【发布时间】：2014-04-19 01:55:53
【问题描述】：
正如标题所说，我想知道什么会导致 setadapter() 方法导致 nullexception。我正在编写一个 android 应用程序，我正在尝试填充一个列表视图， 这是我的自定义列表适配器：
private class MyListAdapter extends ArrayAdapter<Grade> {
ArrayList<Student> studentList;
public MyListAdapter(ArrayList<Student> studentlist) {
super(ShowExamActivity.this, R.layout.exam_grade_list_view, theList);
studentList = studentlist;
Log.e("Set Adapter1","Passed");
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View itemView = convertView;
Log.e("before evrything", "!!!!!!!");
if(itemView == null){
itemView = getLayoutInflater().inflate(R.layout.exam_grade_list_view, parent, false);
}
Log.e("before Loop","Inside");
Grade grade = theList.get(position);
Student student = new Student();
for(int i =0; i<studentList.size(); i++){
for(int j =0; j<studentList.get(i).getGradeList().size(); j++){
if(grade.getGrade() == studentList.get(i).getGradeList().get(j).getGrade() && studentList.get(i).getGradeList().get(j).getName().equals(grade)){
student = studentList.get(i);
studentList.remove(i);
break;
}
}
}
Log.e("passed Loop","Inside");
//Fill Name
TextView name = (TextView) itemView.findViewById(R.id.name);
name.setText(student.getFirstName());
Log.e("Set Adapter3","Passed");
//Fill Street
TextView Grade = (TextView) itemView.findViewById(R.id.grade);
Grade.setText(grade.getGrade());
Log.e("Set Adapter4","Passed");
return itemView;
}
这是根据 LogCat 出现空异常的 OnCreate()：
public class ShowExamActivity extends Activity {
TextView average;
TextView stddev;
TextView max;
TextView min;
Exam exam = new Exam();
DSLL<Grade> gradeList = new DSLL<Grade>();
ArrayList<Grade> theList = new ArrayList<Grade>();
DSLL<Student> studentList = new DSLL<Student>();
ArrayList<Student> studentTheList = new ArrayList<Student>();
int position;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_show_exam);
// Show the Up button in the action bar.
setupActionBar();
average = (TextView) findViewById(R.id.nametextview);
stddev = (TextView) findViewById(R.id.lastnametextview);
max = (TextView) findViewById(R.id.max);
min = (TextView) findViewById(R.id.min);
try{
Intent i = getIntent();
exam = (Exam) i.getSerializableExtra("clickedExam");
}
catch (Exception e){
Log.e("problema","con serializacion");
}
average.setText(Double.toString(exam.getAvg()));
stddev.setText(Double.toString(exam.getStdDev()));
max.setText(Double.toString(exam.getMax()));
min.setText(Double.toString(exam.getMin()));
gradeList = exam.getGradelist();
studentList = exam.getStudentlist();
if(gradeList.size() != 0){
ListView lv =(ListView)findViewById(R.id.gradeList);
Log.e("Listview!","created!!!!");
for(int i=0;i<gradeList.size();i++){
theList.add(gradeList.get(i));
}
for(int i=0;i<studentList.size();i++){
studentTheList.add(studentList.get(i));
}
Log.e("for Loop Finished",Integer.toString(studentTheList.size()));
Log.e("for Loop Finished",Integer.toString(theList.size()));
MyListAdapter adapter = new MyListAdapter(studentTheList);
Log.e("ArrayAdapter","Created");
lv.setAdapter(adapter);
Log.e("Set Adapter","Passed");
}
}
出现nullexception的部分在lv.setAdapter(adapter)中
这是我的日志：
04-18 21:17:41.510: E/AndroidRuntime(2318): FATAL EXCEPTION: main
04-18 21:17:41.510: E/AndroidRuntime(2318): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.student_lists/com.example.student_lists.ShowExamActivity}: java.lang.NullPointerException
04-18 21:17:41.510: E/AndroidRuntime(2318): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1960)
04-18 21:17:41.510: E/AndroidRuntime(2318): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1985)
04-18 21:17:41.510: E/AndroidRuntime(2318): at android.app.ActivityThread.access$600(ActivityThread.java:127)
04-18 21:17:41.510: E/AndroidRuntime(2318): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1151)
04-18 21:17:41.510: E/AndroidRuntime(2318): at android.os.Handler.dispatchMessage(Handler.java:99)
04-18 21:17:41.510: E/AndroidRuntime(2318): at android.os.Looper.loop(Looper.java:137)
04-18 21:17:41.510: E/AndroidRuntime(2318): at android.app.ActivityThread.main(ActivityThread.java:4447)
04-18 21:17:41.510: E/AndroidRuntime(2318): at java.lang.reflect.Method.invokeNative(Native Method)
04-18 21:17:41.510: E/AndroidRuntime(2318): at java.lang.reflect.Method.invoke(Method.java:511)
04-18 21:17:41.510: E/AndroidRuntime(2318): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
04-18 21:17:41.510: E/AndroidRuntime(2318): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
04-18 21:17:41.510: E/AndroidRuntime(2318): at dalvik.system.NativeStart.main(Native Method)
04-18 21:17:41.510: E/AndroidRuntime(2318): Caused by: java.lang.NullPointerException
04-18 21:17:41.510: E/AndroidRuntime(2318): at com.example.student_lists.ShowExamActivity.onCreate(ShowExamActivity.java:80)
04-18 21:17:41.510: E/AndroidRuntime(2318): at android.app.Activity.performCreate(Activity.java:4466)
04-18 21:17:41.510: E/AndroidRuntime(2318): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1092)
04-18 21:17:41.510: E/AndroidRuntime(2318): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1924)
04-18 21:17:41.510: E/AndroidRuntime(2318): ... 11 more
【问题讨论】：
-
列表视图为空。这意味着它不在您设置为布局的 xml 文件中，或者您使用了错误的 id。
-
您确定 R.id.gradelist 在 activity_show_exam.xml 文件中吗？
-
你是对的！非常感谢！固定！
标签： android android-intent android-listview custom-adapter