Contents of articles

1、 Error information 2. Error analysis 3. Solutions

1、 Error information

Recently, we have upgraded all the support libraries to

28.0.0

28.0.0

28.0.0 ;

implementation 'com.android.support:recyclerview-v7:28.0.0'

There are a lot of errors in the support library code of kotlin language;

2、 Error analysis

Here, we inherit the recyclerview.itemdecision class and override the getitemoffsets method,

object : RecyclerView.ItemDecoration() {
                    override fun getItemOffsets(outRect: Rect?, view: View?, parent: RecyclerView?, state: RecyclerView.State?) {
                        super.getItemOffsets(outRect, view, parent, state)
}

Note that in the overridden method, the parameter type

outRect: Rect?view: View?parent: RecyclerView?state: RecyclerView.State?

All are nullable types;

Look at the real code of itemdeclaration. The four parameters of getitemoffsets method are all non empty types, and the @ nonnull annotation is added. Therefore, non empty parameters must be passed in here. When inheriting, they are nullable parameters. An error will be reported, and the parameter types are inconsistent;

        public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
            this.getItemOffsets(outRect, ((RecyclerView.LayoutParams)view.getLayoutParams()).getViewLayoutPosition(), parent);
        }

Item decision complete code reference:

    public abstract static class ItemDecoration {
        public ItemDecoration() {
        }

        public void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
            this.onDraw(c, parent);
        }

        /** @deprecated */
        @Deprecated
        public void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent) {
        }

        public void onDrawOver(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
            this.onDrawOver(c, parent);
        }

        /** @deprecated */
        @Deprecated
        public void onDrawOver(@NonNull Canvas c, @NonNull RecyclerView parent) {
        }

        /** @deprecated */
        @Deprecated
        public void getItemOffsets(@NonNull Rect outRect, int itemPosition, @NonNull RecyclerView parent) {
            outRect.set(0, 0, 0, 0);
        }

        public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
            this.getItemOffsets(outRect, ((RecyclerView.LayoutParams)view.getLayoutParams()).getViewLayoutPosition(), parent);
        }
    }

3、 Solutions

Google did not add the @ nonnull annotation to the parameters of the support library method before. In the

28.0.0

28.0.0

In version 28.0.0, the annotation is added, which leads to the incompatibility of inheritance;

The modification method is to set all parameter types to non empty type and delete the question mark in each parameter;