B. Minimum：控制項的sizeHint為控制項的最小尺寸。控制項不能小於這個sizeHint，但是可以
放大。
C. Maximum：控制項的sizeHint為控制項的最大尺寸，控制項不能放大，但是可以縮小到它的最小
的允許尺寸。
D. Preferred：控制項的sizeHint是它的sizeHint，但是可以放大或者縮小
E. Expandint：控制項可以自行增大或者縮小
註：sizeHint（布局管理中的控制項默認尺寸，如果控制項不在布局管理中就為無效的值）
1.QHBoxLayout是水平布局，將從左往右（orright to left for right-to-left languages ）widget布局成水平行
2.QVBoxLayout是垂直布局，從頂部到底部
3.QGridLayout 是二位的網格布局。它可以容納多個單元格：
4.QFormLayout是兩列label-field式的表單布局
代碼舉例：
下面代碼創建QHBoxLayout來管理5個QPushButtons的幾何圖形：
QWidget *window= new QWidget;
QPushButton *button1= new QPushButton("One");
QPushButton *button2= new QPushButton("Two");
QPushButton *button3= new QPushButton("Three");
QPushButton *button4= new QPushButton("Four");
QPushButton *button5= new QPushButton("Five");
QHBoxLayout *layout= new QHBoxLayout;
layout->addWidget(button1);
layout->addWidget(button2);
layout->addWidget(button3);
layout->addWidget(button4);
layout->addWidget(button5);
window->setLayout(layout);
window->show();
QGridLayout示例如下：
QWidget *window = new QWidget;
QPushButton *button1 = new QPushButton("One");
QPushButton *button2 = new QPushButton("Two");
QPushButton *button3 = new QPushButton("Three");
QPushButton *button4 = new QPushButton("Four");
QPushButton *button5 = new QPushButton("Five");
QGridLayout *layout = new QGridLayout;
layout->addWidget(button1, 0, 0);
layout->addWidget(button2, 0, 1);
layout->addWidget(button3, 1, 0, 1, 2);
layout->addWidget(button4, 2, 0);
layout->addWidget(button5, 2, 1);
window->setLayout(layout);
window->show();
QFormLayout示例如下：
QWidget *window = new QWidget;
QPushButton *button1 = new QPushButton("One");
QLineEdit *lineEdit1 = new QLineEdit();
QPushButton *button2 = new QPushButton("Two");
QLineEdit *lineEdit2 = new QLineEdit();
QPushButton *button3 = new QPushButton("Three");
QLineEdit *lineEdit3 = new QLineEdit();
QFormLayout *layout = new QFormLayout;
layout->addRow(button1, lineEdit1);
layout->addRow(button2, lineEdit2);
layout->addRow(button3, lineEdit3);
window->setLayout(layout);
window->show();
The use of rich text in a label widget can introduce some problemsto the layout of its parent widget. Problems occur due to the way rich text ishandled by Qt's layout managers when the label is word wrapped.
Incertain cases the parent layout is put into QLayout::FreeResize mode, meaningthat it will not adapt the layout of its contents to fit inside small sizedwindows, or even prevent the user from making the window too small to beusable. This can be overcome by subclassing the problematic widgets, andimplementing suitable sizeHint() andminimumSizeHint() functions.
Insome cases, it is relevant when a layout is added to a widget. When you set thewidget of a QDockWidget ora QScrollArea (with QDockWidget::setWidget() andQScrollArea::setWidget()), the layout mustalready have been set on the widget. If not, the widget will not be visible.
在一些情況下，當布局被添加到widget時需要特別注意。當設置QDockWidget ora QScrollArea widget時（用QDockWidget::setWidget() andQScrollArea::setWidget())，布局必須已經被設置到widget上。否則，這些widget將不可見。
頭文件
card.h
#ifndef CARD_H
#define CARD_H
#include <QtGui>
#include <QList>
class CardLayout : public QLayout
{
public:
CardLayout(QWidget *parent, int dist): QLayout(parent, 0, dist) {}
CardLayout(QLayout *parent, int dist): QLayout(parent, dist) {}
CardLayout(int dist): QLayout(dist) {}
~CardLayout();
void addItem(QLayoutItem *item);
QSize sizeHint() const;
QSize minimumSize() const;
int count() const;
QLayoutItem *itemAt(int) const;
QLayoutItem *takeAt(int);
void setGeometry(const QRect &rect);
private:
QList<QLayoutItem*> list;
};
#endif
實現文件
card.cpp
#include "card.h"
int CardLayout::count() const
{
// QList::size() returns the number of QLayoutItems in the list
return list.size();
}
int CardLayout::count() const
{
// QList::size() returns the number of QLayoutItems in the list
return list.size();
}
int CardLayout::count() const
{
// QList::size() returns the number of QLayoutItems in the list
return list.size();
}
CardLayout::~CardLayout()
{
QLayoutItem *item;
while ((item = takeAt(0)))
delete item;
}
void CardLayout::setGeometry(const QRect &r)
{
QLayout::setGeometry(r);
if (list.size() == 0)
return;
int w = r.width() - (list.count() - 1) * spacing();
int h = r.height() - (list.count() - 1) * spacing();
int i = 0;
while (i < list.size()) {
QLayoutItem *o = list.at(i);
QRect geom(r.x() + i * spacing(), r.y() + i * spacing(), w, h);
o->setGeometry(geom);
++i;
}
}
QSize CardLayout::sizeHint() const
{
QSize s(0,0);
int n = list.count();
if (n > 0)
s = QSize(100,70); //start with a nice default size
int i = 0;
while (i < n) {
QLayoutItem *o = list.at(i);
s = s.expandedTo(o->sizeHint());
++i;
}
return s + n*QSize(spacing(), spacing());
}
QSize CardLayout::minimumSize() const
{
QSize s(0,0);
int n = list.count();
int i = 0;
while (i < n) {
QLayoutItem *o = list.at(i);
s = s.expandedTo(o->minimumSize());
++i;
}
return s + n*QSize(spacing(), spacing());
}
