RecyclerView 局部刷新的坑

前言

相信童鞋们都用过RecyclerView，假设说要我们做一个列表更新Item的功能，相信大部分同学都会这么写的：

  /**
     * 更新列表数据某一项的packageName
     *
     * @param position    下标
     * @param packageName 要替换的文本名
     */
    public void updateItem(int position, String packageName) {
        if (position >= 0 && position < data.size()) {
            data.get(position).setPackageName(packageName);
        }
        notifyDataSetChanged();
    }复制代码

踩坑

而我们要做的是一个下载列表，在下载的callback里面我们要去更新列表的progressBar还有Button的文本：

Activity中获取到下载的callback：

 @Override
        public void onProgress(long finished, long total, int progress) {
            XLog.e(mInfoBean.getDownLoadUrl() + "-----------||||||" + progress);
            String downloadPerSize = Kits.File.getDownloadPerSize(finished, total);
            mInfoBean.setDownLoadStatus(STATUS_DOWNLOADING);
            mInfoBean.setDownloadPerSize(downloadPerSize);
            mInfoBean.setProgress(progress);
            if (isCurrentListViewItemVisible(mPosition)) {
                mTestDownLoadAdapter.setProgress(progress, mPosition, downloadPerSize);
            }
        }复制代码

适配器中暴露的用于更新progressBar进度的方法

  /**
     * 暴露用于修改进度值的方法
     *
     * @param progress
     * @param position
     * @param progressStr
     */
    public void setProgress(int progress, int position, String progressStr) {
        data.get(position).setProgress(progress);
        data.get(position).setDownloadPerSize(progressStr);
        notifyItemChanged(position);
    }复制代码

适配器的onBindViewHolder()中处理数据结果

 @Override
    public void onBindViewHolder(final TestDownLoadHolder holder, final int position) {
        final AppInfoBean appInfoBean = data.get(position);
        if (appInfoBean != null) {
            ILFactory.getLoader().loadNet(holder.mIvDownPic, appInfoBean.getDownLoadPic(), ImgOptions.getDefImaOptions());
            holder.mPbDownProgress.setProgress(appInfoBean.getProgress());
            holder.mBtDownLoad.setText(appInfoBean.getDownloadPerSize());
            holder.mBtDownLoad.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    if (getRecItemClick() != null) {
                        getRecItemClick().onItemClick(position, appInfoBean, 0, holder);
                    }
                }
            });
        }

    }复制代码

这里我们使用的是notifyItemChanged局部刷新而不是notifyDataSetChanged。讲道理我们到了这一步就已经可以满足需求了，然而...事实不讲道理：

一闪一闪亮晶晶
额...原谅demo画得太丑了。这里我们可以发现....为毛我的图片...一闪一闪的，亮瞎我的狗眼了。
至于为什么会闪动？
猜测：

1. ImageView的宽高问题，重新计算导致了闪动
2. 更新到了ImageView，然后glide又重新加载了一次图片。
3. 刷新到了ImageView，这个item渲染了一次。

解疑：

• 采用了写死宽高的方法，但是！页面还是会闪动...gif就不传了，录制好麻烦。猜测1已经否决了。
• 注释掉

  ILFactory.getLoader().loadNet(holder.mIvDownPic, appInfoBean.getDownLoadPic(), ImgOptions.getDefImaOptions());复制代码

  在xml中写入

  android:src="@mipmap/ic_launcher"复制代码

  测试下，结果还是会闪动...那猜测2又不对了！
• 重新理下，我们需要更新的是Button和progressBar，其实ImageView我们是不需要额外去更新的。

那我们的问题就聚焦在如何只更新一部分控件，其他控件不动

解决

至于怎么解决呢...扒源码：

   /**
         * Notify any registered observers that the item at position has changed.
         * Equivalent to calling notifyItemChanged(position, null);.
         *
         * 
This is an item change event, not a structural change event. It indicates that any
         * reflection of the data at position is out of date and should be updated.
         * The item at position retains the same identity.
         *
         * @param position Position of the item that has changed
         *
         * @see #notifyItemRangeChanged(int, int)
         */
        public final void notifyItemChanged(int position) {
            mObservable.notifyItemRangeChanged(position, 1);
        }复制代码

 /**
         * Notify any registered observers that the item at position has changed with an
         * optional payload object.
         *
         * 
This is an item change event, not a structural change event. It indicates that any
         * reflection of the data at position is out of date and should be updated.
         * The item at position retains the same identity.
         * 
         *
         * 

         * Client can optionally pass a payload for partial change. These payloads will be merged
         * and may be passed to adapter's {@link #onBindViewHolder(ViewHolder, int, List)} if the
         * item is already represented by a ViewHolder and it will be rebound to the same
         * ViewHolder. A notifyItemRangeChanged() with null payload will clear all existing
         * payloads on that item and prevent future payload until
         * {@link #onBindViewHolder(ViewHolder, int, List)} is called. Adapter should not assume
         * that the payload will always be passed to onBindViewHolder(), e.g. when the view is not
         * attached, the payload will be simply dropped.
         *
         * @param position Position of the item that has changed
         * @param payload Optional parameter, use null to identify a "full" update
         *
         * @see #notifyItemRangeChanged(int, int)
         */
        public final void notifyItemChanged(int position, Object payload) {
            mObservable.notifyItemRangeChanged(position, 1, payload);
        }复制代码

在这里我们看到一句话：

   @param payload Optional parameter, use null to identify a "full" update复制代码

传入“null”就是更新全部！那我们调用的时候是传入什么呢！看下：

  public final void notifyItemChanged(int position) {
            mObservable.notifyItemRangeChanged(position, 1);
        }复制代码

继而调用：

 public void notifyItemRangeChanged(int positionStart, int itemCount) {
            notifyItemRangeChanged(positionStart, itemCount, null);
        }复制代码

继而调用：

  public void notifyItemRangeChanged(int positionStart, int itemCount, Object payload) {
            // since onItemRangeChanged() is implemented by the app, it could do anything, including
            // removing itself from {@link mObservers} - and that could cause problems if
            // an iterator is used on the ArrayList {@link mObservers}.
            // to avoid such problems, just march thru the list in the reverse order.
            for (int i = mObservers.size() - 1; i >= 0; i--) {
                mObservers.get(i).onItemRangeChanged(positionStart, itemCount, payload);
            }
        }复制代码

[捂脸] 一个大写的null...

OK，那我们修改下我们的调用方法：

 /**
     * 暴露用于修改进度值的方法
     *
     * @param progress
     * @param position
     * @param progressStr
     */
    public void setProgress(int progress, int position, String progressStr) {
        data.get(position).setProgress(progress);
        data.get(position).setDownloadPerSize(progressStr);
        notifyItemChanged(position, 1);
    }

    /**
     * 暴露用于修改按钮文字值的方法
     *
     * @param position
     * @param buttonStr
     */
    public void setButtonStatus(int position, String buttonStr) {
        data.get(position).setDownloadPerSize(buttonStr);
        notifyItemChanged(position, 1);
    }复制代码

这里我们传入了一个 “1”,这个1是随意传入的，其他值也可以。

继而我们需要重写onBindViewHolder方法如下：

 @Override
    public void onBindViewHolder(TestDownLoadHolder holder, int position, List