Changing the length of the array using OnClick method

Question

I am making an Android piano app (my first) and here is my problem. I want to change the number of piano keys by pressing a specific button. Keys are declared as arrays

Button[] whiteKeys = new Button[8];

For the keys I am using View.OnClickListener

View.OnClickListener btnClicked = new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        switch(v.getId())
        {
            case 1:
                 //Here I want to change the length of my whiteKeys array from 8 to 16}

How can I do that? I am completly new to Java so this may be a bit noobish question.

You can't increase the size of an array... You have to make a new array — OneCricketeer
– OneCricketeer, Commented May 5, 2017 at 19:56
the size of an array is fixed you can use List or ArrayList in which you can dynamically change the contents of ArrayList — Kunal Puri
– Kunal Puri, Commented May 5, 2017 at 20:02

Tezra · Accepted Answer · 2017-05-05 20:55:20Z

3

In Java, there is a thing called an ArrayList. It gives methods for accessing it like an array or a list. So adding a key is just list.add(key) or list.add(index, key), remove with list.remove(list.size() - 1), and then get with list.get(key_number).

Of course, you can also just initialize your key array to MAX_KEYS (where MAX_KEYS is a constant you define for most keys you will allow on your keyboard, and then you just have to track which keys are visible)

P.S.
You may also want to become familiar with the synchronize key word. In your example, you don't strictly need it, but ArrayList is not thread safe. (so spamming it may cause weird things)

edited May 5, 2017 at 20:55

answered May 5, 2017 at 19:59

Tezra

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D M · Accepted Answer · 2017-05-05 20:51:15Z

1

If you don't want to use an ArrayList, you can still do this using arrays.

One obvious try is:

whiteKeys = new Button[16];

Now your array has 16 elements. The problem is that you just wiped out whatever was in the old array. To prevent that, we can first copy it over to a new array. So instead, you'd do this:

Button[] temp = new Button[16];
System.arraycopy(whiteKeys, 0, temp, 0, whiteKeys.length);
whiteKeys = temp;

answered May 5, 2017 at 20:51

D M

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Camilo Ortegón · Accepted Answer · 2017-05-05 20:12:40Z

0

Arrays in Java are size fixed, so you will have to either declare a new Array or use a dynamic structure like ArrayList. Using ArrayList you can call .get(index), .add(newButton) and .remove(index).

Make sure to add your new Buttons in the main thread. In this case your public void onClick(View v) is running in the main thread, but for better performance you can also add all the piano keys from the beginning and modify only the visibility:

pianoKey.setVisibility(View.VISIBLE);
pianoKey.setVisibility(View.INVISIBLE);

answered May 5, 2017 at 20:12

Camilo Ortegón

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