滚动后的无序 RecycleView 列表

【问题标题】：An unordered RecycleView list after scrolling滚动后的无序 RecycleView 列表
【发布时间】：2020-06-13 11:04:16
【问题描述】：

如果我用鼠标滚轮滚动这个列表RecycleView，我在列表中的项目看起来像是无序的。 我不懂为什么？

An incorrect clicked item in the new activity from RecycleView

我尝试创建单独的类CrimeAdapter extends RecyclerView.Adapter<CrimeAdapter.CrimeHolder> 和 class CrimeHolder extends RecyclerView.ViewHolder implements View.OnClickListener 在单独的文件中，但我做错了。 不幸的是，我没有足够的经验。

方法public void onClick(View v)不知道怎么写正确的代码

Crime.java

package com.bignerdranch.android.criminalintent;

import java.util.Date;
import java.util.UUID;

public class Crime{

    private UUID mId;
    private String mTitle;
    private Date mDate;
    private boolean mSolved;
    private boolean mRequiresPolice;

    public Crime() {
        // Generate unique identifier
        this(UUID.randomUUID());
    }

    public Crime(UUID id) {
        mId = id;
        mDate = new Date();
    }

    public UUID getId() {
        return mId;
    }

    public String getTitle() {
        return mTitle;
    }

    public void setTitle(String title) {
        mTitle = title;
    }

    public Date getDate() {
        return mDate;
    }

    public void setDate(Date date) {
        mDate = date;
    }

    public boolean isSolved() {
        return mSolved;
    }

    public void setSolved(boolean solved) {
        mSolved = solved;
    }

    public boolean isRequiresPolice() {
        return mRequiresPolice;
    }

    public void setRequiresPolice(boolean requiresPolice) {
        mRequiresPolice = requiresPolice;
    }
}

CrimeLab.java

package com.bignerdranch.android.criminalintent;

import android.content.Context;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.UUID;


public class CrimeLab {

    private static CrimeLab sCrimeLab;
    private List<Crime> mCrimes;

    public static CrimeLab get(Context context) {
        if (sCrimeLab == null) {
            sCrimeLab = new CrimeLab(context);
        }
        return sCrimeLab;
    }

    private CrimeLab(Context context){

        mCrimes = new ArrayList<>();
        for (int i = 0; i < 100; i++) {
            Crime crime = new Crime();
            crime.setTitle("Crime #" + i);
            crime.setSolved(i % 2 == 0); 
            if (i % 4 == 0 ) {crime.setRequiresPolice(true);}
            else {crime.setRequiresPolice(false);}
            mCrimes.add(crime);
        }

    }

    public List<Crime> getCrimes() {
        return mCrimes;
    }

    public  Crime getCrime(UUID id){

        for (Crime crime : mCrimes){
            int rez = id.compareTo(crime.getId());
            if (crime.getId().equals(id)){
                return crime;
            }
        }
        return null;
    }

}

CrimeListFragment.java

package com.bignerdranch.android.criminalintent;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.text.format.DateFormat;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import androidx.annotation.LayoutRes;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import java.util.Date;
import java.util.List;

public class CrimeListFragment extends Fragment {

    private static final int REQUEST_CRIME = 1;

    private static final int NOT_REQUIRES_POLICE = 0;
    private static final int REQUIRES_POLICE = 1;

    private RecyclerView mCrimeRecyclerView;
    private CrimeAdapter mAdapter;
    private TextView mTitleTextView;
    private TextView mDateTextView;
    private ImageView mSolvedImageView;
    private Button mButtonCallPolice;
    private Crime mCrime;
    private CharSequence mDateFormat;
    private  int layout;

    @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 class CrimeHolder extends RecyclerView.ViewHolder implements View.OnClickListener {


         public CrimeHolder(int layout, LayoutInflater inflater, ViewGroup parent ) {


            super(inflater.inflate(layout, parent, false));

            mTitleTextView = (TextView) itemView.findViewById(R.id.crime_title);
            mDateTextView = (TextView) itemView.findViewById(R.id.crime_date);
            mSolvedImageView = (ImageView) itemView.findViewById(R.id.crime_solved);

            if (itemView.findViewById(R.id.call_police)!=null) {
                mButtonCallPolice = (Button) itemView.findViewById(R.id.call_police);
            }

            itemView.setOnClickListener(this);
        }

        public void bind(Crime crime) {

            mCrime = crime;
            mTitleTextView.setText(mCrime.getTitle());
            mDateFormat = DateFormat.format("EEE, MMM dd, yyyy", mCrime.getDate());

            mDateTextView.setText(mDateFormat);
            mSolvedImageView.setVisibility(mCrime.isSolved() ? View.VISIBLE :
                    View.GONE);

            if(mCrime.isRequiresPolice()){
                mButtonCallPolice.setEnabled(true);
            }
        }

        @Override
        public void onClick(View view) {

            Intent intent = CrimePagerActivity.newIntent(getActivity(),
                    CrimeLab.get(requireActivity()).getCrimes().get((getAdapterPosition())).getId());

            startActivityForResult(intent, REQUEST_CRIME);
        }

    }

    private class CrimeAdapter extends RecyclerView.Adapter<CrimeHolder> {


        private List<Crime> mCrimes;
        public CrimeAdapter(List<Crime> crimes) {
            mCrimes = crimes;
        }

       @Override
        public CrimeHolder onCreateViewHolder(ViewGroup parent, int viewType) {

            LayoutInflater layoutInflater = LayoutInflater.from(getActivity());

            if (viewType==1) { layout =  R.layout.list_item_crime_police;}

            else {             layout =  R.layout.list_item_crime;       }

            return new CrimeHolder (layout, 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();
        }


        public int getItemViewType(int position) {

            Crime crime = mCrimes.get(position);

            return (crime.isRequiresPolice()) ? 1 : 0;

        }

    }


    @Override
    public void onResume() {
        super.onResume();
        updateUI();
    }

    private void updateUI() {
        CrimeLab crimeLab = CrimeLab.get(getActivity());
        List<Crime> crimes = crimeLab.getCrimes();
        if (mAdapter == null) {
            mAdapter = new CrimeAdapter(crimes);
            mCrimeRecyclerView.setAdapter(mAdapter);
        } else {

            mAdapter.notifyDataSetChanged();

        }
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {

        if (requestCode == REQUEST_CRIME) {
            // Обработка результата
        }

    }

    public void returnResult() {
        getActivity().setResult(Activity.RESULT_OK, null);
    }

}

CrimePagerActivity.java

package com.bignerdranch.android.criminalintent;

import android.content.Context;
import android.content.Intent;
import android.os.Bundle;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentStatePagerAdapter;

import androidx.viewpager.widget.ViewPager;

import java.util.List;
import java.util.UUID;

public class CrimePagerActivity extends AppCompatActivity {

    private static final String EXTRA_CRIME_ID = "com.bignerdranch.android.criminalintent.crime_id";

    private ViewPager mViewPager;
    private List<Crime> mCrimes;
    MyAdapter mAdapter;

    public static Intent newIntent(Context packageContext, UUID crimeId) {
        Intent intent = new Intent(packageContext, CrimePagerActivity.class);
        intent.putExtra(EXTRA_CRIME_ID, crimeId);
        return intent;
    }

    @Override
    protected void onCreate( Bundle savedInstanceState ) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_crime_pager);

        UUID crimeId = (UUID) getIntent().getSerializableExtra(EXTRA_CRIME_ID);

        mViewPager = (ViewPager) findViewById(R.id.crime_view_pager);

        mCrimes = CrimeLab.get(this).getCrimes();

        mAdapter = new MyAdapter(getSupportFragmentManager(),mCrimes);
        mViewPager.setAdapter(mAdapter);

        for (int i = 0; i < mCrimes.size(); i++) {
            if (mCrimes.get(i).getId().equals(crimeId)) {
                mViewPager.setCurrentItem(i);
                break;
            }
        }

    }

    public static class MyAdapter extends FragmentStatePagerAdapter {

        private List<Crime> mCrimesCopy;

        public MyAdapter(FragmentManager fm, List<Crime> mCrimesParametr) {
            //super(fm);
            super(fm, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
            this.mCrimesCopy = mCrimesParametr;

        }

        @Override
        public int getCount() {
            return mCrimesCopy.size();
        }

        @Override
        public Fragment getItem(int position) {
            Crime crime = mCrimesCopy.get(position);
            return CrimeFragment.newInstance(crime.getId());
        }
    }
}

fragment_crime_list.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.recyclerview.widget.RecyclerView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/crime_recycler_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

fragment_crime.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_margin="16dp"
    android:orientation="vertical">
    <TextView
        style="?android:listSeparatorTextViewStyle"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/crime_title_label"/>
    <EditText
        android:id="@+id/crime_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="@string/crime_title_hint"
        android:inputType=""
        android:autofillHints="" />
    <TextView
        style="?android:listSeparatorTextViewStyle"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/crime_details_label"/>
    <Button
        android:id="@+id/crime_date"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
    <CheckBox
        android:id="@+id/crime_solved"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/crime_solved_label"/>
</LinearLayout>

list_item_crime_police.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/linearLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

    <TextView
        android:id="@+id/crime_title"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="8dp"
        android:text="@string/crime_title"
        android:textColor="@android:color/black"
        android:textSize="18sp"
        app:layout_constraintEnd_toStartOf="@+id/crime_solved"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/crime_date"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:text="@string/crime_date"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/crime_solved" />

    <Button
        android:id="@+id/call_police"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:layout_marginBottom="8dp"
        android:text="@string/call_police"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/crime_date" />

    <ImageView
        android:id="@+id/crime_solved"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="8dp"
        android:layout_marginBottom="16dp"
        android:contentDescription="@string/todo"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/ic_solved" />

</androidx.constraintlayout.widget.ConstraintLayout>

list_item_crime.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/linearLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

        <TextView
            android:id="@+id/crime_title"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="16dp"
            android:layout_marginTop="16dp"
            android:layout_marginEnd="8dp"
            android:text="@string/crime_title"
            android:textColor="@android:color/black"
            android:textSize="18sp"
            app:layout_constraintEnd_toStartOf="@+id/crime_solved"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/crime_date"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="16dp"
            android:layout_marginTop="8dp"
            android:layout_marginEnd="8dp"
            android:text="@string/crime_date"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/crime_solved" />

        <ImageView
            android:id="@+id/crime_solved"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="16dp"
            android:layout_marginEnd="8dp"
            android:layout_marginBottom="16dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:srcCompat="@drawable/ic_solved"
            android:contentDescription="@string/todo" />

</androidx.constraintlayout.widget.ConstraintLayout>

activity_crime_pager.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.viewpager.widget.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/crime_view_pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

</androidx.viewpager.widget.ViewPager>

activity_fragment.xml

<?xml version="1.0" encoding="utf-8"?>
    <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fragment_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

【问题讨论】：

  • 您应该直接在此处发布相关代码，以便可以独立于您的其他问题阅读此问题。
  • 不要相信来自模拟器的视觉效果：D
  • 我已经在我的智能手机中检查了这个应用程序，我得到了类似的结果。
  • @ВладГ_VladG，正如我所说，您没有将 CrimeHolder 和 CrimeAdapter 类移动到单独的文件 CrimeAdapter.java。在您在此处发布的代码中，CrimeAdapter 仍在 CrimeFragment 类中。

标签： java android android-recyclerview


【解决方案1】：

我认为RecyclerView 中的项目是无序的，因为在您的list_item_crime_police.xml 或list_item_crime.xml 布局文件中存在的views 的引用被声明为CrimeListFragment 的类成员，而不是在CrimeHolder 中类为：

public class CrimeListFragment extends Fragment {

    // your other views and variables related declarations
    // these are problematic declaration that keeps on being reused
    private TextView mTitleTextView;
    private TextView mDateTextView;
    private ImageView mSolvedImageView;
    private Button mButtonCallPolice;
    // your other declarations

    // your other code
}

这就是为什么每个CrimeHolder 实例都重复使用相同的view 实例，例如mTitleTextView、mDateTextView、mSolvedImageView、mButtonCallPolice 等，从而导致列表中的项目无序. 现在，为了解决这个问题，您可以简单地将这些行代码移动到 CrimeHolder 类作为类变量，这将确保每个新的 CrimeHolder 实例都有上述视图的单独实例 作为：

private class CrimeHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
         // declare all of them here so there will be unique instances of these views for unique viewholder
         private TextView mTitleTextView;
         private TextView mDateTextView;
         private ImageView mSolvedImageView;
         private Button mButtonCallPolice;

         public CrimeHolder(int layout, LayoutInflater inflater, ViewGroup parent ) {

            View itemView = inflater.inflate(layout, parent, false));
            super(itemView);

            mTitleTextView = (TextView) itemView.findViewById(R.id.crime_title);
            mDateTextView = (TextView) itemView.findViewById(R.id.crime_date);
            mSolvedImageView = (ImageView) itemView.findViewById(R.id.crime_solved);

            if (itemView.findViewById(R.id.call_police)!=null) {
                mButtonCallPolice = (Button) itemView.findViewById(R.id.call_police);
            }

            itemView.setOnClickListener(this);
        }

        public void bind(Crime crime) {

            mCrime = crime;
            mTitleTextView.setText(mCrime.getTitle());
            mDateFormat = DateFormat.format("EEE, MMM dd, yyyy", mCrime.getDate());

            mDateTextView.setText(mDateFormat);
            mSolvedImageView.setVisibility(mCrime.isSolved() ? View.VISIBLE :
                    View.GONE);

            if(mCrime.isRequiresPolice()){
                mButtonCallPolice.setEnabled(true);
            }
        }

        @Override
        public void onClick(View view) {

            Intent intent = CrimePagerActivity.newIntent(getActivity(),
                    CrimeLab.get(requireActivity()).getCrimes().get((getAdapterPosition())).getId());

            startActivityForResult(intent, REQUEST_CRIME);
        }

    }

它解决了我的问题，我希望它也能解决你的问题。

【讨论】：

  • 2cgb_pandey，非常感谢。你的建议很有用。我解决了这个问题。祝你好运！！！
  • 很高兴能为您提供帮助。
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