Loader QML Element

The Loader item allows dynamically loading an Item-based subtree from a URL or Component.More...

• List of all members, including inherited members

Properties

• item : Item
• progress : real
• source : url
• sourceComponent : Component
• status : enumeration

Signals

• onLoaded()

Detailed Description

Loader is used to dynamically load visual QML components. It can load a QML file (using thesource property) or aComponent object (using thesourceComponent property). It is useful for delaying the creation of a component until it is required: for example, when a component should be created on demand, or when a component should not be created unnecessarily for performance reasons.

Here is a Loader that loads "Page1.qml" as a component when theMouseArea is clicked:

import QtQuick 1.0Item {width:200;height:200Loader {id:pageLoader }MouseArea {anchors.fill:parentonClicked:pageLoader.source="Page1.qml"    }}

The loaded item can be accessed using theitem property.

If thesource orsourceComponent changes, any previously instantiated items are destroyed. Settingsource to an empty string or settingsourceComponent toundefined destroys the currently loaded item, freeing resources and leaving the Loader empty.

Loader sizing behavior

Loader is like any other visual item and must be positioned and sized accordingly to become visible.

• If an explicit size is not specified for the Loader, the Loader is automatically resized to the size of the loaded item once the component is loaded.
• If the size of the Loader is specified explicitly by setting the width, height or by anchoring, the loaded item will be resized to the size of the Loader.

In both scenarios the size of the item and the Loader are identical. This ensures that anchoring to the Loader is equivalent to anchoring to the loaded item.

import QtQuick 1.0Item {width:200;height:200Loader {// Explicitly set the size of the Loader to the parent item's sizeanchors.fill:parentsourceComponent:rect    }Component {id:rectRectangle {width:50height:50color:"red"        }    }}

import QtQuick 1.0Item {width:200;height:200Loader {// position the Loader in the center of the parentanchors.centerIn:parentsourceComponent:rect    }Component {id:rectRectangle {width:50height:50color:"red"        }    }}

Receiving signals from loaded items

Any signals emitted from the loaded item can be received using theConnections element. For example, the followingapplication.qml loadsMyItem.qml, and is able to receive themessage signal from the loaded item through aConnections object:

import QtQuick 1.0Item {width:100;height:100Loader {id:myLoadersource:"MyItem.qml"    }Connections {target:myLoader.itemonMessage:console.log(msg)    }}

import QtQuick 1.0Rectangle {id:myItem   signalmessage(string msg)width:100;height:100MouseArea {anchors.fill:parentonClicked:myItem.message("clicked!")   }}

Alternatively, sinceMyItem.qml is loaded within the scope of the Loader, it could also directly call any function defined in the Loader or its parentItem.

Focus and key events

Loader is a focus scope. Itsfocus property must be set totrue for any of its children to get theactive focus. (Seethe focus documentation page for more details.) Any key events received in the loaded item should likely also beaccepted so they are not propagated to the Loader.

For example, the followingapplication.qml loadsKeyReader.qml when theMouseArea is clicked. Notice thefocus property is set totrue for the Loader as well as theItem in the dynamically loaded object:

import QtQuick 1.0Rectangle {width:200;height:200Loader {id:loaderfocus:true    }MouseArea {anchors.fill:parentonClicked:loader.source="KeyReader.qml"    }Keys.onPressed: {console.log("Captured:",event.text);    }}

import QtQuick 1.0Item {Item {focus:trueKeys.onPressed: {console.log("Loaded item captured:",event.text);event.accepted=true;        }    }}

OnceKeyReader.qml is loaded, it accepts key events and setsevent.accepted totrue so that the event is not propagated to the parentRectangle.

See alsoDynamic Object Creation.

Property Documentation

Item {Component {id:redSquareRectangle {color:"red";width:10;height:10 }    }Loader {sourceComponent:redSquare }Loader {sourceComponent:redSquare;x:10 }}

Signal Documentation