Detailed Explanation of State Expressions in Qt Style Sheets: Normal State, Hover State, Pressed State

# Introduction to Qt Style Sheets

### 1.1 Basic Concepts of Qt Style Sheets

Qt style sheets are a mechanism for defining and setting the appearance of the Qt application interface. Based on CSS syntax rules, they allow developers to change the look and behavior of widgets by setting style properties and values. Qt style sheets can be applied to the entire application or specific windows and controls, giving them a custom style.

### 1.2 Role and Application Scenarios of Qt Style Sheets

The role of Qt style sheets is to make the application interface more attractive, intuitive, and customizable. By using style sheets, developers can easily adjust the attributes of widgets such as color, font, size, and layout, achieving personalized customization of the interface. Qt style sheets are commonly used in the following scenarios:

- Desktop application interface design: Style sheets can be used to design the theme style of the entire application, including the appearance and interactive effects of widgets like buttons, labels, and text boxes.
- Interface adaptation for mobile device applications: Style sheets can adapt different interface layouts and styles according to the screen size and pixel density of the device, ensuring good display results across various devices.
- Unified interface for cross-platform applications: Style sheets can be used to achieve a consistent interface for cross-platform applications, giving them the same appearance and interactive effects across different operating systems.

In the subsequent chapters, we will delve into the various uses and examples of Qt style sheets.

# 2. Overview of State Expressions in Qt Style Sheets

### 2.1 Role and Significance of State Expressions

In Qt style sheets, state expressions are used to set corresponding styles based on different states of widgets. By using state expressions, we can define the appearance and behavior of widgets in normal, hover, or pressed states, thereby achieving interactive effects and visual changes in the interface.

The state of a widget is usually triggered by mouse events, keyboard events, or other interactive operations. For different types of widgets, some common state expressions are applicable. Mastering the basic syntax and usage of these state expressions can help us control the UI interface more flexibly.

### 2.2 Common State Expressions in Qt

In Qt, common state expressions include the following:

- `:enabled`: Indicates that the widget is in an enabled state.
- `:disabled`: Indicates that the widget is in a disabled state.
- `:hover`: Indicates that the mouse is hovering over the widget.
- `:pressed`: Indicates that the mouse has pressed the widget.
- `:checked`: Indicates that the widget is in a selected state.
- `:unchecked`: Indicates that the widget is in an unselected state.
- `:readOnly`: Indicates that the widget is in a read-only state.

By combining and using these state expressions, we can define the styles of widgets in different states according to different scenarios and needs.

Next, we will introduce the usage of each state expression and demonstrate through examples how to set widget style sheets.

# 3. Style Sheet Settings for Normal State

### 3.1 Style Sheet Syntax for Normal State

In Qt, style sheets can be used to set the appearance of widgets in their normal state. The normal state refers to the default state of the widget, that is, when the user has not interacted with the widget. Here is the syntax for setting styles in the normal state:

selector {
     property: value;
     ...
}

In this syntax, the selector represents the widget or set of widgets that need to be styled, the property represents the style property to be set, and the value represents the value of the property.

### 3.2 Example Demonstration: How to Set Style Sheets for Normal State

Next, we will demonstrate how to set style sheets for a button widget in its normal state by using a simple button control as an