Question

我有这个自定义适配器，我不知道为什么如果视图在布局中膨胀会引发异常。

然后我使用适配器而不是一个新类来显示listview。什么是null？

    import android.app.Activity;
    import android.content.Context;
    import android.content.res.Resources;
    import android.util.Log;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ArrayAdapter;
    import android.widget.BaseAdapter;
    import android.widget.ImageView;
    import android.widget.ProgressBar;
    import android.widget.TextView;

    import com.save.coinch.R;
    import com.save.coinch.SQLiteDB;
    import com.save.coinch.responses.Saving;
    import com.save.coinch.responses.Transaction;
    import com.save.coinch.responses.User;
    import com.save.coinch.utils.CacheUtils;
    import com.save.coinch.utils.CommonUtils;

    import java.text.DateFormat;
    import java.text.SimpleDateFormat;
    import java.util.ArrayList;
    import java.util.Calendar;
    import java.util.Date;
    import java.util.GregorianCalendar;
    import java.util.List;

    public class TransactionsAdapter extends BaseAdapter {
        private List<Transaction> items;
        LayoutInflater li;

        public TransactionsAdapter(Context context, List<Transaction> items) {
            super();
            this.items = items;
            this.li = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        }

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

        @Override
        public Object getItem(int position) {
            return null;
        }

        @Override
        public long getItemId(int position) {
            return 0;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View v = convertView;
            ViewHolder holder;

            if (v == null) {
                holder = new ViewHolder();
                //LayoutInflater li = LayoutInflater.from(getContext());
                v = li.inflate(R.layout.trans_item, parent, false);

null pointer exception here

                holder.txtViewAmount = (TextView) convertView.findViewById(R.id.trans_amount);
                holder.txtViewDate = (TextView) convertView.findViewById(R.id.trans_date);
                holder.txtViewTitle = (TextView) convertView.findViewById(R.id.trans_title);

                convertView.setTag(holder);
            }else
                holder = (ViewHolder) convertView.getTag();

            Transaction app = items.get(position);

            if (app != null) {


                holder.txtViewDate.setText(app.getDate());
                holder.txtViewAmount.setText(Float.toString(app.getAmount()));
                holder.txtViewTitle.setText(app.getTitle());


            }
            return v;
        }

        public static class ViewHolder {

            TextView txtViewAmount;
            TextView txtViewDate;
            TextView txtViewTitle;

        }

    }

Trans_Item.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:padding="5dip">
    <!-- ListRow Left side Thumbnail image -->



    <TextView
        android:id="@+id/trans_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:gravity="center"
        android:text="@string/tit_prin"
        android:textAlignment="center"
        android:textColor="#ff902020"
        android:textSize="10sp"
        android:textStyle="bold"
        android:typeface="sans"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />


    <TextView
        android:id="@+id/trans_date"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/tit_prin"
        android:textSize="15sp"
        android:textStyle="bold"
        android:layout_alignBottom="@+id/trans_amount"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />


    <TextView
        android:id="@+id/trans_amount"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/tit_prin"
        android:textSize="25sp"
        android:textStyle="bold"
        android:layout_centerVertical="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true" />

    <!--</LinearLayout>-->


</RelativeLayout>

ShowList.java

import android.app.Activity;
import android.app.ListActivity;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.util.Log;
import android.widget.ListView;
import android.widget.Toast;

import com.save.coinch.adapters.TransactionsAdapter;
import com.save.coinch.interfaces.RequestCallBack;
import com.save.coinch.network.FetchDataListener;
import com.save.coinch.network.FetchDataTask;
import com.save.coinch.network.Request;
import com.save.coinch.responses.Savings;
import com.save.coinch.responses.Transaction;
import com.save.coinch.responses.Transactions;
import com.save.coinch.responses.User;
import com.save.coinch.utils.CacheUtils;
import com.save.coinch.utils.CommonUtils;

import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;



/**
 * Created by Joel_2 on 07/05/2015.
 */
public class TransRecord extends ListActivity implements FetchDataListener {

    ListView data;
    TransactionsAdapter adapter;
    JSONArray json;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.trans_data);

        initView();

        //data = (ListView) findViewById(R.id.trans_all);
       // adapter = new TransactionsAdapter(this);

        //data.setAdapter(adapter);
    }

    private void initView() {
        // show progress dialog


        String url = CommonUtils.SERVICES.FETCH_TRANSACTIONS;
        FetchDataTask task = new FetchDataTask(this);

        //ArrayList<BasicNameValuePair> params = new ArrayList<BasicNameValuePair>();
        User user = CacheUtils.getUser(this);
        task.setParameters(new BasicNameValuePair("user_id", String.valueOf(user.user_id)));

        task.execute(url);

    }

    @Override
    public void onFetchComplete(List<Transaction> data) {

        // create new adapter
        TransactionsAdapter adapter = new TransactionsAdapter(this, data);

        // set the adapter to list

        setListAdapter(adapter);
    }

    @Override
    public void onFetchFailure(String msg) {
            // show failure message

        Toast.makeText(this, msg, Toast.LENGTH_LONG).show();
    }

请帮助：）

Answer 1

此区域存在例外

 if (v == null) {
            holder = new ViewHolder();
            //LayoutInflater li = LayoutInflater.from(getContext());
            v = li.inflate(R.layout.trans_item, parent, false);

            holder.txtViewAmount = (TextView) convertView.findViewById(R.id.trans_amount);
            holder.txtViewDate = (TextView) convertView.findViewById(R.id.trans_date);
            holder.txtViewTitle = (TextView) convertView.findViewById(R.id.trans_title);

            convertView.setTag(holder);
        }

您必须使用v instaed convertView

自定义适配器无缘无故地抛出nullpointerexception

1 个答案: