Question

您好我继续在item.setProduct(trans.getProduct().getName());上获取NullPointerException 你能说出原因和方法吗？我没有看到任何理由为什么它会为null因为我已经在onPostExecute方法中设置了我的适配器。谢谢！

private class TransactionTask extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... params) {

        BackendService service = BackendAPI.serviceApi();
        TransactionObject transactionList;

        Log.e("AsyncTask", "I'm called");

        try {
            transactionList = service.listTransactions(15);
            if (transactionList != null) {
                Log.e(TAG, transactionList.toString());
                loadListViewData(transactionList);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }

        return null;
    }

    public void loadListViewData(TransactionObject transObj) {

        item = new SalesItem();

        Iterator<Transaction> transactionList = transObj.getTransactions().iterator();
        Transaction trans = null;

        while (transactionList.hasNext()) {
            trans = transactionList.next();

            item.setProduct(trans.getProduct().getName());
            item.setCost(trans.getCost());
            item.setName(trans.getUser().getName());
            item.setDate(trans.getCreated_at());
            item.setId(trans.getId());
            transaction.add(item);
        }

    }

    @Override
    protected void onPostExecute(String s) {
        super.onPostExecute(s);
        adapter = new SalesListAdapter(getActivity(), transaction);
        listview.setAdapter(adapter);
    }
}

这是我的日志

`03-03 07:40:52.604    2011-2033/net.payswitch.switchmobile W/System.err﹕ java.lang.NullPointerException
03-03 07:40:52.604    2011-2033/net.payswitch.switchmobile W/System.err﹕ at net.payswitch.switchmobile.fragments.SalesDataFragment$TransactionTask.loadListViewData(SalesDataFragment.java:188)
03-03 07:40:52.604    2011-2033/net.payswitch.switchmobile W/System.err﹕ at net.payswitch.switchmobile.fragments.SalesDataFragment$TransactionTask.doInBackground(SalesDataFragment.java:166)
03-03 07:40:52.604    2011-2033/net.payswitch.switchmobile W/System.err﹕ at net.payswitch.switchmobile.fragments.SalesDataFragment$TransactionTask.doInBackground(SalesDataFragment.java:152)
03-03 07:40:52.604    2011-2033/net.payswitch.switchmobile W/System.err﹕ at android.os.AsyncTask$2.call(AsyncTask.java:287)
03-03 07:40:52.604    2011-2033/net.payswitch.switchmobile W/System.err﹕ at java.util.concurrent.FutureTask.run(FutureTask.java:234)
03-03 07:40:52.604    2011-2033/net.payswitch.switchmobile W/System.err﹕ at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
03-03 07:40:52.604    2011-2033/net.payswitch.switchmobile W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
03-03 07:40:52.604    2011-2033/net.payswitch.switchmobile W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
03-03 07:40:52.604    2011-2033/net.payswitch.switchmobile W/System.err﹕ at java.lang.Thread.run(Thread.java:856)`

Answer 1

这是一个跟进:( SalesItem类在不同的文件上）

public class SalesItem {

private String product;
private String cost;
private String name;
private String date;
private String id;

public String getProduct() {
    return product;
}

public void setProduct(String product) {
    this.product = product;
}

public String getCost() {
    return cost;
}

public void setCost(String cost) {
    this.cost = cost;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getDate() {
    return date;
}

public void setDate(String date) {
    this.date = date;
}

public String getId() {
    return id;
}

public void setId(String id) {
    this.id = id;
}

}

下面的声明位于父类中，因此它们被全局声明

private ArrayList<SalesItem> transaction;
private SalesItem item;

Answer 2

item出现问题。您创建一个new SalesItem()，然后循环遍历事务列表。这意味着在第一个SalesItem添加到transaction之后，您将修改已SalesItem中的transaction，并再次添加。当然，这不是预期的行为。解决方案是在new SalesItem()循环中移动while。

对于NullPointerException，如果要继续查看列表中的下一个元素，或者执行{{1}，请为每个步骤添加一个检查null并记录显式错误如果不应该发生，请使用assert进行记录：

Log.wtf(...)

AsyncTask doInBackground响应的nullPointerException

2 个答案: