QTreeView no show inside QDockWidget

[yuping]

Hi, I want to show are file system using QTreeView on a QDockWidget. Here is my code:

QFile file(":/default.txt");
    file.open(QIODevice::ReadOnly);
    TreeModel model(file.readAll());
    file.close();
 
    QTreeView w;
    w.setModel(&model);
    swatch1->setWidget(&w);
    w.setEnabled(true);
 
    addDockWidget(leftarea, swatch1);

QFile file(":/default.txt");
    file.open(QIODevice::ReadOnly);
    TreeModel model(file.readAll());
    file.close();

    QTreeView w;
    w.setModel(&model);
    swatch1->setWidget(&w);
    w.setEnabled(true);

    addDockWidget(leftarea, swatch1);

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swatch1 is of type QDockWidget. The above code is inside a function of MainWindow. The code runs smoothly, and the tree does not show up.

I also tried another way: putting QTreeView into a QLayout, which in turn be put into QDockWidget. This 2nd code also runs smoothly, and the tree does not show up.

This code is copied from a working example on Qt Creator IDE, and I tested working. The only difference is, in the original QTreeView example, the above code is placed inside the main() { ..... } function.

Does anyone has a working example, putting QTreeView into QDockWidget and working? Thanks in advance.