How to assign unique ids to dynamically created Views?

Question

In my app I am creating Views - in this case an EditText - dynamically. But every View I add needs to have a unique id.

EditText editText = new EditText(context);
LayoutParams params = new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
editText.setLayoutParams(params);

// Which value am I supposed to use here?
editText.setId(value);

layout.addView(editText);

I am afraid of conflicts if I assign a random value and I cannot think of any way to generate ids without the possibility of conflicts.

Please not that I know that one can define a fixed set of ids in res/values/ids.xml, but that is not what I want! I need to create the ids dynamically! I have no idea how many I need.

So is there any safe way to generate ids?

Answer 1

There are multiple ways you can reliably generate ids for your Views. Some can be used to dynamically generate ids at runtime, others can be used to statically define a fixed number of ids. I will go over a few solutions in this answer.

---

Statically creating a fixed number of ids

Create a new xml file in res/values called ids.xml and add elements with the type id:

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <item name="name" type="id" />     <!-- Creates the id R.id.name -->
    <item name="example" type="id" />  <!-- Creates the id R.id.example -->

</resources>

You can generate ids for other resources as well! Just change the type.

---

Dynamically generating ids from API level 17+

With API level 17 a new method was added to the View class:

int id = View.generateViewId();

With it you can create as many ids as you need dynamically!

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Dynamically generating ids before API level 17

As @Apoorv suggested you can view the source code of generateViewId() here. By copying the code we can use this method even before API level 17:

private static final AtomicInteger sNextGeneratedId = new AtomicInteger(1);

public static int generateViewId() {
    for (; ; ) {
        final int result = sNextGeneratedId.get();

        // aapt-generated IDs have the high byte nonzero; clamp to the range under that.
        int newValue = result + 1;
        if (newValue > 0x00FFFFFF) newValue = 1; // Roll over to 1, not 0.

        if (sNextGeneratedId.compareAndSet(result, newValue)) {
            return result;
        }
    }
}

Just include it in a helper class and you are all set!

Answer 2

Assign id via code (programmatically)

• Manually set ids using someView.setId(int);
• The int must be positive, but is otherwise arbitrary- it can be whatever you want (keep reading if this is frightful.)
• For example, if creating and numbering several views representing items, you could use their item number.

Normally we do:

To assign id -

for(int i =0 ; i < yourIDcount ; i++){
    yourView.setId(i);
}

To get id -

View.findViewById(yourView.getId());

Also,

API 17 introduced View.generateViewId() which generates a unique ID.

Check:

how-can-i-assign-an-id-to-a-view-programmatically and android-assign-and-retrieve-ids-dynamically.