关于android中ListView的Adapter如何设计能通

我们都知道，在安卓中使用ListView显示多条数据的时候，必须要用一个适配器作为Data和View的桥梁,这种设计非常好， 能很简单就把ui和data分离开来，为ui的复用和维护代码提供方便。
但是每次写一个适配器，都要实现一大堆的重复逻辑，下面是一个常规的实现：
foo_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 
xmlns:android="http://schemas.android.com/apk/res/android"    
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="@dimen/activity_horizontal_margin"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical">   
 <TextView
android:id="@+id/txtTitle"
android:layout_width="match_parent"
android:layout_height="wrap_content"
tools:text="今天好天气" />
<TextView
android:id="@+id/txtContent"
android:layout_marginTop="10dp"
tools:text="我是一名android开发者"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>

适配器：

public class FooNormalAdapter extends BaseAdapter {

    private List<FooBean> datas = new ArrayList<>();
    private Context _context;

    public FooNormalAdapter(Context context) {
        this._context = context;
    }

    public Context getContext() {
        return _context;
    }

    public void setDataSource(List<FooBean> fooBeens) {
        setDataSource(fooBeens,true);
    }

    public void setDataSource(List<FooBean> fooBeens,boolean isClear) {
        if(isClear) this.datas.clear();
        this.datas.addAll(fooBeens);
        notifyDataSetChanged();
    }

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

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

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        FooViewHolder viewHolder = null;
        if (convertView == null) {
            convertView = View.inflate(getContext(), R.layout.foo_item, null);
            convertView.setTag(new FooViewHolder(convertView));
        } else {
            viewHolder = (FooViewHolder) convertView.getTag();
        }
        FooBean fb = (FooBean) getItem(position);
        viewHolder.txtTitle.setText(fb.getTitle());
        viewHolder.txtContent.setText(fb.getContent());
        return convertView;
    }

    public static class FooViewHolder {
        private TextView txtTitle;
        private TextView txtContent;

        public FooViewHolder(View convertView) {
            this.txtTitle = (TextView) convertView.findViewById(R.id.txtTitle);
            this.txtContent = (TextView) convertView.findViewById(R.id.txtContent);
        }
    }
}

嗯，看起来没有什么问题，但是如果有十个adapter,就要写十次这种无意义的代码，我们不能干体力活啊~怎么办？
先分析一下adapter需要哪些元素:
1.首先要inflateView就必须用到Context.
2.需要一个数组来存储用于显示的数据源
3.需要一个viewholder来优化程序性能
4.可能有不同的viewType
分析完这个，代码随之而来：

public abstract class LBaseAdapter<E, V extends LBaseAdapter.BaseViewHolder> extends BaseAdapter {

    private Context context;
    private List<E> dataSource = new ArrayList<>(); //初始化一个防止getCount()空指针

    public LBaseAdapter(Context context) {
        this.context = context;
    }

    public Context getContext() {
        return context;
    }

    //替换原有数据源
    public void setDataSource(List<E> dataSource) {
        setDataSource(dataSource,true);
    }

    //如果isClear==true,则替换原有数据源，否则加到数据源后面
    public void setDataSource(List<E> dataSource, boolean isClear) {
        if (isClear) this.dataSource.clear();
        this.dataSource = dataSource;
        notifyDataSetChanged();
    }

    //只加一个数据
    public void addData(E data) {
        this.dataSource.add(data);
        notifyDataSetChanged();
    }

    //通过下标移除一条数据
    public void removeData(int position) {
        this.dataSource.remove(position);
        notifyDataSetChanged();
    }

    //通过对象移除一条数据
    public void removeData(E data) {
        this.dataSource.remove(data);
        notifyDataSetChanged();
    }


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


    @Override
    public E getItem(int position) {
        return this.dataSource.get(position);
    }


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


    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        V viewHolder = null;
        if (convertView == null) {
            viewHolder = createViewHolder(position, parent);
            if (viewHolder == null || viewHolder.getRootView() == null) {
                throw new NullPointerException("createViewHolder不能返回null或view为null的实例");
            }
            convertView = viewHolder.getRootView();
            convertView.setTag(viewHolder);
        }else{
            viewHolder = (V) convertView.getTag();
        }
        //给当前复用的holder一个正确的position
        viewHolder.setPosition(position);
        bindViewHolder(viewHolder,position,getItem(position));
        return viewHolder.getRootView();
    }

    protected abstract V createViewHolder(int position, ViewGroup parent);

    protected abstract void bindViewHolder(V holder,int position, E data);

    public static class BaseViewHolder {
        private View rootView;
        private SparseArray<View> viewCache = new SparseArray<>();
        private int position = -1;

        public View getRootView() {
            return rootView;
        }

        void setPosition(int position) {
            this.position = position;
        }

        public int getPosition() {
            return position;
        }

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

        public <R> R getView(@IdRes int viewID) {
            View cachedView = viewCache.get(viewID);
            if(null == cachedView) {
                cachedView = rootView.findViewById(viewID);
                viewCache.put(viewID, cachedView);
            }
            return (R) cachedView;
        }
    }
}

1.我加一个构造函数，强制传context,并提供getContext()方法
2.加一个泛型E,允许子类提供随意实体类型
3.加一个BaseViewHolder,并提供一些常用方法
4.重写getView(),在父类里面把复用逻辑搞定，并提供两个抽象方法用于让子类提供viewholder,和绑定具体数据，嗯，我是仿着RecyclerView来的。:)
ok,这个通用的父类怎么使用呢？
代码说话：

public class FooSuperAdapter extends LBaseAdapter<FooBean, LBaseAdapter.BaseViewHolder> {

    public FooSuperAdapter(Context context) {
        super(context);
    }

    @Override
    protected BaseViewHolder createViewHolder(int position, ViewGroup parent) {
        return new BaseViewHolder(View.inflate(getContext(), R.layout.foo_item,null));
    }

    @Override
    protected void bindViewHolder(BaseViewHolder holder, int position, FooBean data) {
        TextView txtTitle = holder.getView(R.id.txtTitle);
        TextView txtContent = holder.getView(R.id.txtContent);

        txtTitle.setText(data.getTitle());
        txtContent.setText(data.getContent());
    }
}

之前的一大堆东西，现在都不用关心了， 只管设置itemview,和绑定数据就好了，是不是好看多了呢？
通用adapter用于了泛型，如果不了解可以留言，我将出一个泛型的专题来讨论希望我的博客能帮到你 :)