The Qt 6 Book

# Layout Items

QML provides a flexible way to layout items using anchors. The concept of anchoring is fundamental to Item, and is available to all visual QML elements. Anchors act like a contract and are stronger than competing geometry changes. Anchors are expressions of relativeness; you always need a related element to anchor with.

An element has 6 major anchor lines (top, bottom, left, right, horizontalCenter, verticalCenter). Additionally, there is the baseline anchor for text in Text elements. Each anchor line comes with an offset. In the case of the top, bottom, left, and right anchors, they are called margins. For horizontalCenter, verticalCenter and baseline they are called offsets.

  • (1) An element fills a parent element.

    GreenSquare {
    BlueSquare {
        width: 12
        anchors.fill: parent
        anchors.margins: 8
        text: '(1)'
    }
}

  • (2) An element is left aligned to the parent.

    GreenSquare {
    BlueSquare {
        width: 48
        y: 8
        anchors.left: parent.left
        anchors.leftMargin: 8
        text: '(2)'
    }
}

  • (3) An element's left side is aligned to the parent’s right side.

    GreenSquare {
    BlueSquare {
        width: 48
        anchors.left: parent.right
        text: '(3)'
    }
}

  • (4) Center-aligned elements. Blue1 is horizontally centered on the parent. Blue2 is also horizontally centered, but on Blue1, and its top is aligned to the Blue1 bottom line.

    GreenSquare {
    BlueSquare {
        id: blue1
        width: 48; height: 24
        y: 8
        anchors.horizontalCenter: parent.horizontalCenter
    }
    BlueSquare {
        id: blue2
        width: 72; height: 24
        anchors.top: blue1.bottom
        anchors.topMargin: 4
        anchors.horizontalCenter: blue1.horizontalCenter
        text: '(4)'
    }
}

  • (5) An element is centered on a parent element

    GreenSquare {
    BlueSquare {
        width: 48
        anchors.centerIn: parent
        text: '(5)'
    }
}

  • (6) An element is centered with a left-offset on a parent element using horizontal and vertical center lines

    GreenSquare {
    BlueSquare {
        width: 48
        anchors.horizontalCenter: parent.horizontalCenter
        anchors.horizontalCenterOffset: -12
        anchors.verticalCenter: parent.verticalCenter
        text: '(6)'
    }
}

# Hidden Gems

Our squares have been magically enhanced to enable dragging. Try the example and drag around some squares. You will see that (1) can’t be dragged as it’s anchored on all sides (although you can drag the parent of (1), as it’s not anchored at all). (2) can be vertically dragged, as only the left side is anchored. The same applies to (3). (4) can only be dragged vertically, as both squares are horizontally centered. (5) is centered on the parent, and as such, can’t be dragged. The same applies to (6). Dragging an element means changing its x,y position. As anchoring is stronger than setting the x,y properties, dragging is restricted by the anchored lines. We will see this effect later when we discuss animations.

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