好吧，我创建了自己的custumadapter类以便在listview中使用，我在第178行得到了一个nullpointerexception，它说“if（inputSearch.getText（）。toString（）。isEmpty（））” 有人可以帮我看看为什么我会这样做吗？
这是我的代码：
package com.example.student_lists;
import java.util.ArrayList;
import java.util.Locale;
import com.resources.student_list.Student;
import android.app.ActionBar;
import android.app.FragmentTransaction;
import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.NavUtils;
import android.support.v4.view.ViewPager;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.Filter;
import android.widget.Filterable;
import android.widget.ListView;
import android.widget.TextView;
public class MainActivity extends FragmentActivity implements ActionBar.TabListener {
/**
* The {@link android.support.v4.view.PagerAdapter} that will provide
* fragments for each of the sections. We use a
* {@link android.support.v4.app.FragmentPagerAdapter} derivative, which
* will keep every loaded fragment in memory. If this becomes too memory
* intensive, it may be best to switch to a
* {@link android.support.v4.app.FragmentStatePagerAdapter}.
*/
SectionsPagerAdapter mSectionsPagerAdapter;
/**
* The {@link ViewPager} that will host the section contents.
*/
ViewPager mViewPager;
EditText inputSearch;
// static ListView lv;
// static EditText inputSearch;
//static MyListAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Set up the action bar.
final ActionBar actionBar = getActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
// Create the adapter that will return a fragment for each of the three
// primary sections of the app.
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mSectionsPagerAdapter);
// When swiping between different sections, select the corresponding
// tab. We can also use ActionBar.Tab#select() to do this if we have
// a reference to the Tab.
mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
@Override
public void onPageSelected(int position) {
actionBar.setSelectedNavigationItem(position);
}
});
// For each of the sections in the app, add a tab to the action bar.
for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
// Create a tab with text corresponding to the page title defined by
// the adapter. Also specify this Activity object, which implements
// the TabListener interface, as the callback (listener) for when
// this tab is selected.
actionBar.addTab(
actionBar.newTab()
.setText(mSectionsPagerAdapter.getPageTitle(i))
.setTabListener(this));
}
}
private class MyListAdapter extends ArrayAdapter<Student> implements Filterable{
private final Context context;
public ArrayList<Student> displayValues;
public ArrayList<Student> originalValues;
public MyListAdapter(Context context, int textViewResourceId, ArrayList<Student> values) {
super(context, textViewResourceId, values);
this.context = context;
this.displayValues = values;
this.originalValues = (ArrayList<Student>) values.clone();
}
public int getCount(){
return this.displayValues.size();
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
//----This method sets each row of the list individually----
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View itemView = inflater.inflate(R.layout.list_view, parent, false);
if(displayValues.size() > 0)
{
Student student = displayValues.get(position);
// //Fill Name
TextView name = (TextView) itemView.findViewById(R.id.contactName);
name.setText(student.getFirstName() + " " + student.getLastName());
}
return itemView;
}
public Filter getFilter() {
Filter contactFilter = new Filter() {
@Override
protected FilterResults performFiltering(CharSequence constraint) {
FilterResults filterResults = new FilterResults();
ArrayList<Student> filteredList = new ArrayList<Student>();
//Filter the list
if(constraint != null && originalValues !=null) {
if(!constraint.toString().isEmpty())
{
String constraintLowerCase = constraint.toString().toLowerCase();
for(Student c: originalValues)
{
String cName = c.getFirstName().toLowerCase() ;
String cLName = c.getLastName().toLowerCase();
if(cName.startsWith(constraintLowerCase) || cLName.startsWith(constraintLowerCase))
{
//Add the row to the list if filtered items
filteredList.add(c);
}
}
}
//Important steps to store the filtered list
filterResults.values = filteredList;
filterResults.count = filteredList.size();
}
return filterResults;
}
@SuppressWarnings("unchecked")
@Override
protected void publishResults(CharSequence contraint, FilterResults results) {
if (results.count > 0)
{
//Display the filtered list
MyListAdapter.this.displayValues = (ArrayList<Student>) results.values;
notifyDataSetChanged();
}
else
{
if(inputSearch.getText().toString().isEmpty())
{
//Display the original list
MyListAdapter.this.displayValues = (ArrayList<Student>) MyListAdapter.this.originalValues.clone();
}
else
{
//Display an empty list
MyListAdapter.this.displayValues.clear();
}
notifyDataSetInvalidated();
}
}
};
return contactFilter;
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
// When the given tab is selected, switch to the corresponding page in
// the ViewPager.
mViewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
}
@Override
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
}
/**
* A {@link FragmentPagerAdapter} that returns a fragment corresponding to
* one of the sections/tabs/pages.
*/
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a DummySectionFragment (defined as a static inner class
// below) with the page number as its lone argument.
Fragment fragment = new DummySectionFragment();
Bundle args = new Bundle();
args.putInt(DummySectionFragment.ARG_SECTION_NUMBER, position + 1);
fragment.setArguments(args);
return fragment;
}
@Override
public int getCount() {
// Show 3 total pages.
return 3;
}
@Override
public CharSequence getPageTitle(int position) {
Locale l = Locale.getDefault();
switch (position) {
case 0:
return getString(R.string.title_section1).toUpperCase(l);
case 1:
return getString(R.string.title_section2).toUpperCase(l);
case 2:
return getString(R.string.title_section3).toUpperCase(l);
}
return null;
}
}
/**
* A dummy fragment representing a section of the app, but that simply
* displays dummy text.
*/
public static class DummySectionFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
public static final String ARG_SECTION_NUMBER = "section_number";
public DummySectionFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main_dummy, container, false);
switch(getArguments().getInt(ARG_SECTION_NUMBER)){
case 0:
case 1:
Student andres = new Student();
andres.setFirstName("Andres");
andres.setLastName("Blanco");
Student ondria = new Student();
ondria.setFirstName("Ondria");
ondria.setLastName("Arias");
ArrayList<Student> studentList = new ArrayList<Student>();
studentList.add(andres);
studentList.add(ondria);
MainActivity mainactivity = new MainActivity();
ListView lv = (ListView) rootView.findViewById(R.id.list);
final MyListAdapter adapter = mainactivity.new MyListAdapter(getActivity(), R.layout.list_view, studentList);
lv.setAdapter(adapter);
lv.setTextFilterEnabled(true);
EditText inputSearch = (EditText) rootView.findViewById(R.id.inputSearch);
inputSearch.addTextChangedListener(new TextWatcher() {
@Override
public void onTextChanged(CharSequence cs, int arg1, int arg2, int arg3) {
// When user changed the Text
adapter.getFilter().filter(cs);
}
@Override
public void beforeTextChanged(CharSequence arg0, int arg1, int arg2,
int arg3) {
// TODO Auto-generated method stub
}
@Override
public void afterTextChanged(Editable arg0) {
// TODO Auto-generated method stub
}
});
return rootView;
case 2:
}
return rootView;
}
}
}
答案 0 :(得分：3)
您需要首先初始化EditText：
@Override
protected void onCreate(Bundle savedInstanceState) {
EditText inputSearch = (EditText) this.findViewById(R.id.inputSearch);
}
然后，而不是：
if (inputSearch.getText().toString().isEmpty())
你应该这样做：
if (inputSearch.getText() != null) {
// Do something
} else {
// Do something else
}
答案 1 :(得分：1)
我不知道你在哪里初始化inputSearch。如果您没有初始化它，那么它将是null，当您在其上调用getText()时，您将收到NullPointerException。
修改
你有这一行：
EditText inputSearch = (EditText) rootView.findViewById(R.id.inputSearch);
这只是一个局部变量，与inputSearch中的变量不同publishResults将此行更改为
inputSearch = (EditText) rootView.findViewById(R.id.inputSearch);