How to create forms

AvailableBox.java

public class AvailableBox extends Checkbox implements FormField, OnCheckChangeListener {

  private ErrorCallback errorCallback;
  private User user;
  
  //use the constructor with 1 argument for using only on java and the constructor with 2 arguments for using on xml
  public AvailableBox(...) {
    //you can add any MUST HAVE behaviour in the constructor
    setOnCheckChangedListener(this);
  }
  
  @Override
  onCheckChangedListener(boolean cbValue) {
    //This user is the same that in the View
    user.setAvailability(cbValue)
    if (cbValue) {
      removeError();
    } else {
      setError();
    }
  }
  
  @Override
  boolean isValid() {
    if (!isChecked) {
      setError();
      errorCallback.fiedlPosition(getBottom());
    }
    return isChecked();
  }
  
  @Override
  void setError(){//set the error somehow}
   
  @Override
  void removeError(){//remove error somehow}
    
  @Override
  void setErrorCallback(ErrorCallback errorCallback) {
    this.errorCallback = errorCallback;
  }
    
  void setUser(User user) {
    this.user = user;
  }
  
  
}

ComplexField.java

class ComplexField extends LinearLayout implements FormField {

  //The same one argument or two arguments
  public ComplexField() {
    LayoutInflater inflater = LayoutInflater.from(context);
    //true is auto attach
    inflater.inflate(R.layout.your_layout, this, true);
    //this way you can add a more complex layout if needed
  }

}

FormField.java

//This interface has every common aspect between fields
interface FormField {

//is valid can be called by the View (activity or fragment)
boolean isValid();
void setError();
void removeError();
//this callback can be triggered when isValid is false and make the View scroll to the missing field
void setCallback(ErrorCallback errorCallback);
//for this example, let's say we are creating a user
void setUser(User user);

  interface ErrorCallback {
    void fiedlPosition(int bottom);
  }
  
}

TheActivity.java

public class TheActivity extends AppCompatActivity implements FormField.ErrorCallback {

  private List<FormField> fields = new ArrayList();
  private User user;
  
  onCreate() {
    //here you can iterate all the views, something like
    LinearLayout container = findViewById(R.id.root);
    user = (User) getIntent().getSerializableExtra(USER);
    user = (user != null) ? user : new User();
    //either editing or creating, we can pass the object and change it on the fields
    //java objects work as reference, if any field change the user, then this user change as weel
    viewIterator(container, user);
  }
  
  //This make using fragments easy, anyway you can find your form fields programatically
  private void viewIterator(ViewGroup group, User user) {
    int count = group.getChildCount();
    for (int i = 0; i < count; i++) {
       if (group.childAt(i) instanceOf FormField) {
         FormField field = group.childAt(i);
         //We can pass the user so the field will modify it
         field.setUser(user);
         fields.add(field);
       }
       if (group.childAt(i) instanceOf VieGroupd) viewIterator(group.childAt(i), user);
    }
  }
  
  //Call something like this when the user press the save button
  private void onSave() {
    for (FormField field : fields) {
      if (!field.isValid()) return
    }
    //validation say everything is ok, now save
    //we can user the field user because is modified by each field
    sendData(user);
  }
 
 @Override
 void fiedlPosition(int bottom) {
  //remember to scroll to the field, this will be triggered on inner field validation
 }

}