Qt布局-调整大小时保持小部件的宽高比 [英] Qt layouts - Keep widget aspect ratio while resizing
本文介绍了Qt布局-调整大小时保持小部件的宽高比的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我想在QGroupBox上保持长宽比为16/9(在下面的屏幕截图的左侧).为了进行测试，我编写了一个简单的程序，该程序具有4个垂直排列的分组框，所有水平排列的分组框:
main.cpp
#include "MainWindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
MainWindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
MainWindow.cpp
#include "MainWindow.h"
#include "ui_MainWindow.h"
#include <QDebug>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
qDebug() << "horizontalLayout->hasHeightForWidth: " << ui->horizontalLayout->hasHeightForWidth();
}
MainWindow::~MainWindow()
{
delete ui;
}
MainWindow.ui
<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>MainWindow</class>
<widget class="QMainWindow" name="MainWindow">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>1000</width>
<height>703</height>
</rect>
</property>
<property name="windowTitle">
<string>MainWindow</string>
</property>
<widget class="QWidget" name="centralWidget">
<layout class="QHBoxLayout" name="horizontalLayout">
<item>
<widget class="GroupBoxHFW" name="groupBox_1">
<property name="title">
<string>GroupBox</string>
</property>
</widget>
</item>
<item>
<layout class="QVBoxLayout" name="verticalLayout">
<item>
<widget class="QGroupBox" name="groupBox_2">
<property name="minimumSize">
<size>
<width>485</width>
<height>204</height>
</size>
</property>
<property name="maximumSize">
<size>
<width>485</width>
<height>204</height>
</size>
</property>
<property name="title">
<string>GroupBox</string>
</property>
</widget>
</item>
<item>
<widget class="QGroupBox" name="groupBox_3">
<property name="minimumSize">
<size>
<width>485</width>
<height>204</height>
</size>
</property>
<property name="maximumSize">
<size>
<width>485</width>
<height>204</height>
</size>
</property>
<property name="title">
<string>GroupBox</string>
</property>
</widget>
</item>
<item>
<widget class="QGroupBox" name="groupBox_4">
<property name="minimumSize">
<size>
<width>485</width>
<height>204</height>
</size>
</property>
<property name="maximumSize">
<size>
<width>485</width>
<height>204</height>
</size>
</property>
<property name="title">
<string>GroupBox</string>
</property>
</widget>
</item>
<item>
<spacer name="verticalSpacer">
<property name="orientation">
<enum>Qt::Vertical</enum>
</property>
<property name="sizeHint" stdset="0">
<size>
<width>20</width>
<height>40</height>
</size>
</property>
</spacer>
</item>
</layout>
</item>
</layout>
</widget>
<widget class="QMenuBar" name="menuBar">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>1000</width>
<height>21</height>
</rect>
</property>
</widget>
<widget class="QToolBar" name="toolBar">
<property name="windowTitle">
<string>toolBar</string>
</property>
<attribute name="toolBarArea">
<enum>TopToolBarArea</enum>
</attribute>
<attribute name="toolBarBreak">
<bool>false</bool>
</attribute>
</widget>
<widget class="QStatusBar" name="statusBar"/>
</widget>
<layoutdefault spacing="6" margin="11"/>
<customwidgets>
<customwidget>
<class>GroupBoxHFW</class>
<extends>QGroupBox</extends>
<header>GroupBoxHFW.h</header>
<container>1</container>
</customwidget>
</customwidgets>
<resources/>
<connections/>
</ui>
GroupBoxHFW.h
#ifndef GROUPBOXHFW_H
#define GROUPBOXHFW_H
#include <QGroupBox>
class GroupBoxHFW : public QGroupBox
{
public:
GroupBoxHFW(QWidget * parent = 0);
GroupBoxHFW(const QString & title, QWidget * parent = 0);
int heightForWidth(int w) const;
bool hasHeightForWidth() const;
};
#endif // GROUPBOXHFW_H
GroupBoxHFW.cpp
#include "GroupBoxHFW.h"
#include <QDebug>
GroupBoxHFW::GroupBoxHFW(QWidget * parent) : QGroupBox(parent)
{
QSizePolicy policy(this->sizePolicy());
policy.setHeightForWidth(true);
this->setSizePolicy(policy);
}
GroupBoxHFW::GroupBoxHFW(const QString & title, QWidget * parent) : QGroupBox(title, parent)
{
QSizePolicy policy(this->sizePolicy());
policy.setHeightForWidth(true);
this->setSizePolicy(policy);
}
int GroupBoxHFW::heightForWidth(int w) const
{
qDebug() << "GroupBoxHFW::heightForWidth called";
return 9.f / 16.f * w;
}
bool GroupBoxHFW::hasHeightForWidth() const
{
qDebug() << "GroupBoxHFW::hasHeightForWidth called";
return true;
}
如您所见，我重新实现了虚函数int heightForWidth(int w) const和bool hasHeightForWidth() const，希望我的QGroupBox可以自动调整为16/9的宽高比.不幸的是，它不起作用. GroupBoxHFW::heightForWidth()在程序启动时仅被调用一次，甚至不调整窗口小部件的大小.
这是程序的输出:
GroupBoxHFW::hasHeightForWidth called
horizontalLayout->hasHeightForWidth: true
GroupBoxHFW::hasHeightForWidth called
GroupBoxHFW::heightForWidth called
GroupBoxHFW::hasHeightForWidth called
GroupBoxHFW::hasHeightForWidth called
GroupBoxHFW::hasHeightForWidth called
GroupBoxHFW::hasHeightForWidth called
更奇怪的是，当我调整窗口大小，而QGroupBox调整大小时，上面的函数(hasHeightForWidth()和heightForWidth()都没有被调用.
怎么了?
解决方案
如果此组框位于垂直布局内，则您的方法可以工作.
顾名思义，当高度取决于宽度(这是专为文本环绕而设计的)时，hasHeightForWidth的定义是明确的，而不是围绕您的情况的另一种选择.
您能做什么?试试这个(我已经为QGraphicsWidget实现了类似的功能，并且效果很好):
QSize GroupBoxHFW::sizeHint() const {
QSize s = size();
lastHeight = s.height();
s.setWidth((s.height()*16)/9);
s.setHeight(QGroupBox::sizeHint().height());
return s;
}
void GroupBoxHFW::resizeEvent(QResizeEvent * event) {
QGroupBox::resizeEvent(event);
if (lastHeight!=height()) {
updateGeometry(); // it is possible that this call should be scheduled to next iteration of event loop
}
}
小话题:
如果这样做，我将尝试通过QLayout的子类而不是某些QWidget的子类来实现此功能.这样，它可以多次用于不同的小部件.
I want to keep an aspect ratio of 16/9 on a QGroupBox (the one on the left on the screenshot below). For the tests I made a simple program with 4 groupboxes in a vertical layout, all in an horizontal layout:
main.cpp
#include "MainWindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
MainWindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
MainWindow.cpp
#include "MainWindow.h"
#include "ui_MainWindow.h"
#include <QDebug>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
qDebug() << "horizontalLayout->hasHeightForWidth: " << ui->horizontalLayout->hasHeightForWidth();
}
MainWindow::~MainWindow()
{
delete ui;
}
MainWindow.ui
<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>MainWindow</class>
<widget class="QMainWindow" name="MainWindow">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>1000</width>
<height>703</height>
</rect>
</property>
<property name="windowTitle">
<string>MainWindow</string>
</property>
<widget class="QWidget" name="centralWidget">
<layout class="QHBoxLayout" name="horizontalLayout">
<item>
<widget class="GroupBoxHFW" name="groupBox_1">
<property name="title">
<string>GroupBox</string>
</property>
</widget>
</item>
<item>
<layout class="QVBoxLayout" name="verticalLayout">
<item>
<widget class="QGroupBox" name="groupBox_2">
<property name="minimumSize">
<size>
<width>485</width>
<height>204</height>
</size>
</property>
<property name="maximumSize">
<size>
<width>485</width>
<height>204</height>
</size>
</property>
<property name="title">
<string>GroupBox</string>
</property>
</widget>
</item>
<item>
<widget class="QGroupBox" name="groupBox_3">
<property name="minimumSize">
<size>
<width>485</width>
<height>204</height>
</size>
</property>
<property name="maximumSize">
<size>
<width>485</width>
<height>204</height>
</size>
</property>
<property name="title">
<string>GroupBox</string>
</property>
</widget>
</item>
<item>
<widget class="QGroupBox" name="groupBox_4">
<property name="minimumSize">
<size>
<width>485</width>
<height>204</height>
</size>
</property>
<property name="maximumSize">
<size>
<width>485</width>
<height>204</height>
</size>
</property>
<property name="title">
<string>GroupBox</string>
</property>
</widget>
</item>
<item>
<spacer name="verticalSpacer">
<property name="orientation">
<enum>Qt::Vertical</enum>
</property>
<property name="sizeHint" stdset="0">
<size>
<width>20</width>
<height>40</height>
</size>
</property>
</spacer>
</item>
</layout>
</item>
</layout>
</widget>
<widget class="QMenuBar" name="menuBar">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>1000</width>
<height>21</height>
</rect>
</property>
</widget>
<widget class="QToolBar" name="toolBar">
<property name="windowTitle">
<string>toolBar</string>
</property>
<attribute name="toolBarArea">
<enum>TopToolBarArea</enum>
</attribute>
<attribute name="toolBarBreak">
<bool>false</bool>
</attribute>
</widget>
<widget class="QStatusBar" name="statusBar"/>
</widget>
<layoutdefault spacing="6" margin="11"/>
<customwidgets>
<customwidget>
<class>GroupBoxHFW</class>
<extends>QGroupBox</extends>
<header>GroupBoxHFW.h</header>
<container>1</container>
</customwidget>
</customwidgets>
<resources/>
<connections/>
</ui>
GroupBoxHFW.h
#ifndef GROUPBOXHFW_H
#define GROUPBOXHFW_H
#include <QGroupBox>
class GroupBoxHFW : public QGroupBox
{
public:
GroupBoxHFW(QWidget * parent = 0);
GroupBoxHFW(const QString & title, QWidget * parent = 0);
int heightForWidth(int w) const;
bool hasHeightForWidth() const;
};
#endif // GROUPBOXHFW_H
GroupBoxHFW.cpp
#include "GroupBoxHFW.h"
#include <QDebug>
GroupBoxHFW::GroupBoxHFW(QWidget * parent) : QGroupBox(parent)
{
QSizePolicy policy(this->sizePolicy());
policy.setHeightForWidth(true);
this->setSizePolicy(policy);
}
GroupBoxHFW::GroupBoxHFW(const QString & title, QWidget * parent) : QGroupBox(title, parent)
{
QSizePolicy policy(this->sizePolicy());
policy.setHeightForWidth(true);
this->setSizePolicy(policy);
}
int GroupBoxHFW::heightForWidth(int w) const
{
qDebug() << "GroupBoxHFW::heightForWidth called";
return 9.f / 16.f * w;
}
bool GroupBoxHFW::hasHeightForWidth() const
{
qDebug() << "GroupBoxHFW::hasHeightForWidth called";
return true;
}
As you can see, I reimplemented the virtual functions int heightForWidth(int w) const and bool hasHeightForWidth() const, hoping my QGroupBox would resize automatically to a 16/9 aspect ratio. Unfortunately, it doesn't work. GroupBoxHFW::heightForWidth() is called only once when the program starts and it doesn't even resize the widget.
Here is the output of the program:
GroupBoxHFW::hasHeightForWidth called
horizontalLayout->hasHeightForWidth: true
GroupBoxHFW::hasHeightForWidth called
GroupBoxHFW::heightForWidth called
GroupBoxHFW::hasHeightForWidth called
GroupBoxHFW::hasHeightForWidth called
GroupBoxHFW::hasHeightForWidth called
GroupBoxHFW::hasHeightForWidth called
What's even weirder is that none of the functions above (hasHeightForWidth() and heightForWidth() get called when I resize the window, while the QGroupBox is resized.
What's wrong?
解决方案
Your approach could work if this group box was inside vertical layout.
As name says hasHeightForWidth is well defined when height depends on width (this was designed for text wrapping), not another way around (your case).
What you can do? Try this (I've implemented something similar for QGraphicsWidget and it was working quite well):
QSize GroupBoxHFW::sizeHint() const {
QSize s = size();
lastHeight = s.height();
s.setWidth((s.height()*16)/9);
s.setHeight(QGroupBox::sizeHint().height());
return s;
}
void GroupBoxHFW::resizeEvent(QResizeEvent * event) {
QGroupBox::resizeEvent(event);
if (lastHeight!=height()) {
updateGeometry(); // it is possible that this call should be scheduled to next iteration of event loop
}
}
Small off topic:
If I would do that I would try implement this functionality by subclass a QLayout and not as a subclass of some QWidget. This way this it could be used multiple times for different widgets.
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