如何使用 RecyclerView.State 保存 RecyclerView 的滚动位置?

问题描述

我有一个关于 Android 的 RecyclerView.State 的问题.

I have a question about Android's RecyclerView.State.

我正在使用 RecyclerView，如何使用 RecyclerView.State 并将其绑定?

I am using a RecyclerView, how could I use and bind it with RecyclerView.State?

我的目的是保存 RecyclerView 的滚动位置.

推荐答案

你打算如何使用 RecyclerView.State 保存上次保存的位置?

How do you plan to save last saved position with RecyclerView.State?

您始终可以依靠良好的保存状态.扩展 RecyclerView 并覆盖 onSaveInstanceState() 和 onRestoreInstanceState():

You can always rely on ol' good save state. Extend RecyclerView and override onSaveInstanceState() and onRestoreInstanceState():

    @Override
    protected Parcelable onSaveInstanceState() {
        Parcelable superState = super.onSaveInstanceState();
        LayoutManager layoutManager = getLayoutManager();
        if(layoutManager != null && layoutManager instanceof LinearLayoutManager){
            mScrollPosition = ((LinearLayoutManager) layoutManager).findFirstVisibleItemPosition();
        }
        SavedState newState = new SavedState(superState);
        newState.mScrollPosition = mScrollPosition;
        return newState;
    }

    @Override
    protected void onRestoreInstanceState(Parcelable state) {
        super.onRestoreInstanceState(state);
        if(state != null && state instanceof SavedState){
            mScrollPosition = ((SavedState) state).mScrollPosition;
            LayoutManager layoutManager = getLayoutManager();
            if(layoutManager != null){
              int count = layoutManager.getItemCount();
              if(mScrollPosition != RecyclerView.NO_POSITION && mScrollPosition < count){
                  layoutManager.scrollToPosition(mScrollPosition);
              }
            }
        }
    }

    static class SavedState extends android.view.View.BaseSavedState {
        public int mScrollPosition;
        SavedState(Parcel in) {
            super(in);
            mScrollPosition = in.readInt();
        }
        SavedState(Parcelable superState) {
            super(superState);
        }

        @Override
        public void writeToParcel(Parcel dest, int flags) {
            super.writeToParcel(dest, flags);
            dest.writeInt(mScrollPosition);
        }
        public static final Parcelable.Creator<SavedState> CREATOR
                = new Parcelable.Creator<SavedState>() {
            @Override
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }

            @Override
            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
        };
    }

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