- Qt 6.5
- Qt Quick Demo - RESTful Color Palette API client
- Qt 6.5.1 Reference Documentation

# Qt Quick Demo - RESTful Color Palette API client

Example of how to create a RESTful API QML client.

This example shows how to create a basic QML RESTful application with an imaginary color palette service. The application uses RESTful communication with the selected server to request and send data. The REST service is provided as a QML element whose child elements wrap the individual JSON data APIs provided by the server.

#### Application functionality

The example provides the following basic functionalities:

- Select the server to communicate with
- List users and colors
- Login and logout users
- Modify and create new colors

##### Server selection

At start the application presents the options for the color palette server to communicate with. The predefined options are:

- reqres.in, a publicly available REST API test service
- Qt-based REST API server example in QtHttpServer

Once selected, the application issues a test HTTP GET to the color API to check if the service is accessible.

One major difference between the two predefined API options is that the Qt-based REST API server example is a stateful application which allows modifying colors, whereas the reqres.in is a stateless API testing service. In other words, when using the reqres.in backend, modifying the colors has no impact on the UI.

##### List users and colors

The users and colors are paginated resources on the server-side. This means that the server provides the data in chunks called pages. The UI listing reflects this pagination and views the data on pages.

Viewing the data on UI is done with standard QML views:

     ListView {
         model: colors.data

Where the model is a list of JSON data received from the server.

##### Logging in

Logging in happens via the login function provided by the login QML element:

     loginService.login({"email" : userInfo.modelData.email,
                         "password" : "apassword",
                         "id" : userInfo.modelData.id})

Under the hood the login sends a HTTP POST request. Upon receiving a successful response the authorization token is extracted from the response, which in turn is then used in subsequent HTTP requests which require the token.

##### Editing colors

Editing and adding new colors is done in a popup:

Note that uploading the color changes to the server requires that a user has logged in.

#### REST implementation

The example illustrates one way to compose a REST service from individual resource elements. In this example the resources are the paginated user and color resources plus the login service. The resource elements are bound together by the base URL (server URL) and the shared network access manager.

The basis of the REST service is the RestService element whose children items compose the actual service:

     RestService {
         id: paletteService

         PaginatedResource {
             id: users
             path: "/api/users"
         }

         PaginatedResource {
             id: colors
             path: "/api/unknown"
         }

         BasicLogin {
             id: loginService
             loginPath: "/api/login"
             logoutPath: "/api/logout"
         }
     }

Upon instantiation the RestService element loops its children elements and sets them up to use the same network access manager. This way the individual resources share the same access details such as the server URL and authorization token.

The actual communication is done with a rest access manager which implements some convenience functionality to deal specifically with HTTP REST APIs and effectively deals with sending and receiving the QNetworkRequest and QNetworkReply as needed.

#### Running the Example

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.

Example project @ code.qt.io