Android BaseAdapter 封装总结
针对BaseAdapter的封装一般有两类，一种是ListView的Adapter，还有一种是RecyclerView的Adapter。两种Adapter封装的原理都类似。
封装的方式主要包含两方面：
-
一种是对ViewHolder的封装
- 具体的实现参考GitHub上开源库：base-adapter-helper
-
还有就是针对多种类型的viewType，通过模块代理(Delegate)的方式，将不同类型的viewType组装起来。
- 具体的实现参考GitHub上开源库：AdapterDelegates
当然Adapter的封装还可以做更多的工作，比如说:Sticky Head，加载更多 ...
两种封装方式在ListView上的具体实现
1. BaseViewHolder的封装
先看一下普通的ListView的适配器代码
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，提供获取BaseViewHolder实例对象的静态方法
先看下SimpleListAdapter的getView()方法中的一段代码：
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();
}
这段代码重复率非常高，主要作用是：获取与convertView 绑定(bind)在一起的ViewHolder
可以将这段代码提取到我们的BaseViewHolder中,于是我们开始写BaseViewHolder
public class BaseViewHolder {
private View convertView;//adapter中getView() 返回的对象，用于与ListView的数据绑定
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;
}
}
此时我们的SimpleListAdapter的getView()方法中的代码将得到初步的简化
由原来的
@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;
}
简化后的代码如下：
@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提供获取convertView中views的方法，以便在adapter中绘制数据
convertView中的Views我们可以通过如下方式获取到：
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;
}
至此我们的BaseViewHolder封装完成，完成后的代码如下：
public class BaseViewHolder {
private View convertView;//adapter中getView() 返回的对象，用于与ListView的数据绑定
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， 重点看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();
}
}
封装好BaseViewHolder之后，我们开始封装我们的Adapter，定义为CommonAdapter 封装Adapter的代码就比较简单了，直接上封装后的代码
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设置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);
}
});
}
}
