QFileSystemModel always show expandable or expanded icon

[yycking]

Hi all:
I am using QFileSystemModel but it always show expandable or expanded icon

FileBrowser::FileBrowser()
    : QTreeView()
{
    model = new QFileSystemModel;
    model->setRootPath(QDir::rootPath());
    setModel(model);
    setColumnHidden( 1, true );
    setColumnHidden( 2, true );
    setColumnHidden( 3, true );
    setHeaderHidden(true);
}

FileBrowser::FileBrowser()
    : QTreeView()
{
    model = new QFileSystemModel;
    model->setRootPath(QDir::rootPath());
    setModel(model);
    setColumnHidden( 1, true );
    setColumnHidden( 2, true );
    setColumnHidden( 3, true );
    setHeaderHidden(true);
}

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how to fix it
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