为什么每次使用回收器视图时都会显示相同的行？

xdnvmnnf  于 2022-09-21  发布在  Android
关注(0)|答案(3)|浏览(130)

为什么我每次使用RecyclerView都会显示同一行？？

我已经创建了一个ArrayList，名为StudentList，其中存储了从数据库检索的所有数据，但在填充RecyclerView时，只有数据库的第一行被多次填充。

//从数据库文件复制的数据库//1 deveah 79 98 99 96 293 97 A+2 Tejas 78 73 75 78 226 75 A 3 sidhesh 96 56 59 58 173 57 B 4 rishabh 58 78 49 38 165 55 B 5 Devesh 45 79 96 82 257 85 A 6 Akshay 5 99 76 94 269 89 A

数据库帮助器类

package com.devesh.sqlitedatabase.db;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

import androidx.annotation.Nullable;

import com.devesh.sqlitedatabase.db.model.Student;

import java.util.ArrayList;

public class StudentDatabasaeHelper extends SQLiteOpenHelper {
    private static final String STUDENT_DATABASE = "student.db";
    private static final String STUDENT_TABLE = "studentsInfo";

    public StudentDatabasaeHelper( Context context) {
        super(context,STUDENT_DATABASE,null,1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table " + STUDENT_TABLE + " (ID Integer Primary Key AutoIncrement,STUDENT_NAME text,STUDENT_ROLLNO text,CHEMISTRY Integer,PHYSICS Integer,MATH Integer,TOTAL_MARKS Integer,PERCENTAGE Integer,GRADE text)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("drop table if exists " + STUDENT_TABLE);
        onCreate(db);
    }

    public boolean InsertStudentData(String roll_no,String name,int chemistry,int physics, int math,int total_marks,int percentage, String grade){
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put("STUDENT_NAME",name);
        contentValues.put("STUDENT_ROLLNO",roll_no);
        contentValues.put("CHEMISTRY",chemistry);
        contentValues.put("PHYSICS",physics);
        contentValues.put("MATH",math);
        contentValues.put("TOTAL_MARKS",total_marks);
        contentValues.put("PERCENTAGE",percentage);
        contentValues.put("GRADE",grade);

        long result = db.insert(STUDENT_TABLE,null,contentValues);
        if(result == -1) return false;
        else return true;
    }

    public ArrayList<Student> GetStudentData(){
        SQLiteDatabase db = this.getReadableDatabase();
        String query  = "select * from " + STUDENT_TABLE;
        Cursor cursor = db.rawQuery(query,null);

        Student model = new Student();
        ArrayList<Student> allStudents = new ArrayList<Student>();

        while (cursor.moveToNext()){

            model.NAME = cursor.getString(1);
            model.ROLL_NO = cursor.getString(2);
            model.CHEMISTRY = cursor.getInt(3);
            model.PHYSICS = cursor.getInt(4);
            model.MATH = cursor.getInt(5);
            model.TOTAL_MARKS = cursor.getInt(6);
            model.PERCENTAGE = cursor.getInt(7);
            model.GRADE = cursor.getString(8);
            allStudents.add(model);
        }
        return allStudents;
    }

}

学生模范班

package com.devesh.sqlitedatabase.db.model;

public class Student {
    public int ID;
    public String NAME;
    public String ROLL_NO;
    public int CHEMISTRY;
    public int MATH;
    public int PHYSICS;
    public int TOTAL_MARKS;
    public int PERCENTAGE;
    public String GRADE;

//     public Student(int id, String name, String roll_no, int total_marks, int percentage, String grde){
//        this.ID = id;
//        this.NAME = name;
//        this.ROLL_NO = roll_no;
//        this.TOTAL_MARKS = total_marks;
//        this.PERCENTAGE = percentage;
//        this.GRADE = grde;
//    }
//

}

查看活动类

package com.devesh.sqlitedatabase;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;
import android.util.Log;
import android.widget.LinearLayout;

import com.devesh.sqlitedatabase.db.StudentDatabasaeHelper;
import com.devesh.sqlitedatabase.db.model.Student;

import java.util.ArrayList;
import java.util.List;

public class ViewActivity extends AppCompatActivity {

    RecyclerView recyclerView;
    LinearLayoutManager linearLayoutManager;
    ArrayList<Student> studentList;
//    ArrayList<Student> viewList = new ArrayList<>();
    RecyclerAdapter recyclerAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_view);
        initData();
        initRecyclerView();
    }

    private void initData() {
        StudentDatabasaeHelper db = new StudentDatabasaeHelper(this);

        studentList = db.GetStudentData();

//        String name = "",roll_no= "",total_marks= "",percent= "",grade= "";
//        int id=0,total=0,percentage=0;
//        Student obj = new Student();
//        int i=0;
//        while (i != studentList.size()) {
//            obj.ID = studentList.get(i).ID;
//            obj.NAME = studentList.get(i).NAME;
//            obj.ROLL_NO =studentList.get(i).ROLL_NO;
//            obj.TOTAL_MARKS = studentList.get(i).TOTAL_MARKS;
//            // String total_marks = String.valueOf(total);
//            obj.PERCENTAGE = studentList.get(i).PERCENTAGE;
//            //String percent = String.valueOf(percentage);
//            obj.GRADE = studentList.get(i).GRADE;
//            viewList.add(obj);
//            i++;
//        }
        Log.d("rogd", "initData: " + studentList.get(1).NAME );

    }

    private void initRecyclerView() {
        recyclerView = findViewById(R.id.Student_list_recyclerView);
        linearLayoutManager = new LinearLayoutManager(this);
        linearLayoutManager.setOrientation(RecyclerView.VERTICAL);
        recyclerView.setLayoutManager(linearLayoutManager);

        recyclerAdapter = new RecyclerAdapter(studentList);
        recyclerView.setAdapter(recyclerAdapter);
        if(recyclerAdapter !=null){

            recyclerAdapter.notifyDataSetChanged();
        }
    }
}

RecrecerAdapter类

package com.devesh.sqlitedatabase;

import android.content.Context;
import android.database.Cursor;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.devesh.sqlitedatabase.db.model.Student;

import java.util.ArrayList;
import java.util.List;

public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

     ArrayList<Student> studentList;
    public RecyclerAdapter(ArrayList<Student> studentList){
        this.studentList = studentList;
    }

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.row,parent,false);

        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
            Student st = studentList.get(position);
            int id = st.ID;
            String strID = String.valueOf(id);
            String name = st.NAME;
            String roll_no = st.ROLL_NO;
//        int chemistry = studentList.get(position).CHEMISTRY;
//        int math = studentList.get(position).MATH;
//        int physics = studentList.get(position).PHYSICS;
            int total_marks = st.TOTAL_MARKS;
            String strTotal_Marks = String.valueOf(total_marks);
            int percentage = st.PERCENTAGE;
            String strPercentage = percentage + "%";
            String grade = st.GRADE;
            ViewHolder.setData(strID,name,roll_no,strTotal_Marks,strPercentage,grade);

            Log.d("rogd", "onBindViewHolder: " + position);
    }

    @Override
    public int getItemCount() {
        return studentList.size();
    }

    public static class ViewHolder extends RecyclerView.ViewHolder{

        private static TextView srno;
        private static TextView roll_no;
        private static TextView name;
        private static TextView total_marks;
        private static TextView percentage;
        private static TextView grade;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            srno = itemView.findViewById(R.id.srNo_tv);
            roll_no = itemView.findViewById(R.id.rollno_tv);
            percentage = itemView.findViewById(R.id.percentage_tv);
            name = itemView.findViewById(R.id.name_tv);
            total_marks = itemView.findViewById(R.id.totalMarks_tv);
            grade = itemView.findViewById(R.id.grade_tv);
        }

        public static void setData(String ID, String name1, String roll_no1, String total_marks1, String percentage1, String grade1){
            srno.setText(ID);
            name.setText(name1);
            roll_no.setText(roll_no1);
            total_marks.setText(total_marks1);
            percentage.setText(percentage1);
            grade.setText(grade1);
        }
    }
}
android

3条答案

按热度按时间
x33g5p2x

x33g5p2x1#

第一次更改线路从

ViewHolder.setData(strID,name,roll_no,strTotal_Marks,strPercentage,grade);

至

holder.setData(strID,name,roll_no,strTotal_Marks,strPercentage,grade);

第二个-

public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

至

public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ViewHolder> {

第三

public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {

至

public void onBindViewHolder(@NonNull RecyclerAdapter.ViewHolder holder, int position) {
赞(0）分享  回复(0）举报  2022-09-21
gzjq41n4

gzjq41n42#

您应该从ViewHolder类的数据成员中省略static修饰符，因为它会导致您在每次由回收器视图适配器为每一行调用onBindViewHolder()时更新同一组数据成员。

赞(0）分享  回复(0）举报  2022-09-21
5hcedyr0

5hcedyr03#

在StudentDatabasaeHelper内的GetStudentData()中

public ArrayList<Student> GetStudentData(){
    SQLiteDatabase db = this.getReadableDatabase();
    String query  = "select * from " + STUDENT_TABLE;
    Cursor cursor = db.rawQuery(query,null);

    Student model = new Student();
    ArrayList<Student> allStudents = new ArrayList<Student>();

    while (cursor.moveToNext()){

      // Student model should be here 
        Student model = new Student();

     ...// rest of your code 

        allStudents.add(model);
    }
    return allStudents;
}

学生模型对象只能在while loop之外创建一次，它应该在while loop内。

Student model = new Student();

发生的情况是，学生类对象被创建并分配了一个引用，当添加最后一个学生记录时，相同的对象(named model in your case)被添加到具有不同学生记录的列表中，它被分配给最后一个学生记录的所有其他对象。

示例

Student model = new Student();

model.ID = 1;
list.add(model)

model.ID = 2;
list.add(model)

model.ID = 3;
list.add(model)

model.ID = 4;
list.add(model)

列表的大小将是4，但当我尝试迭代并打印模型.id时，它总是给我ID = 4。

赞(0）分享  回复(0）举报  2022-09-21
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