所以我有以下类,代码如下:
private List<Medicines> meds = new ArrayList<Medicines>();//for loading the list
private List<Medicines> medDummy = new ArrayList<Medicines>();//for loading the list to a class
DatabaseHandler db;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.medicine_list);
populateMedicines();// Null Pointer Exception
populateListView();
}
private void populateMedicines(){
meds = db.getOnQuery("post", "SY");// Null Pointer Exception
for(Medicines medList: meds){
medDummy.add(new Medicines(medList.getBrand(), medList.getDescription(), medList.getCategory()));
}
}
public void populateListView(){
ArrayAdapter<Medicines> adapter = new MyListAdapter();
ListView list = (ListView)findViewById(R.id.medicineList);
list.setAdapter(adapter);
}
public class MyListAdapter extends ArrayAdapter<Medicines>{
public MyListAdapter(){
super(TabsandCapsList.this, R.layout.med_layout, medDummy);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
View itemView = convertView;
if(itemView == null){
itemView = getLayoutInflater().inflate(R.layout.med_layout, parent, false);
}
Medicines listMed = medDummy.get(position);
//textview
TextView header = (TextView)itemView.findViewById(R.id.list_header);
header.setText(listMed.getBrand());
TextView description = (TextView)itemView.findViewById(R.id.list_description);
description.setText(listMed.getDescription());
TextView category = (TextView)itemView.findViewById(R.id.list_category);
category.setText(listMed.getCategory());
return itemView;
}
}
方法getOnQuery:
//Getting on query medical entries
public List<Medicines> getOnQuery(String query, String value){
List<Medicines> medList = new ArrayList<Medicines>();
//Query
String queryString = "SELECT * FROM "+TABLE_MEDICINE+" WHERE "+query+" = "+"'"+value+"'";
SQLiteDatabase db = this.getWritableDatabase();
Cursor c = db.rawQuery(queryString, null);
if(c.moveToFirst()){
do{
Medicines med = new Medicines();
med.setID(Integer.parseInt(c.getString(0)));
med.setBrand(c.getString(1));
med.setDescription(c.getString(2));
med.setCategory(c.getString(3));
med.setPost(c.getString(4));
medList.add(med);
}while(c.moveToNext());
}
return medList;
}
我正在尝试使用我创建的内部数据库填充ListView。该数据库包含以下列: 一个。 ID 湾品牌 C。类别 d。描述 即交
上面的函数返回List中的onQuery结果。这个函数适用于我正在使用的其他类。但是在上面显示的类中,下面给出了一个NPE:
09-21 23:01:25.474: E/AndroidRuntime(29321): FATAL EXCEPTION: main
09-21 23:01:25.474: E/AndroidRuntime(29321): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.geneticalabs/com.geneticalabs.TabsandCapsList}: java.lang.NullPointerException
09-21 23:01:25.474: E/AndroidRuntime(29321): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
09-21 23:01:25.474: E/AndroidRuntime(29321): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2211)
09-21 23:01:25.474: E/AndroidRuntime(29321): at android.app.ActivityThread.access$600(ActivityThread.java:149)
09-21 23:01:25.474: E/AndroidRuntime(29321): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1300)
09-21 23:01:25.474: E/AndroidRuntime(29321): at android.os.Handler.dispatchMessage(Handler.java:99)
09-21 23:01:25.474: E/AndroidRuntime(29321): at android.os.Looper.loop(Looper.java:153)
09-21 23:01:25.474: E/AndroidRuntime(29321): at android.app.ActivityThread.main(ActivityThread.java:4987)
09-21 23:01:25.474: E/AndroidRuntime(29321): at java.lang.reflect.Method.invokeNative(Native Method)
09-21 23:01:25.474: E/AndroidRuntime(29321): at java.lang.reflect.Method.invoke(Method.java:511)
09-21 23:01:25.474: E/AndroidRuntime(29321): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:821)
09-21 23:01:25.474: E/AndroidRuntime(29321): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:584)
09-21 23:01:25.474: E/AndroidRuntime(29321): at dalvik.system.NativeStart.main(Native Method)
09-21 23:01:25.474: E/AndroidRuntime(29321): Caused by: java.lang.NullPointerException
09-21 23:01:25.474: E/AndroidRuntime(29321): at com.geneticalabs.TabsandCapsList.populateMedicines(TabsandCapsList.java:75)
09-21 23:01:25.474: E/AndroidRuntime(29321): at com.geneticalabs.TabsandCapsList.onCreate(TabsandCapsList.java:37)
09-21 23:01:25.474: E/AndroidRuntime(29321): at android.app.Activity.performCreate(Activity.java:5020)
09-21 23:01:25.474: E/AndroidRuntime(29321): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
09-21 23:01:25.474: E/AndroidRuntime(29321): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
09-21 23:01:25.474: E/AndroidRuntime(29321): ... 11 more
第37行:
populateMedicines();
第75行:
meds = db.getOnQuery("post", "SY");
答案 0 :(得分:2)
您的db
未初始化
DatabaseHandler db;
在onCreate
db = new DatabaseHandler(ActivityName.this); // initialize db