How to call a method in UniApp and get the return value

UniApp is a cross-platform development framework that can develop iOS, Android and Web applications in one code base. Calling methods and getting return values ​​is a common requirement in UniApp. This article will introduce how to call methods in UniApp and get the return value.

Calling methods in UniApp

The process of calling methods in UniApp can be divided into two steps:

1. Calling methods in JavaScript code.
2. Execute the method in Native code and return the result.

The following is a simple example that demonstrates how to call a Native method in UniApp:

1. Call a Native method in JavaScript:

uni.invokeMethod("testPlugin", "testMethod", "args", function(res){
    console.log(res);
})

• uni.invokeMethod(plugin, method, args, callback)The method is used to call Native methods.
• pluginThe parameter refers to the ID of the Native plug-in, such as "testPlugin".
• methodThe parameter refers to the name of the Native method, such as "testMethod".
• argsParameters refer to the parameters required by the method, such as "args".
• callbackThe parameter refers to the callback function after the method is executed, where the res parameter represents the return value.

2. Asynchronous execution method in Native:

public class TestPlugin implements IModule {
    @JSMethod(uiThread = false)
    public void testMethod(JSCallback callback, String args){
        String result = "Hello " + args;
        callback.invoke(result);
    }
}

• Define a class in Java TestPlugin for implementing Native plugin.
• @JSMethod(uiThread = false)The annotation indicates that this method will be executed in a non-UI thread.
• JSCallback is a callback interface used to return results in JavaScript.
• invoke method is used to return the result to JavaScript.

Get the return value of the calling method

In order to get the return value of the calling method, we need to use the callback function in the Native code to return the value. The parameters in the callback function are the method's return value. In JavaScript code, we need to use the return value in the callback function to perform corresponding processing.

The following is an example of code that obtains the return value of a calling method:

1. Use Promise in JavaScript to call Native methods:

export function testMethod(args){
    return new Promise((resolve, reject) => {
        uni.invokeMethod("testPlugin", "testMethod", args, function(res){
            resolve(res);
        })
    })
}

• We use Promise in ES6 to asynchronously obtain the return value of the method. The
• resolve function represents a processing function that returns asynchronous results.

2. Execute the method asynchronously in Native and return the result:

public class TestPlugin implements IModule {
    @JSMethod(uiThread = false)
    public void testMethod(JSCallback callback, String args){
        String result = "Hello " + args;
        callback.invoke(result);
    }
}

• In the callback function we use the invoke method to return result.

3. Using return values ​​in JavaScript:

testMethod('world')
    .then(res => {
        console.log(res);
    })
    .catch(error => {
        console.error(error);
    });

• We use Promise’s then method after calling the method asynchronously Get the return value and process it in the callback function.
• If an error occurs, we use Promise's catch method to capture the error and output it to the console.

Summary

Calling methods and getting return values ​​is a common requirement in UniApp. Although UniApp allows us to use callback functions to obtain the results of calling methods, using Promise and async/await can make the code more concise and readable. In order to get the return value of the calling method, we can use Promise in JavaScript code to handle asynchronous results, and use callback functions in Native code to return the results.

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