Question

您好我知道之前已发布但我似乎无法找到错误。我创建了一个List<Objects>，我想用它来填充一个微调器。我的代码

public class RegisterActivity extends AppCompatActivity {

    private Toolbar tb;
    private Spinner spinner;
    private List<Swmata> lista;
    private BaseAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_register);
        spinner = (Spinner)findViewById(R.id.spinner3);
        tb = (Toolbar)findViewById(R.id.toolBar);
        lista = new ArrayList<Swmata>();
        tb.setTitle("Λελέμετρο");
        setSupportActionBar(tb);
        populateSpinner();
        adapter = new MyAdapter(RegisterActivity.this, lista);
        spinner.setAdapter(adapter);
    }

    private void populateSpinner() {
        lista.add(new Swmata(R.drawable.peziko, "Πεζικό(ΠΖ)"));
        lista.add(new Swmata(R.drawable.eidikesdinameis, "Ειδικές Δυνάμεις(ΕΔ)"));
        lista.add(new Swmata(R.drawable.tethwrakismena, "Τεθωρακισμένα(ΤΘ)"));
        lista.add(new Swmata(R.drawable.piroboliko, "Πυροβολικό(ΠΒ)"));
        lista.add(new Swmata(R.drawable.mixaniko, "Μηχανικό(ΜΧ)"));
        lista.add(new Swmata(R.drawable.aeroporia, "Αεροπορία Στρατού(ΑΣ)"));
        lista.add(new Swmata(R.drawable.texniko, "Τεχνικό(ΤΧ)"));
        lista.add(new Swmata(R.drawable.efodiasmou, "Εφοδιασμού Μεταφορών(ΕΜ)"));
        lista.add(new Swmata(R.drawable.ylikou, "Υλικού Πολέμου(ΥΠ)"));
        lista.add(new Swmata(R.drawable.ygeionomiko, "Υγειονομικό(ΥΓ)"));
        lista.add(new Swmata(R.drawable.diabibaseis, "Διαβιβάσεων(ΔΒ)"));
        lista.add(new Swmata(R.drawable.stratonomia, "Στρατονομία(ΣΝ)"));
    }

适配器：

public class MyAdapter extends BaseAdapter {

    private List<Swmata> objects;
    private Context context;

    public MyAdapter(Context context, List objects) {
        this.context = context;
        this.objects = objects;
    }

    @Override
    public int getCount() {
        return objects.size();
    }

    @Override
    public Object getItem(int position) {
        return objects.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

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

        if (convertView == null){
            LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            inflater.inflate(R.layout.spinner_item, parent, false);
            holder = new SwmataHolder();
            holder.imageView = (ImageView)convertView.findViewById(R.id.imageSpinner5);
            holder.textView = (TextView)convertView.findViewById(R.id.textSpinner5);
            convertView.setTag(holder);
        }else {
            holder = (SwmataHolder)convertView.getTag();
        }

        Swmata swma = (Swmata) getItem(position);
        holder.imageView.setImageResource(swma.getImage());
        holder.textView.setText(swma.getName());
        return convertView;
    }

    static class SwmataHolder{
        ImageView imageView;
        TextView textView;
    }
}

错误：

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
            at com.project.matrix.lelemetroga.MyAdapter.getView(MyAdapter.java:46)

第46行：holder.imageView = (ImageView)convertView.findViewById(R.id.imageSpinner5);

布局文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal" android:layout_width="match_parent"
    android:padding="15dp"
    android:layout_height="wrap_content">

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/aeroporia"
        android:layout_weight="1"
        android:id="@+id/imageSpinner5" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Medium Text"
        android:layout_weight="1"
        android:id="@+id/textSpinner5" />
</LinearLayout>

现在我不知道我做错了什么，但因为我在其他项目中使用相同的方法，它实际上看起来很有趣，我找不到我的错误。如果有人能指出它我宁愿赞赏。在此先感谢!!!

Answer 1

在此代码段中，您测试convertView是否为空，但是您继续并取消引用它：

    if (convertView == null){
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        inflater.inflate(R.layout.spinner_item, parent, false);
        holder = new SwmataHolder();
        holder.imageView = (ImageView)convertView.findViewById(R.id.imageSpinner5);
        holder.textView = (TextView)convertView.findViewById(R.id.textSpinner5);
        convertView.setTag(holder);
    }else {

我认为您打算为convertView分配一个值，如下所示：

    if (convertView == null){
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.spinner_item, parent, false);
        holder = new SwmataHolder();
        holder.imageView = (ImageView)convertView.findViewById(R.id.imageSpinner5);
        holder.textView = (TextView)convertView.findViewById(R.id.textSpinner5);
        convertView.setTag(holder);
    }else {

Answer 2

您忘记将膨胀值分配给convertView变量。

此：

inflater.inflate(R.layout.spinner_item, parent, false);

应该是这样的：

convertView = inflater.inflate(R.layout.spinner_item, parent, false);

Answer 3

你需要

convertView = inflater.inflate(R.layout.spinner_item, parent, false);

在if声明中。

您在NPE上获得convertView.findViewById()，因为您从未初始化convertView，因此它是第一次null。在膨胀View时需要给它一个值。

不能填充一个微调器

3 个答案: