Appinventor development

Why develop and expand ？

Want to use appinventor There are only two ways beyond the functions supported by the standard .

1. Directly modifying appinventor Source code , Add new features , Then use this private customized server .

2. Write and expand , Can be added to anything that works appinventor Service .

The advantage of the second is obvious , The expansion form of official support , It eliminates the need for users to build appinventor Service effort .

Expand the development environment

If you have built a standard appinventor service , You can directly use this environment for development .

But if you haven't built it yet appinventor service , Because the overall service construction process is slow after all , And contains redundant service parts （2G many ）, So we can use it to do extension Development environment of ：

GitHub - mit-cml/extension-template: Template repository for creating App Inventor extensionshttps://github.com/mit-cml/extension-template

Basic development steps

First download the library ：

git clone --recurse-submodules https://github.com/mit-cml/extension-template.git my-extension

And then in src New in folder MyExtension.java project ：

package cn.temp;

import com.google.appinventor.components.annotations.*;// annotation 
import com.google.appinventor.components.common.ComponentCategory; // Component category 
import com.google.appinventor.components.runtime.*;
ava Utility class library for java.util package . In this bag ,Java Some practical methods and data structures are provided . for example ,Java Provide date (Data) class 、 The calendar (Calendar) Class to generate and get the date and time , Provide random numbers (Random) Class generates various types of random numbers , A stack is also provided (Stack)、 vector (Vector) 、 Bit set (Bitset) And hash table (Hashtable) And other classes to represent the corresponding data structure .
import com.google.appinventor.components.runtime.util.*;
import com.google.appinventor.components.runtime.errors.YailRuntimeError;

@DesignerComponent(version = MyExtension.VERSION, // Designer component 
    description = "by Aheadtechs.",  // remarks , describe 
    category = ComponentCategory.EXTENSION, // Category ： On display in appinventor Which module of 
    nonVisible = true, // invisible 
    iconName = "images/extension.png") // Component icon 

@SimpleObject(external = true) // External plug-ins 

public class MyExtension extends AndroidNonvisibleComponent {
    public static final int VERSION = 1; // If a data is both static again final, Then it will have an unchangeable storage space 
    private static final String LOG_TAG = "MyExtension";

    public MyExtension(ComponentContainer container) { // Memory skills ：contain  contain , accommodate  + er  Watch things  →  Containers 
        // You can call the properties or methods of the parent class through super keyword . adopt super To get the private properties of the parent class 
        super(container.$form());
    }
  // Calculation a+b The sum of is then converted into a string 
    @SimpleFunction(description = "add up a and b")
    public String addab(int a,int b) {
        return ""+(a+b);
    }
}

Then it can be called ：

ant extensions

After the compilation is successful, a... Will be generated in the root directory of the project  out Folder , Among them is what we need .aix Postfix file .

Note that the form of expansion is .aix Postfix file .

Advanced development

Although it can meet our basic needs , But the real development process needs more than a simple example of this , We may need to add third-party libraries ！

For example, a special communication protocol ：opcua And so on. .

The specific steps are as follows ：

1. Download the corresponding library jar file , And copy to lib/deps Folder ：

And then in Myextension.java Add... To the file ：

@SimpleObject(external = true) // External plug-ins 
// You can't put it in this position ！ Must be in SimpleObject below 
@UsesLibraries(libraries = "opc-ua-stack-1.4.1-224.jar,slf4j-api-1.7.0.jar")

  Recompile , You can put the jar Add the content of to the generated .aix In file , You can easily see from the size of the file .

The call is the same as a normal call ：

import org.opcfoundation.ua.application.Client;
...

Reference documents ：

https://saitwalshreyash19.medium.com/writing-extensions-for-app-inventor-2-and-kodular-7d20092bff16https://saitwalshreyash19.medium.com/writing-extensions-for-app-inventor-2-and-kodular-7d20092bff16