I have 1 listview in 1 fragment. When I call that listview in MainActivity, I get an error "java.lang.NullPointerException: Attempting to invoke virtual method 'void android.widget.AdapterView.setEmptyView (android.view.View)' on a reference object null"
Error at line:
listViewGhiChu. setEmptyView (findViewById (R.id.textViewRong)); and listViewGhiChu.setAdapter (ghiChuAdapter);
Kindly review my code and give feedback, How can I fix this?
This is my code:
**MainActivity class:**
public class MainActivity extends AppCompatActivity {
ListView listViewGhiChu;
ImageView imageViewThem;
Button buttonXoaTatCa;
public static Database database;
public static ArrayList<GhiChu> ghiChuArrayList;
public static GhiChuAdapter ghiChuAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listViewGhiChu = (ListView) findViewById(R.id.listViewGhiChu);
imageViewThem = (ImageView) findViewById(R.id.imageViewThem);
buttonXoaTatCa = (Button) findViewById(R.id.buttonXoaTatCa);
listViewGhiChu.setEmptyView(findViewById(R.id.textViewRong));
// Cài đặt ListView và Adapter
ghiChuArrayList = new ArrayList<>();
ghiChuAdapter = new GhiChuAdapter(this, R.layout.line_layout_ghichu, ghiChuArrayList);
listViewGhiChu.setAdapter(ghiChuAdapter);
// Tạo database
database = new Database(this, "GhiChu.sqlite", null, 1);
// Tạo table
database.QueryData("CREATE TABLE IF NOT EXISTS GhiChutbl(Id INTEGER PRIMARY KEY, TieuDe VARCHAR(200)" +
", NoiDung VARCHAR(200))");
LoadDuLieu();
SettupViewPager();
}
private void SettupViewPager() {
TabLayout tabLayout = findViewById(R.id.tabLayout);
PagerAdapter pagerAdapter = new PagerAdapter(getSupportFragmentManager(), tabLayout.getTabCount());
ViewPager viewPager = findViewById(R.id.viewPager);
viewPager.setAdapter(pagerAdapter);
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
}
public static void LoadDuLieu() {
// Tạo con trỏ duyệt từng phần tử trong table
Cursor cursor = database.GetData("SELECT * FROM GhiChutbl");
ghiChuArrayList.clear();
while (cursor.moveToNext()) {
int id = cursor.getInt(0);
String tieude = cursor.getString(1);
String noidung = cursor.getString(2);
ghiChuArrayList.add(new GhiChu(id, tieude, noidung));
}
ghiChuAdapter.notifyDataSetChanged();
}
**PagerAdapter class**
public class PagerAdapter extends FragmentPagerAdapter {
private int numOfTabs;
public PagerAdapter(FragmentManager fm, int numOfTabs) {
super(fm);
this.numOfTabs = numOfTabs;
}
@Override
public Fragment getItem(int i) {
switch (i) {
case 0:
return new GhiChuFragment();
case 1:
return new HinhAnhFragment();
case 2:
return new PaintFragment();
default:
return null;
}
}
@Override
public int getCount() {
return numOfTabs;
}
}
**activity_main.xml**
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".GhiChu.MainActivity">
<android.support.design.widget.TabLayout
android:id="@+id/tabLayout"
android:layout_width="359dp"
android:layout_height="46dp"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
<android.support.design.widget.TabItem
android:id="@+id/tabGhiChu"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Ghi chú" />
<android.support.design.widget.TabItem
android:id="@+id/tabHinhAnh"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hình ảnh" />
<android.support.design.widget.TabItem
android:id="@+id/tabPaint"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Vẽ" />
</android.support.design.widget.TabLayout>
<android.support.v4.view.ViewPager
android:id="@+id/viewPager"
android:layout_width="355dp"
android:layout_height="509dp"
android:layout_marginStart="4dp"
android:layout_marginLeft="4dp"
android:layout_marginTop="1dp"
android:layout_marginBottom="2dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/tabLayout"
app:layout_constraintVertical_bias="0.0" />
</android.support.constraint.ConstraintLayout>
**fragment_tab_ghi_chu.xml**
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".TabFragment.TabGhiChu">
<TextView
android:id="@+id/textViewRong"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="104dp"
android:layout_marginLeft="104dp"
android:layout_marginTop="236dp"
android:text="Chưa có nội dung"
android:textColor="#000"
android:textSize="20sp"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ListView
android:id="@+id/listViewGhiChu"
android:layout_width="359dp"
android:layout_height="477dp"
android:layout_marginStart="1dp"
android:layout_marginLeft="1dp"
android:layout_marginTop="1dp"
android:layout_marginEnd="5dp"
android:layout_marginRight="5dp"
android:layout_marginBottom="10dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ImageView
android:id="@+id/imageViewThem"
android:layout_width="65dp"
android:layout_height="55dp"
android:layout_marginEnd="8dp"
android:layout_marginRight="8dp"
android:layout_marginBottom="16dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:srcCompat="@drawable/button_add" />
<Button
android:id="@+id/buttonXoaTatCa"
android:layout_width="96dp"
android:layout_height="48dp"
android:layout_marginStart="8dp"
android:layout_marginLeft="8dp"
android:layout_marginBottom="16dp"
android:background="@drawable/custom_button"
android:text="Xóa tất cả"
android:textAllCaps="false"
android:textColor="#fff"
android:textSize="17sp"
android:textStyle="bold"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent" />
</android.support.constraint.ConstraintLayout>
