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java - NULL 指针异常错误应用程序在单击回收器列表项后崩溃

问题描述

我正在开发一个在 Recycle List View Holder 中显示数据的 android 应用程序。当我单击 Recycler View Holder 中的列表项时，应用程序崩溃。

public class UserRecyclerAdapterSavedUsers extends RecyclerView.Adapter<UserRecyclerAdapterSavedUsers.UserViewHolder> {

private List<User> listUsers;
Context mContext;
ItemClickListenerLongPressed itemClickListenerLongPressed;

public UserRecyclerAdapterSavedUsers(List<User> listUsers) {
    this.listUsers = listUsers;
}


@Override
public UserViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View itemView = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.item_user_recycler_second, parent, false);

    return new UserViewHolder(itemView);
}



@Override
public void onBindViewHolder(UserViewHolder holder, int position) {
    holder.textViewID.setText(listUsers.get(position).getUserid());
    holder.textViewName.setText(listUsers.get(position).getName());
    holder.textViewPassword.setText(listUsers.get(position).getPassword());
    holder.textViewRole.setText(listUsers.get(position).getRole());

}

public void setItemClickListenerLongPressed(ItemClickListenerLongPressed itemClickListenerLongPressed){
    this.itemClickListenerLongPressed=itemClickListenerLongPressed;
}

@Override
public int getItemCount() {
    Log.v(UserRecyclerAdapterSavedUsers.class.getSimpleName(),""+listUsers.size());
    return listUsers.size();
}

/**
 * ViewHolder class
 */
public class UserViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

    //public AppCompatTextView ID;
    public AppCompatTextView textViewID;
    public AppCompatTextView textViewName;
    public AppCompatTextView textViewPassword;
    public AppCompatTextView textViewRole;

    public UserViewHolder(View view) {
        super(view);

        textViewID = (AppCompatTextView) view.findViewById(R.id.textViewID);
        textViewName = (AppCompatTextView) view.findViewById(R.id.textViewName);
        textViewPassword = (AppCompatTextView) view.findViewById(R.id.textViewPassword);
        textViewRole = (AppCompatTextView) view.findViewById(R.id.textViewRole);
    }

    @Override
    public void onClick(View v) {
        if (itemClickListenerLongPressed != null) itemClickListenerLongPressed.onClick(v, getAdapterPosition());
        Toast.makeText(mContext, "USMAN", Toast.LENGTH_SHORT).show();

    }
}

}

这是用户列表活动

public class UsersListActivity extends AppCompatActivity implements ItemClickListenerLongPressed{

AppCompatActivity activity = UsersListActivity.this;

AppCompatTextView textViewName;
RecyclerView mRecyclerView;
AppCompatButton textViewButtonNewUser;
UserRecyclerAdapterSavedUsers userRecyclerAdapterSavedUsers;
List<User> listUsers;

DatabaseHelper databaseHelper;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_user_record_updated_list);
    mRecyclerView= (RecyclerView) findViewById(R.id.recyclerViewUsers);
    mRecyclerView.setAdapter(userRecyclerAdapterSavedUsers);
    userRecyclerAdapterSavedUsers.setItemClickListenerLongPressed(this);

    initViews();
    initObjects();
}

@Override
public void onBackPressed() {
    super.onBackPressed();
    startActivity(new Intent(UsersListActivity.this,AdminMain.class));
    finish();
}

@Override
protected void onRestart() {
    super.onRestart();
}


/**
 * This method is to initialize views
 */
private void initViews() {
    textViewName = (AppCompatTextView) findViewById(R.id.textViewName);
    textViewButtonNewUser = (AppCompatButton) findViewById(R.id.btnaddnew);
    mRecyclerView = (RecyclerView) findViewById(R.id.recyclerViewUsers);
    textViewButtonNewUser.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            startActivity(new Intent(UsersListActivity.this,UserRecordSaveActivity.class));
        }
    });

}

/**
 * This method is to initialize objects to be used
 */
private void initObjects() {
    listUsers = new ArrayList<>();
    userRecyclerAdapterSavedUsers = new UserRecyclerAdapterSavedUsers(listUsers);

    RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
    mRecyclerView.setLayoutManager(mLayoutManager);
    mRecyclerView.setItemAnimator(new DefaultItemAnimator());
    mRecyclerView.setHasFixedSize(true);
    mRecyclerView.setAdapter(userRecyclerAdapterSavedUsers);
    databaseHelper = new DatabaseHelper(activity);

    String emailFromIntent = getIntent().getStringExtra("USERS");
    textViewName.setText(emailFromIntent);

    getDataFromSQLite();
}

/**
 * This method is to fetch all user records from SQLite
 */
private void getDataFromSQLite() {
    // AsyncTask is used that SQLite operation not blocks the UI Thread.
    new AsyncTask<Void, Void, Void>() {
        @Override
        protected Void doInBackground(Void... params) {
            listUsers.clear();
            listUsers.addAll(databaseHelper.getAllUser());

            return null;
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            super.onPostExecute(aVoid);
            userRecyclerAdapterSavedUsers.notifyDataSetChanged();
        }
    }.execute();
}

@Override
public void onClick(View view, int position) {

}

}

当我单击列表项时，它崩溃了，错误是由 Toast 引起的。当我删除 toast 时，由于使用了未单击的 try catch 项，因此出现错误。

这是错误的图像。

删除 try catch 后再次显示错误，但这次错误显示在 AlertDialog 上。生成器。这是没有尝试捕获的错误图像。

删除 try and catch 后的图像

点击删除吐司前的错误

添加 toast 后的图像 logcat 添加 Toast 后的错误图像

错误现在出现在用户列表活动 图像上

移除点击监听时列表中的实际数据 移除点击监听 后列表中的实际数据

这是我的回收站布局文件

<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
card_view:cardCornerRadius="4dp">
<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@color/Indigo"
    android:orientation="vertical"
    android:padding="16dp">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <android.support.v7.widget.AppCompatTextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="2"
            android:text="User ID"
            android:textColor="@color/colorTextHint" />

        <android.support.v7.widget.AppCompatTextView
            android:id="@+id/textViewID"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="User ID"
            android:textColor="@android:color/darker_gray" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="5dp"
        android:orientation="horizontal">

        <android.support.v7.widget.AppCompatTextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="2"
            android:text="Name"
            android:textColor="@color/colorTextHint" />

        <android.support.v7.widget.AppCompatTextView
            android:id="@+id/textViewName"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Name"
            android:textColor="@android:color/darker_gray" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="5dp"
        android:orientation="horizontal">

        <android.support.v7.widget.AppCompatTextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="2"
            android:text="@string/hint_password"
            android:textColor="@color/colorTextHint" />

        <android.support.v7.widget.AppCompatTextView
            android:id="@+id/textViewPassword"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="@string/hint_password"
            android:textColor="@android:color/darker_gray" />
    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="5dp"
        android:orientation="horizontal">

        <android.support.v7.widget.AppCompatTextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="2"
            android:text="Role"
            android:textColor="@color/colorTextHint" />

        <android.support.v7.widget.AppCompatTextView
            android:id="@+id/textViewRole"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Role"
            android:textColor="@android:color/darker_gray" />
    </LinearLayout>


</LinearLayout>

这是Logcat的图像

更新数据时的 Logcat 图像

这是 IMEIRecord 保存活动适配器，如用户记录..

public class IMEIRecyclerAdapter extends RecyclerView.Adapter<IMEIRecyclerAdapter.ImeiViewHolder> {

private List<User> ListImei;
Context mContext;
ItemClickListenerLongPressed itemClickListenerLongPressed;
View itemView;

public IMEIRecyclerAdapter(List<User> ListImei) {
    this.ListImei = ListImei;
}


@Override
public ImeiViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    itemView = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.item_user_recycler_imei, parent, false);

    return new ImeiViewHolder(itemView);
}

@Override
public void onBindViewHolder(ImeiViewHolder holder, int position) {
    final User user= ListImei.get(position);
    holder.textViewImeiId.setText(ListImei.get(position).getImeiid());
     holder.textViewImeiNo.setText(ListImei.get(position).getImei());
}

public void setItemClickListenerLongPressed(ItemClickListenerLongPressed itemClickListenerLongPressed) {
    this.itemClickListenerLongPressed = itemClickListenerLongPressed;
}

@Override
public int getItemCount() {
    Log.v(UsersRecyclerAdapter.class.getSimpleName(),""+ListImei.size());
    return ListImei.size();
}

public void displayingAlertDialogimei() {
    final User user= new User();
    //displaying alert dialog box
    AlertDialog.Builder builder = new AlertDialog.Builder(itemView.getContext());
    builder.setTitle("Choose Option");
    builder.setMessage("Update or Delete?");
    builder.setPositiveButton("Update", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {

            //go to update activity
            goToUpdateActivity(user.getUserid());
            dialog.cancel();

        }
    });
    builder.setNeutralButton("Delete", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {

            //go to update activity
            dialog.cancel();

        }
    });
    builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            dialog.dismiss();
        }
    });
    AlertDialog alert11 = builder.create();
    alert11.show();
}

private void goToUpdateActivity(String userid) {
    Intent goToUpdate = new Intent(mContext, RoughUser.class);
    goToUpdate.putExtra("USER_ID", userid);
    mContext.startActivity(goToUpdate);

}


public class ImeiViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener{

    public AppCompatTextView textViewImeiId;
    public AppCompatTextView textViewImeiNo;
    LinearLayout layout;


    public ImeiViewHolder(View view) {
        super(view);
        textViewImeiId = (AppCompatTextView) view.findViewById(R.id.textViewImeiId);
        textViewImeiNo = (AppCompatTextView) view.findViewById(R.id.textViewImeiNo);
        layout = (LinearLayout) view.findViewById(R.id.list_view_imei);

        layout.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        displayingAlertDialogimei();
    }
}

}

标签： javaandroidlistviewandroid-recyclerview

解决方案

您尚未mContext在适配器类中声明。在 Adapter 类的构造函数中可能会像这样改变。

public UserRecyclerAdapterSavedUsers(List<User> listUsers,Context context) {
    this.mContext= context;
    this.listUsers1 = listUsers;
    user= new User();
}

和你必须改变的回收视图活动类

UserRecyclerAdapterSavedUsers myAdapter = new RecyclerViewAdapter(yourList,this);

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