What is the usage of Qt’s stylesheet?

Stylesheet in Qt is a mechanism used to define the appearance of controls. It allows defining the style of controls, including background color, foreground color, font, borders, spacing, etc., using CSS syntax.

Stylesheets can be utilized to achieve the following functions:

1. Define the background color, foreground color, font, and border styles of the control.
2. Define the style of the control in different states, such as hover, pressed, selected, etc.
3. Define the layout style of the control, such as setting the control’s margins, padding, alignment, etc.

In Qt, you can apply stylesheets by using the following method:

1. Define styles in a separate .qss file, load the file in the code, and apply it to the desired controls.
2. apply a style sheet

For instance, you can use a stylesheet to customize the appearance of a QPushButton.

QPushButton *button = new QPushButton("Click me");
button->setStyleSheet("background-color: red; color: white; border: 1px solid black;");

This sets the background color of the button to red, the font color to white, and the border to black.

In addition to directly setting styles, you can also define the styles of controls in different states using pseudo-classes. For example, you can define the style when the mouse hovers over a button using the :hover pseudo-class.

QPushButton *button = new QPushButton("Click me");
button->setStyleSheet("QPushButton:hover { background-color: blue; }");

When the mouse hovers over the button, the background color of the button will change to blue.

Overall, the stylesheet mechanism in Qt offers a simple and flexible way to define the style of controls, helping developers achieve a personalized appearance for the controls.