NullPointerException：尝试在空对象引用上调用虚方法＆＃39; void android.widget.ListView.setAdapter

Question

我试图用我的数组服务填充listView，数组服务填充了＆＃34;概念＆＃34;和＆＃34; priceDo＆＃34;从EditText获取的变量，它被初始化的服务数组。我已经在stackOverflow和Google搜索了这里，但我找不到有用的东西。 当我编译并运行应用程序时，它会抛出空指针 在这一行：

mainListView.setAdapter(my);

这是我的代码：

public class ConceptsActivity extends AppCompatActivity{
private int i=0;
private AutoCompleteTextView actv;
private TextView tvConcept;
private TextView tvConcept2;
private TextView warning;
private TextView tvPrice;
private EditText price;
private Button addConcept;
private String concept;
private double priceDo;
private List<AddConceptsListView> myConcept = new ArrayList<AddConceptsListView>();
private Service[] service = new Service[100];
private ListView mainListView ;

public ConceptsActivity(){

}

public ConceptsActivity(Service service[]){
    this.service = service;
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    setTitle(R.string.TitleSer);
    super.onCreate(savedInstanceState);
    setContentView(R.layout.concepts_layout);

    for(int j=0; j<service.length; j++){
        service[j] = new Service();
        if(service[j].getName() != null){
            i++;
        }
    }
    mainListView = (ListView) findViewById( R.id.list2 );

    actv = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextViewConcept);
    tvConcept = (TextView) findViewById(R.id.textViewConcept);
    tvConcept2 = (TextView) findViewById(R.id.textViewConcept2);
    warning = (TextView) findViewById(R.id.textViewWarning);
    tvPrice = (TextView) findViewById(R.id.textViewPrice);
    price = (EditText) findViewById(R.id.editTextPrice);
    addConcept = (Button) findViewById(R.id.buttonAddConcept);

    //Autocomplete Textview
    String[] services = getResources().getStringArray(R.array.services_array);
    ArrayAdapter<String> adapter =
            new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, services);
    actv.setAdapter(adapter);

    actv.setOnEditorActionListener(new TextView.OnEditorActionListener() {
        @Override
        public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
            boolean handled = false;
            if (actionId == EditorInfo.IME_ACTION_DONE) {
                //make items visible
                tvConcept.setVisibility(View.VISIBLE);
                tvConcept2.setVisibility(View.VISIBLE);
                tvPrice.setVisibility(View.VISIBLE);
                price.setVisibility(View.VISIBLE);
                addConcept.setVisibility(View.VISIBLE);

                concept = actv.getText()+"";
                tvConcept2.setText(concept);
                //To hide the keyboard
                InputMethodManager imm = (InputMethodManager) v.getContext().getSystemService(Context.INPUT_METHOD_SERVICE);
                imm.hideSoftInputFromWindow(v.getWindowToken(), 0);

                handled = true;
            }
            return handled;
        }
    });
}

public void onClickAddConcept(View view){
    if(price.getText().toString().equals("")){
        warning.setVisibility(View.VISIBLE);
    }
    else {
        warning.setVisibility(View.INVISIBLE);

        priceDo = Double.parseDouble(price.getText().toString());
        Toast.makeText(getApplicationContext(),"Precio: " + priceDo+ "" + "\n"
                + "Concepto: " + concept,Toast.LENGTH_SHORT).show();

        service[i].setName(concept);
        service[i].setPrice(priceDo);
        i++;

        for(int j=0; j<service.length; j++){
            if(service[j].getName() != null || service[j].getPrice() != null){
                Toast.makeText(getApplicationContext(), "Array" + j + "nameConcept: " + service[j].getName() +
                        "\n" + "Array price: " + service[j].getPrice(), Toast.LENGTH_SHORT).show();
            }
        }
    }

    ArrayAdapter<Service> my = new ArrayAdapter<Service>(this, android.R.layout.simple_list_item_1, service);
    mainListView.setAdapter(my);

}

}