1. 异常

• 开启 ItemIsUserCheckable以后，界面上没有出现多选框。

	QTreeWidgetItem *item = new QTreeWidgetItem();
    item->setText(0, "hello");
    item->setFlags(Qt::ItemIsUserCheckable | Qt::ItemIsSelectable |
                   Qt::ItemIsEnabled | Qt::ItemIsAutoTristate);
    ui->treeWidget->addTopLevelItem(item);

2. 正常

• 添加 item->setCheckState(0, Qt::Unchecked);

	QTreeWidgetItem *item = new QTreeWidgetItem();
    item->setText(0, "hello");
    item->setFlags(Qt::ItemIsUserCheckable | Qt::ItemIsSelectable |
                   Qt::ItemIsEnabled | Qt::ItemIsAutoTristate);
    item->setCheckState(0, Qt::Unchecked);  //重要
    ui->treeWidget->addTopLevelItem(item);