这里我想创建一个包含listview的应用程序。 我已经定义了使用此列表视图所需的所有内容，但我不知道为什么，当我运行应用程序时，我收到了此错误报告：
处理：com.gook.ever_ncn.cashflow，PID：11882 java.lang.RuntimeException：无法启动活动ComponentInfo {com.gook.ever_ncn.cashflow / com.gook.ever_ncn.cashflow.Reminder}：java.lang.NullPointerException：尝试调用虚方法＆＃39; void android.widget .ListView.setAdapter（android.widget.ListAdapter）＆＃39;在null对象引用上 在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2325） 在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2390） 在android.app.ActivityThread.access $ 800（ActivityThread.java:151） 在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1303） 在android.os.Handler.dispatchMessage（Handler.java:102） 在android.os.Looper.loop（Looper.java:135） 在android.app.ActivityThread.main（ActivityThread.java:5257） at java.lang.reflect.Method.invoke（Native Method） 在java.lang.reflect.Method.invoke（Method.java:372） 在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:903） 在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:698） 引起：java.lang.NullPointerException：尝试调用虚方法＆＃39; void android.widget.ListView.setAdapter（android.widget.ListAdapter）＆＃39;在null对象引用上 在com.gook.ever_ncn.cashflow.Reminder.displayData（Reminder.java:83） 在com.gook.ever_ncn.cashflow.Reminder.onCreate（Reminder.java:54）
我知道它只是一个空指针异常，但我再次检查我的代码很多次，我认为它不会有空指针异常错误。
请高手帮帮我，我必须做些什么？
先谢谢。
NB。到目前为止，这是我的代码Reminder.java（包含listview的活动）：
public class Reminder extends ActionBarActivity {
Button btnReminder;
Button btnDateReminder;
EditText txtRemindAbout;
private ListView listRemind;
static final int DIALOG_ID=0;
private ArrayList<String> arrRemindId = new ArrayList<String>();
private ArrayList<String> arrRemindDateMentah = new ArrayList<String>();
private ArrayList<String> arrRemindDate = new ArrayList<String>();
private ArrayList<String> arrRemindAbout = new ArrayList<String>();
SQLiteDatabase db;
DatabaseHelper dBHelper = new DatabaseHelper(this);
private AlertDialog.Builder build;
public static String month, monthZ, dayZ ;
public static String dateSelected, dateSelectedShow;
int year_x, month_x, day_x;
private boolean isUpdateTrans;
String id, dateMentah, dateShow, about;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_reminder);
listRemind = (ListView) findViewById(android.R.id.list);
btnDateReminder = (Button)findViewById(R.id.btnDateRemind);
btnReminder = (Button) findViewById(R.id.btnAddTrans);
displayData();
onButtonClickButtonListener();
onLongClickListener();
selectDate();
}
private void displayData() {
db = dBHelper.getReadableDatabase();
Cursor mCursor = db.rawQuery("SELECT * FROM " + dBHelper.TABLE_Reminder_NAME + " WHERE DateMentah = "+dateSelected, null);
arrRemindId.clear();
arrRemindDateMentah.clear();
arrRemindDate.clear();
arrRemindAbout.clear();
if (mCursor.moveToFirst()) {
do {
arrRemindId.add(mCursor.getString(mCursor.getColumnIndex(dBHelper.ROL1)));
arrRemindDateMentah.add(mCursor.getString(mCursor.getColumnIndex(dBHelper.ROL2)));
arrRemindDate.add(mCursor.getString(mCursor.getColumnIndex(dBHelper.ROL3)));
arrRemindAbout.add(mCursor.getString(mCursor.getColumnIndex(dBHelper.ROL4)));
} while (mCursor.moveToNext());
}
DisplayAdapterRemind disadptr = new DisplayAdapterRemind(Reminder.this, arrRemindId, arrRemindDateMentah, arrRemindDate,
arrRemindAbout);
//listRemind = (ListView) listRemind.findViewById(R.id.listRemind);
listRemind = (ListView) findViewById(android.R.id.list);
listRemind.setAdapter(disadptr);
mCursor.close();
listRemind.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
id = arrRemindId.get(arg2);
dateSelected = arrRemindDateMentah.get(2);
dateSelectedShow = arrRemindDate.get(2);
txtRemindAbout.setText(arrRemindAbout.get(2));
isUpdateTrans = true;
// belum di coba, klo nda bisa yaudh dsni tampung pke string dlu baru lempar ke method lain nanti disana
//yang dateSelectedShwo di set ke Btn nya
}
});
}
public void updateReminder(){
Bundle bundle= getIntent().getExtras();
if(bundle!= null) {
isUpdateTrans = getIntent().getExtras().getBoolean("update");
if (isUpdateTrans) {
System.out.print("isUpdate di NewTrans");
id = getIntent().getExtras().getString("remindId");
dateMentah = getIntent().getExtras().getString("dateMentah");
dateShow = getIntent().getExtras().getString("dateShow");
about = getIntent().getExtras().getString("about");
btnDateReminder.setText(dateShow);
}
}
}
public void onButtonClickButtonListener() {
btnReminder.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
if (isUpdateTrans) {
//update
boolean isInserted = dBHelper.updateReminder(id, dateSelected, dateSelectedShow,
txtRemindAbout.getText().toString(), null);
if (isInserted == true) {
clearText();
Toast.makeText(Reminder.this, "Updated", Toast.LENGTH_LONG).show();
} else
Toast.makeText(Reminder.this, "Not Inserted", Toast.LENGTH_LONG).show();
} else {
//insert
boolean isInserted = dBHelper.insertReminder(dateSelected, dateSelectedShow,
txtRemindAbout.getText().toString(), null);
if (isInserted == true) {
clearText();
Toast.makeText(Reminder.this, "Inserted", Toast.LENGTH_LONG).show();
} else
Toast.makeText(Reminder.this, "Not Inserted", Toast.LENGTH_LONG).show();
}
}
});
}
private void selectDate(){
final Calendar cal = Calendar.getInstance();
SimpleDateFormat df = new SimpleDateFormat("dd-MM-yyyy");
String date = df.format(cal.getTime());
year_x = cal.get(Calendar.YEAR);
month_x = cal.get(Calendar.MONTH);
day_x = cal.get(Calendar.DAY_OF_MONTH);
switchMonth(month_x + 1);
monthZero(month_x + 1);
dayZero(day_x);
btnDateReminder = (Button)findViewById(R.id.btnDate);
btnDateReminder.setText("Date : " + date);
//btnIDate.setText("Date : " + day_x + "-" + month + "-" + year_x);
dateSelected = (year_x+"-"+monthZ+"-"+dayZ);
dateSelectedShow = dayZ + "-" +month+"-"+year_x;
}
@Override
protected Dialog onCreateDialog(int id){
if (id == DIALOG_ID)
return new DatePickerDialog(this, dpickerListener , year_x, month_x, day_x);
return null;
}
public DatePickerDialog.OnDateSetListener dpickerListener
= new DatePickerDialog.OnDateSetListener() {
@Override
public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) {
year_x= year;
month_x = monthOfYear + 1;
day_x = dayOfMonth;
switchMonth(month_x);
monthZero(month_x);
dayZero(day_x);
Log.d("Month", "Anjret" + month_x);
btnDateReminder.setText("Date : " + day_x + "-" + month + "-" + year_x);
dateSelected = (year_x+"-"+monthZ+"-"+dayZ);
dateSelectedShow = dayZ + "-" +month+"-"+year_x;
displayData();
}
};
private void onLongClickListener(){
ListView list = (ListView)findViewById(android.R.id.list);
list.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
public boolean onItemLongClick(AdapterView<?> arg0, View arg1, final int arg2, long arg3) {
build = new AlertDialog.Builder(Reminder.this);
build.setTitle("Delete " + arrRemindAbout.get(arg2));
build.setMessage("Do you want to delete ?");
build.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
Toast.makeText(getApplicationContext(),
arrRemindId.get(arg2) + " is deleted.", Toast.LENGTH_LONG).show();
db.delete(
dBHelper.TABLE_Trans_NAME, dBHelper.TOL1 + "=" + arrRemindId.get(arg2), null);
//String catSelected = mainAct.getCatSelected();
displayData();
dialog.cancel();
}
});
build.setNegativeButton("No", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
AlertDialog alert = build.create();
alert.show();
return true;
}
});
}
private String switchMonth(Integer month_x){
switch(month_x){
case 1 : month = "Jan";
break;
case 2 : month = "Feb";
break;
case 3 : month = "Mar";
break;
case 4 : month = "Apr";
break;
case 5 : month = "Mei";
break;
case 6 : month = "Jun";
break;
case 7 : month = "Jul";
break;
case 8 : month = "Aug";
break;
case 9 : month = "Sep";
break;
case 10 : month = "Okt";
break;
case 11 : month = "Nov";
break;
case 12 : month = "Des";
break;
}
return month;
}
private String monthZero(Integer month_x){//untuk nambahin 0 di depan bulan satu bilangan
switch(month_x){
case 1 : monthZ = "0"+month_x;
break;
case 2 : monthZ = "0"+month_x;
break;
case 3 : monthZ = "0"+month_x;
break;
case 4 : monthZ = "0"+month_x;
break;
case 5 : monthZ = "0"+month_x;
break;
case 6 : monthZ = "0"+month_x;
break;
case 7 : monthZ = "0"+month_x;
break;
case 8 : monthZ = "0"+month_x;
break;
case 9 : monthZ = "0"+month_x;
break;
case 10 : monthZ = String.valueOf(month_x);
break;
case 11 : monthZ = String.valueOf(month_x);
break;
case 12 : monthZ = String.valueOf(month_x);
break;
}
return monthZ;
}
private String dayZero(Integer day_x){//untuk nambahin 0 di depan bulan satu bilangan
if(day_x < 10){
switch(day_x) {
case 1:
dayZ = "0" + day_x;
break;
case 2:
dayZ = "0" + day_x;
break;
case 3:
dayZ = "0" + day_x;
break;
case 4:
dayZ = "0" + day_x;
break;
case 5:
dayZ = "0" + day_x;
break;
case 6:
dayZ = "0" + day_x;
break;
case 7:
dayZ = "0" + day_x;
break;
case 8:
dayZ = "0" + day_x;
break;
case 9:
dayZ = "0" + day_x;
break;
}
}else{
dayZ = String.valueOf(month_x);
}
return dayZ;
}
private void clearText() {
txtRemindAbout.setText("");
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_reminder, menu);
return true;
}
@Override
public void onBackPressed()
{
super.onBackPressed();
startActivity(new Intent(Reminder.this, MainActivity.class));
finish();
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if(id == android.R.id.home){
finish();
}
switch (id) {
case R.id.action_settings:
Intent intentCategSetting = new Intent(Reminder.this, CategorySetting.class);
startActivity(intentCategSetting);
finish();
break;
case R.id.menu_rate:
Toast.makeText(Reminder.this, "Rate Broo", Toast.LENGTH_LONG);
break;
case R.id.menu_about:
Intent intentAbout = new Intent(Reminder.this, AboutUs.class);
startActivity(intentAbout);
finish();
break;
} return super.onOptionsItemSelected(item);
}
}
activity_reminder.xml文件：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.gook.ever_ncn.cashflow.Reminder">
<include
android:id="@+id/app_bar"
layout="@layout/app_bar"
/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Reminder List"
android:id="@+id/textView14"
android:layout_below="@+id/app_bar"
android:layout_centerHorizontal="true"
android:layout_marginTop="40dp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="New Reminder"
android:id="@+id/textView18"
android:layout_marginBottom="60dp"
android:layout_above="@+id/editText3"
android:layout_alignRight="@+id/btnRemindMe"
android:layout_alignEnd="@+id/btnRemindMe" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/editText3"
android:hint="Reminder About"
android:layout_above="@+id/btnRemindMe"
android:layout_centerHorizontal="true" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Remind Me"
android:id="@+id/btnRemindMe"
android:layout_marginBottom="53dp"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:background="@drawable/custom_button"/>
<Button
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Date"
android:id="@+id/btnDateRemind"
android:layout_above="@+id/editText3"
android:layout_centerHorizontal="true"
android:background="@drawable/custom_button"/>
<ListView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/listRemind"
android:layout_below="@+id/textView14"
android:layout_centerHorizontal="true"
android:layout_above="@+id/textView18" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="Reminder"
android:id="@+id/textView19"
android:textColor="#f325272f"
android:textStyle="bold"
android:layout_below="@+id/app_bar"
android:layout_centerHorizontal="true" />
答案 0 :(得分：1)
你在这里做错了
listRemind = (ListView) findViewById(android.R.id.list);
应该是
listRemind = (ListView) findViewById(R.id.listRemind);
答案 1 :(得分：0)
在你的活动的onCreate（）中
ListView listRemind = findViewById(R.id.listRemind);
这是你在运行时得到空引用的原因......