多列表视图 android

Question

我尝试创建多个 ListView，但我有 java.lang.NullPointerException。好像还行吧

主要：

for(int i = 0; i < 10; i++) {
            ActivityObject ao = new ActivityObject();
            if(i%2 == 0) {
                ao.setType("0");
                ao.setTitle("Im null");
            } else {
                ao.setType("1");
                ao.setTitle("Im one");
            }

            dataActivity.add(ao);
        }

        ActivityAdapter adapter = new ActivityAdapter(getApplicationContext(), dataActivity);
        listActivity.setAdapter(adapter);

超级适配器

public class ActivityAdapter extends ArrayAdapter {

    private Context context;
    private ArrayList<ActivityObject> object;
    LayoutInflater vi;

    public ActivityAdapter(Context context, ArrayList<ActivityObject> object) {
        super(context, 0, object);

        this.context = context;
        this.object = object;

        vi = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        ViewHolder holder = null;

        if(convertView == null) {

            if(object.get(position).equals("0")) {
                convertView = vi.inflate(R.layout.p_activity_detected, null);
                holder.textActivity = (TextView) convertView.findViewById(R.id.detected_text);
            }

            if(object.get(position).equals("1")) {
                convertView = vi.inflate(R.layout.p_activity_people, null);
                holder.textPeople = (TextView) convertView.findViewById(R.id.people_text);
            }

            holder = new ViewHolder();
            convertView.setTag(holder);

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

        //set text
        if(object.get(position).getType().equals("0")) {
            holder.textActivity.setText(object.get(position).getTitle());
        }

        if(object.get(position).getType().equals("1")) {
            holder.textPeople.setText(object.get(position).getTitle());
        }

        return convertView;
    }

    static class ViewHolder {
        public TextView textActivity;
        public TextView textPeople;
    }
}

错误

FATAL EXCEPTION: main
    java.lang.NullPointerException
            at adapters.ActivityAdapter.getView(ActivityAdapter.java:54)

这是线 convertView.setTag(holder);

Answer 1

把你的支架移到上面。我认为它会起作用。在我看来，您还必须使用 else 语句。

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    if(convertView == null) {
                holder = new ViewHolder();
                Log.d("object.get(position) = ", object.get(position));
                if(object.get(position).equals("0")) {
                    convertView = vi.inflate(R.layout.p_activity_detected, null);
                    holder.textActivity = (TextView) convertView.findViewById(R.id.detected_text);
                }
                else if(object.get(position).equals("1")) {
                    convertView = vi.inflate(R.layout.p_activity_people, null);
                    holder.textPeople = (TextView) convertView.findViewById(R.id.people_text);
                }
                else{
                    //set defualt holder.textPeople here
                }


                convertView.setTag(holder);

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

    //set text
    if(object.get(position).getType().equals("0")) {
        holder.textActivity.setText(object.get(position).getTitle());
    }

    if(object.get(position).getType().equals("1")) {
        holder.textPeople.setText(object.get(position).getTitle());
    }

    return convertView;
}

Answer 2

用这些代码替换你的适配器

public class ActivityAdapter extends ArrayAdapter {

private Context context;
private ArrayList<ActivityObject> object;
LayoutInflater vi;

ViewHolder holder;

public ActivityAdapter(Context context, ArrayList<ActivityObject> object) {
    super(context, 0, object);

    this.context = context;
    this.object = object;

    vi = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    holder = new ViewHolder();;

    if(convertView == null) {

        if(object.get(position).equals("0")) {
            convertView = vi.inflate(R.layout.p_activity_detected, null);
            holder.textActivity = (TextView) convertView.findViewById(R.id.detected_text);
        }

        if(object.get(position).equals("1")) {
            convertView = vi.inflate(R.layout.p_activity_people, null);
            holder.textPeople = (TextView) convertView.findViewById(R.id.people_text);
        }


        convertView.setTag(holder);

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

    //set text
    if(object.get(position).getType().equals("0")) {
        holder.textActivity.setText(object.get(position).getTitle());
    }

    if(object.get(position).getType().equals("1")) {
        holder.textPeople.setText(object.get(position).getTitle());
    }

    return convertView;
}

static class ViewHolder {
    public TextView textActivity;
    public TextView textPeople;
    }
   }

Answer 3

您的代码无法保证 convertView 不会为空：

  if(convertView == null) {

        if(object.get(position).equals("0")) {
            convertView = vi.inflate(R.layout.p_activity_detected, null);
            holder.textActivity = (TextView) convertView.findViewById(R.id.detected_text);
        }

        if(object.get(position).equals("1")) {
            convertView = vi.inflate(R.layout.p_activity_people, null);
            holder.textPeople = (TextView) convertView.findViewById(R.id.people_text);
        }

        holder = new ViewHolder();
        convertView.setTag(holder);

如果上述none个条件成立，则convertView仍为null。你确定条件正是你想要做的吗？根据您的声明

private ArrayList<ActivityObject> object;

object 是一个 ActivityObject 的列表，但您正在将它们与 strings“0”和“1”进行比较

object.get(position).equals("0"))
...
object.get(position).equals("1"))

也许您想将它们转换为 ActivityObject 并将字段类型与字符串进行比较？

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