how to execute code only after some asynchronous has finished executed?

Question

I am new in programming and in Android development. I have 3 asynchronous method to get data from server in my MainActivity, let say it is called

getUserDataFromServer()
getProductsDataFromServer()
getBannersFromServer()

if every request takes 1 second, then it needs 3 seconds to complete those 3 request If I chain it one after the other (in series).

so what I want is.... I want to make those 3 request asynchronously (in parallel) then if those 3 request has been done (either failed or success) then I want to do something else, let say to show up the Toast message. so I can finish it faster, maybe it just need around 1,2 s, not 3 s.

I don't know how to do it or what the special method called to wrap it in Android ?

how to do that in Java or Kotlin ?

Answer 1

The following code should help you get started for your purposes. It also has explanations of what is happening. You can change the parameters as required:

Executing the Task:

MyTask myTask = new MyTask();
myTask.execute(String1);

//OR:
new MyTask().execute(String1, String2, String3...);

Creating the Task:

//The first type in AsyncTask<> is for specifying the type of input given.
//Second parameter: Type of data to give to onProgressUpdate.
//Third parameter: Type of data to give to onPostExecute.
private class MyTask extends AsyncTask<String, String, String> {

    private String resp;
    ProgressDialog progressDialog;

    @Override
    protected String doInBackground(String... params) {
        publishProgress("Processing ..."); // Calls onProgressUpdate()
        //params is the input you've given that can be used for processing.

        getUserDataFromServer()
        getProductsDataFromServer()
        getBannersFromServer()

        //Result is the String to give onPostExecute when the task is done executing.
        String result = "Done Processing";
        return result;
    }

    @Override
    protected void onPostExecute(String result) {
        // Get the result from your task after it is done running.
        progressDialog.dismiss();
        //IMPORTANT: As you asked in your question, you can now execute whatever code you 
        //want since the task is done running.

    }

    @Override
    protected void onProgressUpdate(String... text) {
        //Progress has been updated. You can update the proggressDialog.       
    }
}