LayoutInflater 修复 RecyclerView 是正确的解决方案吗?
Was LayoutInflater fix for RecyclerView was correct solution?
我正在使用这个教程:
https://www.youtube.com/watch?v=I2eYBtLWGzc
https://mzgreen.github.io/2015/06/23/How-to-hideshow-Toolbar-when-list-is-scrolling(part3)/
起初我遇到错误:
java.lang.NullPointerException: Attempt to invoke virtual method android.view.View android.view.LayoutInflater.inflate(int, android.view.ViewGroup, boolean)' on a null object reference
at pl.michalz.hideonscrollexample.adapter.parttwo.MyAdapter.onCreateViewHolder(MyAdapter.java:37)
at pl.michalz.hideonscrollexample.adapter.parttwo.MyAdapter.onCreateViewHolder(MyAdapter.java:18)
我对以下内容进行了更改:
@Override
public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
Log.w("myApp", "onCreateViewHolder ");
View view = layoutInflater.inflate(R.layout.recycler_item, parent, false);
return new ViewHolder(view);
}
至:
View view = layoutInflater.from(parent.getContext()).inflate(R.layout.recycler_item, parent, false);
它修复了错误,但只是在几次之后我厌倦了模拟应用程序。我真的很难完成这项工作,所以我不知道这是正确的修复还是我的代码不好,以后可能会出错。
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
private LayoutInflater layoutInflater;
private ArrayList<Receptas> receptasL = new ArrayList<>();
public MyAdapter(Context context) {
//layoutInflater = layoutInflater.from(context);
}
public void setReceptasList(ArrayList<Receptas> receptasL ){
this.receptasL = receptasL;
notifyItemRangeChanged(0, receptasL.size());
}
@Override
public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
Log.w("myApp", "onCreateViewHolder ");
View view = layoutInflater.from(parent.getContext()).inflate(R.layout.recycler_item, parent, false);
return new ViewHolder(view);
}
@Override
public void onBindViewHolder(MyAdapter.ViewHolder holder, int position) {
Receptas receptas = receptasL.get(position);
holder.itemTextViewPav.setText(receptas.getPav());
holder.itemTextViewIngred_sk.setText(receptas.getIngred_sk());
}
@Override
public int getItemCount() {
return receptasL == null ? 0 : receptasL.size();
}
public static class ViewHolder extends RecyclerView.ViewHolder {
TextView itemTextViewPav, itemTextViewIngred_sk;
public ViewHolder(View itemView) {
super(itemView);
itemTextViewPav = (TextView) itemView.findViewById(R.id.itemTextViewPav);
itemTextViewIngred_sk = (TextView) itemView.findViewById(R.id.itemTextViewIngred_sk);
}
}
}
这是用于显示 RecyclerView 的片段 class:
public class PartThreeFragment extends Fragment {
private final String url = "http://smkbaig.esy.es/get_info_test.php";
//pridetas
ArrayList<Receptas> receptasAList = new ArrayList<>();
MyAdapter myAdapter;
RecyclerView recyclerView;
RequestQueue requestQueue;
Receptas receptas;
public static PartThreeFragment createInstance() {
PartThreeFragment partThreeFragment = new PartThreeFragment();
Log.w("myApp", ">>partThree)");
return partThreeFragment;
}
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
Log.w("myApp", "partThree>>");
View view = inflater.inflate(R.layout.fragment_part_three, container, false);
recyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
myAdapter = new MyAdapter(getActivity());
recyclerView.setAdapter(myAdapter);
requestQueue = Volley.newRequestQueue(this.getActivity());
volleyJson();
return view;
}
public void volleyJson() {
JsonObjectRequest jsObjRequest = new JsonObjectRequest
(Request.Method.GET, url, (String) null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
try {
JSONArray ja = response.getJSONArray("receptai");
for (int i = 0; i < ja.length(); i++) {
JSONObject jsonObject = ja.getJSONObject(i);
receptas = new Receptas();
receptas.setPav(jsonObject.getString("pav"));
//receptas.setApras(jsonObject.getString("apras"));
receptas.setIngred_sk(jsonObject.getString("ingred_sk"));
receptasAList.add(receptas);
Log.w("myApp", "receptasAList.add(receptas); " + receptasAList.get(0).getPav());
}
} catch (JSONException e) {
e.printStackTrace();
}
//atliekamas po getRecceptas()
Log.w("myApp", "myAdapter.setReceptasList(receptasAList);");
myAdapter.setReceptasList(receptasAList);
// myAdapter.notifyDataSetChanged();
//mTextView.setText("Response: " + response.toString());
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
// TODO Auto-generated method stub
}
}
);
requestQueue.add(jsObjRequest);
}
}
还有mainactivityclass不过我觉得没必要
如果这个问题不正确,我不知道还能怎么问,但我非常感谢任何帮助。
public MyAdapter(Context context) {
//layoutInflater = layoutInflater.from(context);
}
您在这里混淆了静态方法和实例方法,这是您的问题。此时,字段 layoutInflater
为空。然后您尝试取消引用它并对其调用 .from()
(这是一个静态方法)。
这总是会因 NullPointerException
而崩溃,因为 layoutInflater
为空(此行用于分配它)。
由于 .from()
是一个静态方法,您应该改为使用:
// Note the capitalization -- I'm using the LayoutInflater class to
// reference the static method, not the layoutInflater field.
layoutInflater = LayoutInflater.from(context);
我正在使用这个教程: https://www.youtube.com/watch?v=I2eYBtLWGzc
https://mzgreen.github.io/2015/06/23/How-to-hideshow-Toolbar-when-list-is-scrolling(part3)/
起初我遇到错误:
java.lang.NullPointerException: Attempt to invoke virtual method android.view.View android.view.LayoutInflater.inflate(int, android.view.ViewGroup, boolean)' on a null object reference
at pl.michalz.hideonscrollexample.adapter.parttwo.MyAdapter.onCreateViewHolder(MyAdapter.java:37)
at pl.michalz.hideonscrollexample.adapter.parttwo.MyAdapter.onCreateViewHolder(MyAdapter.java:18)
我对以下内容进行了更改:
@Override
public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
Log.w("myApp", "onCreateViewHolder ");
View view = layoutInflater.inflate(R.layout.recycler_item, parent, false);
return new ViewHolder(view);
}
至:
View view = layoutInflater.from(parent.getContext()).inflate(R.layout.recycler_item, parent, false);
它修复了错误,但只是在几次之后我厌倦了模拟应用程序。我真的很难完成这项工作,所以我不知道这是正确的修复还是我的代码不好,以后可能会出错。
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
private LayoutInflater layoutInflater;
private ArrayList<Receptas> receptasL = new ArrayList<>();
public MyAdapter(Context context) {
//layoutInflater = layoutInflater.from(context);
}
public void setReceptasList(ArrayList<Receptas> receptasL ){
this.receptasL = receptasL;
notifyItemRangeChanged(0, receptasL.size());
}
@Override
public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
Log.w("myApp", "onCreateViewHolder ");
View view = layoutInflater.from(parent.getContext()).inflate(R.layout.recycler_item, parent, false);
return new ViewHolder(view);
}
@Override
public void onBindViewHolder(MyAdapter.ViewHolder holder, int position) {
Receptas receptas = receptasL.get(position);
holder.itemTextViewPav.setText(receptas.getPav());
holder.itemTextViewIngred_sk.setText(receptas.getIngred_sk());
}
@Override
public int getItemCount() {
return receptasL == null ? 0 : receptasL.size();
}
public static class ViewHolder extends RecyclerView.ViewHolder {
TextView itemTextViewPav, itemTextViewIngred_sk;
public ViewHolder(View itemView) {
super(itemView);
itemTextViewPav = (TextView) itemView.findViewById(R.id.itemTextViewPav);
itemTextViewIngred_sk = (TextView) itemView.findViewById(R.id.itemTextViewIngred_sk);
}
}
}
这是用于显示 RecyclerView 的片段 class:
public class PartThreeFragment extends Fragment {
private final String url = "http://smkbaig.esy.es/get_info_test.php";
//pridetas
ArrayList<Receptas> receptasAList = new ArrayList<>();
MyAdapter myAdapter;
RecyclerView recyclerView;
RequestQueue requestQueue;
Receptas receptas;
public static PartThreeFragment createInstance() {
PartThreeFragment partThreeFragment = new PartThreeFragment();
Log.w("myApp", ">>partThree)");
return partThreeFragment;
}
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
Log.w("myApp", "partThree>>");
View view = inflater.inflate(R.layout.fragment_part_three, container, false);
recyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
myAdapter = new MyAdapter(getActivity());
recyclerView.setAdapter(myAdapter);
requestQueue = Volley.newRequestQueue(this.getActivity());
volleyJson();
return view;
}
public void volleyJson() {
JsonObjectRequest jsObjRequest = new JsonObjectRequest
(Request.Method.GET, url, (String) null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
try {
JSONArray ja = response.getJSONArray("receptai");
for (int i = 0; i < ja.length(); i++) {
JSONObject jsonObject = ja.getJSONObject(i);
receptas = new Receptas();
receptas.setPav(jsonObject.getString("pav"));
//receptas.setApras(jsonObject.getString("apras"));
receptas.setIngred_sk(jsonObject.getString("ingred_sk"));
receptasAList.add(receptas);
Log.w("myApp", "receptasAList.add(receptas); " + receptasAList.get(0).getPav());
}
} catch (JSONException e) {
e.printStackTrace();
}
//atliekamas po getRecceptas()
Log.w("myApp", "myAdapter.setReceptasList(receptasAList);");
myAdapter.setReceptasList(receptasAList);
// myAdapter.notifyDataSetChanged();
//mTextView.setText("Response: " + response.toString());
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
// TODO Auto-generated method stub
}
}
);
requestQueue.add(jsObjRequest);
}
}
还有mainactivityclass不过我觉得没必要
如果这个问题不正确,我不知道还能怎么问,但我非常感谢任何帮助。
public MyAdapter(Context context) {
//layoutInflater = layoutInflater.from(context);
}
您在这里混淆了静态方法和实例方法,这是您的问题。此时,字段 layoutInflater
为空。然后您尝试取消引用它并对其调用 .from()
(这是一个静态方法)。
这总是会因 NullPointerException
而崩溃,因为 layoutInflater
为空(此行用于分配它)。
由于 .from()
是一个静态方法,您应该改为使用:
// Note the capitalization -- I'm using the LayoutInflater class to
// reference the static method, not the layoutInflater field.
layoutInflater = LayoutInflater.from(context);