Android: Programmatically reading view IDs for LayoutParams

Question

What I am trying to do is programmatically creating a row of buttons with a constraint view. I am creating two buttons and I want to have them next to each other without doing something to the .xml file, since the number of buttons can vary depending on the user.

I want to use something like (this code is part of an Activity):

ConstraintLayout layout = findViewById(R.id.layout);

Button btn1 = new Button(this);
Button btn2 = new Button(this);

ConstraintLayout.LayoutParams params1 = new ConstraintLayout.LayoutParams(ConstraintLayout.LayoutParams.WRAP_CONTENT,ConstraintLayout.LayoutParams.WRAP_CONTENT);
ConstraintLayout.LayoutParams params2 = new ConstraintLayout.LayoutParams(ConstraintLayout.LayoutParams.WRAP_CONTENT,ConstraintLayout.LayoutParams.WRAP_CONTENT);

layout.addView(btn1, 1, params1);   

params2.topToTop = btn1.getId();
params2.leftToRight = btn1.getId();

layout.addView(btn2, 2, params2);

Setting the two params2 values does not work because apparently I cannot really access the ID of button1. What would be a working solution to this? Things I have read and tried:

• Using tags instead of ids
• Accessing the buttons using an ArrayList of all the created buttons as a private member for the Activity
• Giving some random id (that I have chosen) to the Views using setId()

Using something like this works, because I have predefined that btn3 in the xml file:

params2.topToTop = layout.findViewById(R.id.btn3).getId();
params2.leftToRight = layout.findViewById(R.id.btn3).getId();

But in all the other cases my btn2 just lands on top of btn1 (or rather on the top left edge of the layout)

Thank you in advance!

Answer 1

You can use the following method to generate view id programmatically:

private static final AtomicInteger nextGeneratedId = new AtomicInteger(10000);
public static int generateViewId() {
    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR1) {
        for (;;) {
            final int result = nextGeneratedId.get();
            // aapt-generated IDs have the high byte nonzero; clamp to the range under that.
            int newValue = result + 1;
            if (newValue > 0x00FFFFFF) newValue = 10000; // Roll over to 10000, not 0.
            if (nextGeneratedId.compareAndSet(result, newValue)) {
                return result;
            }
        }
    } else {
        return View.generateViewId();
    }
}

call .setId(generatedId) for the buttons you create.