Android 在ViewPager中引用EditText会创建空指针异常
我想做什么:Android 在ViewPager中引用EditText会创建空指针异常,android,android-fragments,nullpointerexception,android-viewpager,findviewbyid,Android,Android Fragments,Nullpointerexception,Android Viewpager,Findviewbyid,我想做什么: 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.view
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.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.widget.EditText;
public class SwipeEnterResults extends FragmentActivity {
ResultsPagerAdapter mResultsPagerAdapter;
ViewPager mViewPager;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.swipe_enter_results);
mResultsPagerAdapter = new ResultsPagerAdapter(getSupportFragmentManager());
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mResultsPagerAdapter);
}
public void onResume() {
super.onResume();
//Declare EditText(s)
final EditText txt1= (EditText) mViewPager.findViewById(R.id.txt1);
final EditText txt2= (EditText) mViewPager.findViewById(R.id.txt2);
final EditText txt3= (EditText) mViewPager.findViewById(R.id.txt3);
final EditText rvw1= (EditText) mViewPager.findViewById(R.id.rvw1);
final EditText rvw2= (EditText) mViewPager.findViewById(R.id.rvw2);
final EditText rvw3= (EditText) mViewPager.findViewById(R.id.rvw3);
mViewPager.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
rvw1.setText(txt1.getText().toString());
rvw2.setText(txt2.getText().toString());
rvw3.setText(txt3.getText().toString());
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) { }
@Override
public void onPageScrollStateChanged(int arg0) { }
});
}
public class ResultsPagerAdapter extends FragmentPagerAdapter{
public ResultsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
Fragment f = new Fragment();
switch (position) {
case 0:
f = new Swipe1();
break;
case 1:
f = new Swipe2();
break;
case 2:
f = new Swipe3();
break;
case 3:
f = new SwipeReviewResults();
break;
}
return f;
}
@Override
public int getCount() {
return 4;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return getString(R.string.str1);
case 1:
return getString(R.string.str2);
case 2:
return getString(R.string.str3);
case 3:
return getString(R.string.strReview);
default:
return "Page " + (position + 1);
}
}
}
}
让用户在3个不同的片段上输入数据,然后在第4个片段上,用户将在提交到数据库之前查看输入到前3个片段中的所有数据
我遇到的问题:
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.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.widget.EditText;
public class SwipeEnterResults extends FragmentActivity {
ResultsPagerAdapter mResultsPagerAdapter;
ViewPager mViewPager;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.swipe_enter_results);
mResultsPagerAdapter = new ResultsPagerAdapter(getSupportFragmentManager());
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mResultsPagerAdapter);
}
public void onResume() {
super.onResume();
//Declare EditText(s)
final EditText txt1= (EditText) mViewPager.findViewById(R.id.txt1);
final EditText txt2= (EditText) mViewPager.findViewById(R.id.txt2);
final EditText txt3= (EditText) mViewPager.findViewById(R.id.txt3);
final EditText rvw1= (EditText) mViewPager.findViewById(R.id.rvw1);
final EditText rvw2= (EditText) mViewPager.findViewById(R.id.rvw2);
final EditText rvw3= (EditText) mViewPager.findViewById(R.id.rvw3);
mViewPager.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
rvw1.setText(txt1.getText().toString());
rvw2.setText(txt2.getText().toString());
rvw3.setText(txt3.getText().toString());
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) { }
@Override
public void onPageScrollStateChanged(int arg0) { }
});
}
public class ResultsPagerAdapter extends FragmentPagerAdapter{
public ResultsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
Fragment f = new Fragment();
switch (position) {
case 0:
f = new Swipe1();
break;
case 1:
f = new Swipe2();
break;
case 2:
f = new Swipe3();
break;
case 3:
f = new SwipeReviewResults();
break;
}
return f;
}
@Override
public int getCount() {
return 4;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return getString(R.string.str1);
case 1:
return getString(R.string.str2);
case 2:
return getString(R.string.str3);
case 3:
return getString(R.string.strReview);
default:
return "Page " + (position + 1);
}
}
}
}
我尝试设置或从EditText中获取的每个方法都会创建一个NullPointerException
我的问题:
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.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.widget.EditText;
public class SwipeEnterResults extends FragmentActivity {
ResultsPagerAdapter mResultsPagerAdapter;
ViewPager mViewPager;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.swipe_enter_results);
mResultsPagerAdapter = new ResultsPagerAdapter(getSupportFragmentManager());
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mResultsPagerAdapter);
}
public void onResume() {
super.onResume();
//Declare EditText(s)
final EditText txt1= (EditText) mViewPager.findViewById(R.id.txt1);
final EditText txt2= (EditText) mViewPager.findViewById(R.id.txt2);
final EditText txt3= (EditText) mViewPager.findViewById(R.id.txt3);
final EditText rvw1= (EditText) mViewPager.findViewById(R.id.rvw1);
final EditText rvw2= (EditText) mViewPager.findViewById(R.id.rvw2);
final EditText rvw3= (EditText) mViewPager.findViewById(R.id.rvw3);
mViewPager.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
rvw1.setText(txt1.getText().toString());
rvw2.setText(txt2.getText().toString());
rvw3.setText(txt3.getText().toString());
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) { }
@Override
public void onPageScrollStateChanged(int arg0) { }
});
}
public class ResultsPagerAdapter extends FragmentPagerAdapter{
public ResultsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
Fragment f = new Fragment();
switch (position) {
case 0:
f = new Swipe1();
break;
case 1:
f = new Swipe2();
break;
case 2:
f = new Swipe3();
break;
case 3:
f = new SwipeReviewResults();
break;
}
return f;
}
@Override
public int getCount() {
return 4;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return getString(R.string.str1);
case 1:
return getString(R.string.str2);
case 2:
return getString(R.string.str3);
case 3:
return getString(R.string.strReview);
default:
return "Page " + (position + 1);
}
}
}
}
对于我试图做的,什么是正确的方法来调用一个片段中EditText的文本值,并在页面更改时在另一个片段中的EditText中设置该文本
注意事项:
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.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.widget.EditText;
public class SwipeEnterResults extends FragmentActivity {
ResultsPagerAdapter mResultsPagerAdapter;
ViewPager mViewPager;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.swipe_enter_results);
mResultsPagerAdapter = new ResultsPagerAdapter(getSupportFragmentManager());
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mResultsPagerAdapter);
}
public void onResume() {
super.onResume();
//Declare EditText(s)
final EditText txt1= (EditText) mViewPager.findViewById(R.id.txt1);
final EditText txt2= (EditText) mViewPager.findViewById(R.id.txt2);
final EditText txt3= (EditText) mViewPager.findViewById(R.id.txt3);
final EditText rvw1= (EditText) mViewPager.findViewById(R.id.rvw1);
final EditText rvw2= (EditText) mViewPager.findViewById(R.id.rvw2);
final EditText rvw3= (EditText) mViewPager.findViewById(R.id.rvw3);
mViewPager.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
rvw1.setText(txt1.getText().toString());
rvw2.setText(txt2.getText().toString());
rvw3.setText(txt3.getText().toString());
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) { }
@Override
public void onPageScrollStateChanged(int arg0) { }
});
}
public class ResultsPagerAdapter extends FragmentPagerAdapter{
public ResultsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
Fragment f = new Fragment();
switch (position) {
case 0:
f = new Swipe1();
break;
case 1:
f = new Swipe2();
break;
case 2:
f = new Swipe3();
break;
case 3:
f = new SwipeReviewResults();
break;
}
return f;
}
@Override
public int getCount() {
return 4;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return getString(R.string.str1);
case 1:
return getString(R.string.str2);
case 2:
return getString(R.string.str3);
case 3:
return getString(R.string.strReview);
default:
return "Page " + (position + 1);
}
}
}
}
为了便于复制和解析代码,我简化了代码,使每个片段上只反映一个EditText
代码:
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.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.widget.EditText;
public class SwipeEnterResults extends FragmentActivity {
ResultsPagerAdapter mResultsPagerAdapter;
ViewPager mViewPager;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.swipe_enter_results);
mResultsPagerAdapter = new ResultsPagerAdapter(getSupportFragmentManager());
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mResultsPagerAdapter);
}
public void onResume() {
super.onResume();
//Declare EditText(s)
final EditText txt1= (EditText) mViewPager.findViewById(R.id.txt1);
final EditText txt2= (EditText) mViewPager.findViewById(R.id.txt2);
final EditText txt3= (EditText) mViewPager.findViewById(R.id.txt3);
final EditText rvw1= (EditText) mViewPager.findViewById(R.id.rvw1);
final EditText rvw2= (EditText) mViewPager.findViewById(R.id.rvw2);
final EditText rvw3= (EditText) mViewPager.findViewById(R.id.rvw3);
mViewPager.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
rvw1.setText(txt1.getText().toString());
rvw2.setText(txt2.getText().toString());
rvw3.setText(txt3.getText().toString());
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) { }
@Override
public void onPageScrollStateChanged(int arg0) { }
});
}
public class ResultsPagerAdapter extends FragmentPagerAdapter{
public ResultsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
Fragment f = new Fragment();
switch (position) {
case 0:
f = new Swipe1();
break;
case 1:
f = new Swipe2();
break;
case 2:
f = new Swipe3();
break;
case 3:
f = new SwipeReviewResults();
break;
}
return f;
}
@Override
public int getCount() {
return 4;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return getString(R.string.str1);
case 1:
return getString(R.string.str2);
case 2:
return getString(R.string.str3);
case 3:
return getString(R.string.strReview);
default:
return "Page " + (position + 1);
}
}
}
}
不要将
EditText
s设为最终文本。尝试使用以下代码代替当前的onResume
:
EditText txt1= (EditText) mViewPager.findViewById(R.id.txt1);
EditText txt2= (EditText) mViewPager.findViewById(R.id.txt2);
EditText txt3= (EditText) mViewPager.findViewById(R.id.txt3);
EditText rvw1= (EditText) mViewPager.findViewById(R.id.rvw1);
EditText rvw2= (EditText) mViewPager.findViewById(R.id.rvw2);
EditText rvw3= (EditText) mViewPager.findViewById(R.id.rvw3);
不要将
EditText
s设为最终文本。尝试使用以下代码代替当前的onResume
:
EditText txt1= (EditText) mViewPager.findViewById(R.id.txt1);
EditText txt2= (EditText) mViewPager.findViewById(R.id.txt2);
EditText txt3= (EditText) mViewPager.findViewById(R.id.txt3);
EditText rvw1= (EditText) mViewPager.findViewById(R.id.rvw1);
EditText rvw2= (EditText) mViewPager.findViewById(R.id.rvw2);
EditText rvw3= (EditText) mViewPager.findViewById(R.id.rvw3);
可能您的ViewPager没有id为R.id.txt1、R.id.rvw1、
确保您已在swipe\u enter\u results.xml文件中定义了所有编辑文本。否则,某些对象(可能全部)将等于null,您将得到NullPointerException。您的ViewPager可能没有id为R.id.txt1、R.id.rvw1、 确保您已在swipe\u enter\u results.xml文件中定义了所有编辑文本。否则,某些对象(可能全部)将等于null,您将得到一个NullPointerException。以下几点:
ResultsPagerAdapter
的getItem
方法时,都会创建一个具有自己视图的新片段。。。因此,在创建新片段视图时,您的活动可能会引用过时的EditText视图Swipe
片段的onPause()
方法中,您可以将其EditText值存储在缓存中,而在SwipeReviewResults
片段的onResume()
方法中,可以从缓存中提取所有更新的EditText值default
块返回空的new Fragment()
,而不是不必要地预先创建它ResultsPagerAdapter
的getItem
方法时,都会创建一个具有自己视图的新片段。。。因此,在创建新片段视图时,您的活动可能会引用过时的EditText视图Swipe
片段的onPause()
方法中,您可以将其EditText值存储在缓存中,而在SwipeReviewResults
片段的onResume()
方法中,可以从缓存中提取所有更新的EditText值default
块返回空的new Fragment()
,而不是不必要地预先创建它我希望这对你有所帮助。我最后尝试了几件事。我添加了
mviewpage.setOffscreenPageLimit(3)
然后将我的代码放入一个条件为position==3
的if
语句中,这似乎解决了nullpointerexception的所有问题。谢谢大家的帮助
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.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.widget.CheckBox;
import android.widget.EditText;
public class SwipeEnterResults extends FragmentActivity {
ResultsPagerAdapter mResultsPagerAdapter;
ViewPager mViewPager;
//Declare EditText for reviewing data on Fragment SwipeReviewResults
EditText txt1;
EditText rvw1;
EditText txt2;
EditText rvw2;
EditText txt3;
EditText rvw3;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.swipe_enter_results);
//Set up ViewPager and allow app to hold prior pages when off screen
mResultsPagerAdapter = new ResultsPagerAdapter(getSupportFragmentManager());
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mResultsPagerAdapter);
mViewPager.setOffscreenPageLimit(3);
//When SwipeReviewResults is displayed, fill EditText's with data from other fragments
mViewPager.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
if (position == 3) {
//set values to EditTexts to pull data from 3 entry fragments and display in SwipeReviewResults
EditText txt1 = (EditText) mViewPager.findViewById(R.id.txt1);
EditText rvw1 = (EditText) mViewPager.findViewById(R.id.rvw1);
EditText txt2 = (EditText) mViewPager.findViewById(R.id.txt2);
EditText rvw2 = (EditText) mViewPager.findViewById(R.id.rvw2);
EditText txt3 = (EditText) mViewPager.findViewById(R.id.txt3);
EditText rvw3 = (EditText) mViewPager.findViewById(R.id.rvw3);
//Set EditText's on SwipeReviewResults
rvw1.setText(txt1.getText().toString());
rvw2.setText(txt2.getText().toString());
rvw3.setText(txt3.getText().toString());
}
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) { }
@Override
public void onPageScrollStateChanged(int arg0) { }
});
}
public class ResultsPagerAdapter extends FragmentPagerAdapter{
public ResultsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
Fragment f;
switch (position) {
case 0:
f = new Swipe1();
break;
case 1:
f = new Swipe2();
break;
case 2:
f = new Swipe3();
break;
case 3:
f = new SwipeReviewResults();
break;
default:
f = new Fragment();
break;
}
return f;
}
@Override
public int getCount() {
return 4;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return getString(R.string.str1);
case 1:
return getString(R.string.str2);
case 2:
return getString(R.string.str3);
case 3:
return getString(R.string.strReview);
default:
return "Page " + (position + 1);
}
}
}
}
我最后尝试了几件事。我添加了
mviewpage.setOffscreenPageLimit(3)
然后将我的代码放入一个条件为position==3
的if
语句中,这似乎解决了nullpointerexception的所有问题。谢谢大家的帮助
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.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.widget.CheckBox;
import android.widget.EditText;
public class SwipeEnterResults extends FragmentActivity {
ResultsPagerAdapter mResultsPagerAdapter;
ViewPager mViewPager;
//Declare EditText for reviewing data on Fragment SwipeReviewResults
EditText txt1;
EditText rvw1;
EditText txt2;
EditText rvw2;
EditText txt3;
EditText rvw3;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.swipe_enter_results);
//Set up ViewPager and allow app to hold prior pages when off screen
mResultsPagerAdapter = new ResultsPagerAdapter(getSupportFragmentManager());
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mResultsPagerAdapter);
mViewPager.setOffscreenPageLimit(3);
//When SwipeReviewResults is displayed, fill EditText's with data from other fragments
mViewPager.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
if (position == 3) {
//set values to EditTexts to pull data from 3 entry fragments and display in SwipeReviewResults
EditText txt1 = (EditText) mViewPager.findViewById(R.id.txt1);
EditText rvw1 = (EditText) mViewPager.findViewById(R.id.rvw1);
EditText txt2 = (EditText) mViewPager.findViewById(R.id.txt2);
EditText rvw2 = (EditText) mViewPager.findViewById(R.id.rvw2);
EditText txt3 = (EditText) mViewPager.findViewById(R.id.txt3);
EditText rvw3 = (EditText) mViewPager.findViewById(R.id.rvw3);
//Set EditText's on SwipeReviewResults
rvw1.setText(txt1.getText().toString());
rvw2.setText(txt2.getText().toString());
rvw3.setText(txt3.getText().toString());
}
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) { }
@Override
public void onPageScrollStateChanged(int arg0) { }
});
}
public class ResultsPagerAdapter extends FragmentPagerAdapter{
public ResultsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
Fragment f;
switch (position) {
case 0:
f = new Swipe1();
break;
case 1:
f = new Swipe2();
break;
case 2:
f = new Swipe3();
break;
case 3:
f = new SwipeReviewResults();
break;
default:
f = new Fragment();
break;
}
return f;
}
@Override
public int getCount() {
return 4;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return getString(R.string.str1);
case 1:
return getString(R.string.str2);
case 2:
return getString(R.string.str3);
case 3:
return getString(R.string.strReview);
default:
return "Page " + (position + 1);
}
}
}
}
有4个具有不同ID的独立xml布局。这不是问题所在。在我的完整设计中,总共有近60个EditText,每个EditText最后都是空的。这不是问题所在。在我的完整设计中,总共有近60个EditText,它们中的每一个都是空的。当我尝试引用EditText进行更改时,会出现一个错误。当我尝试引用EditText进行更改时,会出现一个错误。如下所示:
@Override public Fragment getItem(int position){Fragment f;switch(位置){case 0:f=new SwipeChemicalsApplied();break;case 1:f=new SwipeRaw();break;case 2:f=new swipeefinished();break;case 3:f=new SwipeReviewResults();break;default:f=new Fragment();break;}返回f;}