Bound view is null when using Butterknife in fragment

问题

I am using Butterknife to bind a single view in one of my fragments. I have used Butterknife with no issue in a separate fragment, but for some reason in this fragment the bound view is null. I am trying to add a child layout to it and I am receiving a NPE and I cannot figure out why. The setup I have in this fragment is the same as I have in my other fragment that works perfectly.

This is a snippet from the fragment including the Butterknife code.

private View view;
@BindView(R.id.layoutHolder)
LinearLayout layoutHolder;

public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    view = inflater.inflate(R.layout.fragment_log, container, false);
    ButterKnife.setDebug(true);
    ButterKnife.bind(this, view);
    return view;
}

This is the method that is throwing the NPE.

private void addLayoutToHolder(LinearLayout layout) {
    layoutHolder.addView(layout, 0);
}

Here is the error:

java.lang.NullPointerException: Attempt to invoke virtual method 
'void android.widget.LinearLayout.addView(android.view.View, int)'
on a null object reference

at com.omitted.LogFragment.addLayoutToHolder(LogFragment.java:101)

Here is the output from Butterknife.setdebug, which seems to be fine.

Looking up view binder for com.omitted.LogFragment
HIT: Loaded view binder class.
Looking up view binder for com.omitted.CalculatorFragment
HIT: Loaded view binder class.

I also checked to make sure that layoutHolder is indeed null, and it is. But for the life of me I cannot figure out why.

I can assign layoutHolder right before I add a layout to it, and it works just fine.

private void addLayoutToHolder(LinearLayout layout) {
    layoutHolder = ButterKnife.findById(view, R.id.layoutHolder); 
    layoutHolder.addView(layout, 0);
}

So it works for now, but I do not understand why in the hell Butterknife.bind in my onCreateView is not binding the view correctly.

I hope I described this problem well enough...

Thanks for any insight.

回答1:

I had the same problem and I solved it adding the butterknife-compiler as apt. You can see it in the readme of ButterKnife

回答2:

Be sure that you are implementing the dependency like this

dependencies {
    /* ... */
    implementation 'com.jakewharton:butterknife:8.8.1'
    annotationProcessor 'com.jakewharton:butterknife-compiler:8.8.1'
}

The annotationProcessor line is very important

回答3:

My guess is that you are calling addLayoutToHolder before the ButterKnife binding has taken place, that's why layoutHolder is null. At what point of the lifecycle are you calling that method?