之前在《一步步打造自己的通用上拉載入佈局》（如果沒有看過，建議先看下這一篇）寫到如何實現一個通用的上拉載入佈局，本文將基於此進行擴充套件，實現 RecyclerView 的上拉載入及自動載入。

在之前的《一步步打造自己的通用上拉載入佈局》已經提到，下拉重新整理是將獲取到的資料替換掉原有的資料，而上拉載入則是將獲取到的資料插入到原來資料的末尾與底部提示載入的 View（如FooterView）之間，它們的展現方式的不同，使得上拉出來用於提示載入的 View，對於列表類檢視如 ListView 或 RecyclerView 而言，適合作為它們的 FooterView 而不適合封裝到我們的上拉布局中。因此，我們需要繼承 LoadMoreLayout

準備工作

由於在 LoadMoreLayout 中已經把上拉的邏輯都封裝好，因此這裡主要是對 RecyclerView 的 FooterView 及自動載入的封裝。在這裡，對於帶 FooterView 的 Adapter，我是通過包裝原有的 Adapter 來實現，這樣在使用的時候就不需要把原來的 Adapter 改成我們的上拉載入中的 Adapter，以減少對程式碼的侵入。這個 Adapter 程式碼如下。這個類程式碼可不必細看，它是上拉載入的副產品，不是主要邏輯，於這裡貼出只是交底。

/*
 * Copyright (c) 2017. Xi'an iRain IOT Technology service CO., Ltd (ShenZhen). All Rights Reserved.
 */
 

package com.githang.recycleradapter;

import android.support.v7.widget.RecyclerView;
import android.view.ViewGroup;

/**
 * @author Geek_Soledad ([email protected])
 * @since 2017-05-03 0.1
 */
public abstract class HiRecyclerAdapter extends RecyclerView.Adapter {
    /**
     * 由於RecyclerView的靈活性，可能會出現不同的Adapter的巢狀，而因此可能導致viewType重複。
     * 因此在這裡嘗試為每個Adapter定義一個區間，而避免它們的重複問題。
     */
 

    public static final int TYPE_SECTION = 2 << 10;

    /**
     * 從2<<20開始，留足夠的type值給content使用。
     */
    private static final int HEADER_OFFSET = TYPE_SECTION << 10;
    private static final int FOOTER_OFFSET = HEADER_OFFSET + TYPE_SECTION;

    private int mHeaderCount;
    private int mContentCount;
    private int mFooterCount;

    private RecyclerView.Adapter mWrapperAdapter;
    private RecyclerView.AdapterDataObserver mDataObserver;

    public HiRecyclerAdapter(RecyclerView.Adapter wrapperAdapter) {
        mWrapperAdapter = wrapperAdapter;
        mDataObserver = new RecyclerView.AdapterDataObserver() {
            @Override
            public void onChanged() {
                notifyDataSetChanged();
            }

            @Override
            public void onItemRangeChanged(int positionStart, int itemCount) {
                notifyItemRangeChanged(positionStart + mHeaderCount, itemCount);
            }

            @Override
            public void onItemRangeChanged(int positionStart, int itemCount, Object payload) {
                notifyItemRangeChanged(positionStart + mHeaderCount, itemCount, payload);
            }

            @Override
            public void onItemRangeInserted(int positionStart, int itemCount) {
                notifyItemRangeInserted(positionStart + mHeaderCount, itemCount);
            }

            @Override
            public void onItemRangeRemoved(int positionStart, int itemCount) {
                notifyItemRangeRemoved(positionStart + mHeaderCount, itemCount);
            }

            @Override
            public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
                notifyItemMoved(fromPosition + mHeaderCount, toPosition + mHeaderCount);
            }
        };
        mWrapperAdapter.registerAdapterDataObserver(mDataObserver);
    }

    public RecyclerView.Adapter getWrapperAdapter() {
        return mWrapperAdapter;
    }

    public int getContentPosition(int position) {
        return position - mHeaderCount;
    }

    @Override
    public final RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if (viewType >= HEADER_OFFSET && viewType < HEADER_OFFSET + TYPE_SECTION) {
            return onCreateHeaderHolder(parent, viewType - HEADER_OFFSET);
        } else if (viewType >= FOOTER_OFFSET && viewType < FOOTER_OFFSET + TYPE_SECTION) {
            return onCreateFooterHolder(parent, viewType - FOOTER_OFFSET);
        } else {
            return mWrapperAdapter.onCreateViewHolder(parent, viewType);
        }
    }

    /**
     * Called when RecyclerView needs a new header {@link RecyclerView.ViewHolder} of the given type to
     * represent an item.
     *
     * @param parent   The ViewGroup into which the new View will be added after it is bound to
     *                 an adapter position.
     * @param viewType The view type of the new View.
     * @return A new ViewHolder that holds a View of the given view type.
     */
    protected abstract RecyclerView.ViewHolder onCreateHeaderHolder(ViewGroup parent, int viewType);

    /**
     * Called when RecyclerView needs a new footer {@link RecyclerView.ViewHolder} of the given type to
     * represent an item.
     *
     * @param parent   The ViewGroup into which the new View will be added after it is bound to
     *                 an adapter position.
     * @param viewType The view type of the new View.
     * @return A new ViewHolder that holds a View of the given view type.
     */
    protected abstract RecyclerView.ViewHolder onCreateFooterHolder(ViewGroup parent, int viewType);

    @Override
    public final void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if (position < mHeaderCount) {
            onBindHeaderHolder(holder, position);
        } else if (position < mHeaderCount + mContentCount) {
            mWrapperAdapter.onBindViewHolder(holder, position - mHeaderCount);
        } else {
            onBindFooterHolder(holder, position - mHeaderCount - mContentCount);
        }
    }

    /**
     * Called by RecyclerView to display the header at the specified position. This method should
     * update the contents of the {@link RecyclerView.ViewHolder#itemView} to reflect the header
     * item at the given position.
     *
     * @param holder   The ViewHolder which should be updated to represent the contents of the
     *                 item at the given position in the data set.
     * @param position The position of the item within the adapter's data set.
     */
    protected abstract void onBindHeaderHolder(RecyclerView.ViewHolder holder, int position);

    /**
     * Called by RecyclerView to display the footer at the specified position. This method should
     * update the contents of the {@link RecyclerView.ViewHolder#itemView} to reflect the footer
     * item at the given position.
     *
     * @param holder   The ViewHolder which should be updated to represent the contents of the
     *                 item at the given position in the data set.
     * @param position The position of the item within the adapter's data set.
     */
    protected abstract void onBindFooterHolder(RecyclerView.ViewHolder holder, int position);

    public int getHeaderCount() {
        return 0;
    }

    public final int getContentCount() {
        return mWrapperAdapter.getItemCount();
    }

    public int getFooterCount() {
        return 0;
    }

    @Override
    public final int getItemCount() {
        mHeaderCount = getHeaderCount();
        mContentCount = mWrapperAdapter.getItemCount();
        mFooterCount = getFooterCount();
        return mHeaderCount + mContentCount + mFooterCount;
    }

    @Override
    public final int getItemViewType(int position) {
        if (position < mHeaderCount) {
            return validateViewType(getHeaderViewType(position)) + HEADER_OFFSET;
        } else if (position < mHeaderCount + mContentCount) {
            return validateViewType(mWrapperAdapter.getItemViewType(position - mHeaderCount));
        } else {
            return validateViewType(getFooterViewType(position - mHeaderCount - mContentCount)) + FOOTER_OFFSET;
        }
    }

    private int validateViewType(int viewType) {
        if (viewType < 0 || viewType >= TYPE_SECTION) {
            throw new IllegalStateException("viewType must be between 0 and " + TYPE_SECTION);
        }
        return viewType;
    }

    protected int getHeaderViewType(int position) {
        return 0;
    }

    protected int getFooterViewType(int position) {
        return 0;
    }

    public void notifyFooterInsert(int positionStart) {
        notifyItemInserted(mHeaderCount + mContentCount + positionStart);
    }

    public void notifyFooterRemoved(int positionStart) {
        notifyItemRemoved(mHeaderCount + mContentCount + positionStart);
    }
}

接下來，繼承自這個 Adapter，實現對 FooterView 新增，程式碼如下：

/*
 * Copyright (c) 2017. Xi'an iRain IOT Technology service CO., Ltd (ShenZhen). All Rights Reserved.
 */
package com.githang.hiloadmore.recyclerview;

import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.view.ViewGroup;

import com.githang.recycleradapter.HiRecyclerAdapter;

import java.util.ArrayList;
import java.util.List;

/**
 * @author Geek_Soledad ([email protected])
 * @since 2017-05-03 0.1
 */
public class FooterRecyclerAdapter extends HiRecyclerAdapter {

    private List<View> mFooterViews = new ArrayList<>();

    public FooterRecyclerAdapter(RecyclerView.Adapter wrapperAdapter) {
        super(wrapperAdapter);
    }

    @Override
    protected RecyclerView.ViewHolder onCreateHeaderHolder(ViewGroup parent, int viewType) {
        return null;
    }

    @Override
    protected RecyclerView.ViewHolder onCreateFooterHolder(ViewGroup parent, int viewType) {
        return new FooterViewHolder(mFooterViews.get(viewType));
    }

    @Override
    protected void onBindHeaderHolder(RecyclerView.ViewHolder holder, int position) {
    }

    @Override
    protected void onBindFooterHolder(RecyclerView.ViewHolder holder, int position) {
    }

    @Override
    protected int getFooterViewType(int position) {
        return position;
    }

    @Override
    public int getFooterCount() {
        return mFooterViews.size();
    }

    void addFooterView(View view) {
        if (!mFooterViews.contains(view)) {
            mFooterViews.add(view);
            notifyFooterInsert(mFooterViews.indexOf(view));
        }
    }

    void removeFooterView(View view) {
        if (mFooterViews.contains(view)) {
            int index = mFooterViews.indexOf(view);
            mFooterViews.remove(view);
            notifyFooterRemoved(index);
        }
    }

    static FooterRecyclerAdapter wrapper(RecyclerView.Adapter adapter) {
        if (adapter instanceof FooterRecyclerAdapter) {
            return (FooterRecyclerAdapter) adapter;
        } else {
            return new FooterRecyclerAdapter(adapter);
        }
    }

    static class FooterViewHolder extends RecyclerView.ViewHolder {

        FooterViewHolder(View itemView) {
            super(itemView);
            RecyclerView.LayoutParams lp = (RecyclerView.LayoutParams) itemView.getLayoutParams();
            if (lp == null) {
                lp = new RecyclerView.LayoutParams(
                        ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
                itemView.setLayoutParams(lp);
            }
        }
    }
}

然後，實現一個預設的 FooterView。它的佈局檔案很簡單，就是一個 TextView，如下：

<?xml version="1.0" encoding="utf-8"?>
<TextView
    android:id="@+id/footer_text"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="48dp"
    android:gravity="center"
    android:textColor="#666"
    android:textSize="12sp"/>

它需要實現 LoadMoreUIHandler 介面，Java 程式碼如下：

/*
 * Copyright (c) 2017. Xi'an iRain IOT Technology service CO., Ltd (ShenZhen). All Rights Reserved.
 */
package com.githang.hiloadmore.recyclerview;

import android.content.Context;
import android.support.annotation.NonNull;
import android.view.LayoutInflater;
import android.widget.FrameLayout;
import android.widget.TextView;

import com.githang.hiloadmore.LoadMoreUIHandler;
import com.githang.hiloadmore.R;

/**
 * @author Geek_Soledad ([email protected])
 * @since 2017-05-03 0.1
 */
public class RecyclerFooterView extends FrameLayout implements LoadMoreUIHandler {
    private TextView mText;

    public RecyclerFooterView(@NonNull Context context) {
        super(context);
        LayoutInflater.from(context).inflate(R.layout.hlm_footer_load_more, this, true);
        mText = findViewById(R.id.footer_text);
        mText.setText(R.string.hlm_pull_to_load_more);
    }

    @Override
    public void onPrepare() {
        mText.setText(R.string.hlm_pull_to_load_more);
    }

    @Override
    public void onBegin() {
        mText.setText(R.string.hlm_tip_loading_more);
    }

    @Override
    public void onComplete(boolean hasMore) {
        mText.setText(hasMore ? R.string.hlm_pull_to_load_more : R.string.hlm_tip_load_finish);
    }

    @Override
    public void onPositionChange(int offsetY, int offsetToLoadMore) {
        if (Math.abs(offsetY) > offsetToLoadMore) {
            mText.setText(R.string.hlm_release_to_load_more);
        } else {
            mText.setText(R.string.hlm_pull_to_load_more);
        }
    }
}

上拉載入的 FooterView 擴充套件

前面這些，都只是對 FooterView 顯示的準備工作。最後，才是對 LoadMoreLayout 實現支援 RecyclerView 的擴充套件。如果你不需要這個FooterView，那麼直接使用 LoadMoreLayout 也是可以的。當然，這裡的擴充套件過程也很簡單，繼承 LoadMoreLayout，然後重寫 protected void onFinishInflate() 方法，限定子 View 只能是 RecyclerView，再定義一個設定 FooterView 的方法，如此即可，程式碼如下：

/*
 * Copyright (c) 2017. Xi'an iRain IOT Technology service CO., Ltd (ShenZhen). All Rights Reserved.
 */
package com.githang.hiloadmore.recyclerview;

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

import com.githang.hiloadmore.LoadMoreLayout;

/**
 * RecyclerView的上拉載入以及自動載入實現。
 *
 * @author Geek_Soledad ([email protected])
 * @since 2017-05-03 0.1
 */
public class LoadMoreRecyclerViewContainer extends LoadMoreLayout {
    private View mFooterView;

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

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        View content = getContentView();
        if (!(content instanceof RecyclerView)) {
            throw new IllegalStateException("LoadMoreRecyclerViewContainer only support RecyclerView");
        }
    }

    public void setFooterView(final View footer) {
        final RecyclerView recyclerView = (RecyclerView) getContentView();
        final FooterRecyclerAdapter adapter = FooterRecyclerAdapter.wrapper(recyclerView.getAdapter());
        if (mFooterView != null && mFooterView != footer) {
            adapter.removeFooterView(mFooterView);
        }
        adapter.addFooterView(footer);
        mFooterView = footer;
        recyclerView.setAdapter(adapter);
        footer.post(new Runnable() {
            @Override
            public void run() {
                int height = footer.getHeight();
                if (height > 0) {
                    setOffsetYToLoadMore(height);
                }
            }
        });
    }
}

這就完成了上拉載入的擴充套件。

實現自動載入

接下來實現自動載入，這個也很簡單，思路就是監聽 RecyclerView 的滾動，如果到達底部，則主動觸發上拉載入。這裡只需要定義一個表示是否需要自動載入的成員變數，新增其 setter 方法，然後修改上面重寫的 protected void onFinishInflate() 方法，給 RecyclerView 加一個監聽器即可，如下：

    private View mFooterView;

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        View content = getContentView();
        if (content instanceof RecyclerView) {
            ((RecyclerView) content).addOnScrollListener(new RecyclerView.OnScrollListener() {

                private LinearLayoutManager mLinearLayoutManager;

                @Override
                public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                    if (!mAutoLoadMore || !hasMore()) {
                        return;
                    }
                    if (mLinearLayoutManager == null) {
                        RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
                        if (layoutManager instanceof LinearLayoutManager) {
                            mLinearLayoutManager = (LinearLayoutManager) layoutManager;
                        }
                    }
                    if (mLinearLayoutManager == null) {
                        return;
                    }

                    if ((mLinearLayoutManager.getItemCount() - recyclerView.getChildCount())
                            <= mLinearLayoutManager.findFirstVisibleItemPosition()) {
                        triggerToLoadMore();
                    }
                }
            });
        } else {
            throw new IllegalStateException("LoadMoreRecyclerViewContainer only support RecyclerView");
        }
    }

    public void setAutoLoadMore(boolean autoLoadMore) {
        mAutoLoadMore = autoLoadMore;
    }

這樣就擴充套件完成了。

使用示例

以上程式碼已提交至 Github 上的 hi-loadmore 專案，並且已釋出至 bintray。使用方式如下：

首先新增 Gradle 依賴：

    compile 'com.githang:hi-loadmore:0.1.1'
    // OR
    implementation 'com.githang:hi-loadmore:0.1.1'

然後在佈局中使用 LoadMoreRecyclerViewContainer作為 RecyclerView 的父佈局。接下來在 Java 程式碼中新增配置：

        RecyclerFooterView footerView = new RecyclerFooterView(this);
        mLoadMoreLayout.setFooterView(footerView);
        mLoadMoreLayout.setLoadMoreUIHandler(footerView);
        mLoadMoreLayout.setHasMore(true);

然後設定觸發了上拉載入後的處理：

        mLoadMoreLayout.setLoadMoreHandler(new LoadMoreHandler() {
            @Override
            public void onLoadMore() {
                // 在這裡請求資料
            }
        });

最後看下執行結果：