我创建了一个由教师列表视图组成的应用程序，其中数据是sqlite。当我点击其中一个列表视图时，将显示教师的个人资料，其中有一个学生列表。 BTW教师的个人资料有一个滚动，因为它有很多信息。我申请the top answer here，因此列表视图将自动延长，具体取决于教师的学生人数。但是当我申请时，我得到了错误。我将在下面发布错误和我的代码。
public class MainActivity extends AppCompatActivity {
Button btnback, btnnext, btnbackprofile;
TextView profileteacher;
List<TeacherModel> GetAllTeacher;
List<StudentModel> GetTeacherStudent;
Context context = this;
DatabaseHelper dbhelper;
DatabaseHelper db = new DatabaseHelper(this);
ListView lv,lv2;
View TeacherListView,TeacherProfileView;
int index = 0;
private int currentPageIndex = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbhelper = new DatabaseHelper(MainActivity.this);
try{
dbhelper.createDataBase();
}
catch(IOException e){
e.printStackTrace();
}
try {
dbhelper.openDataBase();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//Till here
GetAllTeacher = dbhelper.getAllTeacher(index);
lv = (ListView) findViewById(R.id.teacher_list);
lv.setAdapter(new ViewAdapter());
/****************************************************************************************
* TEACHER PROFILE
****************************************************************************************/
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view,final int i, long l) {
GetTeacherStudent = dbhelper.getTeacherStudent(GetAllTeacher.get(i).getid());
TeacherListView = findViewById(R.id.teacherlayout);
ViewGroup parent = (ViewGroup) TeacherListView.getParent();
parent.removeView(TeacherListView);
// inflate your profile view (or get the reference to it if it's already inflated)
TeacherProfileView = getLayoutInflater().inflate(R.layout.profile_teacher, parent, false);
// add it to the parent
parent.addView(TeacherProfileView);
ListView listView = (ListView)view.findViewById(R.id.profileStudentList);
setListViewHeightBasedOnChildren(listView);
listView.setAdapter(new ViewAdapter2());
btnbackprofile = (Button) findViewById(R.id.profileTeacherBack);
btnbackprofile.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (TeacherProfileView != null && TeacherProfileView.getParent() != null) {
// remove your profile view
ViewGroup parent = (ViewGroup) TeacherProfileView.getParent();
parent.removeView(TeacherProfileView);
// a reference to yourListView has to be saved somewhere; just get it
// add your listview to the parent
parent.addView(TeacherListView);
} else {
}
}
});
profileteacher = (TextView) findViewById(R.id.profileTeacherName);
profileteacher.setText(GetAllTeacher.get(i).getname());
}
});
btnback = (Button) findViewById(R.id.teacherBack);
btnnext = (Button) findViewById(R.id.teacherNext);
btnback.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View convertView) {
currentPageIndex -= 20;
GetAllTeacher = dbhelper.getAllTeacher(currentPageIndex);
lv = (ListView) findViewById(R.id.teacher_list);
lv.setAdapter(new ViewAdapter());
}
});
btnnext.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View convertView) {
currentPageIndex += 20;
GetAllTeacher = dbhelper.getAllTeacher(currentPageIndex);
lv = (ListView) findViewById(R.id.teacher_list);
lv.setAdapter(new ViewAdapter());
}
});
}
/****************************************************************************************
* CODE IN THE LINK THAT I APPLY
****************************************************************************************/
public static void setListViewHeightBasedOnChildren(ListView listView) {
ListAdapter listAdapter = listView.getAdapter();
if (listAdapter == null)
return;
int desiredWidth = View.MeasureSpec.makeMeasureSpec(listView.getWidth(), View.MeasureSpec.UNSPECIFIED);
int totalHeight = 0;
View view = null;
for (int i = 0; i < listAdapter.getCount(); i++) {
view = listAdapter.getView(i, view, listView);
if (i == 0)
view.setLayoutParams(new ViewGroup.LayoutParams(desiredWidth, AbsListView.LayoutParams.WRAP_CONTENT));
view.measure(desiredWidth, View.MeasureSpec.UNSPECIFIED);
totalHeight += view.getMeasuredHeight();
}
ViewGroup.LayoutParams params = listView.getLayoutParams();
params.height = totalHeight + (listView.getDividerHeight() * (listAdapter.getCount() - 1));
listView.setLayoutParams(params);
}
/****************************************************************************************
* CUSTOM LIST
****************************************************************************************/
public class ViewAdapter extends BaseAdapter {
LayoutInflater mInflater;
public ViewAdapter() {
mInflater = LayoutInflater.from(context);
}
@Override
public int getCount() {
return GetAllTeacher.size();
}
@Override
public Object getItem(int position) {
return null;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = mInflater.inflate(R.layout.item_teacher,null);
}
final TextView names = (TextView) convertView.findViewById(R.id.teacherlist_name);
final TextView gender = (TextView) convertView.findViewById(R.id.teacherlist_gender);
names.setText("Dr. "+GetAllTeacher.get(position).getname());
gender.setText(GetAllTeacher.get(position).getgender());
return convertView;
}
}
public class ViewAdapter2 extends BaseAdapter {
LayoutInflater mInflater;
public ViewAdapter2() {
mInflater = LayoutInflater.from(context);
}
@Override
public int getCount() {
return GetTeacherStudent.size();
}
@Override
public Object getItem(int position) {
return null;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = mInflater.inflate(R.layout.item_teacherstudent,null);
}
final TextView names = (TextView) convertView.findViewById(R.id.teacherlist_name);
names.setText(GetTeacherStudent.get(position).getstudent());
return convertView;
}
}
}
错误
尝试调用虚方法'android.widget.ListAdapter android.widget.ListView.getAdapter（）'在null对象引用上 com.example.jathniel.studentlist.MainActivity.setListViewHeightBasedOnChildren（MainActivity.java:243） 在 com.example.jathniel.studentlist.MainActivity $ 1.onItemClick（MainActivity.java:100）
第243行：ListAdapter listAdapter = listView.getAdapter（）;
第100行：setListViewHeightBasedOnChildren（listView）;
答案 0 :(得分：2)
为什么要在setListViewHeightBasedOnChildren中输入列表视图，将其更改为setListViewHeightBasedOnChildren()，并在oncreate() ListView listView = (ListView)view.findViewById(R.id.profileStudentList);中声明
然后试试
修改
在你的方法中将其更改为：
public static void setListViewHeightBasedOnChildren() {
ListAdapter listAdapter = listView.getAdapter();
if (listAdapter == null)
return;
和oncreate（）方法
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbhelper = new DatabaseHelper(MainActivity.this);
listView = (ListView)findViewById(R.id.profileStudentList);
答案 1 :(得分：0)
交换您的第100行和第101行。 作为第101行设置适配器到listView。
第100行尝试从listView获取适配器。
但是在第100行的时候，没有适配器设置为列表视图。所以它会抛出空指针异常。
所以代码就像这样
listView.setAdapter(new ViewAdapter2());
setListViewHeightBasedOnChildren(listView);