将项目加载到微调器时为空指针异常
这是我的活动类，我有spinner.I需要加载数据库值到微调，所以使用ArrayList和ArrayAdapter，我做到了。
但是当我运行我的应用程序时，它提供了Null指针异常。
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);
}
}
这是我在DBHelper数据库类中的方法
public class DBhelper extends SQLiteOpenHelper{
static final String DATABASE = "wedding9.db";
static final int VERSION = 9;
static final String TABLE1 = "Category";
static final String TABLE2 = "Budget";
static final String C_ID = "_id";
static final String Name = "name";
static final String B_ID = "_id";
static final String Description = "description";
static final String Amount = "amount";
public DBhelper(Context context){
super(context, DATABASE, null, VERSION);
}
public void onCreate(SQLiteDatabase db){
db.execSQL("CREATE TABLE " + TABLE1+ "(" +C_ID
+ " INTEGER PRIMARY KEY AUTOINCREMENT," +Name+ " text unique not null)");
db.execSQL("CREATE TABLE " + TABLE2+ "(" +B_ID
+ " INTEGER PRIMARY KEY AUTOINCREMENT," +Description+ " text,"
+Amount+ " text, FOREIGN KEY ("+Description+") REFERENCES "+TABLE1+"("+Name+"));");
// db.execSQL("CREATE TABLE " + TABLE2+ "(" +B_ID
// + " INTEGER PRIMARY KEY AUTOINCREMENT," +Amount+ " text )");
}
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("drop table " + TABLE1);
onCreate(db);
}
public ArrayList<category> getCategories(){
ArrayList<category> arrayList = new ArrayList<category>();
SQLiteDatabase db = getReadableDatabase();
Cursor c = db.query(DBhelper.TABLE1, null, null, null, null, null, null);
// c.moveToFirst();
while (c.moveToNext()) {
category cat = new category(c.getInt(0),c.getString(1));
arrayList.add(cat);
}
return arrayList;
}
public boolean checkIdExist(String name) {
SQLiteDatabase db = getReadableDatabase();
Cursor c = db.query(DBhelper.TABLE1, null, null, null, null, null, null);
// c.moveToFirst();
while (c.moveToNext()) {
if(c.getString(1).equals(name))
return false;
}
return true;
}
}
这是类别类
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;
}
}
下面是一个例外，我运行应用程序时得到了这个例外
10-23 08：29：21.482 3075-3075 / com.example.username.weddingplanning E / AndroidRuntime：FATAL EXCEPTION：主要java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.username.weddingplanning / com.example .username.weddingplanning.addexpense}：android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2250）上的android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2304）处于android.app.ActivityThread的java.lang.NullPointerException。在android.os.Looper.loop上的android.os.Handler.dispatchMessage（Handler.java:99）处访问$ 700（ActivityThread.java:152）android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1284）在java.lang.reflect.Method.invoke处使用java.lang.reflect.Method.invokeNative（Native Method）处理android.app.ActivityThread.main（ActivityThread.java:5299）（Method.java：Looper.java:176） 511）at com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1102）at com.android.internal.os.ZygoteInit.main（ZygoteInit.java:869） 在dalvik.system.NativeStart.main（Native方法）引发：java.lang.NullPointerException at com.example.username.weddingplanning.addexpense.onCreate（addexpense.java:43）at android.app.Activity.performCreate（Activity。在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2304）处的android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2213）处的android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1097）处的java：5326） android.app.ActivityThread.access $ 700（ActivityThread.java:152）at android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1284）at android.os.Handler.dispatchMessage（Handler.java:99）at android。 os.Looper.loop（Looper.java:176）at android.app.ActivityThread.main（ActivityThread.java:5299）at java.lang.reflect.Method.invokeNative（Native Method）at java.lang.reflect.Method。在com.android.internal调用（Method.java:511） .os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1102）at com.android.internal.os.ZygoteInit.main（ZygoteInit.java:869）at dalvik.system.NativeStart.main（Native Method）
首先创建你的帮助器实例。
helper在helper.getCategories(); 是问题。
你必须实现Array适配器（扩展到ArrayAdapter）。 并重写getDropDownView。
这是为了示例。
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);
}
}
}
}
使用适配器
categorySpinnerAdapter = new CategorySpinnerAdapter(this, R.layout.category_spinner_row, new Category[]{});
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