react-navigation/android/src/main/java/com/swmansion/rnscreens/ScreenStackHeaderSubview.java

package com.swmansion.rnscreens;

import android.view.View;
import android.view.ViewParent;

import com.facebook.react.bridge.ReactContext;
import com.facebook.react.uimanager.UIManagerModule;
import com.facebook.react.views.view.ReactViewGroup;

public class ScreenStackHeaderSubview extends ReactViewGroup {

  public class Measurements {
    public int width;
    public int height;
  }

  public enum Type {
    LEFT,
    CENTER,
    TITLE,
    RIGHT,
    BACK
  }

  private int mReactWidth, mReactHeight;
  private final UIManagerModule mUIManager;

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    if (MeasureSpec.getMode(widthMeasureSpec) == MeasureSpec.EXACTLY &&
            MeasureSpec.getMode(heightMeasureSpec) == MeasureSpec.EXACTLY) {
      // dimensions provided by react
      mReactWidth = MeasureSpec.getSize(widthMeasureSpec);
      mReactHeight = MeasureSpec.getSize(heightMeasureSpec);
      ViewParent parent = getParent();
      if (parent != null) {
        forceLayout();
        ((View) parent).requestLayout();
      }
    }
    setMeasuredDimension(mReactWidth, mReactHeight);
  }

  @Override
  protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
    if (changed && (mType == Type.CENTER || mType == Type.TITLE)) {
      Measurements measurements = new Measurements();
      measurements.width = right - left;
      if (mType == Type.CENTER) {
        // if we want the view to be centered we need to account for the fact that right and left
        // paddings may not be equal.
        View parent = (View) getParent();
        int parentWidth = parent.getWidth();
        int rightPadding = parentWidth - right;
        int leftPadding = left;
        measurements.width = Math.max(0, parentWidth - 2 * Math.max(rightPadding, leftPadding));
      }
      measurements.height = bottom - top;
      mUIManager.setViewLocalData(getId(), measurements);
    }
    super.onLayout(changed, left, top, right, bottom);
  }

  private Type mType = Type.RIGHT;

  public ScreenStackHeaderSubview(ReactContext context) {
    super(context);
    mUIManager = context.getNativeModule(UIManagerModule.class);
  }

  public void setType(Type type) {
    mType = type;
  }

  public Type getType() {
    return mType;
  }
}