如果之前有人问过这个问题,我很抱歉,但我似乎找不到该问题的解决方案。
我正在 Android Studio 中工作,并遵循一本有关开发应用程序和使用 RecyclerView 的书中的教程,并且该应用程序正在停止,即使它在 Android Studio 中编译。
该代码与书中的代码完全相同,因此我检查了 Logcat 给出了以下类型的错误:
FATAL EXCEPTION: main Process: ndroid.bignerdranch.com, PID: 17436 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference at ndroid.bignerdranch.com.CrimeListFragment$CrimeHolder.bind (CrimeListFragment.java:62) at ndroid.bignerdranch.com.CrimeListFragment$CrimeAdapter.onBindViewHolder** (CrimeListFragment.java:91)** at ndroid.bignerdranch.com.CrimeListFragment$CrimeAdapter.onBindViewHolder** (CrimeListFragment.java:74)** at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7056) at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7098) at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6010)
这里是 CrimeListFragment 类代码,似乎有错误:
package ndroid.bignerdranch.com; import android.os.Bundle; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.TextView; import android.widget.Toast; import java.util.List; import androidx.fragment.app.Fragment; import androidx.recyclerview.widget.LinearLayoutManager; import androidx.recyclerview.widget.RecyclerView; import ndroid.bignerdranch.com.R; public class CrimeListFragment extends Fragment { private RecyclerView mCrimeRecyclerView; private CrimeAdapter mAdapter; @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View view = inflater.inflate(R.layout.fragment_crime_list, container, false); mCrimeRecyclerView = (RecyclerView) view .findViewById(R.id.crime_recycler_view); mCrimeRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity())); updateUI(); return view; } private void updateUI() { CrimeLab crimeLab = CrimeLab.get(getActivity()); List crimes = crimeLab.getCrimes(); mAdapter = new CrimeAdapter(crimes); mCrimeRecyclerView.setAdapter(mAdapter); } private class CrimeHolder extends RecyclerView.ViewHolder implements View.OnClickListener { private Crime mCrime; private TextView mTitleTextView; private TextView mDateTextView; public CrimeHolder(LayoutInflater inflater, ViewGroup parent) { super(inflater.inflate(R.layout.list_item_crime, parent, false)); itemView.setOnClickListener(this); mTitleTextView = (TextView) itemView.findViewById(R.id.crime_title); mDateTextView = (TextView) itemView.findViewById(R.id.crime_date); } public void bind(Crime crime) { mCrime = crime; mTitleTextView.setText(mCrime.getTitle()); mDateTextView.setText(mCrime.getDate().toString()); } @Override public void onClick(View view) { Toast.makeText(getActivity(), mCrime.getTitle() + " clicked!", Toast.LENGTH_SHORT) .show(); } } private class CrimeAdapter extends RecyclerView.Adapter { private List mCrimes; public CrimeAdapter(List crimes) { mCrimes = crimes; } @Override public CrimeHolder onCreateViewHolder(ViewGroup parent, int viewType) { LayoutInflater layoutInflater = LayoutInflater.from(getActivity()); return new CrimeHolder(layoutInflater, parent); } @Override public void onBindViewHolder(CrimeHolder holder, int position) { Crime crime = mCrimes.get(position); holder.bind(crime); } @Override public int getItemCount() { return mCrimes.size(); } } }
最佳答案
您的mTitleTextView
为null,并且您尝试调用null的方法。变量在上面的方法中被赋值:
mTitleTextView = (TextView) itemView.findViewById(R.id.crime_title);
当 findViewById
方法在调用它的 View (在您的情况下为 itemView
)内找不到具有给定 id 的 View 时,它会返回 null。我在您的代码中找不到此 View 的来源,但您需要检查并确保 ID 为 crime_title
的 View 实际上是其中的一部分。
关于java - 应用程序在 Android Studio 中停止,但它可以编译,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/57944657/