![](/img/trans.png)
[英]Sending json data into db and display in listview throws “null pointer exception”
[英]Listview button click throws null pointer exception
在我的UpdateSupervitionActivity
類中, CallAdapter()
方法來生成listview
。 listview
的每個item
都有一個按鈕,用於刪除item
。 加載listview
后,當我嘗試通過單擊列表視圖按鈕從listview
刪除項目時,它將引發nullpointer
異常,並且應用程序崩潰。
具有CallAdapter()方法的Java類 :
package bd.edu.bubt.regup;
public class UpdateSupervitionActivity extends AppCompatActivity {
EditText fac_code, s_intake, s_section;
ListView listView;
Button search, addlist, update;
Spinner shift;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_update_supervition);
fac_code = (EditText) findViewById(R.id.sh_code);
s_intake = (EditText) findViewById(R.id.intake);
s_section = (EditText) findViewById(R.id.section);
listView = (ListView) findViewById(R.id.faclistview);
shift = (Spinner) findViewById(R.id.shift);
addlist = (Button) findViewById(R.id.addlist);
search = (Button) findViewById(R.id.search);
update = (Button) findViewById(R.id.update);
}
public void CallAdapter(Context context)
{
adapterlist.clear();
if(daylist.size() == 0)
{
//no intake list for day shift
if(evelist.size() == 0)
{
//no intake list for evening shift
}
else if(evelist.size() > 0)
{
for (int i=0;i<evelist.size();i++)
{
String s = evelist.get(i);
int p = s.indexOf("-");
String intake = s.substring(0,p);
String section = s.substring(p+1,s.length());
adapterlist.add(new UpdateSupervisionItem(intake, section, "Evening"));
}
}
}
else if(daylist.size() > 0)
{
for (int i=0;i<daylist.size();i++)
{
String s = daylist.get(i);
int p = s.indexOf("-");
String intake = s.substring(0,p);
String section = s.substring(p+1,s.length());
adapterlist.add(new UpdateSupervisionItem(intake, section, "Day"));
}
if(evelist.size() == 0)
{
//no intake list for evening shift
}
else if(evelist.size() > 0)
{
for (int i=0;i<evelist.size();i++)
{
String s = evelist.get(i);
int p = s.indexOf("-");
String intake = s.substring(0,p);
String section = s.substring(p+1,s.length());
adapterlist.add(new UpdateSupervisionItem(intake, section, "Evening"));
}
}
}
UpdateSupervisionAdapter updateSupervisionAdapter = new UpdateSupervisionAdapter(context, R.layout.update_supervision_list_view_layout, adapterlist);
listView.setAdapter(updateSupervisionAdapter);
}
}
適配器類:
package bd.edu.bubt.regup;
public class UpdateSupervisionAdapter extends ArrayAdapter<UpdateSupervisionItem> {
ArrayList<UpdateSupervisionItem> adapterlist = new ArrayList<>();
Context context;
public UpdateSupervisionAdapter(Context context, int textViewResourceId, ArrayList<UpdateSupervisionItem> objects) {
super(context, textViewResourceId, objects);
this.context = context;
adapterlist = objects;
}
@Override
public int getCount() {
return super.getCount();
}
@Override
public View getView(final int position, View convertView, ViewGroup parent){
View v = convertView;
LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
v = inflater.inflate(R.layout.update_supervision_list_view_layout, null);
TextView intake = (TextView) v.findViewById(R.id.intake);
TextView section = (TextView) v.findViewById(R.id.section);
TextView shift = (TextView) v.findViewById(R.id.shift);
final Button remove = (Button) v.findViewById(R.id.remove);
remove.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Animation animation = AnimationUtils.loadAnimation(getContext(), R.anim.blink_anim);
remove.startAnimation(animation);
UpdateSupervisionItem updateSupervisionItem = getItem(position);
String in_take = updateSupervisionItem.getIntake();
String sec_tion = updateSupervisionItem.getSection();
String shi_ft = updateSupervisionItem.getShift();
UpdateSupervitionActivity updateSupervitionActivity = new UpdateSupervitionActivity();
if(TextUtils.equals(shi_ft,"Day"))
{
updateSupervitionActivity.daylist.remove(in_take+ "-" +sec_tion);
updateSupervitionActivity.CallAdapter(context);
}
else if(TextUtils.equals(shi_ft,"Evening"))
{
updateSupervitionActivity.evelist.remove(in_take+ "-" +sec_tion);
updateSupervitionActivity.CallAdapter(context);
}
}
});
intake.setText("Intake: " +adapterlist.get(position).getIntake());
section.setText("Section: " +adapterlist.get(position).getSection());
shift.setText("Shift: " +adapterlist.get(position).getShift());
return v;
}
}
錯誤日志:
FATAL EXCEPTION: main
Process: bd.edu.bubt.regup, PID: 31219
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at bd.edu.bubt.regup.UpdateSupervitionActivity.CallAdapter(UpdateSupervitionActivity.java:352)
at bd.edu.bubt.regup.UpdateSupervisionAdapter$1.onClick(UpdateSupervisionAdapter.java:70)
at android.view.View.performClick(View.java:5637)
at android.view.View$PerformClick.run(View.java:22429)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
出現此錯誤的原因是id找不到listview。 看來您的適配器是首先從另一個活動初始化的,這是使用listview進行布局的真實上下文。 有兩種解決方法:1)您應該通過以下方法在更新類中初始化listview
ListView listView = context.findViewById(R.id.faclistview)
2)您可以將CallAdapter移到適配器的實際上下文活動中
更新嘗試:
ListView listView = (ListView) ((ActivityWhereAdapterIsForstInitialized) context).findViewById(R.id.faclistview)
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.