无法使用ViewPager和FragmentPagerAdapter访问片段视图
[英]Unable to access View of Fragment with ViewPager and FragmentPagerAdapter
问题描述
Trying to learn Android development by poking around so please forgive if the query is too simple. 
尝试通过探索来学习Android开发，所以如果查询太简单，请原谅。
I have the following code which keeps crashing due to NullPointerException - I hve tried several ways to access the View of the Fragment but I always get null. 我有以下代码，由于NullPointerException导致崩溃 - 我已经尝试了几种方法来访问片段的视图，但我总是得到null。 Can anyone help me out with what I'm doing wrong? 任何人都能帮我解决我做错的事吗？
What I'm trying to do is save the contents of the EditText to SharedPreferences when the page is scrolled. 我正在尝试做的是在滚动页面时将EditText的内容保存到SharedPreferences。 For the life of me, I can't seem to access the View of the fragment that is loaded when the tab is displayed. 对于我的生活，我似乎无法访问显示选项卡时加载的片段的视图。
public class ViewPagerAdapter extends FragmentPagerAdapter {
final int PAGE_COUNT = 3;
// Tab Titles
private String tabtitles[] = new String[] { "Profile", "Address",
"Security"};
Context context;
public ViewPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public int getCount() {
return PAGE_COUNT;
}
@Override
public Fragment getItem(int position) {
switch (position) {
// Open FragmentTab1.java
case 0:
CreateUserFragmentProfile fragmenttab1 = new
CreateUserFragmentProfile();
return fragmenttab1;
// Open FragmentTab2.java
case 1:
CreateUserFragmentLocation fragmenttab2 = new
CreateUserFragmentLocation();
return fragmenttab2;
// Open FragmentTab3.java
case 2:
CreateUserFragmentSecurity fragmenttab3 = new
CreateUserFragmentSecurity();
return fragmenttab3;
}
return null;
}
@Override
public CharSequence getPageTitle(int position) {
return tabtitles[position];
}
}
The Fragment code extends Fragment, and does pretty much nothing. Fragment代码扩展了Fragment，并且几乎没有做任何事情。
public class CreateUserFragmentSecurity extends Fragment {
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup
container, @Nullable Bundle savedInstanceState) {
//return super.onCreateView(inflater, container,
savedInstanceState);
View view = inflater.inflate(R.layout.create_fragment_security,
container, false);
return view;
}
public void storeData(){
}
}
The Activity code is as follows: 活动代码如下：
public class CreateUser extends AppCompatActivity {
public SharedPreferences preferences;
public SharedPreferences.Editor editor;
public View currView;
public String fname, lname, dob, gender, email, addr1, addr2, addr3,
addrstate, city, passwd, passwdPlain;
public Long mobile, pin;
//public FragmentPagerAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_create_user);
preferences = getSharedPreferences("Reviv", MODE_PRIVATE);
editor = preferences.edit();
// Locate the viewpager in activity_create_user.xml
final ViewPager viewPager = (ViewPager) findViewById(R.id.pager);
// Set the ViewPagerAdapter into ViewPager
final FragmentPagerAdapter adapter = new
ViewPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(adapter);
viewPager.setOffscreenPageLimit(3);
viewPager.addOnPageChangeListener(new
ViewPager.OnPageChangeListener() {
@Override
public void onPageScrolled(int position, float positionOffset,
int positionOffsetPixels) {
boolean hasChanged = false;
switch (position){ // store data on tab switch
case 0: // Profile tab
//currView =
viewPager.getChildAt(viewPager.getCurrentItem()); // returns
null
currView =
adapter.getItem(viewPager.getCurrentItem()).getView(); //
crashes, returns null
EditText etFname =
currView.findViewById(R.id.etFname);
fname = etFname.getText().toString();
hasChanged = false;
if(!StringUtils.isEmpty(fname)) {
editor.putString("fname", fname);
hasChanged = true;
}
if(hasChanged == true) editor.commit();
break;
case 1: // Address tab
// currView =
viewPager.getChildAt(viewPager.getCurrentItem()); // returns
null
currView =
adapter.getItem(viewPager.getCurrentItem()).getView();
EditText etAddr1 =
currView.findViewById(R.id.etAddr1);
addr1 = etAddr1.getText().toString();
hasChanged = false;
if(!StringUtils.isEmpty(addr1)) {
editor.putString("addr1", addr1);
hasChanged = true;
}
if(hasChanged == true) editor.commit();
break;
case 2: // Security tab
//currView =
viewPager.getChildAt(viewPager.getCurrentItem()); // returns null
currView =
adapter.getItem(viewPager.getCurrentItem()).getView();
EditText etPasswd =
currView.findViewById(R.id.etPasswd);
passwd = etPasswd.getText().toString();
hasChanged = false;
if(!StringUtils.isEmpty(passwd)) {
editor.putString("passwd", passwd);
hasChanged = true;
}
if(hasChanged == true) editor.commit();
break;
}
}
@Override
public void onPageSelected(int position) {
// do nothing
}
@Override
public void onPageScrollStateChanged(int state) {
// do nothing
}
});
}
}
My Stack trace is as follows: 我的堆栈跟踪如下：
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference at com.portmanteau.reviv.CreateUser$1.onPageScrolled(CreateUser.java:58) at android.support.v4.view.ViewPager.dispatchOnPageScrolled(ViewPager.java:1921) at android.support.v4.view.ViewPager.onPageScrolled(ViewPager.java:1895) at android.support.v4.view.ViewPager.pageScrolled(ViewPager.java:1833) at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:690) at android.support.v4.view.ViewPager.onLayout(ViewPager.java:1777) at android.view.View.layout(View.java:19678) at android.view.ViewGroup.layout(ViewGroup.java:6057) at android.support.constraint.ConstraintLayout.onLayout(ConstraintLayout.java:1197) at android.view.View.layout(View.java:19678) at android.view.ViewGroup.layout(ViewGroup.java:6057) at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323) at android.widget.FrameLayout.onLayout(FrameLayout.java:261) at andr
2 个解决方案
解决方案1
3 已采纳 2017-10-23 13:12:55
Try something like this: 尝试这样的事情：
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
boolean hasChanged = false;
if (positionOffset > 0) {
currView = getSupportFragmentManager().findFragmentByTag("android:switcher:" + R.id.pager + ":" + position).getView();
if (currView != null) {
EditText editText = null;
if (position == 0) editText = currView.findViewById(R.id.etPasswdPlain);
else if (position == 1) editText = currView.findViewById(R.id.etAddr1);
else if (position ==2) editText = currView.findViewById(R.id.etFname);
if (editText != null) {
String value = editText.getText().toString();
Log.d("TAG", "Value is " + value);
}
}
}
}
Note that this will work only if you are doing left to right swipe ( from page 1 to page 2 and page 2 to page 3). 请注意，仅当您从左向右滑动 （从第1页到第2页，第2页到第3页）时，此功能才有效。
ie when you are swiping from page 1 to page 2 , data in page 1 is saved and 即当你从第1页刷卡第2页 ， 第1页的数据被保存，
when you are swiping from page 2 to page 3 , data in page 2 will be saved. 当您从第2 页滑动到第3 页时，将保存第2 页中的数据。
For right to left swipe assuming that you have to save page 3 data when swiping from page 3 to page 2 and save page 2 data when swiping from page 2 to page 1 , you have to do some logic but you can get the idea from here. 对于right to left swipe假设您必须在从第3页到第2页滑动时保存第3 页数据并在从第2页到第1页滑动时保存第2页数据，您必须执行一些逻辑，但您可以从此处获取相关信息。
解决方案2
0 2017-10-21 12:46:52
Try calling 试着打电话
((EditText) viewPager.getChildAt(viewPager.getCurrentItem())
.findViewById(R.id.etFname)).getText().toString()
rather than 而不是
adapter.getItem(viewPager.getCurrentItem()).getView();
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