如何设置QTreeWidget的宽度

怎么设置QTreeWidget的宽度

QTreeWidget *treeWidget = new QTreeWidget;
    treeWidget->setColumnCount(1);
    treeWidget->setColumnWidth(0,100);
 //   treeWidget->setRootIsDecorated(false);
    treeWidget->setSelectionMode(QAbstractItemView::ExtendedSelection);
    treeWidget->setHeaderLabel(tr("医院列表"));
    QTreeWidgetItem *imageItem1 = new QTreeWidgetItem(treeWidget,QStringList(QString("北京")));
    QTreeWidgetItem *imageItem2_1 = new QTreeWidgetItem(imageItem1,QStringList(QString("Band1"))); //子节点1
    QTreeWidgetItem *imageItem2_2 = new QTreeWidgetItem(imageItem1,QStringList(QString("Band2"))); //子节点2
    imageItem1->addChild(imageItem2_1);  //添加子节点
    imageItem1->addChild(imageItem2_2);
  //  treeWidget->setColumnWidth(0,100);

    treeWidget->expandAll(); //结点全部展开

    QHBoxLayout *btnLayout=new QHBoxLayout;
 //   btnLayout->addStretch(1);
    btnLayout->addWidget(hos_manage);
    btnLayout->addWidget(search);
    btnLayout->addWidget(gather);
    btnLayout->addStretch(1);
    btnLayout->addWidget(quit);
  //  btnLayout->addStretch(1);

    QHBoxLayout *btnLayout1=new QHBoxLayout;
    btnLayout1->addWidget(treeWidget);
    btnLayout1->addWidget(tabWidget);

    QVBoxLayout *mainLayout=new QVBoxLayout;
    mainLayout->addLayout(btnLayout);
    mainLayout->addLayout(btnLayout1);

    setLayout(mainLayout);

这是我的一段代码，我已经用 treeWidget->setColumnWidth(0,100)但是运行以后并没有实现不知道为什么，是不是和布局有关系呀，求高手解释

------解决方案--------------------
你的treewidget就一列，该列的宽度默认等于treewidget的宽度

两列以上的话才起作用。