自定义ListView适配器空对象参考 [英] Custom ListView Adapter Null Object Reference

问题描述

不确定在这里还没有初始化什么，我想我必须在列表本身上手动创建一个新行，但是我不知道如何开始.这是我用来创建和调用适配器的代码:

 /***检索适配器UI** @param position当前位置与列表* @param convertView视图* @param父容器* @return视图，UI元素*/@Overridepublic View getView(最终int位置，最终View convertView，最终ViewGroup父级){最终的ViewHolder处理程序= new ViewHolder();//开始查看行= convertView;if(row == null){LayoutInflater inflator =(LayoutInflater)this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);row = inflator.inflate(R.layout.fragment_delivery_collect_item，parent，false);}row.setTag(handler);final Order.Item itemRow =(Order.Item)super.getItem(位置);if(itemRow！= null){handler.mName =(TextView)convertView.findViewById(R.id.item_name);handler.mSize =(TextView)convertView.findViewById(R.id.item_size);handler.mQty =(TextView)convertView.findViewById(R.id.item_qty);handler.mPrice =(TextView)convertView.findViewById(R.id.item_price);handler.mName.setText(itemList.get(position).getName());如果(itemList.get(position).getSize()！= null){handler.mSize.setText(itemList.get(position).getSize());}handler.mQty.setText(itemList.get(position).getQty());handler.mPrice.setText(String.format(£％s"，itemList.get(position).getPrice()));}返回行}公共布尔cleanAll(){尝试 {itemList.clear();notifyDataSetChanged();返回true；}捕获(异常除外){Log.i("cleanAll"，ex.getMessage());返回false；}}类ViewHolder {查看mView;TextView mName，mSize，mQty，mPrice；} 

我正在尝试使用"Order.Item"中的信息填充页面上的4个TextView，该类非常简单，但是如果您也需要我展示它，那就问吧.

这是我收到的错误消息:

 致命异常:主要流程:uk.ac.plymouth.www.deliveryapplication，PID:21370java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法"android.view.View android.view.View.findViewById(int)"在uk.ac.plymouth.www.deliveryapplication.adapters.CollectListViewAdapter.getView(CollectListViewAdapter.java:96) 

这是我在片段中创建适配器的地方:

  ListView returnItem =(ListView)rootView.findViewById(R.id.list);CollectListViewAdapter适配器=新的CollectListViewAdapter(getActivity().getApplicationContext()，R.layout.fragment_delivery_collect_item，true，this);对于(Order.Item i:currOrder.getITEMS()){adapter.add(i);}returnItem.setAdapter(adapter); 

解决方案

您的 convertView 为空.您没有在 convertView

中分配布局视图

请尝试使用该行:

  row = inflator.inflate(R.layout.fragment_delivery_collect_item，parent，false); 

这样做:

  if(row！= null){handler.mName =(TextView)row.findViewById(R.id.item_name);handler.mSize =(TextView)row.findViewById(R.id.item_size);handler.mQty =(TextView)row.findViewById(R.id.item_qty);handler.mPrice =(TextView)row.findViewById(R.id.item_price); 

Not sure what hasn't been initialised here, I'm guessing I have to manually create a new row on the list itself but I have no clue how to even start on that. Here is the code I use to create and call the adapter:

/**
 * Retrieve adapter UI
 *
 * @param position current position with the list
 * @param convertView view
 * @param parent container
 * @return view, UI elements
 */
@Override
public View getView(final int position, final View convertView, final ViewGroup parent) {

    final ViewHolder handler = new ViewHolder();

    //start
    View row = convertView;
    if(row == null) {
        LayoutInflater inflator = (LayoutInflater) this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        row = inflator.inflate(R.layout.fragment_delivery_collect_item, parent, false);

    }
    row.setTag(handler);


    final  Order.Item itemRow = (Order.Item) super.getItem(position);
    if(itemRow != null) {
        handler.mName = (TextView) convertView.findViewById(R.id.item_name);
        handler.mSize = (TextView) convertView.findViewById(R.id.item_size);
        handler.mQty = (TextView) convertView.findViewById(R.id.item_qty);
        handler.mPrice = (TextView) convertView.findViewById(R.id.item_price);

        handler.mName.setText(itemList.get(position).getName());
        if (itemList.get(position).getSize() != null) {
            handler.mSize.setText(itemList.get(position).getSize());
        }
        handler.mQty.setText(itemList.get(position).getQty());
        handler.mPrice.setText(String.format("£%s", itemList.get(position).getPrice()));
    }
    return row;
}

public Boolean cleanAll(){
    try {
        itemList.clear();
        notifyDataSetChanged();
        return true;
    }catch (Exception ex){
        Log.i("cleanAll",ex.getMessage());
        return false;
    }
}

class ViewHolder {
    View mView;
    TextView mName, mSize, mQty, mPrice;
}

I'm trying to populate the 4 TextViews on a page with information from "Order.Item," that class Is pretty simple but if you need me to show that too just ask.

Here is the error message I'm getting:

FATAL EXCEPTION: main
Process: uk.ac.plymouth.www.deliveryapplication, PID: 21370
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at uk.ac.plymouth.www.deliveryapplication.adapters.CollectListViewAdapter.getView(CollectListViewAdapter.java:96)

And here is where I create the adapter in the fragment:

ListView returnedItem = (ListView) rootView.findViewById(R.id.list);
    CollectListViewAdapter adapter = new CollectListViewAdapter(getActivity().getApplicationContext(), R.layout.fragment_delivery_collect_item, true, this);
    for (Order.Item i : currOrder.getITEMS()) {
        adapter.add(i);
    }
    returnedItem.setAdapter(adapter);

解决方案

your convertView is null. You are not assigning your layout view in convertView

try use the row as you are using:

row = inflator.inflate(R.layout.fragment_delivery_collect_item, parent, false);

so do:

if(row!= null) {
    handler.mName = (TextView) row.findViewById(R.id.item_name);
    handler.mSize = (TextView) row.findViewById(R.id.item_size);
    handler.mQty = (TextView) row.findViewById(R.id.item_qty);
    handler.mPrice = (TextView) row.findViewById(R.id.item_price);

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