新手啊请求帮助，在自定义适配器里面设置数据的时候都是报错，读不到listDate数据

package com.example.baseadapter;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;


public class MainActivity extends Activity {
    private ListView listView=null;
    private List<Map<String, Object>> listdata = null;

    //    private final static String TAG="MyAdapter";
    private int[] icon = {R.drawable.jinniu, R.drawable.juxie, R.drawable.tiancheng, R.drawable.tianxie, R.drawable.chunv,
            R.drawable.baiyang, R.drawable.funv, R.drawable.numa, R.drawable.shuangyu, R.drawable.shizi, R.drawable.sheshou, R.drawable.shuangyu1};
    private String[] title = {"金牛座", "巨蟹座", "天秤座", "天蝎座", "双子座", "白羊座", "处女座", "摩羯座", "水瓶座", "狮子座", "射手座", "双鱼座"};
    private String[] descrip = {"jiuniuzuo", "juxiezuo", "tianchengzuo", "tianxiezuo", "shuangzizuo", "baiyangzuo", "chunvzuo", "mojiezuo", "shuipingzuo", "shizizuo", "sheshouzuo", "shuangyuzuo"};

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        listView = (ListView) findViewById(R.id.list_view);

//        data = new ArrayList<Map<String,Object>>();
        listdata = getDate();
        MyAdapter adapter = new MyAdapter(this);
        listView.setAdapter(adapter);
    }

    public List<Map<String, Object>> getDate() {
        List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
        Map<String, Object> map;
        for (int i = 0; i < 12; i++) {
            map = new HashMap<String, Object>();
            map.put("icon", icon[i]);
            map.put("title", title[i]);
            map.put("descrip", descrip[i]);
            list.add(map);
        }
        return list;
    }

    public class MyAdapter extends BaseAdapter {
        LayoutInflater inflater = null;

        //        private Context mContext;
        public MyAdapter(Context context) {
//            this.mContext = context;
            this.inflater = LayoutInflater.from(context);
        }

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

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

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

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            ViewHolder holder = null;
            if (convertView == null) {
                convertView = inflater.inflate(R.layout.items, null);
                holder = new ViewHolder();
                holder.icon = (ImageView) findViewById(R.id.iv_img);
                holder.title = (TextView) findViewById(R.id.tv_title);
                holder.descrip = (TextView) findViewById(R.id.tv_descrip);
                holder.button = (Button) findViewById(R.id.button);
                convertView.setTag(holder);
            } else {
                holder = (ViewHolder) convertView.getTag();
            }

            holder.icon.setBackgroundResource((Integer) listdata.get(position).get("icon"));
            holder.title.setText(listdata.get(position).get("title").toString());
            holder.descrip.setText((String) listdata.get(position).get("descrip"));


            return convertView;
        }
    }

    final class ViewHolder {
        public ImageView icon;
        public TextView title;
        public TextView descrip;
        public Button button;
    }
}