() const;virtual QString codeTemplate() const;virtual QString domXml() const;virtual QString group() const;virtual QString includeFile() const;virtual QString name() const;virtual QString toolTip() const;virtual QString whatsThis() const;virtual void initialize( QDesignerFormEditorInterface * );protected:bool d_isContainer{false};QString d_name;QString d_include;QString d_toolTip;QString d_whatsThis;QString d_domXml;QString d_codeTemplate;QString d_goup = "ysyyrps";QIcon d_icon;private:bool d_isInitialized;};class CustomWidgetCollectionInterface: public QObject,public QDesignerCustomWidgetCollectionInterface{Q_OBJECTQ_INTERFACES( QDesignerCustomWidgetCollectionInterface )#if QT_VERSION >= 0x050000Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QDesignerCustomWidgetCollectionInterface" )#endifpublic:CustomWidgetCollectionInterface( QObject *parent = NULL );virtual QList<QDesignerCustomWidgetInterface*> customWidgets() const;private:QList<QDesignerCustomWidgetInterface*> d_plugins;};//子项目继承class SwitchInterface: public CustomWidgetInterface{Q_OBJECTQ_INTERFACES( QDesignerCustomWidgetInterface )public:SwitchInterface( QObject *parent );virtual QWidget *createWidget( QWidget *parent );};#endif // LQCFCJXPLUGIN_H
具体实现为：
#include "lqcfcjxplugin.h"#include <QtPlugin>CustomWidgetInterface::CustomWidgetInterface( QObject *parent ):QObject( parent ),d_isInitialized( false ){}bool CustomWidgetInterface::isContainer() const{return d_isContainer;}bool CustomWidgetInterface::isInitialized() const{return d_isInitialized;}QIcon CustomWidgetInterface::icon() const{return d_icon;}QString CustomWidgetInterface::codeTemplate() const{return d_codeTemplate;}QString CustomWidgetInterface::domXml() const{return d_domXml;}QString CustomWidgetInterface::group() const{return d_goup;}QString CustomWidgetInterface::includeFile() const{return d_include;}QString CustomWidgetInterface::name() const{return d_name;}QString CustomWidgetInterface::toolTip() const{return d_toolTip;}QString CustomWidgetInterface::whatsThis() const{return d_whatsThis;}void CustomWidgetInterface::initialize(QDesignerFormEditorInterface *){if ( d_isInitialized )return;d_isInitialized = true;}CustomWidgetCollectionInterface::CustomWidgetCollectionInterface(QObject *parent ):QObject( parent ){d_plugins.append(new SwitchInterface(this));}QList<QDesignerCustomWidgetInterface*>CustomWidgetCollectionInterface::customWidgets( void ) const{return d_plugins;}SwitchInterface::SwitchInterface(QObject *parent): CustomWidgetInterface(parent){d_name = "Switch";d_include = "switch.h";d_icon = QPixmap( ":/icons/switch.png" );d_isContainer = true;d_domXml ="<widget class=\"Switch\" name=\"switch\">\n"" <property name=\"geometry\">\n"" <rect>\n"" <x>0</x>\n"" <y>0</y>\n"" <width>100</width>\n"" <height>30</height>\n"" </rect>\n"" </property>\n""</widget>\n";}QWidget *SwitchInterface::createWidget(QWidget *parent){return new Switch(parent);}#if QT_VERSION < 0x050000Q_EXPORT_PLUGIN2(lqcfcjx, lqcfcjxPlugin)#endif // QT_VERSION < 0x050000
然后点击构建，就会在对应的Debug或Release文件夹下生成对应的dll和lib文件。
然后将lqcfcjx.dll，lqcfcjxd.dll，lqcfcjx.lib，lqcfcjxd.lib文件放到Qt安装的designer目录下即可。如C:\install\Qt\5.14.2\msvc\plugins\designer和C:\install\Qt\Tools\QtCreator\bin\plugins\designer。这个是我的Qt的两个目录，然后即可在QtDesigner中使用了。
