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我試圖構建一個應用程序，該應用程序從JSON中填充ListView。當我嘗試使用notifyDataSetChanged更新列表視圖時，出現以下異常。從onCreateView方法外部更新ListView適配器
嘗試上的空對象引用
的ListView的調用虛擬方法 '無效 com.example.android.Wordtrend.CustomArrayAdapter.notifyDataSetChanged（）' 是一個片段的內部。我使用onPostExecute方法來調用片段內的更新方法來更新ArrayAdapter。 UI會加載onCreateView方法中提供的虛擬數據，但在更新過程中會失敗。
我是新手，所以任何建議都會大有幫助。我感到困惑，因爲ArrayAdapter爲null，更新方法中dataArray的大小爲零。
活動：
公共類ClassicActivity延伸AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activitycategory);
getSupportFragmentManager().beginTransaction().replace(R.id.container,new ClassicFragment()).commit();
}
}
片段：
public class ClassicFragment extends Fragment {
CustomArrayAdapter adapter;
ArrayList<dataobjects> dataArray=new ArrayList<>();
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
dataArray.clear();
dataArray.add(new dataobjects("word","Explanation",R.drawable.placeholder,R.raw.color_black));
dataArray.add(new dataobjects("word","Explanation",R.drawable.placeholder,R.raw.color_black));
dataArray.add(new dataobjects("word","Explanation",R.drawable.placeholder,R.raw.color_black));
View rootView=inflater.inflate(R.layout.word_list,container,false);
ListView listView=(ListView)rootView.findViewById(R.id.list);
adapter=new CustomArrayAdapter(getActivity(),dataArray,R.color.classic);
listView.setAdapter(adapter);
return rootView;
}
public void update(ArrayList<FinalData> e){
ArrayList<dataobjects> newDataArray=new ArrayList<>(); // update Adapter from JSON
for(int i=0;i<e.size();i++) {
FinalData FinalDataObject = e.get(i);
String word=FinalDataObject.getWord();
String meaning=FinalDataObject.getMeaning();
newDataArray.add(new dataobjects(word,meaning,R.drawable.placeholder,R.raw.color_black));
}
Log.d("Classic"," Size of Data"+dataArray.size()); // Shows zero but im not clearing it manually. Should be two.
dataArray.addAll(newDataArray); // Size changes to 7 as expected.
adapter.notifyDataSetChanged();
}
//從類中調用更新方法Dataprocess
public class Data extends AsyncTask<String,Void,String> {
String Mdata;
@Override
protected void onPostExecute(String s) {
Mdata=s;
Dataprocess d=new Dataprocess();
d.process(Mdata);
super.onPostExecute(s);
}.....}
public class Dataprocess {
Finaldata f;
ArrayList<Finaldata> wordList=new ArrayList<>();
ClassicFragment classicfragment=new ClassicFragment();
public void process(String s){
if(s!=null){
try {
JSONObject data = new JSONObject(s);
JSONArray word = data.getJSONArray("WordArray");
for (int i = 0; i < word.length(); i++){
JSONObject c = word.getJSONObject(i);
String word1=c.getString("word");
String meaning=c.getString("meaning");
f=new Finaldata(word1,meaning);
wordList.add(f);
}
classicfragment.update(wordList);
}catch (Exception e){
}
}
}
}
CustomArray的適配器：
public class CustomArrayAdapter extends ArrayAdapter<dataobjects> {
int color;
public static MediaPlayer mediaPlayer;
static AudioManager am;
private TextToSpeech tts;
static MediaPlayer.OnCompletionListener oncom=new MediaPlayer.OnCompletionListener() {
@Override
public void onCompletion(MediaPlayer mp) {
release();
}
};
public CustomArrayAdapter(Activity context, ArrayList<dataobjects> a, int color) {
super(context,0,a);
this.color=color;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View listitemview=convertView;
if(listitemview==null){
listitemview= LayoutInflater.from(getContext()).inflate(R.layout.customlayout,parent,false);
}
dataobjects currentword=getItem(position);
TextView t1=(TextView)listitemview.findViewById(R.id.textView);
TextView t2=(TextView)listitemview.findViewById(R.id.textView2);
View background1=listitemview.findViewById(R.id.back);
View background2=listitemview.findViewById(R.id.back2);
background1.setBackgroundColor(colorid);
background2.setBackgroundColor(colorid);
int ex=currentword.getImageURL();
int aud=currentword.getSound();
t1.setText(currentword.getWord());
t2.setText(currentword.getTransalation());
int colorid= ContextCompat.getColor(getContext(),color);
ImageView im1=(ImageView)listitemview.findViewById(R.id.media);
im1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
test();
}
});
return listitemview;
}
關鍵是你在哪裏以及如何調用update（），並且該部分丟失了！ – rupps
對不起，我的無知。編輯該帖子的其他細節。 –