我正在尝试从数据库设置数组长度，我得到这个错误:
EE/AndroidRuntime: FATAL EXCEPTION: main
Process: com.cekmekoytipmerkezi.diyetisyen.diyetisyen, PID: 11676
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.cekmekoytipmerkezi.diyetisyen.diyetisyen/com.cekmekoytipmerkezi.diyetisyen.diyetisyen.DiyetisyenActivity}: java.lang.NullPointerException: Attempt to get length of null array
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3253)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349)
at android.app.ActivityThread.access$1100(ActivityThread.java:221)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7224)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: java.lang.NullPointerException: Attempt to get length of null array
at com.cekmekoytipmerkezi.diyetisyen.diyetisyen.AkisArrayAdapter.getCount(AkisArrayAdapter.java:47)
at android.widget.ListView.setAdapter(ListView.java:508)
at com.cekmekoytipmerkezi.diyetisyen.diyetisyen.AkisFragment.onCreateView(AkisFragment.java:136)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:742)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:339)
at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:601)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1265)
at android.app.Activity.performStart(Activity.java:6915)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3216)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349)
at android.app.ActivityThread.access$1100(ActivityThread.java:221)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7224)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
at java.lang.Thread.run(Thread.java:818)
基本上我有一个列表视图，我需要从我的数据库填充。我已经创建了一个自定义适配器。在我的片段中，当我在初始声明中设置String[] ogunler = new String[10];并且在线程中不做任何事情时，我接收到数据，但在实际数据之后我有一堆空列表项。
我的片段代码:
public class AkisFragment extends Fragment
{
String[] ogunler;
int hastaID;
String dayOfTheWeek;
int programID;
AkisArrayAdapter adapter;
public AkisFragment()
{
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View view = inflater.inflate(R.layout.fragment_akis, container, false);
Calendar calendar = Calendar.getInstance();
final int day = calendar.get(Calendar.DAY_OF_WEEK);
String SQL = "SELECT email, sifre, ID FROM Hasta WHERE Hasta.email = '";
Bundle bundle = this.getArguments();
if (bundle != null)
{
hastaID = bundle.getInt("hastaID");
}
...
new Thread(new Runnable()
{
public void run()
{
try
{
Class.forName("net.sourceforge.jtds.jdbc.Driver");
Connection conn = DriverManager.getConnection(getResources().getString(R.string.db_connection));
dayOfTheWeek = "Pazartesi";
String SQL = "SELECT ID FROM Program Where hastaID = " + Integer.toString(hastaID) + "AND gun = '" + dayOfTheWeek + "'";
Log.w(dayOfTheWeek, "123");
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(SQL);
int counter = 0;
while (rs.next())
{
programID = rs.getInt(1);
}
String SQLcounter = "SELECT ID FROM Program Where hastaID = " + Integer.toString(hastaID) + "AND gun = '" + dayOfTheWeek + "'";
Statement stmtCounter = conn.createStatement();
ResultSet rsCounter = stmtCounter.executeQuery(SQLcounter);
int arrSize = 0;
while(rsCounter.next())
{
arrSize++;
}
ogunler = new String[arrSize];
SQL = "SELECT ogunTipi, ogunIcerik FROM Ogun WHERE programID = " + Integer.toString(programID);
Statement stmt2 = conn.createStatement();
ResultSet rs2 = stmt2.executeQuery(SQL);
int counter2 = 0;
while (rs2.next())
{
ogunler[counter2] = rs2.getString(2) + " " + rs2.getString(1);
//Log.w(ogunler[counter2], "123");
counter2++;
}
getActivity().runOnUiThread(new Runnable()
{
public void run()
{
adapter.notifyDataSetChanged();
}
});
conn.close();
} catch (ClassNotFoundException e)
{
e.printStackTrace();
} catch (SQLException e)
{
e.printStackTrace();
}
}
}).start();
ListView list = (ListView) view.findViewById(R.id.lvAkis);
adapter = new AkisArrayAdapter(getActivity(), ogunler);
list.setAdapter(adapter);
return view;
}
}
定制适配器:
public class AkisArrayAdapter extends BaseAdapter
{
String items[];
int programID;
LayoutInflater mInflater;
public AkisArrayAdapter(Context context, String[] _items)
{
mInflater = LayoutInflater.from(context);
this.items = _items;
}
@Override
public int getCount()
{
return items.length;
}
@Override
public Object getItem(int position)
{
return position;
}
@Override
public long getItemId(int position)
{
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent)
{
ViewHolder holder;
if(convertView == null)
{
convertView = mInflater.inflate(R.layout.aks_list_item, parent, false);
holder = new ViewHolder();
holder.tv = (TextView) convertView.findViewById(R.id.tvOgun);
holder.iv = (ImageView) convertView.findViewById(R.id.ivOgun);
convertView.setTag(holder);
}
else
{
holder = (ViewHolder) convertView.getTag();
}
holder.tv.setText(items[position]);
if (holder.tv.getText().toString().endsWith("Ana Öğün"))
{
holder.iv.setImageResource(R.mipmap.ana);
}
else if (holder.tv.getText().toString().endsWith("Ara Öğün"))
{
holder.iv.setImageResource(R.mipmap.ara);
}
else if (holder.tv.getText().toString().endsWith("Ek Öğün"))
{
holder.iv.setImageResource(R.mipmap.ek);
}
return convertView;
}
static class ViewHolder
{
ImageView iv;
TextView tv;
}
}
我做错了什么?
以异步方式获取数据。这意味着Android试图为你创建一个视图，但还没有数据。所以如果你一开始就提供一个空数组，这是可行的。然后在以后的体育场中，您可以设置适配器的结果并调用适配器上的notifyDataSetChanged()。
所以首先要解决NullPointerException，适配器中的项需要一个初始值。
public class AkisArrayAdapter extends BaseAdapter {
String[] items = {};
...
...
}
那么我认为您应该将新项设置为适配器。所以给适配器添加setter
public void setItems(String[] newItems) {
this.items = newItems;
}