nullpointerexception

问题 Basically this app is supposed to ask for your name, with an option to save, which when click, an alert dialog pops up and asks 'are you sure?', when yes is clicked, it should say 'welcome + whatever name put'. my problem is that the app keeps shutting down before it says welcome. I declared the string as userName and ran it without any function to the string, and it just said 'welcome, null'. but when i did userName=editText.getText().toString(); the app shut down immediately. Please HELP I

问题 I have 4 images as buttons and when the correct button is selected, an arrow button appears which is working fine. My problem is that I'm trying to change the background resource of each button to change when this arrow is clicked but I'm getting a null pointer exception at this line : happybutton.setBackgroundResource(R.drawable.mum1); I have declared the nextArrow button in my java onCreate - nextArrow = (Button) findViewById(R.id.nextArrow); nextArrow.setOnClickListener(onClickListener);

问题 I get nullpointerexception when I try to fill a 2D array with process IDs, it is 2D since there is a unlimited list of PIDs for each system and I need to eventually return that back to my main code (set to void now since just a prototype test function). Any ideas would be great private void testfunctionA (List<String> additionalPC) { // A 2d array that will contain a list of pids for each system - needs to be strings and not integers String[][] pidCollection = new String[additionalPC.size()][

问题 I have a listview that shows the contents of an arraylist. I'm using a simple adaptor to make this possible like so. public static ArrayList<String> homeScreenContacts = new ArrayList<String>(); ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.home_screen_contacts_view, NewContact.homeScreenContacts); The second line is giving me a null pointer exception. I thought about it and I decided it was because the arrayList is empty. So I added the following line between the

问题 Somehow, I cannot add items to my ComboBox variable from another class as it always says either the value of variable is null or the return value of its getter is null. I use Scene Builder to build Sample.fxml, with controller as Controller class, luanch the whole thing form UserInterface class FXML <?xml version="1.0" encoding="UTF-8"?> <?import javafx.scene.control.ComboBox?> <?import javafx.scene.layout.BorderPane?> <BorderPane xmlns="http://javafx.com/javafx/11.0.1" xmlns:fx="http:/

问题 If I have a line like this: var.getSomething().getSomethingElse().setNewValue(stuff.getValue().getWhatever()); If that line creates a NullPointerException , is there any way of finding out which method is returning a null value? I believe I was able to split the line at every dot and get the exception showing which line was failing. But I can't get that to work anymore (maybe I remember incorrectly). Is the only good debugging possibility to write it like this? a = var.getSomething(); b = a

问题 I'm trying to mock a file creation , FileWriter operation and CsvWriter operation. I'm using EasyMock to mock file creation , PowerMockito to mock FileWriter and CSVWriter operations. Even after mocking the file creation, junit showing NullPointerException.. My code is, package example.mypackage.rms.utility; import java.io.FileNotFoundException; import java.io.FileWriter; import java.io.IOException; import au.com.bytecode.opencsv.CSVWriter; public class CSVBeanUtil { public static boolean

问题 I've got a float array camObjCoord declared as.. public static float camObjCoord[] = new float[8000]; I'm then filling it's indexes in a class that does something like the following.. camObjCoord[1] = 2.5; I'm then calling makeview() public void makeview() { Intent myIntent = new Intent(this, GLCamTest.class); this.startActivity(myIntent); Bundle b = new Bundle(); b.putFloatArray("tweets", camObjCoord); } and then in the new class it's doing... public void onCreate(Bundle savedInstanceState)

问题 I simply want to call a Fragment method from my MainActivity. So I tried to use an Interface. public interface MyInterface { void testMethod(); } In my Fragment (TestFragment.java) I implement the interface and overrite the testMethod method. @Override public void testMethod() { Toast.makeText(getActivity(), "Test", Toast.LENGTH_LONG).show(); } but now I want to call this method from my MainActivity as soon as the onRewardedVideoCompleted get's called, but I'm not sure how to do it. I tried

问题 I'm creating an Android application. The problem is that when I press the button and pass the data to the new array, it goes to black and giving me this error: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.add (java.lang.Object) 'on a null object reference By debugging, it gives me something in the string: mExampleList.add(Ticket) My ExampleAdapter class: public class ExampleAdapter extends RecyclerView.Adapter<ExampleAdapter