Java 将项目加载到微调器时出现空指针异常
这是我的活动类，其中有微调器。我需要将数据库值加载到微调器，所以使用ArrayList和ArrayAdapter，我做到了这一点 但当我运行我的应用程序时，它会给出空指针异常Java 将项目加载到微调器时出现空指针异常,java,android,android-studio,nullpointerexception,Java,Android,Android Studio,Nullpointerexception,这是我的活动类，其中有微调器。我需要将数据库值加载到微调器，所以使用ArrayList和ArrayAdapter，我做到了这一点 但当我运行我的应用程序时，它会给出空指针异常 public class addexpense extends ActionBarActivity { DBhelper helper; SQLiteDatabase db; Spinner spinner; @Override /** Called when the activ
public class addexpense extends ActionBarActivity {
DBhelper helper;
SQLiteDatabase db;
Spinner spinner;
@Override
/** Called when the activity is first created. */
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.addexpenses);
ArrayList<category> mArrayList = helper.getCategories();
Spinner sp =(Spinner)findViewById(R.id.spinner);
ArrayAdapter adapter =new ArrayAdapter(this,R.layout.spinner_row,mArrayList);
sp.setAdapter(adapter);
}
}
首先创建助手实例。
helper在
helper.getCategories（）处为空就是问题所在。必须实现阵列适配器（扩展到ArrayAdapter）。并覆盖getDropDownView
这是样品
public class CategorySpinnerAdapter extends ArrayAdapter<Category> {
List<Category> list = new ArrayList<>();
private Context context;
public CategorySpinnerAdapter(Context context, int resource, Category[] categories) {
super(context, resource, categories);
this.context = context;
}
@Override
public View getDropDownView(int position, View convertView, ViewGroup parent) {
return getMyView(position, convertView, parent);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
return getMyView(position, convertView, parent);
}
private View getMyView(int position, View convertView, ViewGroup parent){
CSViewHolder viewHolder;
if(convertView == null){
convertView = LayoutInflater.from(parent.getContext()).inflate(R.layout.category_spinner_row, parent, false);
viewHolder = new CSViewHolder(convertView);
convertView.setTag(viewHolder);
}else{
viewHolder = (CSViewHolder)convertView.getTag();
}
viewHolder.fill(list.get(position));
return convertView;
}
/**
* Load channel list
* @param cursor
*/
public void setList(Cursor cursor){
list.clear();
Log.i(getClass().getName(), String.valueOf(cursor));
for(cursor.moveToFirst(); !cursor.isAfterLast(); cursor.moveToNext()) {
// The Cursor is now set to the right position
Category category = new Category();
category.setTitle(CursorUtil.getStringColumnFromCursor(cursor, GoftagramContract.CategoryEntry.COLUMN_TITLE));
category.setId(CursorUtil.getStringColumnFromCursor(cursor, GoftagramContract.CategoryEntry.COLUMN_SERVER_ID));
list.add(category);
}
}
@Override
public int getCount() {
return list.size();
}
@Override
public Category getItem(int position) {
return list.get(position);
}
class CSViewHolder{
private TextView titleView;
private ImageView thumbnailView;
public CSViewHolder(View itemView){
titleView = (TextView)itemView.findViewById(R.id.category_spinner_row_title);
thumbnailView = (ImageView)itemView.findViewById(R.id.category_spinner_row_image);
}
public void fill(Category category){
titleView.setText(category.getTitle());
if(!TextUtils.isEmpty(category.getThumbnail())){
Glide.with(context)
.load(category.getThumbnail())
.into(thumbnailView);
}else{
thumbnailView.setImageResource(R.drawable.ic_discuss);
}
}
}
}
10-23 09:06:59.571 8798-8798/com.example.username.weddingplanning E/ArrayAdapter﹕ 您必须为TextView 10-23 09:06:59.601 8798-8798/com.example.username.weddingplanning E/AndroidRuntime提供资源ID﹕ 致命异常：main java.lang.IllegalStateException:ArrayAdapter要求资源ID为TextView
`ArrayAdapter=new ArrayAdapter（this，R.layout.spinner_row，R.ID.tv，mArrayList）；`在我更改这一行之后，它开始工作，但是在微调器com.example.username.weddingplan中。category@41a1da80
此格式的值在addexpense中的按钮在哪里？你能把它寄出去吗？
public class category
{
private int id;
private String name;
public category(int id, String name) {
this.id = id;
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
public class CategorySpinnerAdapter extends ArrayAdapter<Category> {
List<Category> list = new ArrayList<>();
private Context context;
public CategorySpinnerAdapter(Context context, int resource, Category[] categories) {
super(context, resource, categories);
this.context = context;
}
@Override
public View getDropDownView(int position, View convertView, ViewGroup parent) {
return getMyView(position, convertView, parent);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
return getMyView(position, convertView, parent);
}
private View getMyView(int position, View convertView, ViewGroup parent){
CSViewHolder viewHolder;
if(convertView == null){
convertView = LayoutInflater.from(parent.getContext()).inflate(R.layout.category_spinner_row, parent, false);
viewHolder = new CSViewHolder(convertView);
convertView.setTag(viewHolder);
}else{
viewHolder = (CSViewHolder)convertView.getTag();
}
viewHolder.fill(list.get(position));
return convertView;
}
/**
* Load channel list
* @param cursor
*/
public void setList(Cursor cursor){
list.clear();
Log.i(getClass().getName(), String.valueOf(cursor));
for(cursor.moveToFirst(); !cursor.isAfterLast(); cursor.moveToNext()) {
// The Cursor is now set to the right position
Category category = new Category();
category.setTitle(CursorUtil.getStringColumnFromCursor(cursor, GoftagramContract.CategoryEntry.COLUMN_TITLE));
category.setId(CursorUtil.getStringColumnFromCursor(cursor, GoftagramContract.CategoryEntry.COLUMN_SERVER_ID));
list.add(category);
}
}
@Override
public int getCount() {
return list.size();
}
@Override
public Category getItem(int position) {
return list.get(position);
}
class CSViewHolder{
private TextView titleView;
private ImageView thumbnailView;
public CSViewHolder(View itemView){
titleView = (TextView)itemView.findViewById(R.id.category_spinner_row_title);
thumbnailView = (ImageView)itemView.findViewById(R.id.category_spinner_row_image);
}
public void fill(Category category){
titleView.setText(category.getTitle());
if(!TextUtils.isEmpty(category.getThumbnail())){
Glide.with(context)
.load(category.getThumbnail())
.into(thumbnailView);
}else{
thumbnailView.setImageResource(R.drawable.ic_discuss);
}
}
}
}
categorySpinnerAdapter = new CategorySpinnerAdapter(this, R.layout.category_spinner_row, new Category[]{});