dynamic number of elements layout problem

Question

I'm trying to create an Activity with dynamic number of Buttons, each of them representing a Shadow object.

I'm not sure if it's possible to do with the XML file, so I decided to use Java code instead.

The whole idea of displaying all of the List elements is working - I have a button generated for every Shadow in the list.

My problem is that the buttons are all in the same place, the largest one covers the others. How can I make them display properly, e.g. with 16dp vertical space between them?

Here's the class code:

package com.jackw.nfshadow;

import android.os.Bundle;
import android.support.constraint.ConstraintLayout;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.LinearLayout;

import com.biernacki.nfshadow.tagdiscoveredactivities.Shadow;

import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class ShadowLibrary extends AppCompatActivity {

    private List<Shadow> savedShadows;
    private ConstraintLayout layout;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        if(savedInstanceState != null) {
            super.onCreate(savedInstanceState);
        }else{
            super.onCreate(new Bundle());
        }
        setContentView(R.layout.activity_shadow_library);
        layout  = findViewById(R.id.shadow_library);
        setButtonNames();
    }

    private void setButtonNames() {
        if(Main.savedShadows != null && Main.savedShadows.size() > 0){
            savedShadows = Main.savedShadows.stream()
                    .sorted(Comparator.comparing(Shadow::getName))
                    .collect(Collectors.toList());

            savedShadows.forEach(shadow -> {
                Button button = new Button(this);
                button.setId(View.generateViewId());
                button.setText(shadow.getName());
                layout.addView(button);
            });

        }
    }
}

Since I'm totally new to Android, I'd also appreciate any information about other ways of creating dynamic content/small review of the code I've written above.

UPDATE: I've edited the setButtonNames() a bit, still trying to use ConstraintLayout and connect() method, but for some reason it still doesn't work. I can't find what's wrong with this one.

savedShadows.forEach(shadow -> {
                Button button = new Button(this);
                button.setId(View.generateViewId());
                button.setText(shadow.getName());

                if(shadow == savedShadows.get(0)){
                    previousButtonId = button.getId();
                }else{
                    constraints.connect(button.getId(), ConstraintSet.TOP, previousButtonId, ConstraintSet.BOTTOM, 16);
                    previousButtonId = button.getId();
                }
                constraints.applyTo(layout);
                layout.addView(button);
            });
        }
}

Answer 1

Your problem is you are not adding constraints for your Button. You can do it like in this example, where layout is your ConstraintLayout:

ConstraintSet constraintSet = new ConstraintSet();
constraintSet.clone(layout);
constraintSet.connect(someButton.getId(), ConstraintSet.TOP, 
                       anotherButton.getId(), ConstraintSet.BOTTOM);
constraintSet.applyTo(constraintLayout);

You need to add constraints as you want. Or replace your ConstraintLayout with LinearLayout and it will automatically add buttons correctly without no need to work with constraints.