QML Qt Quick Study Note --- No.2

import與include類似
如果不確定使用某種類型時(shí)應(yīng)當(dāng)導(dǎo)入哪個(gè)模塊， 可以使用Qt assisstant, 查看其所在的Qt Quick模塊, 如下：
Text QML Type
Specifies how to add formatted text to a scene. More...

The generic form of a module import is as follows:

import <ModuleIdentifier> <Version.Number> [as <Qualifier>]

The <ModuleIdentifier> is an identifier specified in dotted URI (Uniform Resource Identifier, 統(tǒng)一資源標(biāo)志符) notation, which uniquely identifies the type namespace provided by the module.

The <Version.Number> is a version of the form MajorVersion.MinorVersion which specifies which definitions of various object types and JavaScript resources will be made available due to the import.

Example: import QtQuick 2.0

The <Qualifier> is an optional local namespace identifier into which the object types and JavaScript resources provided by the module will be installed, if given.

If omitted, the object types and JavaScript resources provided by the module will be installed into the global namespace.

Example: import QtQuick 2.0 as Quick

This import allows multiple modules which provide conflicting type names to be imported at the same time,

however since each usage of a type provided by a module which was imported into a qualified namespace must be preceded by the qualifier,

the conflict is able to be resolved unambiguously by the QML engine.

An example of client code which creates a rectangle after using a qualified module import is as follows:

  import QtQuick 2.0 as Quick

  Quick.Rectangle {

      width: 200

      height: 100

      color: "red"

  }

Importing into a Qualified Local Namespace

The import statement may optionally use the "as" keyword to specify that the types should be imported into a particular document-local namespace.

If a namespace is specified, then any references to the types made available by the import must be prefixed by the local namespace qualifier.

Below, the QtQuick module is imported into the namespace "CoreItems".

Now, any references to types from the QtQuick module must be prefixed with the CoreItems name:

  import QtQuick 2.0 as CoreItems

  CoreItems.Rectangle {

      width: 100; height: 100

      CoreItems.Text { text: "Hello, world!" }

      // WRONG! No namespace prefix - the Text type won't be found

      Text { text: "Hello, world!" }

  }

A namespace acts as an identifier for a module within the scope of the file.

The namespace does not become an attribute of the root object that can be referred to externally as can be done with properties, signals and methods.

The namespaced import is useful if there is a requirement to use two QML types that have the same name but are located in different modules.

In this case the two modules can be imported into different namespaces to ensure the code is referring to the correct type:

  import QtQuick 2.0 as CoreItems

  import "../textwidgets" as MyModule

  CoreItems.Rectangle {

      width: 100; height: 100

      MyModule.Text { text: "Hello from my custom text item!" }

      CoreItems.Text { text: "Hello from Qt Quick!" }

  }

Directory Imports

A directory which contains QML documents may also be imported directly in a QML document.

This provides a simple way for QML types to be segmented into reusable groupings: directories on the filesystem.

The generic form of a directory import is as follows:

import "<DirectoryPath>" [as <Qualifier>]

 Note: Import paths are network transparent: applications can import documents from remote paths just as simply as documents from local paths.

See the general URL resolution rules for Network Transparency in QML documents.

If the directory is remote, it must contain a directory import listing qmldir file as the QML engine cannot determine the contents of a remote directory if that qmldir file does not exist.

JavaScript Resource Imports

JavaScript resources may be imported directly in a QML document. Every JavaScript resource must have an identifier by which it is accessed.

The generic form of a JavaScript resource import is as follows:

  import "<JavaScriptFile>" as <Identifier>

Note that the <Identifier> must be unique within a QML document, unlike the local namespace qualifier which can be applied to module imports.

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