NullPointerException学生类组织者android

-1

所以我正在为学生做一个简单的班级经理，我无法弄清楚这一点。从主要活动中有一个按钮来添加一个班级，该班级将带您进入添加班级活动，该班级活动有一个添加学生按钮，可让您进入添加学生活动。当我保存学生时，通过返回添加课程活动并将学生姓名添加到名册列表视图中，它可以正常工作。但由于某种原因，当我保存该类时，返回主活动时出现nullPointerException。如果有人有任何想法，我会非常感谢帮助。NullPointerException学生类组织者android

这里的主要活动：

public class MainActivity extends Activity { 

ListView classList; 
Button addClass; 
ArrayAdapter<String> adapterClass; 
ArrayList<Class> currClasses = new ArrayList<Class>(); 
ArrayList<String> currClassNames = new ArrayList<String>(); 
ClassesSingleton myClasses; 
int REQUEST_CODE_ADD = 318; 
int REQUEST_CODE_EDIT = 319; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    classList = (ListView) findViewById(R.id.classList); 
    final Context context = this; 
    adapterClass = new ArrayAdapter<String>(this, R.layout.single_list_item, R.id.label, currClassNames); 

    classList.setAdapter(adapterClass); 

    addClass = (Button) this.findViewById(R.id.addClass); 

    classList.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
     public void onItemClick(AdapterView <?> arg0, View view, int position, long id){ 
      Intent intent = new Intent(MainActivity.this, ShowClass.class); 
      startActivityForResult(intent, REQUEST_CODE_EDIT); 
     } 
    }); 

    addClass.setOnClickListener(new OnClickListener() { 

     public void onClick(View arg0){ 
      Intent intent = new Intent(MainActivity.this, AddClass.class); 
      startActivityForResult(intent, REQUEST_CODE_ADD); 
     } 
    }); 
} 

protected void onActivityResult(int requestCode, int resultCode, Intent data){ 
    super.onActivityResult(requestCode, resultCode, data); 

    if(resultCode == RESULT_OK && requestCode == REQUEST_CODE_ADD){ 
     Class newClass = new Class(); 
     if(data.hasExtra("className")){ 
      newClass.setName(data.getExtras().getString("name")); 
     } 
     if(data.hasExtra("number")){ 
      newClass.setNumber(data.getExtras().getInt("number")); 
     } 
     if(data.hasExtra("students")){ 
      ArrayList<Student> s = data.getExtras().getParcelableArrayList("students"); 
      newClass.setStudents(s); 
     } 
     if(data.hasExtra("names")){ 
      ArrayList<String> sn = data.getExtras().getStringArrayList("names"); 
      newClass.setStudentNames(sn); 
     } 

     myClasses = ClassesSingleton.getInstance(); 
     updateClassList(newClass, newClass.getName()); 
     myClasses.setClassArray(currClasses); 
     myClasses.setClassNames(currClassNames); 
    } 

    //else if(resultCode == RESULT_OK && requestCode == REQUEST_CODE_EDIT){ 

    //} 
} 

public void updateClassList(Class n, String s){ 

    adapterClass = null; 
    currClasses.add(n); 
    currClassNames.add(s); 
    adapterClass = new ArrayAdapter<String>(this, R.layout.single_list_item, R.id.label, currClassNames); 
    classList.setAdapter(adapterClass); 
    adapterClass.notifyDataSetChanged(); 
} 
}

这里的添加类活动：

public class AddClass extends Activity{ 

Button addStudent, saveClass, cancelClass; 
EditText className, classNumber; 
ListView studentList; 
ArrayAdapter<String> adapterStudent; 
ArrayList<Student> currStudents = new ArrayList<Student>(); 
ArrayList<String> studNames = new ArrayList<String>(); 
int REQUEST_CODE_ADDSTU = 317; 
int REQUEST_CODE_EDSTU = 316; 

public void onCreate(Bundle savedInstanceState){ 
    super.onCreate(savedInstanceState); 
    Intent intent = getIntent(); 
    setContentView(R.layout.new_class); 

    addStudent = (Button) findViewById(R.id.addStudent); 
    saveClass = (Button) findViewById(R.id.confirmClassAdd); 
    cancelClass = (Button) findViewById(R.id.cancelClass); 
    className = (EditText) findViewById(R.id.newClassName); 
    classNumber = (EditText) findViewById(R.id.newClassNumber); 
    studentList = (ListView) findViewById(R.id.newStudentList); 
    adapterStudent = new ArrayAdapter<String>(this, R.layout.single_list_item, R.id.label, studNames); 

    studentList.setAdapter(adapterStudent); 

    studentList.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
     public void onItemClick(AdapterView <?> arg0, View view, int position, long id){ 
      Intent intent2 = new Intent(AddClass.this, EditStudent.class); 
      startActivityForResult(intent2, REQUEST_CODE_EDSTU); 
     } 
    }); 

    addStudent.setOnClickListener(new OnClickListener() { 

     public void onClick(View arg0){ 
      Intent intent2 = new Intent(AddClass.this, AddStudent.class); 
      startActivityForResult(intent2, REQUEST_CODE_ADDSTU); 
     } 
    }); 

    saveClass.setOnClickListener(new OnClickListener() { 
     public void onClick(View arg0){ 
      Intent data = new Intent(); 
      int numData = 0; 
      if(className.getText().toString().matches("") != true && classNumber.getText().toString().matches("") != true && currStudents.isEmpty() != true && studNames.isEmpty() != true){ 
       String nameData = className.getText().toString(); 
       String numStr = classNumber.getText().toString(); 
       ArrayList<Student> students = currStudents; 
       ArrayList<String> studentNames = studNames; 

       boolean intTrue = true; 
       try{ 
        numData = Integer.parseInt(numStr); 
       }catch(NumberFormatException e){ 
        Toast.makeText(AddClass.this, "Please be sure to enter a numberic value in the number field.", Toast.LENGTH_LONG).show(); 
        intTrue = false; 
       } 

       if(intTrue){ 
        data.putExtra("className", nameData); 
        data.putExtra("number", numData); 
        data.putStringArrayListExtra("names", studentNames); 
        data.putParcelableArrayListExtra("students", students); 
        setResult(RESULT_OK, data); 
        finish(); 
       } 
      } 
      else{ 
       Toast.makeText(AddClass.this, "Don't leave your class name, number field, or student roster blank!", Toast.LENGTH_LONG).show(); 
      } 
     } 
    }); 
} 

//onActivityResult callback 
protected void onActivityResult(int requestCode, int resultCode, Intent data){ 
    super.onActivityResult(requestCode, resultCode, data); 

    if(resultCode == RESULT_OK && requestCode == REQUEST_CODE_ADDSTU){ 
     Student newStudent = new Student(); 
     if(data.hasExtra("name")){ 
      newStudent.setName(data.getExtras().getString("name")); 
     } 
     if(data.hasExtra("id")){ 
      newStudent.setId(data.getExtras().getInt("id")); 
     } 

     updateStudentList(newStudent, newStudent.getName()); 
    } 
} 

public void updateStudentList(Student s, String n){ 
    adapterStudent = null; 
    currStudents.add(s); 
    studNames.add(n); 
    adapterStudent = new ArrayAdapter<String>(this, R.layout.single_list_item, R.id.label, studNames); 
    studentList.setAdapter(adapterStudent); 
    adapterStudent.notifyDataSetChanged(); 
} 

}

这里的附加学生活动：

public class AddStudent extends Activity{ 

EditText studentName, studentId; 
Button saveStudent, cancelStudent; 

public void onCreate(Bundle savedInstanceState){ 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.new_student); 

    studentName = (EditText) findViewById(R.id.newStudentName); 
    studentId = (EditText) findViewById(R.id.newStudentId); 
    saveStudent = (Button) findViewById(R.id.confirmStudentAdd); 
    cancelStudent = (Button) findViewById(R.id.cancelStudent); 

    saveStudent.setOnClickListener(new OnClickListener() { 
     public void onClick(View arg0){ 
      Intent data = new Intent(); 
      int idData = 0; 

      if(studentName.getText().toString().matches("") != true && studentId.getText().toString().matches("") != true){ 
       String nameData = studentName.getText().toString(); 
       String idStr = studentId.getText().toString(); 

       boolean intTrue = true; 
       try{ 
        idData = Integer.parseInt(idStr); 
       }catch(NumberFormatException e){ 
        Toast.makeText(AddStudent.this, "Please be sure to enter a numeric value in the ID field.", Toast.LENGTH_LONG).show(); 
        intTrue = false; 
       } 

       if(intTrue){ 
        data.putExtra("name", nameData); 
        data.putExtra("id", idData); 
        setResult(RESULT_OK, data); 
        finish(); 
       } 
      } 
      else{ 
       Toast.makeText(AddStudent.this, "Don't leave your student name or ID field blank!", Toast.LENGTH_LONG).show(); 
      } 
     } 
    }); 
} 
}

这里的堆栈跟踪：

FATAL EXCEPTION: main 
Process: com.example.congelassign2, PID: 1664 
java.lang.NullPointerException 
at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:394) 
at android.widget.ArrayAdapter.getView(ArrayAdapter.java:362) 
at android.widget.AbsListView.obtainView(AbsListView.java:2263) 
at android.widget.ListView.makeAndAddView(ListView.java:1790) 
at android.widget.ListView.fillDown(ListView.java:691) 
at android.widget.ListView.fillFromTop(ListView.java:752) 
at android.widget.ListView.layoutChildren(ListView.java:1616) 
at android.widget.AbsListView.onLayout(AbsListView.java:2091) 
at android.view.View.layout(View.java:14785) 
at android.view.ViewGroup.layout(ViewGroup.java:4631) 
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671) 
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525) 
at android.widget.LinearLayout.onLayout(LinearLayout.java:1434) 
at android.view.View.layout(View.java:14785) 
at android.view.ViewGroup.layout(ViewGroup.java:4631) 
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453) 
at android.widget.FrameLayout.onLayout(FrameLayout.java:388) 
at android.view.View.layout(View.java:14785) 
at android.view.ViewGroup.layout(ViewGroup.java:4631) 
at com.android.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:374) 
at android.view.View.layout(View.java:14785) 
at android.view.ViewGroup.layout(ViewGroup.java:4631) 
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453) 
at android.widget.FrameLayout.onLayout(FrameLayout.java:388) 
at android.view.View.layout(View.java:14785) 
at android.view.ViewGroup.layout(ViewGroup.java:4631) 
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:1985) 
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1742) 
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998) 
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5582) 
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749) 
at android.view.Choreographer.doCallbacks(Choreographer.java:562) 
at android.view.Choreographer.doFrame(Choreographer.java:532) 
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735) 
at android.os.Handler.handleCallback(Handler.java:733) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:137) 
at android.app.ActivityThread.main(ActivityThread.java:4998) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:515) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593) 
at dalvik.system.NativeStart.main(Native Method)

来源

2014-03-03 user3349697

调试我的朋友。 – NewUser

哪个方法抛出exception.Exception堆栈跟踪不清 – Kick

哪一行抛出错误？ – Piyush

看着异常看起来像'ListView classList'不是在onCreate方法中使用的初始化。

来源

2014-03-03 06:12:52 Mak

它显示错误，因为您试图在您的ArrayAdapter类中显示自定义布局。要使用ArrayAdapter中的自定义布局，您需要创建单独的自定义适配器类，该类可以扩展ArrayAdapter类并将布局充气到该适配器类中。

你试图夸大布局的方式是错误的，这就是为什么你得到错误at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:394)因为它将引用android布局将数据绑定到列表视图。

此外，您的ArrayList ArrayList<String> currClassNames = new ArrayList<String>();和ArrayList<String> studNames = new ArrayList<String>();都为空。

来源

2014-03-03 06:13:20 GrIsHu

NullPointerException学生类组织者android

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