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enter code here`
公共类MainActivity延伸AppCompatActivity {为什么我越来越尝试调用空对象引用的接口方法'int java.util.List.size（）'？
private RecyclerView recyclerView;
private AlbumAdapter adapter;
public List<Album> list;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
new MovieAsyncTask().execute("");
adapter = new AlbumAdapter(this, list);
recyclerView.setLayoutManager(new GridLayoutManager(this, 2));
recyclerView.setAdapter(adapter);
}
public class MovieAsyncTask extends AsyncTask<String,Void,List<Album> >
{
public List<Album> getMovieDataFromJson(String str)
{
List<Album> albumArrayList = new ArrayList<>();
String ImageUrilink = "http://image.tmdb.org/t/p/w342/";
final String RELEASE_DATE = "release_date";
final String RATING = "vote_average";
final String POSTER_PATH = "poster_path";
try {
JSONObject jsonObject = new JSONObject(str);
JSONArray jsonArray = jsonObject.getJSONArray("results");
for(int i=0;i<jsonArray.length();i++)
{
JSONObject jsonObject1 = jsonArray.getJSONObject(i);
String releaseDate = jsonObject1.getString(RELEASE_DATE);
String rating = jsonObject1.getDouble(RATING)+"/10";
String image = ImageUrilink+jsonObject1.getString(POSTER_PATH);
albumArrayList.add(new Album(rating,releaseDate,image));
}
String size = jsonArray.length()+" ITEM";
Log.v("SIZE OF ALBUMLIST = ",size);
return albumArrayList;
}
catch (JSONException j)
{
j.printStackTrace();
}
return null;
}
@Override
protected List<Album> doInBackground(String... params) {
BufferedReader reader = null;
HttpURLConnection httpURLConnection = null;
String readJson ;
final String Sortby = "sort_by";
final String APPID_PARAM = "api_key";
try {
String movieUri = "https://api.themoviedb.org/3/discover/movie?";
Uri buildUri = Uri.parse(movieUri).buildUpon().appendQueryParameter(Sortby,"popularity.desc")
.appendQueryParameter(APPID_PARAM,BuildConfig.MOVIE_API_KEY).build();
URL url = new URL(buildUri.toString());
Log.v("LOG_TAG",buildUri.toString());
httpURLConnection = (HttpURLConnection)url.openConnection();
httpURLConnection.setRequestMethod("GET");
httpURLConnection.connect();
InputStream inputStream = httpURLConnection.getInputStream();
StringBuffer stringBuffer = new StringBuffer();
if(inputStream==null)
{
return null;
}
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
// Since it's JSON, adding a newline isn't necessary (it won't affect parsing)
// But it does make debugging a *lot* easier if you print out the completed
// buffer for debugging.
stringBuffer.append(line + "\n");
}
if(stringBuffer==null)
{
return null;
}
readJson = stringBuffer.toString();
return getMovieDataFromJson(readJson);
}catch (IOException I)
{
I.printStackTrace();
}
finally {
if(httpURLConnection!=null)
{
httpURLConnection.disconnect();
}
if(reader!=null)
{
try {
reader.close();
}catch(IOException I)
{
I.printStackTrace();
}
}
}
return null;
}
@Override
protected void onPostExecute(List<Album> albumList) {
if(!albumList.isEmpty())
{
super.onPostExecute(albumList);
list = albumList;
}
}
}
}
公共类AlbumAdapter延伸RecyclerView.Adapter {
private Context mcontext;
private List<Album> albumList;
public class MyViewHolder extends RecyclerView.ViewHolder {
public TextView rating, releaseDate;
public ImageView thumbnail, overflow;
public MyViewHolder(View view) {
super(view);
rating = (TextView) view.findViewById(R.id.title);
releaseDate = (TextView) view.findViewById(R.id.count);
thumbnail = (ImageView) view.findViewById(R.id.thumbnails);
overflow = (ImageView) view.findViewById(R.id.overflow);
}
}
public AlbumAdapter(Context mcontext1, List<Album> albumList1) {
mcontext = mcontext1;
albumList = albumList1;
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(mcontext).inflate(R.layout.album_card, parent, false);
return new MyViewHolder(view);
}
@Override
public void onBindViewHolder(final MyViewHolder holder, int position) {
Album album = albumList.get(position);
holder.rating.setText(album.getRating());
holder.releaseDate.setText(album.getReleaseDate()+" Songs ");
Picasso.with(mcontext).load(album.getThumbnail()).into(holder.thumbnail);
Log.v("IMAGE_URL",album.getThumbnail());
holder.overflow.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
showPopUp(holder.overflow);
}
});
}
/**
* showing popup menu wher tapping on 3 dots
*/
private void showPopUp(View view)
{
PopupMenu popupMenu = new PopupMenu(mcontext,view);
MenuInflater inflater = popupMenu.getMenuInflater();
inflater.inflate(R.menu.menu_album,popupMenu.getMenu());
popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
@Override
public boolean onMenuItemClick(MenuItem item) {
switch (item.getItemId())
{
case R.id.action_add_favourite :
Toast.makeText(mcontext,"Add to favourite",Toast.LENGTH_SHORT).show();
return true;
case R.id.action_play_next :
Toast.makeText(mcontext,"Play next",Toast.LENGTH_SHORT).show();
return true;
}
return false;
}
});
}
@Override
public int getItemCount() {
return albumList.size();
}
}
异常
11-13 15:07:00.587 26661-26661/com.example.sanket3125.cardgridviewexample E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.sanket3125.cardgridviewexample, PID: 26661
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at com.example.sanket3125.cardgridviewexample.AlbumAdapter.getItemCount(AlbumAdapter.java:106)
at android.support.v7.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:3225)
at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:2837)
at android.view.View.measure(View.java:18811)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:716)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:462)
at android.view.View.measure(View.java:18811)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:700)
at android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild(HeaderScrollingViewBehavior.java:90)
at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1364)
at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:765)
at android.view.View.measure(View.java:18811)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
at android.view.View.measure(View.java:18811)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18811)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18811)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18811)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2645)
at android.view.View.measure(View.java:18811)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2127)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1243)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1535)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1134)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6045)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:860)
at android.view.Choreographer.doCallbacks(Choreographer.java:672)
at android.view.Choreographer.doFrame(Choreographer.java:608)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:846)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5441)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)