这个应用程序直接从API获取数据。当它运行时会发生这种类型的错误。基本上我认为错误发生在getItemCount()方法中,但我无法解决问题。我已经附加了错误文件和整个代码。如果您能解决错误,我将非常感激。
java.lang.NullPointerException:尝试在android.support的com.techbrightsoft.database.MyRecyler.getItemCount(MyRecyler.java:36)上的空对象引用上调用接口方法“int java.util.List.size()”。 v7.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:3603)在android.sview.view.measure(View.java:20151)的android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:3103) .support.constraint.ConstraintLayout.internalMeasureChildren(ConstraintLayout.java:934)在android.support.constraint.ConstraintLayout.onMeasure(ConstraintLayout.java:973)在android.view.View.measure(View.java:20151)在机器人。 view.ViewGroup.measureChildWithMargins(ViewGroup.java:6330)在android.widget.FrameLayout.onMeasure(FrameLayout.java:194)在android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)在android.view .View.measure(View.java:20151)位于android.sview.view.measure.View.Stallgins(ViewGroup.java:6330)的android.support.v7.widget.Act ionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:400)在android.view.View.measure(View.java:20151)在android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6330)在android.widget.FrameLayout.onMeasure(的FrameLayout的.java:194)在android.view.View.measure(View.java:20151)在android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6330)在android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)在android.view上的android.widget.Lineout.measureVertical(LinearLayout.java:747),android.view上的android.view.View.measure(View.java:20151)上的android.widget.LinearLayout.onMeasure(LinearLayout.java:629)。 ViewGroup.measureChildWithMargins(ViewGroup.java:6330)在android.widget.FrameLayout.onMeasure(FrameLayout.java:194)在com.android.internal.policy.PhoneWindow $ DecorView.onMeasure(PhoneWindow.java:3158)在android.view .View.measure(View.java:20151)位于android.view.ViewRootImpl.measureHierarchy(vi)的android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2594) ewRootImpl.java:1549)维持在android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1437)在android.view.ViewRootImpl $ TraversalRunnable.run android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1841)(ViewRootImpl.java :7397)在android.view.Choreographer,我在Android.view.Chore上传(知识分子编辑:java:695),在android.view.Choreographer.doCrame(Choreographer.java:631)上的android.view.Choreographer $ CallbackRecord.run(Choreographer.java:950)在Android.google.view.Choreographer $ FrameDisplayEventReceiver.run(Choreographer.java:906)在Android.os.Handler.dispatchMessage(Handler.java:95)的android.os.Handler.handleCallback(Handler.java:739)。 os.Looper.loop(Looper.java:158)位于com.android.internal.os的java.lang.reflect.Method.invoke(Native Method)的android.app.ActivityThread.main(ActivityThread.java:7224)。 ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:1230)at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
public class MyRecyler extends RecyclerView.Adapter<MyRecyler.MyHolder> {
private Context context;
private ArrayList<String> names;
public MyRecyler(Context context, ArrayList<String> names) {
this.context = context;
this.names = names;
}
@Override
public MyHolder onCreateViewHolder(ViewGroup parent, int viewType) {
LayoutInflater inflater = LayoutInflater.from(this.context);
View view = inflater.inflate(R.layout.names, parent, false);
return new MyHolder(view);
}
@Override
public void onBindViewHolder(MyHolder holder, int position) {
holder.name.setText(this.names.get(position));
}
@Override
public int getItemCount() {
return names.size();
}
public class MyHolder extends RecyclerView.ViewHolder {
TextView name;
public MyHolder(View itemView) {
super(itemView);
name = itemView.findViewById(R.id.name);
}
}
public class MainActivity extends AppCompatActivity {
public static ArrayList<String> authors_names ;
RecyclerView recyclerView;
EditText editText;
Button button;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = findViewById(R.id.recyclerView);
// Downloading Data From Internet
DownloadingData downloadingData = new DownloadingData();
downloadingData.execute("https://newsapi.org/v1/articles?source=the-next-web&sortBy=latest&apiKey=a301a9e90c774b4ebf7eb21000cdbdef");
// RecyclerView Set
MyRecyler recyler = new MyRecyler(MainActivity.this,authors_names);
recyclerView.setAdapter(recyler);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyler.notifyDataSetChanged();
}
}
看来这段代码没有正确初始化authors_names
。如果我猜错你的代码逻辑,你想用authors_names
的结果填充downloadingData
。通常,将该列表传递给适配器是一种不好的做法。
我的建议是用空列表初始化names
并定义一个用于更新其内容的addAll()
方法。一个简单而未经优化的实现将是这样的:
private ArrayList<String> names = new ArrayList<>();
public void addAll(ArrayList<String> items) {
names.clear();
names.addAll(items);
notifyDatasetChanged();
}
当addAll()
完成其工作时(通常通过回调),您需要使用主代码中的downloadingData
方法添加项目。