万能适配器和万能ViewHolder配合实现ListView列表数据展示

在适配器的getView方法中使用ViewHolder来保存子布局项的组件信息时，传统的做法是：

 public View getView(int position, View convertView, ViewGroup parent) {        ViewHolder holder;        if(convertView == null){            convertView = inflater.inflate(R.layout.listview_item,parent,false);            holder = new ViewHolder();            holder.title = (TextView) convertView.findViewById(R.id.title);            holder.content = (TextView) convertView.findViewById(R.id.content);            convertView.setTag(holder);        }else{            holder = (ViewHolder) convertView.getTag();        }        holder.title.setText(mDatas.get(position).getTitle());        holder.content.setText(mDatas.get(position).getContent());        return convertView;    }    class ViewHolder{        private TextView title;        private TextView content;    }

在项目开发中需要编写很多个适配器，那么会有很多重复的代码，若使用万能ViewHolder和万能适配器将会减少很多代码，使用方法见下：

1.  编写万能ViewHolder：

public class CommonViewHolder {    private int mPosition;    //  mViews用于存放界面上的组件    private SparseArray<View> mViews;    private View mCconvertView;    public CommonViewHolder(Context context, ViewGroup parent,int layoutId,int position){        this.mPosition = position;        this.mViews = new SparseArray<>();        this.mCconvertView = LayoutInflater.from(context).inflate(layoutId,parent,false);        mCconvertView.setTag(this);    }    // 获取ViewHolder    public static CommonViewHolder getViewHolder(Context context, View convertView,                                                 ViewGroup parent, int layoutId, int position){        CommonViewHolder holder;        if(convertView == null){            holder = new CommonViewHolder(context,parent,layoutId,position);        }else{            holder = (CommonViewHolder)convertView.getTag();            holder.mPosition = position;        }        return holder;    }    //  获取convertView    public View getConvertView(){        return mCconvertView;    }    //  用来获取convertview中的组件  组件存在SparseArray中    public View getView(int viewId){        View view = mViews.get(viewId);        if(view == null){            view = mCconvertView.findViewById(viewId);            mViews.put(viewId,view);        }        return view;    }}

2.  编写万能BaseAdapter适配器代码如下：

public abstract class CommonAdapter<T> extends BaseAdapter{    //  定义这两个属性为protected，是为了让子类能够访问    protected Context mContext;    protected List<T> mDatas;    public CommonAdapter(Context context,List<T> datas){        this.mContext = context;        this.mDatas = datas;    }    @Override    public int getCount() {        return mDatas.size();    }    @Override    public Object getItem(int position) {        return mDatas.get(position);    }    @Override    public long getItemId(int position) {        return position;    }    //  在此定义要具体实现的抽象方法 ，让子类去实现    @Override    public abstract View getView(int position, View convertView, ViewGroup parent);}

在具体实现适配器时，只需要new一个适配器并且继承CommonAdapter，然后在方法getView中具体去实现代码即可，示例如下：

public class MyBaseAdapter extends CommonAdapter{    public MyBaseAdapter(Context context, List datas) {        super(context, datas);    }    @Override    public View getView(int position, View convertView, ViewGroup parent) {        CommonViewHolder holder  = CommonViewHolder.getViewHolder(mContext,convertView,  //  此处使用了万能ViewHolder                parent, R.layout.listview_item,position);        Bean bean = (Bean) mDatas.get(position);        TextView tv1 = (TextView) holder.getView(R.id.title);        tv1.setText(bean.getTitle());        TextView tv2 = (TextView) holder.getView(R.id.content);        tv2.setText(bean.getTitle());        TextView tv3 = (TextView) holder.getView(R.id.time);        tv3.setText(bean.getTitle());        TextView tv4 = (TextView) holder.getView(R.id.tel);        tv4.setText(bean.getTitle());        return holder.getConvertView();    }}

这样我们若想再需要BaseAdapter适配器时，也只需要建立自己的Adapter继承CommonAdapter即可，只要在自己定义的Adapter中实现geView方法，不需要每次都去写ViewHolder和BaseAdapter中那些冗余的代码

Activity中只需要调用下面2行代码即可：

MyBaseAdapter adapter = new MyBaseAdapter(MainActivity.this,beanList);        listView.setAdapter(adapter);