QML 支持很多基本类型。
A
基本类型
是某种简单值的引用,譬如
int
或
string
。这相比
QML 对象类型
, which refers to an object with properties, signals, methods and so on. Unlike an object type, a basic type cannot be used to declare QML objects: it is not possible, for example, to declare an
int{}
对象或
size{}
对象。
Basic types can be used to refer to:
width
and
height
属性)
When a variable or property holds a basic type and it is assigned to another variable or property, then a copy of the value is made. In JavaScript, this value is called a primitive value.
Some basic types are supported by the engine by default and do not require an
import statement
to be used, while others do require the client to import the module which provides them. All of the basic types listed below may be used as a
property
type in a QML document, with the following exceptions:
list
must be used in conjunction with a QML object type
enumeration
cannot be used directly as the enumeration must be defined by a registered QML object type
The basic types supported natively in the QML language are listed below:
二进制 true/false 值 | |
带小数点的数字,以双精度存储 | |
命名枚举值 | |
整数 (如:0、10 或 -20) | |
QML 对象列表 | |
带小数点的数字 | |
自由形式文本字符串 | |
资源定位器 | |
一般特性类型 |
QML modules may extend the QML language with more basic types. For example, the basic types provided by the
QtQuick
module are listed below:
日期值 | |
具有 X 和 Y 属性的值 | |
具有 X、Y、宽度及高度属性的值 | |
具有宽度和高度属性的值 |
The Qt global object provides useful functions for manipulating values of basic types.
Currently only QML modules which are provided by Qt may provide their own basic types, however this may change in future releases of Qt QML. In order to use types provided by a particular QML module, clients must import that module in their QML documents.
一些基本类型拥有特性:例如,
font
类型拥有
pixelSize
,
family
and
bold
properties. Unlike properties of
对象类型
, properties of basic types do not provide their own property change signals. It is only possible to create a property change signal handler for the basic type property itself:
Text { // invalid! onFont.pixelSizeChanged: doSomething() // also invalid! font { onPixelSizeChanged: doSomething() } // but this is ok onFontChanged: doSomething() }
Be aware, however, that a property change signal for a basic type is emitted whenever any of its attributes have changed, as well as when the property itself changes. Take the following code, for example:
Text { onFontChanged: console.log("font changed") Text { id: otherText } focus: true // changing any of the font attributes, or reassigning the property // to a different font value, will invoke the onFontChanged handler Keys.onDigit1Pressed: font.pixelSize += 1 Keys.onDigit2Pressed: font.b = !font.b Keys.onDigit3Pressed: font = otherText.font }
In contrast, properties of an 对象类型 emit their own property change signals, and a property change signal handler for an object-type property is only invoked when the property is reassigned to a different object value.
另请参阅 QML 类型系统 .