RecyclerView 下拉刷新上拉加载（类似PullToRfresh）

自Android5.0出来，大家可能对RecyclerView不陌生了，可是在实际项目中却不敢用，因为不熟悉，

也不会像ListView那样有很多库支持，比如PullToRefreshListiew

现在我们就仿照来自定义PullToRefreshRecyclerView

我们不着急，先看看源代码的上下拉是怎么判断的吧

带着你们找找源码吧，去类库里找到上下拉的基类

PullToRefreshBase

下面重写的代码就是判断上下拉刷新的

isReadyForPullStart  控件是否到顶

isReadyForPullEnd  控件是否到底

@Override
public final boolean demo() {
   if (mMode.showHeaderLoadingLayout() && isReadyForPullStart()) {
      smoothScrollToAndBack(-getHeaderSize() * 2);
      return true;
   } else if (mMode.showFooterLoadingLayout() && isReadyForPullEnd()) {
      smoothScrollToAndBack(getFooterSize() * 2);
      return true;
   }

   return false;
}

我们需要找到这两个方法是如何写的，去参照PullToRefreshListiew类吧

ctrl+f,找到这两个方法，没有找到，那我们就从继承的类里找

public class PullToRefreshListView extends PullToRefreshAdapterViewBase<ListView>
进入到
PullToRefreshAdapterViewBase类中
ctrl+f
protected boolean isReadyForPullEnd() {
   return isLastItemVisible();
}
进入isLastItemVisible()方法如下
private boolean isLastItemVisible() {
   final Adapter adapter = mRefreshableView.getAdapter();//获取adapter

   if (null == adapter || adapter.isEmpty()) {
      if (DEBUG) {
         Log.d(LOG_TAG, "isLastItemVisible. Empty View.");
      }
      return true;
   } else {
      final int lastItemPosition = mRefreshableView.getCount() - 1;//找到最后一个元素对应的位置
      final int lastVisiblePosition = mRefreshableView.getLastVisiblePosition();//最后一个可见元素
对应的位置

      if (lastVisiblePosition >= lastItemPosition - 1) {
         final int childIndex = lastVisiblePosition - mRefreshableView.getFirstVisiblePosition();
         final View lastVisibleChild = mRefreshableView.getChildAt(childIndex);
         if (lastVisibleChild != null) {
            return lastVisibleChild.getBottom() <= mRefreshableView.getBottom();//这是关键代码，
//如果可见元素的y坐标小于等于整个空间的y坐标，就是到了最后一个元素了
         }
      }
   }
   return false;
}
大家可能想，mRefreshableView这个变量哪里来的？不着急，我们后面会写到，同理另一个方法，我直接贴上，就不用解释了


private boolean isFirstItemVisible() {
   final Adapter adapter = mRefreshableView.getAdapter();
   if (null == adapter || adapter.isEmpty()) {
      return true;

   } else {
      if (mRefreshableView.getFirstVisiblePosition() <= 1) {
         final View firstVisibleChild = mRefreshableView.getChildAt(0);
         if (firstVisibleChild != null) {
            return firstVisibleChild.getTop() >= mRefreshableView.getTop();
         }
      }
   }

   return false;
}

好啦，方法看见了，我们直接自定义吧


package b2a.main.widget.RecycleRelating;

import android.content.Context;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
import android.widget.Adapter;

import com.handmark.pulltorefresh.library.PullToRefreshBase;

import b2a.main.R;


/**
 * Created by shf on 2015/7/23.
 */
public class PullToRefreshRecyclerView extends PullToRefreshBase<RecyclerView> {

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

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

    public PullToRefreshRecyclerView(Context context, Mode mode) {
        super(context, mode);
    }

    public PullToRefreshRecyclerView(Context context, Mode mode, AnimationStyle animStyle) {
        super(context, mode, animStyle);
    }

    /**
     * 刷新的方向
     *
     * @return
     */
    @Override
    public Orientation getPullToRefreshScrollDirection() {
        return Orientation.VERTICAL;
    }

    /**
     * 创建刷新内容
     *
     * @param context Context to create view with
     * @param attrs   AttributeSet from wrapped class. Means that anything you
     *                include in the XML layout declaration will be routed to the
     *                created View
     * @return
     */
    @Override
    protected RecyclerView createRefreshableView(Context context, AttributeSet attrs) {
        RecyclerView recycler = new RecyclerView(context, attrs);
        recycler.setId(R.id.recyclerSHF);//在资源文件中配置ids
        return recycler;
    }

    /**
     * 控件是否到底
     *
     * @return
     */

    @Override
    protected boolean isReadyForPullEnd() {
        RecyclerView recycler = getRefreshableView();//获取刷新的view
        final RecyclerView.Adapter adapter = recycler.getAdapter();
        if (null == adapter || adapter.getItemCount() == 0) {
            Log.i("SHF", "因为没有数据控件到底了-->001-->" + adapter.getItemCount());
            return true;
        } else {
            final int lastItemPosition = adapter.getItemCount() - 1;
            final int lastVisiblePosition = ((LinearLayoutManager) recycler.getLayoutManager()).
                    findLastVisibleItemPosition();
            Log.i("SHF", "lastItemPosition-->" + lastItemPosition + "lastVisiblePosition-->" + lastVisiblePosition);
            if (lastVisiblePosition >= lastItemPosition - 1) {
                final int childIndex = lastVisiblePosition -
                        ((LinearLayoutManager) recycler.getLayoutManager()).findFirstVisibleItemPosition();
                final View lastVisibleChild = recycler.getChildAt(childIndex);
                if (lastVisibleChild != null) {
                    Log.i("SHF", "因为数据控件到底了-->002");
                    return lastVisibleChild.getBottom() <= recycler.getBottom();
                }
            }
        }
        Log.i("SHF", "因为数据控件没到底-->003");
        return false;
    }

    @Override
    protected boolean isReadyForPullStart() {
        RecyclerView recycler = getRefreshableView();//获取刷新的view
        final RecyclerView.Adapter adapter = recycler.getAdapter();

        if (null == adapter || adapter.getItemCount() == 0) {
            return true;
        } else {

            if (((LinearLayoutManager) recycler.getLayoutManager()).findFirstVisibleItemPosition() <= 1) {
                final View firstVisibleChild = recycler.getChildAt(0);
                if (firstVisibleChild != null) {
                    return firstVisibleChild.getTop() >= recycler.getTop();
                }
            }
        }
        return false;
    }


}
参照listview我们也写好那两个判断方法即可，这里要提两个地方，
一个是RecyclerView recycler = getRefreshableView();//获取刷新的view
这就是获取控件，上面已经提到啦
另一个是recycler.setId(R.id.recyclerSHF);//在资源文件中配置ids
这里大家依照我写的配置一下就行了
res-->values-->ids.xml  没有的话新建一个
<?xml version="1.0" encoding="utf-8"?>
<resources>
    <item type="id" name="gridview" />
    <item type="id" name="webview" />
    <item type="id" name="scrollview" />
</resources>

大功告成，放心大胆的用吧