Question

好的，这是我的第一篇文章，所以请耐心等待。我搜索过并试过很多东西。我认为另一组眼睛可能会看到我没有的东西。当我调用getText（）函数时，我得到了NPE。我已经包含了我的代码的缩小版本，但同样的错误正在发生。我甚至看到我有正确的观点任何帮助将不胜感激。

MainActivity.java

const string MathCourseName = "Math";

var Student1 = new Student("Alice");
Student1.Infos.Add(new Info(MathCourseName, 4));

var Student2 = new Student("Bob");
Student2.Infos.Add(new Info(MathCourseName, 2));

var Student3 = new Student("Cesar");
Student3.Infos.Add(new Info("English", 3));

var repository = new StudentRepository();

repository.Add(Student1);
repository.Add(Student2);
repository.Add(Student3);

foreach(var kvp in repository.GetCoursesByStudentName(MathCourseName)) {
    Console.WriteLine(kvp.Key + ": " + kvp.Value.Course + " - " + kvp.Value.Grade); 
}

var bobsMathGrade = repository.GetGrade("Bob", MathCourseName);
Console.WriteLine("Bobs math grade: " + bobsMathGrade);

task_add_operations.xml

public class MainActivity extends AppCompatActivity {
   private ArrayList<Task> taskList;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
      setSupportActionBar(toolbar);

      FloatingActionButton fab = (FloatingActionButton)findViewById(R.id.fab);
      fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            LayoutInflater inflater2 = (LayoutInflater)getBaseContext()
                    .getSystemService(LAYOUT_INFLATER_SERVICE);

            View customView2 = inflater2.inflate(R.layout.task_add_operations,null);

            final PopupWindow mPopupWindow2 = new PopupWindow(customView2,
                    RelativeLayout.LayoutParams.WRAP_CONTENT,
                    RelativeLayout.LayoutParams.WRAP_CONTENT, true);


            Button closeButton2 = (Button)customView2.findViewById(R.id.closeButton2);
            closeButton2.setOnClickListener(new Button.OnClickListener() {
                @Override
                public void onClick(View view) {
                    mPopupWindow2.dismiss();
                }
            });

            Button addButton = (Button)customView2.findViewById(R.id.addButton);
            addButton.setOnClickListener(new Button.OnClickListener() {
                @Override
                public void onClick(View customView2) {
                    EditText text = customView2.findViewById(R.id.editText);

                    //This is where my java.lang.NullPointerException pops
                    String title = text.getText().toString();

                    taskList = Task.addTask(taskList, title);

                    mPopupWindow2.dismiss();

                }
            });
            mPopupWindow2.showAtLocation(findViewById(R.id.activityMain),
                    CENTER,0, 0);
        }
    });
}

Answer 1

您需要绑定EditText外addButton.setOnClickListener

EditText text =(EditText) customView2.findViewById(R.id.editText);

或尝试更改view public void onClick(View View2)方法的名称，如下面的代码

Button addButton = (Button)customView2.findViewById(R.id.addButton);
            addButton.setOnClickListener(new Button.OnClickListener() {
                @Override
                public void onClick(View View2) {
                    EditText text = (EditText)customView2.findViewById(R.id.editText);

                    //This is where my java.lang.NullPointerException pops
                    String title = text.getText().toString();

                    taskList = Task.addTask(taskList, title);

                    mPopupWindow2.dismiss();

                }
            });

Answer 2

从查看其他Stack Overflow帖子：

Null Pointer Exception - Getting EditText Value

您可能希望尝试在EditText

中声明OnCreate()

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button addButton = (Button)customView2.findViewById(R.id.addButton);
    EditText text = customView2.findViewById(R.id.editText);            
    addButton.setOnClickListener(new Button.OnClickListener() {
            @Override
            public void onClick(View customView2) {


                //This is where my java.lang.NullPointerException pops
                String title = text.getText().toString();

                taskList = Task.addTask(taskList, title);

                mPopupWindow2.dismiss();

            }
        });

当我尝试获取EditText的文本时，它会抛出一个Null Pointer Exception。

2 个答案: