DataBinding使用指南（三）Listview、RecycleView通用Adapter

在第一章DataBinding使用指南（一）DataBinding基本使用，雙向綁定，ListView RecycleView使用 中我們發現 ListView和RecycleView 的Adapter中代碼都極其相似並和不同數據無特別大的牽扯。故我們想應該可以使用 DataBinding 寫出一個通用Adapter

ListView 通用Adapter

我們直接上代碼

/**
 * 基於 DataBinding 的通用 Adapter
 */
public class CommonListAdapter<T> extends BaseAdapter {

    private ObservableList<T> observableList;
    private int variableId;
    private @LayoutRes int layoutId;

    public CommonListAdapter(@NonNull ObservableList<T> observableList, int variableId, @LayoutRes int layoutId) {
        this.observableList = observableList;
        this.variableId = variableId;
        this.layoutId = layoutId;
    }

    @Override
    public int getCount() {
        return observableList == null ? 0 : observableList.size();
    }

    @Override
    public T getItem(int position) {
        return observableList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Nullable
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        ViewDataBinding binding;
        if (convertView == null) {
            //這裏的最後一個參數必須爲 false
            binding = DataBindingUtil.inflate(LayoutInflater.from(parent.getContext()), layoutId, parent, false);
            convertView = binding.getRoot();
        } else {
            binding = DataBindingUtil.getBinding(convertView);
        }
        binding.setVariable(variableId, getItem(position));
        return convertView;
    }
}

使用方法和普通Adapter的使用方法相同。注意一下構造函數的參數

• observableList這個自然是數據源；
• variableId 這個是 變量的id值列表，類似於R。這個參數用在這裏binding.setVariable(variableId, getItem(position)); 當你的數據項是User的時候，這個參數就會是BR.user。
• layoutId 佈局的ID

RecycleView 通用 Adapter

我還是喜歡直接上代碼，如果你看不懂代碼可以再來問我。

public class CommonRecycleViewAdapter<T> extends RecyclerView.Adapter {
    private ObservableList<T> observableList;
    private int variableId;
    private @LayoutRes int layoutId;
    private OnRecycleViewItemClickListener onRecycleViewItemClickListener;

    public CommonRecycleViewAdapter(@NonNull ObservableList<T> observableList, int variableId, @LayoutRes int layoutId) {
        this.observableList = observableList;
        this.variableId = variableId;
        this.layoutId = layoutId;
        observableList.addOnListChangedCallback(new BaseOnListChangeCallback());
    }

    @NonNull
    @Override
    public BaseViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        //這裏的第四個參數必須爲 false 這在Google
        ViewDataBinding binding = DataBindingUtil.inflate(LayoutInflater.from(viewGroup.getContext()), layoutId, viewGroup, false);
        return new BaseViewHolder(binding.getRoot());
    }

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder viewHolder, final int i) {
        ViewDataBinding binding = DataBindingUtil.getBinding(viewHolder.itemView);
        binding.setVariable(variableId, observableList.get(i));
        //設置item點擊監聽
        binding.getRoot().setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (onRecycleViewItemClickListener != null) {
                    onRecycleViewItemClickListener.itemClick(observableList.get(i), i);
                }
            }
        });
    }

    @Override
    public int getItemCount() {
        return observableList != null ? observableList.size() : 0;
    }

    class BaseViewHolder extends RecyclerView.ViewHolder {

        public BaseViewHolder(@NonNull View itemView) {
            super(itemView);
        }
    }

    public OnRecycleViewItemClickListener getOnRecycleViewItemClickListener() {
        return onRecycleViewItemClickListener;
    }

    public void setOnRecycleViewItemClickListener(OnRecycleViewItemClickListener onRecycleViewItemClickListener) {
        this.onRecycleViewItemClickListener = onRecycleViewItemClickListener;
    }

    //數據變化監聽
    class BaseOnListChangeCallback extends ObservableList.OnListChangedCallback {

        @Override
        public void onChanged(ObservableList sender) {
        }

        @Override
        public void onItemRangeChanged(ObservableList sender, int positionStart, int itemCount) {
            CommonRecycleViewAdapter.this.notifyItemRangeChanged(positionStart, itemCount);
        }

        @Override
        public void onItemRangeInserted(ObservableList sender, int positionStart, int itemCount) {
            CommonRecycleViewAdapter.this.notifyItemRangeInserted(positionStart, itemCount);
        }

        @Override
        public void onItemRangeMoved(ObservableList sender, int fromPosition, int toPosition, int itemCount) {
            CommonRecycleViewAdapter.this.notifyItemMoved(fromPosition, toPosition);
        }

        @Override
        public void onItemRangeRemoved(ObservableList sender, int positionStart, int itemCount) {
            CommonRecycleViewAdapter.this.notifyItemRangeRemoved(positionStart, itemCount);
        }
    }

    /**
     * RecycleView 的 Item 點擊監聽
     * @param <T>
     */
    interface OnRecycleViewItemClickListener<T> {
        /**
         *
         * @param item 點擊的 Item 對應的數據
         * @param position 點擊的 Item 位置
         */
        void itemClick(T item, int position);
    }
    
}

用法和普通的Adapter是一樣的。參數的含義和上面ListView的一樣。
這裏我還貼心的加上了一個 Item 的點擊監聽。你只要在Activity中爲Adapter設置這個監聽就可以了。
來，看代碼

        adapter.setOnRecycleViewItemClickListener(new CommonRecycleViewAdapter.OnRecycleViewItemClickListener<User>() {
            @Override
            public void itemClick(User item, int position) {
                System.out.println(item.getName());
            }
        });

好了，經過上面這些亂七八糟的操作 ListView、RecycleView的通用Adapter就完成了。這樣我們就可以省去很多的重複性代碼。簡直nice啊。