获取空指针异常 - 使用接口将数据从适配器传递到子片段
我有一个Adapter
和一个Sub-Fragment
。我正在使用一个接口将数据从Adapter
传递到Sub-Fragment
。我遇到的问题是我不断收到Null Pointer Exception
。我已阅读了有关这个问题的各种帖子,并且无法弄清楚我出错的地方。我在'passAdapterVariable.passAdapterVariable(mname)'这一行获得了NPE。根据我读过的内容,我怀疑这可能是因为我没有正确初始化passAdapterVariable。我尝试了几种基于其他例子的初始化方法,但我一直在获取NPE。获取空指针异常 - 使用接口将数据从适配器传递到子片段
这里是适配器
public class MatchAdapter extends RecyclerView.Adapter<MatchAdapter.MatchViewHolder> {
//declaration of variables
private Fragment fragment;
private FragmentManager fragmentManager;
private DiscoverPage discoverPage;
private Context context;
private int size;
private int mposition;
private TextView txt_matchname;
private ImageView img_matchpic;
List<String> maImg = new ArrayList<>();
private String mname;
PassAdapterVariable passAdapterVariable;
public interface PassAdapterVariable {
void passAdapterVariable(String mname);
}
//the constructor
public MatchAdapter(List<String> maImg, int size, Context context, DiscoverPage discoverPage){//, PassAdapterVariable passAdapterVariable) {
this.maImg = maImg;
this.context = context;
this.discoverPage = discoverPage;
this.size = size;
//this.passAdapterVariable = (PassAdapterVariable)context;
}
public MatchAdapter(String mname, Context context) {
this.context = context;
this.passAdapterVariable = (PassAdapterVariable)context;
}
//PassAdapterVariable passAdapterVariable = (PassAdapterVariable) context;
@Override
public MatchAdapter.MatchViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.match_items, parent, false);
MatchViewHolder matchViewHolder = new MatchViewHolder(view, maImg, discoverPage);
return matchViewHolder;
}
@Override
public void onBindViewHolder(MatchViewHolder holder, int position) {
Picasso.with(context).load(maImg.get(position)).into(holder.img_match);
holder.setIsRecyclable(false);
}
@Override
public int getItemCount() {
return maImg.size();
}
//viewholder class
public class MatchViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
private static final String TAG = "error";
//declare variables
private DiscoverPage discoverPage;
private ImageView img_match;
//ViewHolder constructor
public MatchViewHolder(View itemView, final List<String> maImg, final DiscoverPage discoverPage) {
super(itemView);
//initialize variables inside the viewholder constructor
this.discoverPage = discoverPage;
img_match = (ImageView) itemView.findViewById(R.id.img_match);
txt_matchname = (TextView) itemView.findViewById(R.id.txt_matchname);
img_matchpic = (ImageView) itemView.findViewById(R.id.img_matchpic);
//set click listener for the img_match
img_match.setOnClickListener(this);
}
@Override
public void onClick(View view) {
if (view == img_match) {
//discoverPage.isHidden();
Fragment currentFragment;
fragment = new ClickedMatch();
fragmentManager = ((AppCompatActivity) context).getSupportFragmentManager();
FragmentTransaction transaction = fragmentManager.beginTransaction();
transaction.replace(android.R.id.content, fragment);
transaction.addToBackStack("DiscoverPage");
if ((currentFragment = ((AppCompatActivity) context).getSupportFragmentManager().findFragmentById(R.id.main_container)) != null) {
transaction.hide(currentFragment);
}
else {
transaction.commit();
}
mname = maImg.get(getAdapterPosition());
mposition = getAdapterPosition();
mname = maImg.get(mposition);
passAdapterVariable.passAdapterVariable(mname);
}
}
}
}
这里是亚片段
public class ClickedMatch extends Fragment implements MatchAdapter.PassAdapterVariable{
//declare variables
private Toolbar toolbar;
private TextView txt_matchname;
private TextView txt_matchprice;
private ImageView img_matchpic;
private String mname;
private String imgmatch;
List<String> maImg = new ArrayList<>();
int size;
Context context;
DiscoverPage discoverPage;
private String pname;
private int i;
MatchAdapter.PassAdapterVariable passAdapterVariable;
public ClickedMatch() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_clicked_match, container, false);
//initialize variables
toolbar = (Toolbar) view.findViewById(R.id.toolbar);
((AppCompatActivity)getActivity()).setSupportActionBar(toolbar);//set toolbar as action bar
txt_matchname = (TextView)view.findViewById(R.id.txt_matchname);
img_matchpic = (ImageView)view.findViewById(R.id.img_matchpic);
//setHasOptionsMenu(true);
toolbar.setNavigationOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
getActivity().onBackPressed();
}
});
if(((AppCompatActivity)getActivity()).getSupportActionBar()!= null){
((AppCompatActivity) getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(true);
((AppCompatActivity)getActivity()).getSupportActionBar().setDisplayShowHomeEnabled(true);
((AppCompatActivity)getActivity()).getSupportActionBar().setHomeButtonEnabled(true);
((AppCompatActivity)getActivity()).getSupportActionBar().setTitle("");
}
// MatchAdapter matAdapter = new MatchAdapter(maImg, size, context, discoverPage,
//passAdapterVariable);
// matAdapter.passAdapterVariable = this;
//passAdapterVariable.passAdapterVariable(mname);
//txt_matchname.setText(pname);
MatchAdapter matAdapter = new MatchAdapter(pname, getContext());
matAdapter.passAdapterVariable = this;
passAdapterVariable(pname);
txt_matchname.setText(pname);
return view;
}
@Override
public void passAdapterVariable(String mname) {
this.pname = mname;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == android.R.id.home) {
this.getActivity().finish();
}
return super.onOptionsItemSelected(item);
}
}
以下是错误日志
08-13 21:53:49.341 12852-12852/com.test.jack E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.test.jack, PID: 12852
java.lang.NullPointerException: Attempt to invoke interface method 'void com.test.jack.MatchAdapter$PassAdapterVariable.passAdapterVariable(java.lang.String)' on a null object reference
at com.test.jack.MatchAdapter$MatchViewHolder.onClick(MatchAdapter.java:138)
at android.view.View.performClick(View.java:5637)
at android.view.View$PerformClick.run(View.java:22429)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
要添加更多的上下文,我有一个主要活动(UserMainPage)。底部导航菜单选择器用一个片段(DiscoverPage)替换UserMainPage。
DiscoverPage调用适配器(MatchAdapter)。点击发现页面上的按钮用一个子片段替换DiscoverPage(ClickedMatch)。
我想将MatchAdapter的变量传递给ClickedMatch。
我能找到没有从那些谁评论或提供洞察到这一问题,并只会展示他们的无能和浪费我的时间帮助解决。
我能够使用Bundle
将数据从适配器传递到子片段。
我修改了代码如下:
在我添加适配器:
fragment = new ClickedMatch();
Bundle bundle = new Bundle();
bundle.putString("matchname",mname);
fragment.setArguments(bundle);
...
transaction.commit();
在我的子片段我说:
Bundle bundle = this.getArguments();
if(bundle != null){
pname = bundle.getString("matchname");
}
没有必要使用一个接口。根据我所研究的内容,我认为(我可能错了)创建接口并实现它的时候,最好在片段之间进行通信时使用,而不是在适配器和子片段之间进行通信。
当您调用passAdapterVariable.passAdapterVariable(mname)时,看起来像字符串“mname”为null。
要么你是列表maImg是空的|| null或提供的适配器位置错误。
尝试登录
Log.d(TAG, "pos: " + getAdapterPosition());
mname = maImg.get(getAdapterPosition());
Log.d(TAG, "name: " + mname);
列表maImg不为空。按照建议实施日志,并且得到值08-13 23:20:59.943 29966-29966/com.test.jack D /错误:pos:0 08-13 23:20:59.943 29966-29966/com.test。杰克D /错误:名称:https://firebasestorage.googleapis.com/v0/b/jack-... @ gekn76 –
PassAdapterVariable passAdapterVariable = (PassAdapterVariable) context;
只是一个声明+赋值语句在你的适配器类。此时,上下文为空。
变量上下文只在您的构造函数中被赋值。将您的passAdapterVariable的上下文之后已分配
public MatchAdapter(List<String> maImg, int size, Context context, DiscoverPage discoverPage) {
this.maImg = maImg;
this.context = context;
this.discoverPage = discoverPage;
this.size = size;
passAdapterVariable = (PassAdapterVariable) context;
}
我分配了上下文后的passAdapterVariable,我仍然得到NPE。 @Arun Shankar –
你可以发布更改后的代码吗?让我编辑我的答案,以显示我的意思是更好 –
已更改的代码已发布。 @Arun Shankar –
You can add Context parameter in constructor of Adapter with String as
public MatchAdapter(String mname, Context context) {
this.context = context;
}
Now get the context from Fragment as
MatchAdapter matAdapter = new MatchAdapter(pname, getActivity());
matAdapter.passAdapterVariable = this;
passAdapterVariable(pname);
txt_matchname.setText(tname);
return view;
尝试建议。我仍然得到NPE。我发布了更新的代码并添加了一些更多的上下文问题。@Sushil Chaudhary –
内MatchAdapter ------ 添加实例在构造你的界面,将工作作为
{
DataInterface passInterface;
Context context;
public MatchAdapter(String mname, Context context1, DataPass pass) {
this.passAdapterVariable = mname;
this.context = context1;
this.passInterface = pass;
}
}
现在获取该接口的实例,而c阿灵适配器
{
MatchAdapter matAdapter = new MatchAdapter(pname, getActivity(),this);
}
当我添加DataInterace passInterface I我不能写“this.passadapterVariable = mname”,它们是不兼容的类型@Sushil Chaudhary –
DataInterface是你创建的接口写入你为接口给出的类名并初始化了passAdapterVariable之前构造函数为 String passAdapterVariable;使用它 –
检查出来@RookyCoder –
您的语境在语句中为空PassAdapterVariable passAdapterVariable =(PassAdapterVariable)context ;,将其移至适配器类构造函数。 – darwin
我移动了PassAdapterVariable passAdapterVariable =(passAdapterVariable)上下文。我有两个构造函数(不知道这是不是好习惯),当我把它放在第二个构造函数时,我得到了相同的NPE。当我将它放在第一个构造函数中时,程序崩溃,并且我收到错误消息User Main Page(这是主要活动)不能转换为MatchAdapter.PassAdapterVariable。 @darwin –
did你在你的Activity中实现了PassAdapterVariable接口吗? – darwin