[Qt UI related] How to control the maximize, minimize and close buttons of the window in Qt? One article takes you to master the usage

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overview

The maximize, minimize, and close buttons for a window are usually controlled by the operating system's window manager, not by the application. The behavior of these buttons (such as clicking the maximize button to resize the window to the size of the screen) is implemented by the window manager, and applications generally cannot change these behaviors.

In Qt, you can use QWidget::setWindowFlagsthe function to set some properties of the window, including whether to display the maximize, minimize and close buttons. However, the actual effect of these properties may be limited by the window manager. For example, some window managers may ignore Qt::WindowMaximizeButtonHintthe flag and always show the maximize button.

If you want to change the behavior of a window's maximize, minimize, or close buttons, you may need to use platform-specific code, or use some special window manager API. However, this usually requires in-depth knowledge of your window manager or graphics system, and may not work on all platforms or window managers.

default behavior

In Qt, the default behavior of the window's minimize, maximize and close buttons is as follows:

1. Minimize button : By default, the minimize button is always enabled unless you explicitly disable it. The minimize button allows the user to minimize the window to the taskbar or the Dock.

2. Maximize button : If the minimum and maximum sizes of the window are different (that is, the size of the window is variable), the maximize button is enabled by default. If the minimum and maximum dimensions of the window are the same (i.e. the size of the window is fixed), the maximize button is disabled by default. This is because maximizing does not make sense if the size of the window is fixed.

3. Close Button : By default, the close button is always enabled unless you explicitly disable it. The close button allows the user to close the window. Note that closing the window does not necessarily exit the application, it depends on the behavior of your application.

The above is Qt's default behavior, but note that this may be affected by the window manager. Different window managers may behave differently, especially in non-mainstream or custom environments. If you experience behavior inconsistent with the above description, you may need to consult your window manager's documentation, or seek specialized help.

Controls in Qt

In Qt, the state (enabled or disabled) of a window's minimize, maximize, and close buttons is usually Qt::WindowFlagsdetermined by the window's window flag ( ). The window flags are a set of bitmasks that control some properties of the window, including whether minimize, maximize, and close buttons are displayed.

Here are some common strategies for these three buttons:

1. Minimize button : If the window's window flag contains Qt::WindowMinimizeButtonHint, the minimize button will usually be displayed and enabled. Qt::WindowMinimizeButtonHintThe minimize button is normally hidden if the window's window flag does not contain it . Note that even if the minimize button is displayed, the user may not be able to minimize the window if the window's window flag contains Qt::MSWindowsFixedSizeDialogHint(on Windows) or Qt::FramelessWindowHint(on all platforms).

2. Maximize button : If the window's window flag contains Qt::WindowMaximizeButtonHint, and the window's minimum and maximum sizes are different, the maximize button will usually be displayed and enabled. Qt::WindowMaximizeButtonHintThe maximize button is usually hidden or disabled if the window's window flag does not contain it , or if the window's minimum and maximum dimensions are the same.

3. Close button : If the window's window flag contains Qt::WindowCloseButtonHint, the close button will usually be displayed and enabled. Qt::WindowCloseButtonHintThe close button is normally hidden if the window's window flag does not contain it . Note that even if the close button is displayed, the user may not be able to close the window if the window's window flag contains Qt::MSWindowsFixedSizeDialogHint(on Windows) or Qt::FramelessWindowHint(on all platforms).

The above is Qt's default behavior, but note that this may be affected by the window manager. Different window managers may behave differently, especially in non-mainstream or custom environments. If you experience behavior inconsistent with the above description, you may need to consult your window manager's documentation, or seek specialized help.

Maximize button control code example

Use Qt::WindowFlagsto disable the maximize button. You can QWidget::setWindowFlagsset the flags of the window through the function. Here is an example:

void MainWindow::onToggleResizeButtonClicked(bool checked)
{
    
    
    if (checked) {
    
    
        // Allow resizing
        setMinimumSize(QSize(0, 0));
        setMaximumSize(QSize(QWIDGETSIZE_MAX, QWIDGETSIZE_MAX));
        // Enable maximize button
        setWindowFlags(windowFlags() | Qt::WindowMaximizeButtonHint);
    } else {
    
    
        // Prevent resizing
        setFixedSize(size());
        // Disable maximize button
        setWindowFlags(windowFlags() & ~Qt::WindowMaximizeButtonHint);
    }
    // Apply the new window flags
    show();
}

In this example, we enable the maximize button toggleResizeButtonby adding the flag when is selected . We disable the maximize button by removing the flag Qt::WindowMaximizeButtonHintwhen toggleResizeButtonis not selected .Qt::WindowMaximizeButtonHint

show()Note that changing the window's logo will hide the window, so we need to call the function to redisplay the window after changing the window's logo .
This method should disable the maximize button, but be aware that this may be limited by your window manager. If your window manager does not support disabling the maximize button, this method may not work.

flickering problem

But when you change the window's flag (e.g. via QWidget::setWindowFlagsthe function), Qt automatically hides and redisplays the window, which may cause the window to flicker. This is because changing a window's flag may change the window's appearance or behavior, and Qt needs to recreate the window to apply the new flag.

The best way to avoid window flickering is to minimize the number of times you change the window's logo. For example, you can set all the required flags when the window is created, instead of changing the flags after the window is already displayed.

If you must change the window flag after the window has already been shown, you may need to use some platform specific method to avoid window flickering. This may involve using the low-level window manager API, or using some special window properties or flags. This usually requires in-depth knowledge of your window manager or graphics system, and may not work on all platforms or window managers.

If window flickering is causing serious problems, you may need to consider other ways to achieve your needs, such as using other UI elements or interaction modes, or adjusting your UI design.

Other button instances

In Qt, you can use QWidget::setWindowFlagsfunctions and Qt::WindowFlagsenumerations to control the minimize and close buttons of windows. Here are some relevant flags:

• Qt::WindowMinimizeButtonHint: If this flag is set, the window will have a minimize button.
• Qt::WindowCloseButtonHint: If this flag is set, the window will have a close button.

|You can set multiple flags by bitwise ORing ( ), for example:

setWindowFlags(Qt::Window | Qt::WindowMinimizeButtonHint | Qt::WindowCloseButtonHint);

This line of code creates a window with minimize and close buttons.

If you want to remove a flag, you can use bitwise AND ( &) and bitwise NOT ( ~), for example:

setWindowFlags(windowFlags() & ~Qt::WindowMinimizeButtonHint);

This line of code removes the window's minimize button.

show()Note that changing the window's flag will hide the window, so you need to call the function to redisplay the window after changing the window's flag . Also, the actual effect of a window's flags may be limited by the window manager.

epilogue

Comprehension is an important step towards the next level in our programming learning journey. However, mastering new skills and ideas always takes time and persistence. From a psychological point of view, learning is often accompanied by continuous trial and error and adjustment, which is like our brain gradually optimizing its "algorithm" for solving problems.

That's why when we encounter mistakes, we should see them as opportunities to learn and improve, not just obsessions. By understanding and solving these problems, we can not only fix the current code, but also improve our programming ability and prevent the same mistakes from being made in future projects.

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