Android BaseAdapter 封裝總結

針對BaseAdapter的封裝一般有兩類，一種是ListView的Adapter，還有一種是RecyclerView的Adapter。兩種Adapter封裝的原理都類似。

封裝的方式主要包含兩方面：

• 一種是對ViewHolder的封裝

  • 具體的實現參考GitHub上開源庫：base-adapter-helper

• 還有就是針對多種類型的viewType，通過模塊代理(Delegate)的方式，將不同類型的viewType組裝起來。

  • 具體的實現參考GitHub上開源庫：AdapterDelegates

當然Adapter的封裝還可以做更多的工作，比如說:Sticky Head，加載更多 ...

兩種封裝方式在ListView上的具體實現

1. BaseViewHolder的封裝

先看一下普通的ListView的適配器代碼

public class SimpleListAdapter extends BaseAdapter {

    private Context context;
    private LayoutInflater layoutInflater;
    private List dataList;


    public SimpleListAdapter(Context context, List dataList) {
        this.context = context;
        this.dataList = dataList;
        layoutInflater = LayoutInflater.from(context);
    }

    @Override
    public int getCount() {
        return dataList.size();
    }

    @Override
    public Object getItem(int position) {
        return dataList.get(position);
    }

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder viewHolder = null;
        if (convertView == null) {
            convertView = layoutInflater.inflate(R.layout.simple_list_item, parent, false);
            viewHolder = new ViewHolder(convertView);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }
        viewHolder.id_tv_title.setText("hello");
        return convertView;
    }


    public static class ViewHolder {
        public View rootView;
        public TextView id_tv_title;

        public ViewHolder(View rootView) {
            this.rootView = rootView;
            this.id_tv_title = (TextView) rootView.findViewById(R.id.id_tv_title);
        }
    }

第一步，提供獲取BaseViewHolder實例對象的靜態方法

先看下SimpleListAdapter的getView()方法中的一段代碼：

ViewHolder viewHolder = null;
if (convertView == null) {
    convertView = layoutInflater.inflate(R.layout.simple_list_item, parent, false);
    viewHolder = new ViewHolder(convertView);
    convertView.setTag(viewHolder);
} else {
    viewHolder = (ViewHolder) convertView.getTag();
}

這段代碼重復率非常高，主要作用是：獲取與convertView 綁定(bind)在一起的ViewHolder

可以將這段代碼提取到我們的BaseViewHolder中,于是我們開始寫BaseViewHolder

public class BaseViewHolder {


    private View convertView;//adapter中getView() 返回的對象，用于與ListView的數據綁定

    public BaseViewHolder(View convertView) {
        this.convertView = convertView;
    }

    public static BaseViewHolder getViewHolder(Context context, int position, View convertView, ViewGroup parent, @LayoutRes int resource) {
        BaseViewHolder baseViewHolder = null;
        if (convertView == null) {
            convertView = LayoutInflater.from(context).inflate(resource, parent, false);
            baseViewHolder = new BaseViewHolder(convertView);
            convertView.setTag(baseViewHolder);
        } else {
            baseViewHolder = (BaseViewHolder) convertView.getTag();
        }
        return baseViewHolder;
    }

    public View getConvertView() {
        return convertView;
    }
}

此時我們的SimpleListAdapter的getView()方法中的代碼將得到初步的簡化

由原來的

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder viewHolder = null;
        if (convertView == null) {
            convertView = layoutInflater.inflate(R.layout.simple_list_item, parent, false);
            viewHolder = new ViewHolder(convertView);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }
        viewHolder.id_tv_title.setText("hello");
        return convertView;
    }

簡化后的代碼如下：

@Override
    public View getView(int position, View convertView, ViewGroup parent) {
        BaseViewHolder baseViewHolder = BaseViewHolder.getViewHolder(context, position, convertView, parent, R.layout.simple_list_item);
        return baseViewHolder.getConvertView();
    }

第二步，BaseViewHolder提供獲取convertView中views的方法，以便在adapter中繪制數據

convertView中的Views我們可以通過如下方式獲取到：

    private SparseArrayCompat<View> viewSparseArrayCompat = new SparseArrayCompat<>();
    
    public View getViewByViewId(@IdRes int viewId) {
        View view = viewSparseArrayCompat.get(viewId);
        if (view == null) {
            view = convertView.findViewById(viewId);
            viewSparseArrayCompat.put(viewId, view);
        }
        return view;
    }

至此我們的BaseViewHolder封裝完成，完成后的代碼如下：

public class BaseViewHolder {

    private View convertView;//adapter中getView() 返回的對象，用于與ListView的數據綁定
    private SparseArrayCompat<View> viewSparseArrayCompat = new SparseArrayCompat<>();

    public BaseViewHolder(View convertView) {
        this.convertView = convertView;
    }

    public static BaseViewHolder getViewHolder(Context context, int position, View convertView, ViewGroup parent, @LayoutRes int resource) {
        BaseViewHolder baseViewHolder;
        if (convertView == null) {
            convertView = LayoutInflater.from(context).inflate(resource, parent, false);
            baseViewHolder = new BaseViewHolder(convertView);
            convertView.setTag(baseViewHolder);
        } else {
            baseViewHolder = (BaseViewHolder) convertView.getTag();
        }
        return baseViewHolder;
    }



    public View getViewByViewId(@IdRes int viewId) {
        View view = viewSparseArrayCompat.get(viewId);
        if (view == null) {
            view = convertView.findViewById(viewId);
            viewSparseArrayCompat.put(viewId, view);
        }
        return view;
    }

    public View getConvertView() {
        return convertView;
    }
}

在SimpleListAdapter中使用如下， 重點看getView()方法：

public class SimpleListAdapter extends BaseAdapter {

    private Context context;
    private LayoutInflater layoutInflater;
    private List dataList;


    public SimpleListAdapter(Context context, List dataList) {
        this.context = context;
        this.dataList = dataList;
        layoutInflater = LayoutInflater.from(context);
    }

    @Override
    public int getCount() {
        return dataList.size();
    }

    @Override
    public Object getItem(int position) {
        return dataList.get(position);
    }

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        BaseViewHolder baseViewHolder = BaseViewHolder.getViewHolder(context, position, convertView, parent, R.layout.simple_list_item);
        TextView textView = (TextView) baseViewHolder.getViewByViewId(R.id.id_tv_title);
        textView.setText("Hello");
        return baseViewHolder.getConvertView();
    }

}

封裝好BaseViewHolder之后，我們開始封裝我們的Adapter，定義為CommonAdapter 封裝Adapter的代碼就比較簡單了，直接上封裝后的代碼

public abstract class CommonAdapter<T> extends BaseAdapter {

    private Context context;
    private int layoutResId;
    private List<T> dataList;

    public CommonAdapter(@NonNull Context context, @LayoutRes int layoutResId, @NonNull List<T> dataList) {
        this.context = context;
        this.layoutResId = layoutResId;
        this.dataList = dataList;
    }

    @Override
    public int getCount() {
        return dataList.size();
    }

    @Override
    public Object getItem(int position) {
        return dataList.get(position);
    }

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        BaseViewHolder baseViewHolder = BaseViewHolder.getViewHolder(context, position, convertView, parent, layoutResId);
        convert(baseViewHolder, dataList.get(position));
        return baseViewHolder.getConvertView();
    }

    protected abstract void convert(BaseViewHolder baseViewHolder, T t);
}

在Fragment中ListView使用CommonAdapter設置Adapter

public class MyBaseAdapterFragment extends BaseFragment {

    private List<String> mDatas = new ArrayList<>(Arrays.asList("Hello", "World", "Welcome"));

    @BindView(R.id.lv)
    ListView listView;


    public static MyBaseAdapterFragment newInstance() {
        MyBaseAdapterFragment fragment = new MyBaseAdapterFragment();
        return fragment;
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_listivew_baseadapter, container, false);
        ButterKnife.bind(this, view);
        initView();
        return view;
    }


    private void initView() {
        listView.setAdapter(new CommonAdapter<String>(getContext(), R.layout.simple_list_item, mDatas) {

            @Override
            protected void convert(BaseViewHolder baseViewHolder, String s) {
                TextView title = (TextView) baseViewHolder.getViewByViewId(R.id.id_tv_title);
                title.setText(s);
            }
        });
    }
}