Use Case - Positioners and Layouts In QML

There are several ways to position items in QML.

Below is a brief overview. For more details, see 重要 Qt Quick 概念 - 位置 .

手动位置

Items can be placed at specific x,y coordinates on the screen by setting their x,y properties. This will setup their position relative to the top left corner of their parent, according to the visual coordinate system 规则。

Combined with using bindings instead of constant values for these properties, relative positioning is also easily accomplished by setting the x and y coordinates to the appropriate bindings.

import QtQuick
Item {
    width: 100; height: 100
    Rectangle {
        // Manually positioned at 20,20
        x: 20
        y: 20
        width: 80
        height: 80
        color: "red"
    }
}
							

锚点

Item type provides the abilitiy to anchor to other Item types. There are seven anchor lines for each item: left , right , vertical center , top , bottom , baseline and horizontal center . The three vertical anchor lines can be anchored to any of the three vertical anchor lines of another item, and the four horizontal anchor lines can be anchored to the horizontal anchor lines of another item.

For full details, see 锚点位置 and the documentation of the anchors property .

import QtQuick
Item {
    width: 200; height: 200
    Rectangle {
        // Anchored to 20px off the top right corner of the parent
        anchors.right: parent.right
        anchors.top: parent.top
        anchors.margins: 20 // Sets all margins at once
        width: 80
        height: 80
        color: "orange"
    }
    Rectangle {
        // Anchored to 20px off the top center corner of the parent.
        // Notice the different group property syntax for 'anchors' compared to
        // the previous Rectangle. Both are valid.
        anchors { horizontalCenter: parent.horizontalCenter; top: parent.top; topMargin: 20 }
        width: 80
        height: 80
        color: "green"
    }
}
							

位置器

For the common case of wanting to position a set of types in a regular pattern, Qt Quick provides some positioner types. Items placed in a positioner are automatically positioned in some way; for example, a Row positions items to be horizontally adjacent (forming a row).

For full details see Item Positioners .

import QtQuick
Item {
    width: 300; height: 100
    Row { // The "Row" type lays out its child items in a horizontal line
        spacing: 20 // Places 20px of space between items
        Rectangle { width: 80; height: 80; color: "red" }
        Rectangle { width: 80; height: 80; color: "green" }
        Rectangle { width: 80; height: 80; color: "blue" }
    }
}
							

布局类型

Layout types function in a similar way as positioners but allow further refinement or restrictions to the layout. Specifically, the layout types allow you to:

  • set the alignment of text and other items
  • resize and fill the allotted application areas automatically
  • set size constraints such as minimum or maximum dimensions
  • set the spacing between items within the layout
GroupBox {
    id: gridBox
    title: "Grid layout"
    Layout.fillWidth: true
    GridLayout {
        id: gridLayout
        rows: 3
        flow: GridLayout.TopToBottom
        anchors.fill: parent
        Label { text: "Line 1" }
        Label { text: "Line 2" }
        Label { text: "Line 3" }
        TextField { }
        TextField { }
        TextField { }
        TextArea {
            text: "This widget spans over three rows in the GridLayout.\n"
                  + "All items in the GridLayout are implicitly positioned from top to bottom."
            Layout.rowSpan: 3
            Layout.fillHeight: true
            Layout.fillWidth: true
        }
    }
}
							

The snippet above comes from the 基本布局 example. The snippet shows the simplicity of adding various fields and items in a layout. The GridLayout can be resized and its format is customizable through various properties.

For more information about the layout types, visit:

注意: Qt Quick Layouts was introduced in Qt 5.1 and requires Qt Quick 2.1.