IllegalStateException: Cannot call this method while RecyclerView is computing a layout or scrolling
最近在使用RecyclerViewAdapter的时候遇到这个问题，这里总结记录一下，先看一下报错日志：
原因是我在Adapter中的item放了一个CheckBox, 并给CheckBox设置了监听，当选中状态改变的时候，在监听回调中直接调用notifyItemChanged就会出现这个问题。代码如下：
@Override
protected void convert(final BaseViewHolder helper, ContactDataSection item) {
final ContactMobileManage mobileContact = item.getEntity();
if (mobileContact != null) {
....
CheckBox checkBox = helper.getView(R.id.ckb_check);
checkBox.setChecked(mobileContact.isChecked());
checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, final boolean isChecked) {
mobileContact.setChecked(isChecked);
notifyItemChanged(helper.getAdapterPosition());
}
});
}
}
我们在RecyclerView源码中找到错误日志中提到的assertNotInLayoutOrScroll方法看一下：
/**
* Checks if RecyclerView is in the middle of a layout or scroll and throws an
* {@link IllegalStateException} if it <b>is</b>.
*
* @param message The message for the exception. Can be null.
* @see #assertInLayoutOrScroll(String)
*/
void assertNotInLayoutOrScroll(String message) {
if (isComputingLayout()) {
if (message == null) {
throw new IllegalStateException("Cannot call this method while RecyclerView is "
+ "computing a layout or scrolling" + exceptionLabel());
}
throw new IllegalStateException(message);
}
if (mDispatchScrollCounter > 0) {
Log.w(TAG, "Cannot call this method in a scroll callback. Scroll callbacks might"
+ "be run during a measure & layout pass where you cannot change the"
+ "RecyclerView data. Any method call that might change the structure"
+ "of the RecyclerView or the adapter contents should be postponed to"
+ "the next frame.",
new IllegalStateException("" + exceptionLabel()));
}
}
可以看到第一行isComputingLayout()方法为true的时候就会抛出这个异常，我们再看一下isComputingLayout()方法的代码：
/**
* Returns whether RecyclerView is currently computing a layout.
* <p>
* If this method returns true, it means that RecyclerView is in a lockdown state and any
* attempt to update adapter contents will result in an exception because adapter contents
* cannot be changed while RecyclerView is trying to compute the layout.
* <p>
* It is very unlikely that your code will be running during this state as it is
* called by the framework when a layout traversal happens or RecyclerView starts to scroll
* in response to system events (touch, accessibility etc).
* <p>
* This case may happen if you have some custom logic to change adapter contents in
* response to a View callback (e.g. focus change callback) which might be triggered during a
* layout calculation. In these cases, you should just postpone the change using a Handler or a
* similar mechanism.
*
* @return <code>true</code> if RecyclerView is currently computing a layout, <code>false</code>
* otherwise
*/
public boolean isComputingLayout() {
return mLayoutOrScrollCounter > 0;
}
它这里的注释写的很清楚了，当这个方法返回值为true时，RecyclerView会处于锁定状态，这时任何尝试更新Adapter内容的方法都将导致异常，因为RecyclerView在计算layout的时候不允许你更新Adapter内容。
后面它又说，你的代码不太可能处于该状态下运行，因为这个状态只有系统framework调用或者响应系统事件的时候才会发生（我信你个鬼哦，可它就是发生了啊，真是shit happens…）
最后，它又补充了一句，说如果确实发生了，那有可能是在你设置了View callback的情况下（如focus change callback），这时你需要使用Handler或类似的方法进行延时处理。
好吧。。。最后它还是承认了自己确实给开发者挖了一个坑。。。不知道RecyclerView还挖了多少坑
接下来就是我们的填坑时间了
解决方法：
@Override
protected void convert(final BaseViewHolder helper, ContactDataSection item) {
final ContactMobileManage mobileContact = item.getEntity();
if (mobileContact != null) {
...
CheckBox checkBox = helper.getView(R.id.ckb_check);
checkBox.setChecked(mobileContact.isChecked());
checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, final boolean isChecked) {
if (mRecyclerView.isComputingLayout()) {
mRecyclerView.post(new Runnable() {
@Override
public void run() {
mobileContact.setChecked(isChecked);
notifyItemChanged(helper.getAdapterPosition());
}
});
} else {
mobileContact.setChecked(isChecked);
notifyItemChanged(helper.getAdapterPosition());
}
}
});
}
}
解决方法比较简单，既然RecyclerView已经给了判断方法了，那我们在onCheckedChanged方法中直接调用isComputingLayout()判断一下就可以了，如果该方法返回为true我们需要进行延时处理这里我直接调用RecyclerView对象的post方法或者你用Handler处理也可以。