Get constraint's id programmatically

Question

Given the following xml:

<ImageView
    android:id="@+id/someTag"
    android:layout_width="10dp"
    android:layout_height="10dp"
    android:layout_marginBottom="12dp"
    android:layout_marginStart="8dp"
    android:tag="someTag"
    app:layout_constraintBottom_toTopOf="@+id/someID"
    app:layout_constraintStart_toEndOf="@+id/someID"

I would like to know how to get the id of

app:layout_constraintBottom_toTopOf

(namely "someID") programatically.

Many thanks!

You want to set `app:layout_constraintBottom_toTopOf` programatically? — Soon Santos, Nov 16 '18 at 19:08
no, get it after it has been constructed manually inside the xml file. — Guy Sharon, Nov 16 '18 at 19:24

score 4 · Accepted Answer · answered Nov 16 '18 at 19:26

That attribute value is held in the ImageView's LayoutParams, which are specifically ConstraintLayout.LayoutParams, in this case, since its parent is the ConstraintLayout.

ConstraintLayout.LayoutParams has the bottomToTop field, which holds the ID of the View for that particular constraint.

Simply get the ImageView's LayoutParams, cast them to ConstraintLayout.LayoutParams, and get your ID from the aforementioned field. For example:

ImageView image = findViewById(R.id.someTag);
ConstraintLayout.LayoutParams lp = (ConstraintLayout.LayoutParams) image.getLayoutParams();
int bottomToTopId = lp.bottomToTop;

If, for some reason, you need the actual resource name for that ID, you can get it per usual with the Resources#getResourceEntryName() method. That is:

String viewIdName = getResources().getResourceEntryName(bottomToTopId); // returns "someID"

Get constraint's id programmatically

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