java/com/android/contacts/common/list/ViewPagerTabStrip.java

/*
 * Copyright (C) 2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License
 */

package com.android.contacts.common.list;

import android.content.Context;
import android.content.res.Resources;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;
import android.widget.LinearLayout;
import com.android.contacts.common.R;

public class ViewPagerTabStrip extends LinearLayout {

  private final Paint mSelectedUnderlinePaint;
  private int mSelectedUnderlineThickness;
  private int mIndexForSelection;
  private float mSelectionOffset;

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

  public ViewPagerTabStrip(Context context, AttributeSet attrs) {
    super(context, attrs);

    final Resources res = context.getResources();

    mSelectedUnderlineThickness = res.getDimensionPixelSize(R.dimen.tab_selected_underline_height);
    int underlineColor = res.getColor(R.color.tab_selected_underline_color);
    int backgroundColor = res.getColor(R.color.contactscommon_actionbar_background_color);

    mSelectedUnderlinePaint = new Paint();
    mSelectedUnderlinePaint.setColor(underlineColor);

    setBackgroundColor(backgroundColor);
    setWillNotDraw(false);
  }

  /**
   * Notifies this view that view pager has been scrolled. We save the tab index and selection
   * offset for interpolating the position and width of selection underline.
   */
  void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    mIndexForSelection = position;
    mSelectionOffset = positionOffset;
    invalidate();
  }

  @Override
  protected void onDraw(Canvas canvas) {
    int childCount = getChildCount();

    // Thick colored underline below the current selection
    if (childCount > 0) {
      View selectedTitle = getChildAt(mIndexForSelection);

      if (selectedTitle == null) {
        // The view pager's tab count changed but we weren't notified yet. Ignore this draw
        // pass, when we get a new selection we will update and draw the selection strip in
        // the correct place.
        return;
      }
      int selectedLeft = selectedTitle.getLeft();
      int selectedRight = selectedTitle.getRight();
      final boolean isRtl = isRtl();
      final boolean hasNextTab =
          isRtl ? mIndexForSelection > 0 : (mIndexForSelection < (getChildCount() - 1));
      if ((mSelectionOffset > 0.0f) && hasNextTab) {
        // Draw the selection partway between the tabs
        View nextTitle = getChildAt(mIndexForSelection + (isRtl ? -1 : 1));
        int nextLeft = nextTitle.getLeft();
        int nextRight = nextTitle.getRight();

        selectedLeft =
            (int) (mSelectionOffset * nextLeft + (1.0f - mSelectionOffset) * selectedLeft);
        selectedRight =
            (int) (mSelectionOffset * nextRight + (1.0f - mSelectionOffset) * selectedRight);
      }

      int height = getHeight();
      canvas.drawRect(
          selectedLeft,
          height - mSelectedUnderlineThickness,
          selectedRight,
          height,
          mSelectedUnderlinePaint);
    }
  }

  private boolean isRtl() {
    return getLayoutDirection() == View.LAYOUT_DIRECTION_RTL;
  }
}