NPE上ArrayAdapter.clear（） [英] NPE on ArrayAdapter.clear()

问题描述

我在该行获得了NPE 如果（adapter.getCount（）！= 0）adapter.clear（）; 就在我已经初始化它。凡我错了，在我的code？我认为，因为我刚刚初始化它，不应该有一个NPE，但我错了..
在这里，我把3种方法相关者适配器：

I get a NPE at the line if(adapter.getCount() != 0) adapter.clear(); just after I have initialized it. Where I'm wrong in my code? I think that because I had just initialized it, there should not be a NPE, but I'm wrong.. Here I put 3 methods relater to the adapter:

    package com.example.app.Fragment;
public class FragmentGestioneCorsa extends Fragment implements AdapterView.OnItemSelectedListener{

@SuppressWarnings("unused")
private static final String TAG = FragmentGestioneCorsa.class.getSimpleName();

private Context context;
private DatabaseLocale db;
private ArrayAdapter<String> adapter;
private  Spinner spnLinee;
private Button aggiornamento;


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    linee = new ArrayList<HashMap<String, String>>();
    context = getActivity();
    return inflater.inflate(R.layout.fragment_gestione_corsa, container, false);
}

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    spnLinee = (Spinner) getView().findViewById(R.id.spinnerLinee);
    ArrayAdapter<String> adapter =new ArrayAdapter<String>(context, android.R.layout.simple_spinner_item);
    spnLinee.setAdapter(adapter);
    spnLinee.setOnItemSelectedListener(this);
    popolamentoSpinner();

    aggiornamento = (Button) getView().findViewById(R.id.buttonAggiornamento);
    aggiornamento.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            // Se scrivo DownloadLinee.execute() ottengo l'errore:
            // If I write DownloadLinee.execute() I get the error:
            // Non-static method cannot be referenced from a static contecxt
            DownloadLinee l = new DownloadLinee();
            l.execute();
        }
    });
}

private void popolamentoSpinner(){
    if(adapter.getCount() != 0) adapter.clear();
    db = new DatabaseLocale(context);
    SQLiteDatabase dbLeggibile = db.getReadableDatabase();
    String[] colonne = {DatabaseLocale.getTagCodiceLinea(), DatabaseLocale.getTagNomeLinea()};
    String tabella = DatabaseLocale.getTableName();
    Cursor cursore = dbLeggibile.query(tabella, colonne, null, null, null, null, null);
    while(cursore.moveToNext()){
        adapter.add(cursore.getString(0) + " " + cursore.getString(1));
    }
    cursore.close();
    db.close();
}
}

为什么这个NPE？
在此先感谢

Why this NPE? Thanks in advance

推荐答案

您正在申报两次 ArrayAdapter＆LT;串GT;适配器，曾经在 onViewCreated 方法，另一次是在类的成员。

You are declaring twice ArrayAdapter<String> adapter, once in the onViewCreated method, and once as a member of the class.

当您在 onViewCreated 初始化它，其实它的初始化它在 popolamentoSpinner 不可见的局部变量。基本上，它是不是在2功能相同的变量，所以实际上你从来没有初始化称为varibale 适配器您在使用 popolamentoSpinner ！

When you initialize it in onViewCreated, in fact it's initializing a local variable which has no visibility in popolamentoSpinner. Basically, it's not the same variable in the 2 functions, so in fact you never initialize the varibale called adapter that you use in popolamentoSpinner!

一个解决办法是去除 onViewCreated 的声明，所以你确信你初始化成员变量：

One solution would be to remove the declaration in onViewCreated so you are sure that you initialize the member variable:

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    spnLinee = (Spinner) getView().findViewById(R.id.spinnerLinee);
    adapter =new ArrayAdapter<String>(context, android.R.layout.simple_spinner_item);
    spnLinee.setAdapter(adapter);
    ...

这篇关于NPE上ArrayAdapter.clear（）的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！