A floating label view which shows some labels on top of the first child.

FloatingLabelLayout.java

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2015 longkai
 *
 * The software shall be used for good, not evil.
 */

package com.example.app.layout;

import android.annotation.TargetApi;
import android.content.Context;
import android.content.res.TypedArray;
import android.os.Build;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import com.example.layout_tester.app.R;

/**
 * A floating label view which shows some labels on top of the first child.
 * 
 * You can drag the tag to adjust the tag' s location. 
 *
 * @author longkai
 */
public class FloatingLabelLayout extends ViewGroup implements View.OnTouchListener {
  private int mTouchSlop;
  private int lastX;
  private int lastY;

  public FloatingLabelLayout(Context context) {
    this(context, null);
  }

  public FloatingLabelLayout(Context context, AttributeSet attrs) {
    super(context, attrs);
    bootstrap(context, attrs, 0, 0);
  }

  @TargetApi(Build.VERSION_CODES.HONEYCOMB)
  public FloatingLabelLayout(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    bootstrap(context, attrs, defStyleAttr, 0);
  }

  @TargetApi(Build.VERSION_CODES.LOLLIPOP)
  public FloatingLabelLayout(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
    super(context, attrs, defStyleAttr, defStyleRes);
    bootstrap(context, attrs, defStyleAttr, defStyleRes);
  }

  private void bootstrap(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
    mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();
  }

  @Override protected void onAttachedToWindow() {
    super.onAttachedToWindow();
    final int count = getChildCount();
    if (count > 1) {
      for (int i = 1; i < count; i++) {
        getChildAt(i).setOnTouchListener(this);
      }
    }
  }

  @Override protected void onDetachedFromWindow() {
    super.onDetachedFromWindow();
    final int count = getChildCount();
    if (count > 1) {
      for (int i = 1; i < count; i++) {
        getChildAt(i).setOnTouchListener(null);
      }
    }
  }

  @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    final int count = getChildCount();
    if (count == 0) {
      // if has no child, rely on system' s impl
      super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    } else {
      // this view' s bound build on top of the first child
      View view = getChildAt(0);
      if (view.getVisibility() == GONE) {
        // if the first view is gone, skip it
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        return;
      }

      measureChild(view, widthMeasureSpec, heightMeasureSpec);
      int width = view.getMeasuredWidth();
      int height = view.getMeasuredHeight();

      // amend padding
      width += getPaddingLeft() + getPaddingRight();
      height += getPaddingTop() + getPaddingBottom();

      // we' re done
      setMeasuredDimension(resolveSize(width, widthMeasureSpec), resolveSize(height, heightMeasureSpec));

      // measure the floating label(s)
      for (int i = 1; i < count; i++) {
        View label = getChildAt(i);
        if (label.getVisibility() != GONE) {
          measureChild(label, widthMeasureSpec, heightMeasureSpec);
        }
      }
    }
  }

  @Override protected void onLayout(boolean changed, int l, int t, int r, int b) {
    // skip if non-changed
    if (!changed) {
      return;
    }

    View view = getChildAt(0);
    // the main layout, if gone, skip layout
    if (view.getVisibility() == GONE) {
      return;
    }

    int width = view.getMeasuredWidth();
    int height = view.getMeasuredHeight();

    l += getPaddingLeft();
    t += getPaddingTop();

    view.layout(l, t, l + view.getMeasuredWidth(), t + view.getMeasuredHeight());

    final int count = getChildCount();
    for (int i = 1; i < count; i++) {
      View label = getChildAt(i);
      if (label.getVisibility() != GONE) {
        // layout label(s)
        LayoutParams lp = (LayoutParams) label.getLayoutParams();
        // NOTE: we simply no check for the x and y, both should be range in [0, 1)
        int x = (int) (lp.x * width);
        int y = (int) (lp.y * height);
        if (lp.centerOrientated) {
          x -= label.getMeasuredWidth() / 2;
          y -= label.getMeasuredHeight() / 2;
        }
        label.layout(l + x, t + y, l + x + label.getMeasuredWidth(), t + y + label.getMeasuredHeight());
      }
    }
  }

  @Override protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
    return p instanceof LayoutParams;
  }

  @Override protected ViewGroup.LayoutParams generateDefaultLayoutParams() {
    return new LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
  }

  @Override public ViewGroup.LayoutParams generateLayoutParams(AttributeSet attrs) {
    return new LayoutParams(getContext(), attrs);
  }

  @Override protected ViewGroup.LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
    return new LayoutParams(p);
  }

  @Override public boolean onTouch(View v, MotionEvent event) {

    switch (event.getAction()) {
      case MotionEvent.ACTION_DOWN:
        lastX = (int) event.getX();
        lastY = (int) event.getY();
        break;
      case MotionEvent.ACTION_MOVE:
        int x = (int) event.getX();
        int y = (int) event.getY();
        int xDiff = x - lastX;
        int yDiff = y - lastY;
        if (Math.abs(xDiff) > mTouchSlop || Math.abs(yDiff) > mTouchSlop) {
          v.layout(v.getLeft() + xDiff, v.getTop() + yDiff, v.getRight() + xDiff, v.getBottom() + yDiff);
          lastX = x;
          lastY = y;
        }
        break;
      case MotionEvent.ACTION_CANCEL:
        lastX = 0;
        lastY = 0;
        break;
      case MotionEvent.ACTION_UP:
        // handle click event
        v.performClick();
        break;
    }
    return true;
  }

  // NOTE: since we use (x, y) coordinate to layout the label, margin is useless
  public static class LayoutParams extends ViewGroup.LayoutParams {
    /** x pos in relative of the layout' s first child */
    public float x;
    /** y pos in relative of the layout' s first child */
    public float y;

    public boolean centerOrientated;

    public LayoutParams(Context c, AttributeSet attrs) {
      super(c, attrs);
      TypedArray array = c.obtainStyledAttributes(attrs, R.styleable.FloatingLabelView_Layout);
      x = array.getFraction(R.styleable.FloatingLabelView_Layout_x, 1, 1, 0f);
      y = array.getFraction(R.styleable.FloatingLabelView_Layout_y, 1, 1, 0f);
      centerOrientated = array.getBoolean(R.styleable.FloatingLabelView_Layout_centerOrientated, false);
      array.recycle();
    }

    public LayoutParams(ViewGroup.LayoutParams source) {
      super(source);
    }

    public LayoutParams(int width, int height) {
      super(width, height);
    }
  }
}