I Custom ListView Layouts(my_list_item,xml) to show my data. It doesnt work. Before I show in acyivity_main.xml, still work. I already create a adapter for list view.
I am a newer of android studio. Maybe is simple question. I try long time still cannot fix. thanks
The error
2020-03-21 00:13:18.227 20079-20079/au.edu.utas.sqlite E/AndroidRuntime: FATAL EXCEPTION: main
Process: au.edu.utas.sqlite, PID: 20079
java.lang.RuntimeException: Unable to start activity ComponentInfo{au.edu.utas.sqlite/au.edu.utas.sqlite.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at au.edu.utas.sqlite.MainActivity.onCreate(MainActivity.java:57)
at android.app.Activity.performCreate(Activity.java:6679)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
MainActivity.java
public class MainActivity extends AppCompatActivity
{
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.my_list_item);
//Open the database, so that we can read and write
Database databaseConnection = new Database(this);
final SQLiteDatabase db = databaseConnection.open();
Property property1 = new Property();
property1.setAddress("742 Evergreen Terrace");
property1.setBedrooms(4); property1.setPrice(250000);
Property property2 = new Property();
property2.setAddress("4352 Wisteria Lane"); property2.setBedrooms(5);
property2.setPrice(500000);
PropertyTable.insert(db, property1);
PropertyTable.insert(db, property2);
final ArrayList<Property> properties = PropertyTable.selectAll(db);
// for(Property element: properties){
// System.out.println(element);
// }
//
// Log.d("TAG", "The debugging message.");
//List parts!
ListView myList = findViewById(R.id.myList);
final PropertyAdapter propertyListAdapter = new PropertyAdapter(getApplicationContext(), R.layout.my_list_item , properties);
myList.setAdapter(propertyListAdapter);
myList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
}
});
}
}
Property.java
public class Property {
private int mPropertyID;
private String mAddress;
private int mPrice, mBedrooms;
public int getPropertyID() { return mPropertyID; }
public void setPropertyID(int s) { this.mPropertyID = s; }
public String getAddress() { return mAddress; }
public void setAddress(String add) { this.mAddress = add; }
public int getPrice() {return mPrice; }
public void setPrice(int pri) {this.mPrice = pri; }
public int getBedrooms() { return mBedrooms; }
public void setBedrooms(int bed) { this.mBedrooms = bed; }
}
PropertyTable.java
public class PropertyTable<c> {
public static final String TABLE_NAME = "property";
public static final String KEY_PROPERTY_ID = "property_id";
public static final String KEY_ADDRESS = "address";
public static final String KEY_PRICE = "price";
public static final String KEY_BEDROOMS = "bedrooms";
public static final String CREATE_STATEMENT = "CREATE TABLE " + TABLE_NAME
+ " (" + KEY_PROPERTY_ID + " integer primary key autoincrement, "
+ KEY_ADDRESS + " string not null, "
+ KEY_PRICE + " int not null, "
+ KEY_BEDROOMS + " string not null " +");";
public static Property createFromCursor(Cursor c) {
if (c == null || c.isAfterLast() || c.isBeforeFirst()) {
return null; }
else {
Property p = new Property();
p.setPropertyID(c.getInt(c.getColumnIndex(KEY_PROPERTY_ID)));
p.setAddress(c.getString(c.getColumnIndex(KEY_ADDRESS)));
p.setPrice(c.getInt(c.getColumnIndex(KEY_PRICE)));
p.setBedrooms(c.getInt(c.getColumnIndex(KEY_BEDROOMS)));
return p;
} }
public static void insert(SQLiteDatabase db, Property p) {
ContentValues values = new ContentValues();
values.put(KEY_ADDRESS, p.getAddress());
values.put(KEY_PRICE, p.getPrice());
values.put(KEY_BEDROOMS, p.getBedrooms());
db.insert(TABLE_NAME, null, values); }
public static ArrayList<Property> selectAll(SQLiteDatabase db) {
ArrayList<Property> results = new ArrayList<Property>();
Cursor c = db.query(TABLE_NAME, null, null, null, null, null, null);
if (c != null) {
c.moveToFirst();
while (!c.isAfterLast()) {
Property p = createFromCursor(c);
results.add(p);
c.moveToNext();
}
}
return results;
}
PropertyAdapter.java
public class PropertyAdapter extends ArrayAdapter<Property> {
private int mLayoutResourceID;
public PropertyAdapter(Context context, int resource, List<Property> objects)
{
super(context, resource, objects);
this.mLayoutResourceID = resource;
}
@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
LayoutInflater layoutInflater = (LayoutInflater) getContext().getSystemService(Service.LAYOUT_INFLATER_SERVICE) ;
View row = layoutInflater.inflate(mLayoutResourceID, parent, false);
Property p = this.getItem(position);
// TextView textView = row.findViewById(android.R.id.text1);
// textView.setText(p.getPropertyID()+": "+p.getAddress());
TextView lblAddress = row.findViewById(R.id.lblAddress);
lblAddress.setText(p.getAddress());
TextView lblBedrooms = row.findViewById(R.id.lblBedrooms);
lblBedrooms.setText(""+p.getBedrooms());
TextView lblPrice = row.findViewById(R.id.lblPrice);
lblPrice.setText("$"+p.getPrice());
return row;
}
}
my_list_item.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="40dp"
android:orientation="horizontal">
<TextView
android:id="@+id/lblAddress"
android:layout_width="80dp"
android:layout_height="40dp"
android:text="lbTitle" />
<TextView
android:id="@+id/lblPrice"
android:layout_width="match_parent"
android:layout_height="40dp"
android:gravity="right"
android:text="lbPrice" />
</LinearLayout>
<TextView
android:id="@+id/lblBedrooms"
android:layout_width="250dp"
android:layout_height="40dp"
android:gravity="right"
android:text="lbBedrooms" />
</LinearLayout>
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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="au.edu.utas.sqlite.MainActivity">
<ListView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/myList" />
</androidx.constraintlayout.widget.ConstraintLayout>
