harmony 鸿蒙app.js

2023-06-24
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app.js

Application Lifecycle⁴⁺

You can implement lifecycle logic specific to your application in the app.js file. Available application lifecycle functions are as follows:

onCreate(): called when an application is created
onDestroy(): called when an application is destroyed

In the following example, logs are printed only in the lifecycle functions.

// app.js
export default {
  onCreate() {
    console.info('Application onCreate');
  },
  onDestroy() {
    console.info('Application onDestroy');
  },
}

Application Object¹⁰⁺

Attribute	Type	Description
getApp	Function	Obtains the data object exposed in app.js from the page JS file. This API works globally.

NOTE

The application object is global data and occupies JS memory before the application exits. Although it facilitates data sharing between different pages, exercise caution when using it on small-system devices, whose memory is small. If they are overused, exceptions may occur due to insufficient memory when the application displays complex pages.

The following is an example:

Declare the application object in app.js.

// app.js
export default {
    data: {
        test: "by getAPP"
    },
    onCreate() {
        console.info('Application onCreate');
    },
    onDestroy() {
        console.info('Application onDestroy');
    },
};

Access the application object on a specific page.

// index.js
export default {
    data: {
        title: ""
    },
    onInit() {
        if (typeof getApp !== 'undefined') {
            var appData = getApp().data;
            if (typeof appData !== 'undefined') {
                this.title = appData.name; // read from app data
            }
        }
    },
    clickHandler() {
        if (typeof getApp !== 'undefined') {
            var appData = getApp().data;
            if (typeof appData !== 'undefined') {
                appData.name = this.title; // write to app data
            }
        }
    }
}

NOTE

To ensure that the application can run properly on an earlier version that does not support getApp, compatibility processing must be performed in the code. That is, before using getApp, check whether it is available.