Qml属性绑定小误区

Item {
    property var car: new Object({wheels: 4})

    Text {
        text: "The car has " + car.wheels + " wheels";
    }

    Component.onCompleted: {
        car.wheels = 6;
    }
}

It is important to note that changes in regular properties of JavaScript objects assigned to a var property will not trigger updates of bindings that access them. 
The example below will display "The car has 4 wheels" as the change to the wheels property will not cause the reevaluation of the binding assigned to the "text" property:

重要注意，
分配给var属性的JavaScript对象的常规属性中的更改不会触发访问它们的绑定的更新。 
下面的示例将显示"The car has 4 wheels"，
因为车轮属性的更改不会导致重新求值分配给“文本”属性的绑定

If the onCompleted handler instead had "car = new Object({wheels: 6})" then the text would be updated to say "The car has 6 wheels", 
since the car property itself would be changed, which causes a change notification to be emitted.

如果onCompleted处理程序具有 "car = new Object({wheels: 6})"，
则该文本将更新为"The car has 6 wheels"，
因为car属性本身将被更改，
这将导致更改通知被发射。