从ViewPager获得专注的视图

Question

我使用ViewPager通过左/右滑动切换视图。

ViewPager需要一个适配器，所以我构建了这个：

public class ListViewPagerAdapter extends PagerAdapter {

protected static final String TAG = "ListViewPagerAdapter";
protected static final int NUM_VIEWS = 3;

protected final Activity mActivity;

public ListViewPagerAdapter(Activity activity) {
    mActivity = activity;
}

@Override
public int getCount() {
    return NUM_VIEWS;
}

@Override
public void startUpdate(View container) {}

@Override
public Object instantiateItem(View container, int position) {
    // ViewPager
    ViewPager viewPager = (ViewPager) container;

    // Wird verwendet, um die Views aufzurufen
    LayoutInflater layoutInflater = mActivity.getLayoutInflater();

    // Standardmäßig ist news eingeblendet
    View view = layoutInflater.inflate(R.layout.news_fragment, null);
    // Falls sich die Position verändert, so verändert sich auch die View
    if (position == 0) {
        view = layoutInflater.inflate(R.layout.favorite_fragment, null);
    } else if (position == 2) {
        view = layoutInflater.inflate(R.layout.videos_fragment, null);
    }

    // View einblenden
    viewPager.addView(view, 0);

    return view;
}

@Override
public void destroyItem(View container, int position, Object object) {
    // ViewPager
    ViewPager viewPager = (ViewPager) container;
    // View
    View view = (View) object;

    // View löschen
    viewPager.removeView(view);
}

@Override
public void finishUpdate(View container) {}

@Override
public boolean isViewFromObject(View view, Object object) {
    View _view = (View) object;
    return view == _view;
}

@Override
public Parcelable saveState() {
    return null;
}

@Override
public void restoreState(Parcelable state, ClassLoader loader) {}
 }

现在，我想通过viewpager获取当前的焦点视图。 我试过getChildAt（x），但它不起作用。

是否有一些示例，或者您是否知道如何获取当前视图？

由于

Answer 1

可以通过覆盖PagerAdapter.setPrimaryItem方法保存当前活动对象（View，Fragment，...）。例如：

private View mCurrentView;

@Override
public void setPrimaryItem(ViewGroup container, int position, Object object) {
    mCurrentView = (View)object;
}

Answer 2

您必须向ViewPager注册听众：

pager.setOnPageChangeListener(new MyPageChangeListener()); 

您必须通过扩展存根侦听器来自定义侦听器：

private int focusedPage = 0;
private class MyPageChangeListener extends ViewPager.SimpleOnPageChangeListener {
    @Override
    public void onPageSelected(int position) {
        focusedPage = position;
    }
}

我通过查看compatibility library中的ViewPager.java源代码找到了这个。我读到我们可以做更多，例如catch onPageScrollStateChanged。

为了构建适配器，我使用了代码on this blog post。你可能想看看。

Answer 3

您可以在instantiateItem方法中为创建的视图添加标记：

view.setTag(position);

稍后您可以通过以下方式访问当前选定的视图：

mPager.findViewWithTag(mPager.getCurrentItem());

Answer 4

我最近需要实现这个确切的解决方案。这就是我做的方式：

Map<Integer, Object> views = Maps.newHashMap();

@Override
public Object instantiateItem(View container, int position) {
  /* Create and add your View here */
  Object result = ???

  views.put(position, result);
  return result;
}

@Override
public void destroyItem(View container, int position, Object object) {
  /** Remove your View here */

  views.remove(position);
}

protected View findViewForPosition(int position) {
  Object object = views.get(position);
  if (object != null) {
    for (int i = 0; i < getChildCount(); i++) {
      View view = getChildAt(i);
      if (isViewFromObject(view, object)) {
        return view;
      }
    }
  }
  return null;
}

Answer 5

试试这个：

public View getCurrentView(ViewPager pager) {
    for (int i = 0; i < pager.getChildCount(); i++) {
        View child = pager.getChildAt(i);
        if (child.getX() <= pager.getScrollX() + pager.getWidth() && 
            child.getX() + child.getWidth() >= pager.getScrollX() + pager.getWidth()) {
            return child;
         }
     }
     return getChildAt(0);
}

Answer 6

为了获得专注的观点，我采用这种方式：

当我在ViewPager上添加视图之前给我的视图充气时，我将标签设置为它。然后我检查这个标签。

private View getCurrentView()
{
    for (int i = 0; i < pager.getChildCount(); i++)
    {
        View v = pager.getChildAt(i);
        if (v != null)
        {
            if (v.getTag().equals(pageList.get(pager.getCurrentItem()).getTag())) return v;
            // pageList is a list of pages that I pass to page adapter
        }
    }
    return null;
}

Answer 7

给定的答案并不适合我，它们都有不必要的副作用。要么我必须添加不必要的变量（我喜欢干净的代码），要么我必须解决Android框架本身。

我的解决方案基于反射，它可以访问ViewPager中所有对象的数组列表，并返回ViewPager中当前选定的对象。它几乎没有副作用（反射很慢，现有类的子类化）并且它保持代码清洁。

public class ViewPagerEx extends ViewPager {

    private static final String TAG = ViewPagerEx.class.getSimpleName();

    public ViewPagerEx(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public ViewPagerEx(Context context) {
        super(context);
    }

    public Object getCurrentObject() {
        try {
            final Field itemsField = ViewPager.class.getDeclaredField("mItems");
            itemsField.setAccessible(true);

            final ArrayList<Object> items = (ArrayList<Object>) itemsField.get(this);

            final int currentItemIndex = getCurrentItem();
            if (currentItemIndex < 0 || currentItemIndex >= items.size()) {
                return null;
            }

            final Object infoItem = items.get(getCurrentItem());

            final Class<?> itemInfoClass = findItemInfoClass(ViewPager.class.getDeclaredClasses());

            final Field objectField = itemInfoClass.getDeclaredField("object");
            objectField.setAccessible(true);
            return objectField.get(infoItem);

        } catch (NoSuchFieldException e) {
            Log.e(TAG, e.toString());
        } catch (IllegalArgumentException e) {
            Log.e(TAG, e.toString());
        } catch (IllegalAccessException e) {
            Log.e(TAG, e.toString());
        }

        return null;
    }

    private Class<?> findItemInfoClass(final Class<?>[] classes) throws IllegalArgumentException {
        for (int i = 0; i < classes.length; i++) {
            if (classes[i].getSimpleName().equals("ItemInfo")) {
                return classes[i];
            }
        }

        throw new IllegalArgumentException("cannot find class ItemInfo");
    }
}

Answer 8

在FragmentStatePagerAdapter内：

    private View mCurrentView;

    @Override
    public void setPrimaryItem(ViewGroup container, int position, Object object) {
        Fragment f = (Fragment) object;
        mCurrentView = f.getView();
    }

Answer 9

您可以使用此代码

viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                Toast.makeText(getContext(), String.valueOf(position), Toast.LENGTH_SHORT).show();
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });

Answer 10

您可以使用：

 viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }

        @Override
        public void onPageSelected(int position) {
            Log.i("maylonsales", "onPageSelected position " + position);
        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    });

Answer 11

如果仔细检查，ViewPager最多可保存3个视图。 您可以通过

轻松获取当前视图

view     = MyActivity.mViewPager.getChildAt(1);

Answer 12

我错过了什么吗？ ViewGroup中只有3个孩子，所以归结为：

int current = viewPager.getCurrentItem();
int childCount = viewPager.getChildCount();
// If there's a single page or we're at the beginning, return the first view
if (childCount == 1 || current == 0) {
  return viewPager.getChildAt(0);
} else { //For any other case, we want the second child. This is either the last page or the page in the middle for any other case.
  return viewPager.getChildAt(1);
}