ConstraintLayout chain does not work if some chained views constrained to another chained view

Question

I am not sure whether it is a bug of ConstraintLayout or not, so I try to ask if somebody knows I made any mistake.

I have a layout which I want to spread evenly on the screen 3 elements. Just like below: 3 chained views

I formed horizontal chains between them and as you can see, they are distributing themselves evenly and working good.

Now I want to place an image plus a TextView centered inside each element, like this: enter image description here

So this is what I tried to do, taking element 1 as example:

Sadly, it seems to "break" the chain of the 3 elements. The 3 elements now does not spread horizontally, but wrapped to a very small size: enter image description here

If I removed the chain between the ImageView and TextView, it works fine. But then I cannot center the ImageView and TextView inside the element.

Does anyone encountered something like this? How do you solve it?

Now, I know I have at least 2 alternatives to solve this problem:
(1) Use one TextView with a compound drawable, instead of ImageView + TextView;
(2) Use a LinearLayout to wrap the ImageView and TextView

But I want to know why it does not work (So that we can have better understanding of ConstraintLayout), instead of finding an alternative.

Thanks!

user_6287910 · Answer

After posting my other answer to this question, I realized that it did not address how to center a multi-line TextView.

Referring to the image above, the leftmost box has a single line TextView. The TextView and the ImageView are centered as a group in the the box. This was accomplished by specifying the following for the TextView.

See this posting regarding the use of app:layout_constraintWidth_default="wrap".

app:layout_constraintWidth_default="wrap" (with width set to 0dp). If set, the widget will have the same size as if using wrap_content, but will be limited by constraints (i.e. it won't expand beyond them)

Update: It looks like the XML above needs to be changed for ConstraintLayout 1.1.0 beta2. See the release update.

I think what we are now looking for in the XML is the following:

I have left the rest of this posting using the pre-1.1.0 beta2 layout. To update, just make the changes mentioned above. The centering issue remains.

This works great for the single line example and the views are centered in the box, but we run into difficulty when the TextView spans multiple lines as it does in the middle box of image above. Although the text within the TextView is wrapped and does not expand beyond its constraints, the ImageView and TextView are not centered like we might expect. In fact, the bounds of the TextView extend to the right of the blue box.

My quick fix for this is to insert a zero-width Space widget to the left of the ImageView in the rightmost box. The chain is that box is now anchored between the Space widget and the righthand side of the box. The ImageView is constrained on the left by the Space.

The Space widget can now be expanded to act like a shim to move the ImageView to the right by the amount that will center the chain. (See right box in the image above.) The getExcessWidth() method of MainActivity calculates how wide the Space widget needs to be.

Here is the XML:

MainActivity.java

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.chained_chains);
        ConstraintLayout layout = (ConstraintLayout) findViewById(R.id.constraintLayout);

        layout.post(new Runnable() {
            @Override
            public void run() {
                final TextView textView = (TextView) findViewById(R.id.text3);
                int excessWidth = getExcessWidth(textView);

                if (excessWidth > 0) {
                    Space spacer = (Space) findViewById(R.id.spacer3);
                    ConstraintLayout.LayoutParams lp = (ConstraintLayout.LayoutParams) spacer.getLayoutParams();
                    lp.width = getExcessWidth(textView) / 2;
                    spacer.setLayoutParams(lp);
                }
            }
        });
    }

    private int getExcessWidth(TextView textView) {

        if (textView.getLineCount() <= 1) {
            return 0;
        }

        Layout layout = textView.getLayout();
        int maxWidth = 0;

        for (int i = 0; i < textView.getLineCount(); i++) {
            maxWidth = Math.max(maxWidth, (int) layout.getLineWidth(i));
        }

        return Math.max(textView.getWidth() - maxWidth, 0);
    }
}

user_6287910 · Answer

ConstraintLayout appears to be working as expected. You don't specify what kind of view the elements are, so I have taken the TextView and ImageView and chained them inside a View. I also changed the width of the TextView from 0dp (match_constraints) to wrap_content. Here is the result:

..and the XML.

If this continues to be a problem for you, it would be helpful if you can post more of your XML including the elements. In the meantime, a couple of thoughts.

First, check to make sure that you are not mixing left/right with start/end constraints. If you supply both, they should agree. There has been an inconsistency in how these have been applied by the designer in the past.

Secondly, you can set up barriers to the left and right of each of your elements and chain the TextView and ImageView between these barriers. See this writeup about barriers in ConstraintLayout.

user_12663117 · Answer

I noticed that you have your inner view chains set to 'packed' with the line

app:layout_constraintHorizontal_chainStyle="packed"

It almost seems like the this functionality is extending out to the parent views (the 'elements in your case').

You should try temporarily removing this line in your markup to see if your problem goes away.

If so, the fix should be easy enough. There are many ways to achieve that same effect without nesting layouts.

user_6891637 · Answer

This is perhaps the closest you can get to centering the ImageView and TextView in the ConstraintLayout without any kind of Nested layouts.

And here is the code that does that

Alternate Solution

A better solution would be to wrap the Image view and Text view in a ConstraintLayout

EDIT

The layout will be positioned correctly only if the chain style is set to app:layout_constraintHorizontal_chainStyle="spread_inside"

This is how the output will look like

ConstraintLayout chain does not work if some chained views constrained to another chained view

4 Answers