Android 在ViewPager中初始化ListView的位置
我试图在viewPager中创建一个listview(从文件夹中获取一些文件名),但初始化listview时遇到问题。 当为ListView设置适配器时,我会得到NullPointerException。 据我所知,我需要在viewPager中初始化ListView,但我已经尝试了很多东西,我仍然得到了NPE。 我必须在哪里初始化它才能停止获取NPE 因此,我在Android 在ViewPager中初始化ListView的位置,android,Android,我试图在viewPager中创建一个listview(从文件夹中获取一些文件名),但初始化listview时遇到问题。 当为ListView设置适配器时,我会得到NullPointerException。 据我所知,我需要在viewPager中初始化ListView,但我已经尝试了很多东西,我仍然得到了NPE。 我必须在哪里初始化它才能停止获取NPE 因此,我在lv1.setAdapter(adapter)处得到NullPointException 这是整个活动,以防你们需要它来解决我的问题 p
lv1.setAdapter(adapter)处得到NullPointException代码>
这是整个活动,以防你们需要它来解决我的问题
public class Gestionare extends Activity {
public List<String> myList;
public File file;
ViewPager vp;
LinearLayout gestionare1;
ListView lv1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_gestionare);
citire();
ActionBar actionBar = getActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
MyPagerAdapter adap = new MyPagerAdapter(this);
vp.setAdapter(adap);
vp.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageScrollStateChanged(int arg0) {
// TODO Auto-generated method stub
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
// TODO Auto-generated method stub
}
@Override
public void onPageSelected(int arg0) {
// TODO Auto-generated method stub
}
});
}
private class MyPagerAdapter extends PagerAdapter {
private ArrayList<LinearLayout> arry;
public MyPagerAdapter(Context context) {
arry = new ArrayList<LinearLayout>();
// arry.add(new ListView1Page(context));
arry.add(new LinearLayout(context));
// views.add(new ListView2Page(context));
arry.add(new LinearLayout(context));
// use this when design done graphically
}
@Override
public void destroyItem(View view, int arg1, Object object) {
((ViewPager) view).removeView((LinearLayout) object);
}
@Override
public int getCount() {
// TODO Auto-generated method stub
return arry.size();
}
@Override
public Object instantiateItem(View collection, int position) {
LayoutInflater inflater = (LayoutInflater) collection.getContext()
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
int resId = 0;
switch (position) {
case 0:
resId = R.layout.activity_gestionare1;
View view = inflater.inflate(resId, null);
gestionare1 = (LinearLayout) view.findViewById(R.id.gestionare1);
lv1=(ListView)view.findViewById(R.id.lv1);
((ViewPager) collection).addView(view, 0);
citire();
return view;
case 1:
resId = R.layout.activity_gestionare2;
View view2 = inflater.inflate(resId, null);
((ViewPager) collection).addView(view2, 0);
return view2;
}
return resId;}
@Override
public boolean isViewFromObject(View arg0, Object arg1) {
return arg0 == arg1;
}
public Parcelable saveState() {
return null;
}
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
Intent intent = new Intent(this, MainActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP
| Intent.FLAG_ACTIVITY_SINGLE_TOP);
startActivity(intent);
return true;
default:
return super.onOptionsItemSelected(item);
}
}
public void citire() {
myList = new ArrayList<String>();
vp = (ViewPager) findViewById(R.id.pager);
lv1=(ListView)findViewById(R.id.lv1);
File directory = android.os.Environment.getExternalStorageDirectory();
file = new File(directory.getAbsolutePath() + "/InterSRL");
File list[] = file.listFiles();
for (int i = 0; i < list.length; i++) {
myList.add(list[i].getName());
}
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, android.R.id.text1, myList);
lv1.setAdapter(adapter);
}
公共类Gestinatore扩展活动{
公开名单;
公共文件;
可视寻呼机;
线性布局示意图1;
ListView lv1;
@凌驾
创建时受保护的void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity\u-gestiatore);
citire();
ActionBar ActionBar=getActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
MyPagerAdapter adap=新的MyPagerAdapter(此);
副总裁setAdapter(adap);
vp.setOnPageChangeListener(新的OnPageChangeListener(){
@凌驾
公共无效onPageScrollStateChanged(int arg0){
//TODO自动生成的方法存根
}
@凌驾
已滚动页面上的公共void(int arg0、float arg1、int arg2){
//TODO自动生成的方法存根
}
@凌驾
已选择页面上的公共无效(int arg0){
//TODO自动生成的方法存根
}
});
}
私有类MyPagerAdapter扩展了PagerAdapter{
私人ArrayList arry;
公共MyPagerAdapter(上下文){
arry=newarraylist();
//arry.add(新列表视图1页(上下文));
添加(新的线性布局(上下文));
//添加(新的ListView2Page(上下文));
添加(新的线性布局(上下文));
//以图形方式完成设计时使用此选项
}
@凌驾
公共项(视图,int arg1,对象){
((ViewPager)视图)。移除视图((LinearLayout)对象);
}
@凌驾
public int getCount(){
//TODO自动生成的方法存根
返回arry.size();
}
@凌驾
公共对象实例化项(视图集合,int位置){
LayoutInflater充气器=(LayoutInflater)集合。getContext()
.getSystemService(上下文布局\充气机\服务);
int剩余=0;
开关(位置){
案例0:
剩余=R.layout.activity\u-gestiator1;
视图=充气机。充气(剩余,空);
Gestional1=(LinearLayout)view.findViewById(R.id.Gestional1);
lv1=(ListView)view.findViewById(R.id.lv1);
((ViewPager)集合).addView(视图,0);
citire();
返回视图;
案例1:
resId=R.layout.activity_-gestatione2;
视图2=充气机充气(剩余,空);
((ViewPager)集合).addView(view2,0);
返回视图2;
}
返回resId;}
@凌驾
公共布尔值isViewFromObject(视图arg0,对象arg1){
返回arg0==arg1;
}
公共包裹存储状态(){
返回null;
}
}
@凌驾
公共布尔值onOptionsItemSelected(菜单项项){
开关(item.getItemId()){
案例android.R.id.home:
意向意向=新意向(此,MainActivity.class);
intent.addFlags(intent.FLAG\u活动\u清除\u顶部
|意图。标记活动(单个顶部);
星触觉(意向);
返回true;
违约:
返回super.onOptionsItemSelected(项目);
}
}
公共证券(花旗银行){
myList=新的ArrayList();
vp=(ViewPager)findViewById(R.id.pager);
lv1=(ListView)findViewById(R.id.lv1);
File directory=android.os.Environment.getExternalStorageDirectory();
file=新文件(directory.getAbsolutePath()+“/InterSRL”);
文件列表[]=File.listFiles();
for(int i=0;i
}当您尝试运行citire()时,lv1
为空:
您是否尝试过将citire()
中的代码移动到instanceItem
方法中?如果将代码移到那里,可能不需要重新初始化lv1
另外,作为一个一般提示,尽量使用局部变量,这将有助于消除很多范围混淆。是的,我尝试了,我得到了这个
构造函数ArrayAdapter(gestorae.MyPagerAdapter,int,int,List)未定义问题是这个。在适配器内部时,您需要将其指向活动(上下文):gestiorae。这改变了这一点,谢谢。但在将其移动到instanceItem方法后,它仍然会给我NPE。。该死的,你把第二个findViewBYId
去掉了吗?是的,唯一的lv1=(ListView)findViewBYId(R.id.lv1)代码>位于实例化方法内部
@Override
public Object instantiateItem(View collection, int position) {
LayoutInflater inflater = (LayoutInflater) collection.getContext()
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
int resId = 0;
switch (position) {
case 0:
resId = R.layout.activity_gestionare1;
View view = inflater.inflate(resId, null);
gestionare1 = (LinearLayout) view.findViewById(R.id.gestionare1);
lv1=(ListView)view.findViewById(R.id.lv1);
((ViewPager) collection).addView(view, 0);
citire();
return view;
case 1:
resId = R.layout.activity_gestionare2;
View view2 = inflater.inflate(resId, null);
((ViewPager) collection).addView(view2, 0);
return view2;
}
return resId;}
public class Gestionare extends Activity {
public List<String> myList;
public File file;
ViewPager vp;
LinearLayout gestionare1;
ListView lv1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_gestionare);
citire();
ActionBar actionBar = getActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
MyPagerAdapter adap = new MyPagerAdapter(this);
vp.setAdapter(adap);
vp.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageScrollStateChanged(int arg0) {
// TODO Auto-generated method stub
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
// TODO Auto-generated method stub
}
@Override
public void onPageSelected(int arg0) {
// TODO Auto-generated method stub
}
});
}
private class MyPagerAdapter extends PagerAdapter {
private ArrayList<LinearLayout> arry;
public MyPagerAdapter(Context context) {
arry = new ArrayList<LinearLayout>();
// arry.add(new ListView1Page(context));
arry.add(new LinearLayout(context));
// views.add(new ListView2Page(context));
arry.add(new LinearLayout(context));
// use this when design done graphically
}
@Override
public void destroyItem(View view, int arg1, Object object) {
((ViewPager) view).removeView((LinearLayout) object);
}
@Override
public int getCount() {
// TODO Auto-generated method stub
return arry.size();
}
@Override
public Object instantiateItem(View collection, int position) {
LayoutInflater inflater = (LayoutInflater) collection.getContext()
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
int resId = 0;
switch (position) {
case 0:
resId = R.layout.activity_gestionare1;
View view = inflater.inflate(resId, null);
gestionare1 = (LinearLayout) view.findViewById(R.id.gestionare1);
lv1=(ListView)view.findViewById(R.id.lv1);
((ViewPager) collection).addView(view, 0);
citire();
return view;
case 1:
resId = R.layout.activity_gestionare2;
View view2 = inflater.inflate(resId, null);
((ViewPager) collection).addView(view2, 0);
return view2;
}
return resId;}
@Override
public boolean isViewFromObject(View arg0, Object arg1) {
return arg0 == arg1;
}
public Parcelable saveState() {
return null;
}
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
Intent intent = new Intent(this, MainActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP
| Intent.FLAG_ACTIVITY_SINGLE_TOP);
startActivity(intent);
return true;
default:
return super.onOptionsItemSelected(item);
}
}
public void citire() {
myList = new ArrayList<String>();
vp = (ViewPager) findViewById(R.id.pager);
lv1=(ListView)findViewById(R.id.lv1);
File directory = android.os.Environment.getExternalStorageDirectory();
file = new File(directory.getAbsolutePath() + "/InterSRL");
File list[] = file.listFiles();
for (int i = 0; i < list.length; i++) {
myList.add(list[i].getName());
}
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, android.R.id.text1, myList);
lv1.setAdapter(adapter);
}
setContentView(R.layout.activity_gestionare);
citire();