Android Open Source - Common-Library Scroll Detectors

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License

The source code is released under:

Apache License

Java Source Code

package com.morgan.library.widget.slidemenu;
/*from   w ww  . ja v a 2  s. com*/
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.WeakHashMap;

import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.View;
import android.webkit.WebView;
import android.widget.HorizontalScrollView;

public class ScrollDetectors {
  private static final WeakHashMap<Class<?>, ScrollDetector> IMPLES = new WeakHashMap<Class<?>, ScrollDetector>();
  private static ScrollDetectorFactory mFactory;

  /**
   * Check the view is horizontal scrollable
   * 
   * @param v
   * @param direction
   * @return
   */
  public static boolean canScrollHorizontal(View v, int direction) {
    ScrollDetector imples = getImplements(v);
    if (null == imples) {
      return false;
    }
    return imples.canScrollHorizontal(v, direction);
  }

  /**
   * Check the view is vertical scrollable
   * 
   * @param v
   * @param direction
   * @return
   */
  public static boolean canScrollVertical(View v, int direction) {
    ScrollDetector imples = getImplements(v);
    if (null == imples) {
      return false;
    }
    return imples.canScrollVertical(v, direction);
  }

  private static ScrollDetector getImplements(View v) {
    Class<?> clazz = v.getClass();
    ScrollDetector imple = IMPLES.get(clazz);

    if (null != imple) {
      return imple;
    }

    if (v instanceof ViewPager) {
      imple = new ViewPagerScrollDetector();
    } else if (v instanceof HorizontalScrollView) {
      imple = new HorizontalScrollViewScrollDetector();
    } else if (v instanceof WebView) {
      imple = new WebViewScrollDetector();
    } else if (null != mFactory) {
      imple = mFactory.newScrollDetector(v);
    } else {
      return null;
    }

    IMPLES.put(clazz, imple);
    return imple;
  }

  private static class ViewPagerScrollDetector implements ScrollDetector {

    @Override
    public boolean canScrollHorizontal(View v, int direction) {
      ViewPager viewPager = (ViewPager) v;
      PagerAdapter pagerAdapter = viewPager.getAdapter();
      if (null == pagerAdapter) {
        return false;
      }

      final int currentItem = viewPager.getCurrentItem();
      return (direction < 0 && currentItem < pagerAdapter.getCount() - 1)
          || (direction > 0 && currentItem > 0);
    }

    @Override
    public boolean canScrollVertical(View v, int direction) {
      // TODO
      return false;
    }

  }

  private static class WebViewScrollDetector implements ScrollDetector {

    @Override
    public boolean canScrollHorizontal(View v, int direction) {
      try {
        // Because this method is protected
        Method computeHorizontalScrollOffsetMethod = WebView.class
            .getDeclaredMethod("computeHorizontalScrollOffset");
        Method computeHorizontalScrollRangeMethod = WebView.class
            .getDeclaredMethod("computeHorizontalScrollRange");
        computeHorizontalScrollOffsetMethod.setAccessible(true);
        computeHorizontalScrollRangeMethod.setAccessible(true);

        final int horizontalScrollOffset = (Integer) computeHorizontalScrollOffsetMethod
            .invoke(v);
        final int horizontalScrollRange = (Integer) computeHorizontalScrollRangeMethod
            .invoke(v);

        return (direction > 0 && v.getScrollX() > 0)
            || (direction < 0 && horizontalScrollOffset < horizontalScrollRange
                - v.getWidth());
      } catch (NoSuchMethodException e) {
        e.printStackTrace();
      } catch (IllegalArgumentException e) {
        e.printStackTrace();
      } catch (IllegalAccessException e) {
        e.printStackTrace();
      } catch (InvocationTargetException e) {
        e.printStackTrace();
      }
      return false;
    }

    @Override
    public boolean canScrollVertical(View v, int direction) {
      // TODO
      return false;
    }

  }

  private static class HorizontalScrollViewScrollDetector implements
      ScrollDetector {

    @Override
    public boolean canScrollHorizontal(View v, int direction) {
      HorizontalScrollView horizontalScrollView = (HorizontalScrollView) v;
      final int scrollX = horizontalScrollView.getScrollX();

      // Without scroll wrapper, can't scroll
      if (0 == horizontalScrollView.getChildCount()) {
        return false;
      }
      return (direction < 0 && scrollX < horizontalScrollView.getChildAt(
          0).getWidth()
          - horizontalScrollView.getWidth())
          || (direction > 0 && scrollX > 0);
    }

    @Override
    public boolean canScrollVertical(View v, int direction) {
      // TODO
      return false;
    }

  }

  /**
   * Factory for create new scroll detector
   * 
   * @param factory
   */
  public static void setScrollDetectorFactory(ScrollDetectorFactory factory) {
    mFactory = factory;
  }

  public interface ScrollDetector {
    public boolean canScrollHorizontal(View v, int direction);

    public boolean canScrollVertical(View v, int direction);
  }
}

Java Source Code List

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