剛學qt，對它的gridlayout功能非常欣賞 -- 不用自己去考慮如何安放控制元件了，layout自動把它們放好。但是今天發現自己對layout的功能並沒完全吃透。以前一直認為控制元件放到layout裡面，只要動用了setColumnStretch和setRowStretch函式，控制元件的尺寸就被按比例縮放了。其實不然。看下面的程式碼：

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QBrush>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QBrush brh(Qt::blue);
    mp_gLayout = new QGridLayout;
    mp_gLayout->setColumnStretch(0,1);
    mp_gLayout->setColumnStretch(1,1);
    mp_gLayout->setColumnStretch(2,1);
    mp_gLayout->setColumnStretch(3,1);
    mp_gLayout->setColumnStretch(4,1);
    mp_gLayout->setColumnStretch(5,1);
    mp_gLayout->setColumnStretch(6,1);
    mp_gLayout->setColumnStretch(7,1);
    mp_gLayout->setColumnStretch(8,1);
    mp_gLayout->setColumnStretch(9,1);

    mp_gLayout->setRowStretch(0,1);
    mp_gLayout->setRowStretch(1,1);
    mp_gLayout->setRowStretch(2,1);
    mp_gLayout->setRowStretch(3,1);
    mp_gLayout->setRowStretch(4,1);
    mp_gLayout->setRowStretch(5,1);
    mp_gLayout->setRowStretch(6,1);
    mp_gLayout->setRowStretch(7,1);
    mp_gLayout->setRowStretch(8,1);
    mp_gLayout->setRowStretch(9,1);

    mp_View = new QGraphicsView;
    mp_View->setBackgroundBrush(brh);

    mp_Scene = new QGraphicsScene;
    mp_Rect = new QGraphicsRectItem;

    mp_Scene->addItem(mp_Rect);

    mp_View->setScene(mp_Scene);
    <span style="color:#ff0000;">mp_gLayout->addWidget(mp_View, 3,3,4,4);
    qDebug("width = %d, viewWidth = %d", width(), mp_View->width());</span>
    ui->centralWidget->setLayout(mp_gLayout);

    mp_Rect->setRect(0,0,mp_View->width()/5,mp_View->height()/5);
    mp_View->show();
}

MainWindow::~MainWindow()
{
    delete mp_Rect;
    delete mp_Scene;
    delete mp_View;
    delete mp_gLayout;
    delete ui;
}