RecyclerView 局部刷新的坑，34岁程序员年薪50w

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• @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();
  }

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);
}
}

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);
  }

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);
}
}
});
}

}

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：

[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-D02S7a5j-1646116102674)(https://user-gold-cdn.xitu.io/2017/10/27/72395e18c6486bb49278862724e630b4?imageView2/0/w/1280/h/960/ignore-error/1)]

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。

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

android:src="@mipmap/ic_launcher"

• 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);
  }

/**

• 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);
  }

在这里我们看到一句话：

@param payload Optional parameter, use null to identify a “full” update

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);
}

继而调用：

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

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);
}
}

[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);
  }

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 payloads) {
XLog.e("--------------------------has payloads");
if (payloads.isEmpty()) {
XLog.e("--------------------------no payloads");
onBindViewHolder(holder, position);
} else {
XLog.e("--------------------------false payloads");
final AppInfoBean appInfoBean = data.get(position);
if (appInfoBean != null) {
holder.mPbDownProgress.setProgress(appInfoBean.getProgress());
holder.mBtDownLoad.setText(appInfoBean.getDownloadPerSize());
}
}
}

@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);
}
}
});
}

}
getDownloadPerSize());
holder.mBtDownLoad.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (getRecItemClick() != null) {
getRecItemClick().onItemClick(position, appInfoBean, 0, holder);
}
}
});
}

}

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