ListView适配器的写法

初级

  • 优点:复用convertView
  • 缺点:每次调用getview()都会去findview,是耗费资源的操作
public class MyAdapter extends BaseAdapter {
    protected List mList;
    protected Context mContext;
    LayoutInflater mInflater;
    
    public MyAdapter(Context context, List list) {
        this.mList = list;
        this.mContext = context;
        mInflater=LayoutInflater.from(context);
    }

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

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

    @Override
    public long getItemId(int position) {
        return position;
    }
    
    public View getView(int position, View convertView, ViewGroup parent) {
        /*----------视图操作--------------*/
        View itemview = null;
        if (convertView == null) {
            //初始化布局
            itemview = mInflater.inflate(R.layout.item, parent, false);
        } else {
            //复用convertView
            itemview = convertView;
        }
         /*-------------- 查找控件 --------------*/
        TextView title = (TextView) itemview.findViewById(R.id.tv_title);
        TextView desc = (TextView) itemview.findViewById(R.id.tv_desc);
    
        /*-------------- 数据绑定 --------------*/
        Bean bean = mList.get(position);
    
        title.setText(bean.tilte);
        desc.setText(bean.desc);
    
        return itemview;
    }
}
  • 简化写法
    public View getView(int position, View convertView, ViewGroup parent) {

        /*----------视图操作--------------*/
        if (convertView == null) {
            //convertView为空,
            convertView = mInflater.inflate(R.layout.item, parent, false);
        }

        /*-------------- 查找控件 --------------*/
        TextView title = (TextView) convertView.findViewById(R.id.tv_title);
        TextView desc = (TextView) convertView.findViewById(R.id.tv_desc);

        /*-------------- 数据绑定 --------------*/
        Bean bean = mList.get(position);

        title.setText(bean.tilte);
        desc.setText(bean.desc);

        return convertView;
    }

中级

  • 优点:利用ViewHolder存储找到的控件,避免多次findViewById
  • 缺点:代码量大
public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder = null;

    /*----------视图操作--------------*/
    if (convertView == null) {
        //解析布局文件
        convertView = mInflater.inflate(R.layout.item, parent, false);
        //创建对象
        holder = new ViewHolder();
        //设置标记
        convertView.setTag(holder);
        
        /*-----------findview ,并存储到holder--------*/ 
        holder.title = (TextView) convertView.findViewById(R.id.tv_title);
        holder.desc = (TextView) convertView.findViewById(R.id.tv_desc);
        
    } else {
        //根据标记,取出holder
        holder = (ViewHolder) convertView.getTag();
    }

    /*-------------- 赋值 --------------*/
    Bean bean = mList.get(position);
    holder.title.setText(bean.tilte);
    holder.desc.setText(bean.desc);

    return convertView;
}

//存放控件,避免多次findViewById
class ViewHolder{
    TextView title;
    TextView desc ;
}

高级

  • holder可通用,减少代码量
public View getView(int position, View convertView, ViewGroup parent) {
        HolderView holderView = null;
        
        /*--------------视图操作--------------------*/
        if (convertView == null) {
            //创建一个holder
            holderView = new HolderView(mContext, R.layout.item, position, parent);
        } else {
            //取出holder
            holderView = (HolderView) convertView.getTag();
            //更新条目位置
            holderView.mPosition=position;
        }

        /*--------------数据绑定--------------------*/
        //数据
        Bean bean = mList.get(position);
        //设置数据
        holderView.setText(R.id.tv_commond, bean.commond)
                .setText(R.id.tv_title, bean.tilte)
                .setText(R.id.tv_desc, bean.desc)
                .setText(R.id.tv_time, bean.time);

        return holderView.mItemView;
}
class HolderView {

    //条目视图
    View mItemView;
    //条目位置
    int mPosition;
    //实质上是存储的HashMap,效率高于HashMap
    SparseArray mArrays;

    public HolderView(Context context,int layoutId,int position,ViewGroup parent) {
        LayoutInflater inflater=LayoutInflater.from(context);
        //初始化布局
        this.mItemView =inflater.inflate(layoutId, parent, false);
        //创建容器
        mArrays = new SparseArray<>();
        //记录条目位置
        mPosition = position;
        //标记
        this.mItemView.setTag(this);
    }

    /**
     * 获取控件
     */
    public  T getView(int viewId) {
        //根据id从容器取出控件
        View view = mArrays.get(viewId);
        if (view == null) {
            //findview
            view = mItemView.findViewById(viewId);
            //缓存
            mArrays.put(viewId, view);
        }
        return (T) view;
    }

    /**
     * 设置文本
     */
    public HolderView setText(int viewId, String string) {
        TextView textView = getView(viewId);
        textView.setText(string);
        return this;
    }
    
    //以后如果有ImageView,Button等空间,可以自行增加方法,进行数据绑定
}

超级

  • 封装通用Adapter
  • 封装通用Holder
public abstract class CommonAdapter extends BaseAdapter {
    protected List mList;
    protected Context mContext;
    /**
     * 布局文件id
     */
    protected int mLayoutId;

    public CommonAdapter(Context context, int layoutId, List list) {
        this.mList = list;
        this.mLayoutId = layoutId;
        this.mContext = context;
    }

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

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

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        //找到holder
        BaseViewHolder holder = BaseViewHolder.get(mContext, mLayoutId, position, convertView, parent);

        T bean = mList.get(position);

        bindData(bean, holder);

        return holder.getItemView();
    }

    /**
     * 数据和控件进行绑定
     *
     * @param bean
     * @param holder
     */
    protected abstract void bindData(T bean, BaseViewHolder holder);

}

public class BaseViewHolder {
    /**
     * 泛型为的HashMap,效率比普通的HashMap高一些
     * 存储子控件
     */
    private SparseArray mArrays;
    /**
     * 条目位置
     */
    private int mPosition;
    /**
     * 条目视图View
     */
    private View mItemView;

    /**
     * 获取条目位置
     */
    public int getPosition() {
        return mPosition;
    }

    /**
     * 获取条目视图
     */
    public View getItemView() {
        return mItemView;
    }

    //构造方法私有,禁止外部创建对象
    //内部创建对象时:进行初始化布局等操作
    private BaseViewHolder(Context context, int resId, int position, ViewGroup parent) {
        //创建容器
        this.mArrays = new SparseArray<>();
        //记录item位置
        this.mPosition = position;
        //初始化布局
        this.mItemView = LayoutInflater.from(context).inflate(resId, parent, false);
        //标记Holder
        this.mItemView.setTag(this);
    }

    /**
     * 获取Holder
     *
     * @param context     上下文
     * @param layoutId    布局id
     * @param position    条目的位置
     * @param convertView 复用的视图,convert(转换的)
     * @param parent      父view
     * @return
     */
    public static BaseViewHolder get(Context context, int layoutId,
                                     int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            //返回一个新创建的Holder
            return new BaseViewHolder(context, layoutId, position, parent);
        } else {
            //返回一个从标记中取出Holder
            BaseViewHolder baseHolder = (BaseViewHolder) convertView.getTag();
            //更新条目位置
            baseHolder.mPosition = position;
            return baseHolder;
        }

    }

    /**
     * 根据控件Id找到控件
     *
     * @param viewId 控件Id
     * @param 
     * @return
     */
    public  T getView(int viewId) {
        //从容器中取出控件
        View view = mArrays.get(viewId);
        //控件为空
        if (view == null) {
            //findview
            view = mItemView.findViewById(viewId);
            //缓存
            mArrays.put(viewId, view);
        }
        return (T) view;
    }

    /**
     * 设置文本
     *
     * @param viewId 控件Id
     * @param text   文本内容
     * @return
     */
    public BaseViewHolder setText(int viewId, String text) {
        TextView textView = getView(viewId);
        textView.setText(text);
        return this;
    }
    
   //更多方法,根据条目id和数据自行创建... 
}

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