I would like to have the working ListView from the MainActivity in the ExpAct (2.Activity).
What I have: Edittext and a Button that creates a new entry to a Listview upon clicking.
The ListView on MainAct is just for checking and will be deleted if ExpAct works.
Upon clicking the "next"Btn I get to ExpAct.
I get a raw use parameter warning. -- And if I were to fix that, it gives me an NPE-crash for the ExpAct, or an empty ListView.
Is the issue that the getter Intent for the String/Array doesnt work? Or does it lie with the creation of the ArrayAdapter?
MainActivity.java
public class MainActivity extends AppCompatActivity {
ListView LV1;
ArrayList < String > listExp;
Button button1, btnext;
EditText ETbc;
ArrayAdapter < String > arrayAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
LV1 = findViewById(R.id.LV1);
button1 = findViewById(R.id.button1);
ETbc = findViewById(R.id.ETbc);
listExp = new ArrayList < String > ();
arrayAdapter = new ArrayAdapter < String > (getApplicationContext(),
android.R.layout.simple_list_item_1, listExp);
button1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String names = ETbc.getText().toString();
listExp.add(names);
LV1.setAdapter(arrayAdapter);
arrayAdapter.notifyDataSetChanged();
Intent inter = new Intent(MainActivity.this, ExpAct.class);
inter.putExtra("key", listExp);
setResult(Activity.RESULT_OK, inter);
}
});
btnext = findViewById(R.id.btnext);
btnext.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, ExpAct.class);
startActivity(intent);
finish();
}
});
}
}
*ExpAct.java: *
public class ExpAct extends MainActivity {
ListView LV2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_exp);
Intent i = getIntent();
listExp = i.getStringArrayListExtra("key");
LV2 = findViewById(R.id.LV2);
ArrayAdapter arrayAdapter = new ArrayAdapter < String > (getApplicationContext(),
android.R.layout.simple_list_item_1, R.id.LV2, listExp); // here without R.id.LV2
LV2.setAdapter(arrayAdapter);
}
}
Logs since it has become red.
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.testcheckbox, PID: 20358
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.testcheckbox/com.example.testcheckbox.ExpAct}.
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2724)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2789)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1527)
at android.os.Handler.dispatchMessage(Handler.java:110)
at android.os.Looper.loop(Looper.java:203)
at android.app.ActivityThread.main(ActivityThread.java:6255)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1063)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:924)
Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:344)
at android.widget.ListView.setAdapter(ListView.java:510)
at com.example.testcheckbox.ExpAct.onCreate(ExpAct.java:27)
at android.app.Activity.performCreate(Activity.java:6670)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2677)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2789)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1527)
at android.os.Handler.dispatchMessage(Handler.java:110)
at android.os.Looper.loop(Looper.java:203)
at android.app.ActivityThread.main(ActivityThread.java:6255)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1063)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:924)
Disconnected from the target VM, address: 'localhost:57662', transport: 'socket'
It looks like you're trying to start the activity without putting the ArrayList as an extra.
btnext = findViewById(R.id.btnext);
btnext.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, ExpAct.class);
// You need to put the extra data here:
intent.putExtra("key", listExp);
startActivity(intent);
finish();
}
});
When you get a NullPointerException, you should first check why would the list be null:
Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
So after looking at your code, I saw that you're not passing the ArrayList with the intent.