Viewpager 在空对象引用上设置适配器

Question

我正在尝试创建一个介绍洛杉矶景点和洛杉矶餐厅的应用程序。主页是景点和餐厅的图片，当您单击其中一个时，它会打开更多景点或餐厅供人们阅读详细信息。我正在实施列表视图，但是我的 setadapter 不起作用。请看看我的代码并帮助新手！谢谢！错误代码如下，之后是我的程序代码。

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference

MainActivity.java:

        package com.example.android.tourguide;

    import android.content.Context;

    import android.content.Intent;

    import android.media.Image;

    import android.support.v7.app.AppCompatActivity;

    import android.os.Bundle;

    import android.view.View;

    import android.widget.ImageView;

    import android.widget.Toast;

    public class MainActivity extends AppCompatActivity {

        @Override

        protected void onCreate(Bundle savedInstanceState) {

            super.onCreate(savedInstanceState);

            setContentView(R.layout.activity_main);

        }

        public void attractionList(View v) {

            Intent intent = new Intent(this, attractionList.class);

            startActivity(intent);

        }

    }

attractionList.java:

    package com.example.android.tourguide;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.widget.ListView;

import java.util.ArrayList;

public class attractionList extends AppCompatActivity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_attraction_list);

        ArrayList<Attraction> attractionArrayList = new ArrayList<>();

        attractionArrayList.add(new Attraction(R.drawable.griffith, R.raw.attraction, "Griffith Observatory"));

        AttractionAdapter attractionAdapter = new AttractionAdapter(this, attractionArrayList);

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

        listView.setAdapter(attractionAdapter);

    }

}

Answer 1

您尝试查找不存在的列表视图，activity_attraction_list.xml因此您的列表视图在您的情况下为空。改变这个public class attractionList extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {&nbsp; &nbsp; super.onCreate(savedInstanceState);&nbsp; &nbsp; setContentView(R.layout.activity_attraction_list); //Change this line到setContentView(R.layout.listview);