Question

我正在编写一个应用程序，其中ArrayList由两个ListViews代表纵向和横向。为此，我一直在使用一个自定义适配器来为其listViews充气。但是，每当实例化NullPointer Exception的自定义适配器时，我都会不断收到landscape ListView。有什么建议么？抛出异常的行：

listLand.setAdapter(customAdapter);

MainActivity

public class MainActivity extends AppCompatActivity {
    ListView listPort;
    ListView listLand;
    ArrayList<Flick> flicks;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        listLand = findViewById(R.id.listLand);
        listPort = findViewById(R.id.listPort);

        flicks = new ArrayList<>();
        flicks.add(new Flick("Wizard of Oz", "Metro-Goldwyn-Mayer", "VARIOUS","1939", "", 98));
        flicks.add(new Flick("Star Wars", "LucasFilm", "George Lucas", "1977","",93));
        flicks.add(new Flick("Psycho","Paramount", "Alfred Hitchcock", "1960", "", 97));
        flicks.add(new Flick("King Kong", "RKO Pictures", "Merian C. Cooper & Ernest B. Schoedsack", "1933", "", 98));
        flicks.add(new Flick("2001: A Space Odyssey", "Metro-Goldwyn-Mayer", "Stanley Kubrick", "1968", "", 93));
        flicks.add(new Flick("Citizen Kane", "RKO Pictures", "Orson Welles", "1941", "", 100));
        flicks.add(new Flick("Snow White and the Seven Dwarfs", "Walt Disney Pictures", "VARIOUS", "1937", "",98));
        flicks.add(new Flick("Casablanca", "Warner Bros.", "Michael Curtiz", "1942", "", 97));
        flicks.add(new Flick("The Godfather", "Paramount", "Francis Ford Coppola", "1972", "", 98));
        flicks.add(new Flick("Jaws", "Universal", "Steven Spielberg", "1975", "", 97));

        CustomAdapter customAdapter = new CustomAdapter(this, R.layout.custom_layout, flicks);
        listPort.setAdapter(customAdapter);
        listLand.setAdapter(customAdapter);
    }
    public class CustomAdapter extends ArrayAdapter<Flick>
    {
        Context context;
        int resource;
        List<Flick> list;

        public CustomAdapter(@NonNull Context context, int resource, @NonNull List<Flick> objects) {
            super(context, resource, objects);
            this.context=context;
            this.resource=resource;
            list=objects;
        }

        @NonNull
        @Override
        public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
            LayoutInflater layoutInflater=(LayoutInflater)context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
            View adapterView=layoutInflater.inflate(resource,null);


            TextView title = adapterView.findViewById(R.id.title);
            ImageView imageView=adapterView.findViewById(R.id.imageView);
            Button up=adapterView.findViewById(R.id.upButton);
            Button down=adapterView.findViewById(R.id.downButton);

            title.setText(list.get(position).getTitle());

            switch(list.get(position).getStudio())
            {
                case "Warner Bros.":
                    imageView.setImageResource(R.drawable.warnerbros);
                    break;
                case "Paramount":
                    imageView.setImageResource(R.drawable.warnerbros);
                    break;
                case "Universal":
                    imageView.setImageResource(R.drawable.warnerbros);
                    break;
                case "LucasFilm":
                    imageView.setImageResource(R.drawable.warnerbros);
                    break;
                case "RKO Pictures":
                    imageView.setImageResource(R.drawable.warnerbros);
                    break;
                case "Walt Disney Pictures":
                    imageView.setImageResource(R.drawable.warnerbros);
                    break;
                case "Metro-Goldwyn-Mayer":
                    imageView.setImageResource(R.drawable.warnerbros);
                    break;
            }

            return adapterView;
        }
    }
}

Answer 1

一个猜测：您有两种不同的布局-一种用于纵向，另一种用于横向。根据设备的方向，将仅通过findViewById加载其中之一。请记住，旋转设备会重新创建活动（并调用onCreate）。设置适配器之前，您应该只检查listPort的{{1}}和listLand。您不会同时使用两者。

类似这样的东西：

null

其中一个应该为非null，前提是其他所有功能均应正常工作。

如果我猜您有一个if (listPort != null) { listPort.setAdapter(customAdapter); // Portrait mode } else { listLand.setAdapter(customAdapter); // Landscape mode }和一个values/activity_main.xml，则可以通过在两个地方使用相同的列表ID来使自己的生活更轻松。例如，

values-land/activity_main.xml

使用自定义适配器和方向接收ListView程序的nullpointer异常？

1 个答案: