获取NullPointerException错误视图寻呼机,同时在视图寻呼机中获取片段方法活动
问题描述:
我知道这是非常普遍的问题,但无法弄清楚什么是错误的。获取NullPointerException错误视图寻呼机,同时在视图寻呼机中获取片段方法活动
片段Java类
// newInstance constructor for creating fragment with arguments
public static BpDetails newInstance(int page) {
BpDetails fragmentFirst = new BpDetails();
Bundle args = new Bundle();
args.putInt("someInt", page);
fragmentFirst.setArguments(args);
return fragmentFirst;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
page = getArguments().getInt("someInt", 0);
}
public String getSystolic(){
return this.systolic.getText().toString();
}
/* public String getDiastolic(){
return this.diastolic.getText().toString();
}*/
// Inflate the view for the fragment based on layout XML
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
final View view = inflater.inflate(R.layout.bp_details, container, false);
Log.i("View ",view.toString());
Log.i("DOB is ",Long.toString(Constants.dob));
systolic =(EditText) view.findViewById(R.id.systolic);
diastolic =(EditText) view.findViewById(R.id.diastolic);
return view;
}
ViewPager活动
vpPager = (ViewPager) findViewById(R.id.view_pager);
adapterViewPager = new MyPagerAdapter(getSupportFragmentManager());
vpPager.setAdapter(adapterViewPager);
findViewById(R.id.btn_prev).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// checking for last page
// if last page home screen will be launched
int current = getItem(-1);
if (current!=0)
prevPage=current-1;
if (current < 4) {
// move to next screen
vpPager.setCurrentItem(current);
} else {
//final reached.
}
}
});
findViewById(R.id.btn_next).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// checking for last page
// if last page home screen will be launched
int current = getItem(+1);
if (current!=0)
prevPage=current-1;
System.out.println("Prev page "+prevPage);
if (current < 4) {
// move to next screen
Fragment bpFragment=adapterViewPager.getItem(vpPager.getCurrentItem());
if (bpFragment instanceof BpDetails){
System.out.println("Current item is "+vpPager.getCurrentItem());
BpDetails fr = (BpDetails)adapterViewPager.getItem(vpPager.getCurrentItem());
**String systolicString = fr.getSystolic();** //error point
Log.i("Systolic is ",systolicString);
}
} else {
//final reached.
}
}
});
}
private int getItem(int i) {
return vpPager.getCurrentItem() + i;
}
public static class MyPagerAdapter extends FragmentPagerAdapter {
private static int NUM_ITEMS = 4;
private static int mSelectedPosition;
public MyPagerAdapter(FragmentManager fragmentManager) {
super(fragmentManager);
//mSelectedPosition=selectedPosition;
}
// Returns total number of pages
@Override
public int getCount() {
return NUM_ITEMS;
}
// Returns the fragment to display for that page
@Override
public Fragment getItem(int position) {
switch (position) {
case 0: // Fragment # 0 - This will show FirstFragment
return BasicDetails.newInstance(0);
case 1:
return BpDetails.newInstance(1);
case 2:
return BslDetails.newInstance(2);
case 3:
return Summary.newInstance(3);
default:
return null;
}
}
}
为什么我收到NullPointerException异常,因为我访问片段的方法,公众才去到下一个片段。 投票前请留下投票原因,以便我可以改进问题。
编辑:
我才知道,因为我调用的GetItem()方法,这就是为什么片段的所有的变量设置为null就是为什么我收到NullPointerException异常。有什么办法可以解决这个问题吗?
答
你应该重写你的ViewPagerAdapter和存储retuened片段
这是因为每次你调用getItem()时间函数返回一个新的片段,而只能由viewpager本身的片段将调用oncreateView调用,所以你调用getItem没有初始化收缩,因此第二次导致NullPointerException异常
供参考:
public static class MyPagerAdapter extends FragmentPagerAdapter {
private static int NUM_ITEMS = 4;
private static int mSelectedPosition;
Map<Integer,Fragment> map= new HashMap<>();
public MyPagerAdapter(FragmentManager fragmentManager) {
super(fragmentManager);
//mSelectedPosition=selectedPosition;
}
// Returns total number of pages
@Override
public int getCount() {
return NUM_ITEMS;
}
// Returns the fragment to display for that page
@Override
public Fragment getItem(int position) {
Fragment f = map.get(position)
if(f!=null){
return f;
}
switch (position) {
case 0: // Fragment # 0 - This will show FirstFragment
f = BasicDetails.newInstance(0);
case 1:
f = return BpDetails.newInstance(1);
case 2:
f = return BslDetails.newInstance(2);
case 3:
f = return Summary.newInstance(3);
default:
return null;
}
map.put(postion,f);
return f;
}
}