3.NativeScript Application Life cycle And Store Data

UseApplication Callbacks

NativeScript applications have thefollowing life cycle events.

• start(): Call the start method  after the module initialization to start application.

//在start()之后调用，如果是点击back键，重新进入则会调用onLaunch(context)，然后调用onResume()

• onLaunch(context): This method is called when application launch.

//点击home键或者back键时调用

• onSuspend(): This method is called when the application is suspended.
• onResume(): This method is called when the application is resumed after it has been suspended.

//当点击back键时，不调用onExit()，只有直接kill掉才会调用

• onExit(): This method is called when the application is about to exit.
• onLowMemory(): This method is called when the memory on the target device is low.
• onUncaughtError(error): This method is called when an uncaught application error is present.

 

Persistand Restore Application Settings

To persist user-defined settings, you need to use the local-settings module. The local-settings module is a staticsingleton hash table that stores key-value pairs for the application.

The getter methods have two parameters: a key and an optional default valueto return if the specified key does not exist. The setter methods have tworequired parameters: a key and value.

Example

• JavaScript
• TypeScript

var localSettings = require("local-settings");

// Event handler for Page "loaded" event attached in main-page.xml.

function pageLoaded(args) {

    localSettings.setString("Name", "John Doe");

    console.log(localSettings.getString("Name")); // Prints "John Doe".

    localSettings.setBoolean("Married", false);

    console.log(localSettings.getBoolean("Married")); // Prints false.

    localSettings.setNumber("Age", 42);

    console.log(localSettings.getNumber("Age")); // Prints 42.

    console.log(localSettings.hasKey("Name")); // Prints true.

    localSettings.remove("Name"); // Removes the Name entry.

    console.log(localSettings.hasKey("Name")); // Prints false.

}

exports.pageLoaded = pageLoaded;