在VIewPager（Android版）（NullPointerException异常）传递两个片段之间的数据 [英] Passing data between two Fragments in a VIewPager (Android) (NullPointerException)
问题描述
所以基本上我的 2 片段 - FragmentConverter 和 FragmentFavourites ，我有有一个 MainActivity 。我试图通过从第一片段4阵列使用名为通讯接口的第二个。具体的片段是下面显示：
公共接口通讯{ 公共无效响应（字符串[]名称，字符串[] codeS，的String []符号，INT []图像）;
}
这是内部的方法 FragmentFavourites ：
@覆盖
公共布尔onOptionsItemSelected（菜单项项）{
// TODO自动生成方法存根 的String [] = checkedNames新的String [窗口];
的String []检查codeS =新的String [窗口];
的String [] = checkedSymbols新的String [窗口];
INT [] = checkedImages新INT [窗口];
COMM =（通讯）getActivity（）;
INT索引= 0;
如果（item.getItemId（）== R.id.action_save）{
的for（int i = 0; I＆LT; checked.size（）;我++）{
如果（checked.get（我）==真）{
checkedNames [指数] =名称[I]
检查codeS [指数] = codeS [I]
checkedSymbols [指数] =符号[I]
checkedImages [指数] =图像[我]
指数++;
} }
comm.respond（checkedNames，检查codeS，checkedSymbols，checkedImages）;
} 返回super.onOptionsItemSelected（项目）;
}
这是在 MainActivity 实现的接口方法：
@覆盖
公共无效响应（字符串[]名称，字符串[] codeS，的String []符号，
INT []图像）{
// TODO自动生成方法存根
FragmentConverter断枝=（FragmentConverter）fragmentPagerAdapter.getItem（1）;
frag.changeData（姓名，codeS，符号，图像）;
}
这是收集数据的方法 FragmentConverter ：
公共无效changeData（字符串[]名称，字符串[] codeS，的String []符号，INT []图像）{
this.names =名称;
这codeS = codeS;
this.symbols =符号;
this.images =图像; Log.d（TEST，symbols.length + names.length + codes.length + images.length +）;
tvOneRate.setText（名称[1]）;
}
现在的问题是，每当我试图改变在 FragmentConverter UI组件，我得到一个 NullPointerException异常，虽然Log.d语句返回正确的结果。
EDIT1：getItem（）时FragmentPagerAdapter方式：
@覆盖
公共片段的getItem（int i）以{
// TODO自动生成方法存根
片段FRAG = NULL;
如果（我== 0）{
FRAG =新FragmentFavourites（）;
}
如果（ⅰ== 1）{
FRAG =新FragmentConverter（）;
}
返回FRAG;
}
编辑：
当你调用 fragmentPagerAdapter.getItem（1）你得到，所以你指的是一个不同的对象片段的新实例。这就是为什么认为是空，你会得到NullPointerException异常。如果你需要的只是2片段的适配器，可以用类似的东西尝试：
公共类YourPagerAdapter扩展android.support.v4.app.FragmentPagerAdapter { 私人FragmentFavourites mFragFavourites;
私人FragmentConverter mFragConverter; 公共YourPagerAdapter（）{ // ...您code以上
this.mFragFavourites =新FragmentFavourites（）;
this.mFragConverter =新FragmentConverter（）;
} @覆盖
公共片段的getItem（INT位置）{ 开关（位置）{
情况下0：
返回mFragFavourites; 情况1：
返回mFragConverter;
默认：
返回null;
}
}
}
So basically I have 2 Fragments - FragmentConverter and FragmentFavourites, and I have one MainActivity. I'm trying to pass 4 arrays from the first fragment to the second one using an Interface called Communicator. The specific snippets are show below:
public interface Communicator {
public void respond(String[] names, String[] codes, String[] symbols, int[] images);
}
This is a method inside FragmentFavourites:
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// TODO Auto-generated method stub
String[] checkedNames = new String[counter];
String[] checkedCodes = new String[counter];
String[] checkedSymbols = new String[counter];
int[] checkedImages = new int[counter];
comm = (Communicator) getActivity();
int index = 0;
if (item.getItemId() == R.id.action_save){
for (int i=0;i<checked.size();i++){
if (checked.get(i) == true){
checkedNames[index] = names[i];
checkedCodes[index] = codes[i];
checkedSymbols[index] = symbols[i];
checkedImages[index] = images[i];
index++;
}
}
comm.respond(checkedNames, checkedCodes, checkedSymbols, checkedImages);
}
return super.onOptionsItemSelected(item);
}
This is the implemented interface method inside MainActivity:
@Override
public void respond(String[] names, String[] codes, String[] symbols,
int[] images) {
// TODO Auto-generated method stub
FragmentConverter frag = (FragmentConverter) fragmentPagerAdapter.getItem(1);
frag.changeData(names, codes, symbols, images);
}
And this is a method that collects the data in FragmentConverter:
public void changeData(String[] names, String[] codes, String[] symbols, int[] images){
this.names = names;
this.codes = codes;
this.symbols = symbols;
this.images = images;
Log.d("TEST", symbols.length + names.length + codes.length + images.length + "");
tvOneRate.setText(names[1]);
}
Now the problem is that whenever I try to change a ui component inside FragmentConverter, I get a NullPointerException, though the Log.d statement returns the correct results.
EDIT1: getItem() method of FragmentPagerAdapter:
@Override
public Fragment getItem(int i) {
// TODO Auto-generated method stub
Fragment frag = null;
if (i == 0){
frag = new FragmentFavourites();
}
if (i == 1){
frag = new FragmentConverter();
}
return frag;
}
EDITED:
When you call fragmentPagerAdapter.getItem(1) you are getting a new instance of the fragment so you are referring to a different object. this is why the view is null and you get the NullPointerException. If you need an adapter for only 2 fragments, you can try with something like that:
public class YourPagerAdapter extends android.support.v4.app.FragmentPagerAdapter {
private FragmentFavourites mFragFavourites;
private FragmentConverter mFragConverter;
public YourPagerAdapter() {
// ... your code above
this.mFragFavourites = new FragmentFavourites();
this.mFragConverter = new FragmentConverter();
}
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return mFragFavourites;
case 1:
return mFragConverter;
default:
return null;
}
}
}
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