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Java 使用parseObject实现RecyclerView但得到一个空白屏幕

java android

Java 使用parseObject实现RecyclerView但得到一个空白屏幕,java,android,android-recyclerview,android-parser,parse-android-sdk,Java,Android,Android Recyclerview,Android Parser,Parse Android Sdk,我正在尝试使用ParseObject实现RecyclerView，但在我的屏幕上没有显示任何内容 以下是要实现recycler视图的活动的代码 AdminShowStudentId.java package com.example.Aphexams; import android.content.Intent; import android.os.Bundle; import android.app.Activity; import andro

我正在尝试使用ParseObject实现RecyclerView，但在我的屏幕上没有显示任何内容

以下是要实现recycler视图的活动的代码

AdminShowStudentId.java

     package com.example.Aphexams;

     import android.content.Intent;
     import android.os.Bundle;
     import android.app.Activity;
     import android.support.v7.widget.GridLayoutManager;
     import android.support.v7.widget.RecyclerView;
     import android.util.Log;
     import android.view.View;
     import android.widget.Adapter;
     import android.widget.Spinner;
     import android.widget.SpinnerAdapter;
     import android.widget.Toast;

     import com.parse.FindCallback;
     import com.parse.GetCallback;
     import com.parse.ParseException;
     import com.parse.ParseObject;
     import com.parse.ParseQuery;
     import com.parse.ParseQueryAdapter;

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

     //import app.android.project.com.olexam.R;



     public class AdminShowStudentId extends Activity {

    private RecyclerView recycleerviewDetails;
    private RecyclerView.LayoutManager layoutManager;
    private StudentIdAdapter studentidAdapter;
    private ArrayList<StudentId> studentidarraylist;
    private boolean notComplete = true;
    private String studId;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_admin_show_student_id);
      final StudentId studentId=new StudentId();
        studentidarraylist=new ArrayList<StudentId>();

            if(notComplete) {


                ParseQuery<ParseObject> query = ParseQuery.getQuery("studAuth");

                query.findInBackground(new FindCallback<ParseObject>() {
                    @Override
                    public void done(List<ParseObject> objects, ParseException e) {
                        if (e == null) {
                            for (ParseObject object : objects) {
                                String studentid = (String) object.get("StudUserName");
                                studentId.setStudentId(studentid);
                                studentidarraylist.add(studentId);


                            }
                            //is it fetching or not

                        } else {
                            Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_SHORT).show();
                        }

                    }
                });
                notComplete=false;
            }


        recycleerviewDetails=(RecyclerView)findViewById(R.id.studentidrecyclerview);
        if (recycleerviewDetails != null)
        {
            recycleerviewDetails.setHasFixedSize(true);
        }

        /*fetching data from the database*/
        studentidAdapter=new StudentIdAdapter(studentidarraylist);
        recycleerviewDetails.setAdapter(studentidAdapter);
        studentidAdapter.notifyDataSetChanged();
        layoutManager=new GridLayoutManager(this,1);
        recycleerviewDetails.setLayoutManager(layoutManager);


        recycleerviewDetails.addOnItemTouchListener(new RecyclerViewListener(AdminShowStudentId.this,new RecyclerViewListener.OnItemClickListener() {
            @Override
            public void onItemClick(View view, int position) {
                studId=studentidarraylist.get(position).getStudentId();
                Intent i=new Intent(AdminShowStudentId.this,ViewStudent.class);
                i.putExtra("studId",studId);
            }
        }));








       }
  }

package com.example.Aphexams;

/**
 * Created by HP on 24-05-2018.
 */

public class StudentId {
    private String StudentId;

    public String getStudentId() {
        return StudentId;
    }

    public void setStudentId(String studentId) {
        StudentId = studentId;
    }
}

As suggested by Thiago Loddi

public class AdminShowStudentId extends Activity {

private RecyclerView recycleerviewDetails;
private RecyclerView.LayoutManager layoutManager;
private StudentIdAdapter studentidAdapter;
private ArrayList<StudentId> studentidarraylist;
private boolean notComplete = true;
private String studId;

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

    recycleerviewDetails=(RecyclerView)findViewById(R.id.studentidrecyclerview);
    if (recycleerviewDetails != null)
    {
        recycleerviewDetails.setHasFixedSize(true);
    }
    layoutManager=new GridLayoutManager(this,1);
    recycleerviewDetails.setLayoutManager(layoutManager);

    studentidarraylist=new ArrayList<StudentId>();

        if(notComplete) {


            ParseQuery<ParseObject> query = ParseQuery.getQuery("studAuth");

            query.findInBackground(new FindCallback<ParseObject>() {
                @Override
                public void done(List<ParseObject> objects, ParseException e) {
                    if (e == null) {

                        for(int i=0;i<objects.size();i++)
                        {
                            String studentidstring = (String) objects.get(i).get("StudUserName");
                            StudentId studentId=new StudentId();
                            studentId.setStudentId(studentidstring);
                            studentidarraylist.add(studentId);
                        }
                        //Now the arraylist is populated!
                        for(int i=0;i<studentidarraylist.size();i++)
                        {
                            Toast.makeText(AdminShowStudentId.this,studentidarraylist.get(i).getStudentId() + "  "+i, Toast.LENGTH_SHORT).show();

                        }
                        studentidAdapter=new StudentIdAdapter(studentidarraylist);
                        recycleerviewDetails.setAdapter(studentidAdapter);
                        studentidAdapter.notifyDataSetChanged();

                        recycleerviewDetails.addOnItemTouchListener(new RecyclerViewListener(AdminShowStudentId.this,new RecyclerViewListener.OnItemClickListener() {
                            @Override
                            public void onItemClick(View view, int position) {
                                studId=studentidarraylist.get(position).getStudentId();
                                Intent i=new Intent(AdminShowStudentId.this,ViewStudent.class);
                                i.putExtra("studId",studId);
                                startActivity(i);
                            }
                        }));

                    } else {
                        Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_SHORT).show();
                    }

                }
            });

            notComplete=false;

        }



}
下面是StudentId.java的代码

     package com.example.Aphexams;

     import android.content.Intent;
     import android.os.Bundle;
     import android.app.Activity;
     import android.support.v7.widget.GridLayoutManager;
     import android.support.v7.widget.RecyclerView;
     import android.util.Log;
     import android.view.View;
     import android.widget.Adapter;
     import android.widget.Spinner;
     import android.widget.SpinnerAdapter;
     import android.widget.Toast;

     import com.parse.FindCallback;
     import com.parse.GetCallback;
     import com.parse.ParseException;
     import com.parse.ParseObject;
     import com.parse.ParseQuery;
     import com.parse.ParseQueryAdapter;

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

     //import app.android.project.com.olexam.R;



     public class AdminShowStudentId extends Activity {

    private RecyclerView recycleerviewDetails;
    private RecyclerView.LayoutManager layoutManager;
    private StudentIdAdapter studentidAdapter;
    private ArrayList<StudentId> studentidarraylist;
    private boolean notComplete = true;
    private String studId;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_admin_show_student_id);
      final StudentId studentId=new StudentId();
        studentidarraylist=new ArrayList<StudentId>();

            if(notComplete) {


                ParseQuery<ParseObject> query = ParseQuery.getQuery("studAuth");

                query.findInBackground(new FindCallback<ParseObject>() {
                    @Override
                    public void done(List<ParseObject> objects, ParseException e) {
                        if (e == null) {
                            for (ParseObject object : objects) {
                                String studentid = (String) object.get("StudUserName");
                                studentId.setStudentId(studentid);
                                studentidarraylist.add(studentId);


                            }
                            //is it fetching or not

                        } else {
                            Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_SHORT).show();
                        }

                    }
                });
                notComplete=false;
            }


        recycleerviewDetails=(RecyclerView)findViewById(R.id.studentidrecyclerview);
        if (recycleerviewDetails != null)
        {
            recycleerviewDetails.setHasFixedSize(true);
        }

        /*fetching data from the database*/
        studentidAdapter=new StudentIdAdapter(studentidarraylist);
        recycleerviewDetails.setAdapter(studentidAdapter);
        studentidAdapter.notifyDataSetChanged();
        layoutManager=new GridLayoutManager(this,1);
        recycleerviewDetails.setLayoutManager(layoutManager);


        recycleerviewDetails.addOnItemTouchListener(new RecyclerViewListener(AdminShowStudentId.this,new RecyclerViewListener.OnItemClickListener() {
            @Override
            public void onItemClick(View view, int position) {
                studId=studentidarraylist.get(position).getStudentId();
                Intent i=new Intent(AdminShowStudentId.this,ViewStudent.class);
                i.putExtra("studId",studId);
            }
        }));








       }
  }

package com.example.Aphexams;

/**
 * Created by HP on 24-05-2018.
 */

public class StudentId {
    private String StudentId;

    public String getStudentId() {
        return StudentId;
    }

    public void setStudentId(String studentId) {
        StudentId = studentId;
    }
}

As suggested by Thiago Loddi

public class AdminShowStudentId extends Activity {

private RecyclerView recycleerviewDetails;
private RecyclerView.LayoutManager layoutManager;
private StudentIdAdapter studentidAdapter;
private ArrayList<StudentId> studentidarraylist;
private boolean notComplete = true;
private String studId;

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

    recycleerviewDetails=(RecyclerView)findViewById(R.id.studentidrecyclerview);
    if (recycleerviewDetails != null)
    {
        recycleerviewDetails.setHasFixedSize(true);
    }
    layoutManager=new GridLayoutManager(this,1);
    recycleerviewDetails.setLayoutManager(layoutManager);

    studentidarraylist=new ArrayList<StudentId>();

        if(notComplete) {


            ParseQuery<ParseObject> query = ParseQuery.getQuery("studAuth");

            query.findInBackground(new FindCallback<ParseObject>() {
                @Override
                public void done(List<ParseObject> objects, ParseException e) {
                    if (e == null) {

                        for(int i=0;i<objects.size();i++)
                        {
                            String studentidstring = (String) objects.get(i).get("StudUserName");
                            StudentId studentId=new StudentId();
                            studentId.setStudentId(studentidstring);
                            studentidarraylist.add(studentId);
                        }
                        //Now the arraylist is populated!
                        for(int i=0;i<studentidarraylist.size();i++)
                        {
                            Toast.makeText(AdminShowStudentId.this,studentidarraylist.get(i).getStudentId() + "  "+i, Toast.LENGTH_SHORT).show();

                        }
                        studentidAdapter=new StudentIdAdapter(studentidarraylist);
                        recycleerviewDetails.setAdapter(studentidAdapter);
                        studentidAdapter.notifyDataSetChanged();

                        recycleerviewDetails.addOnItemTouchListener(new RecyclerViewListener(AdminShowStudentId.this,new RecyclerViewListener.OnItemClickListener() {
                            @Override
                            public void onItemClick(View view, int position) {
                                studId=studentidarraylist.get(position).getStudentId();
                                Intent i=new Intent(AdminShowStudentId.this,ViewStudent.class);
                                i.putExtra("studId",studId);
                                startActivity(i);
                            }
                        }));

                    } else {
                        Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_SHORT).show();
                    }

                }
            });

            notComplete=false;

        }



}
下面是我的活动_admin_show_student_id.xml布局代码

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.NestedScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.Aphexams.AdminShowStudentId">

   <android.support.v7.widget.RecyclerView
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       android:id="@+id/studentidrecyclerview">


   </android.support.v7.widget.RecyclerView>

</android.support.v4.widget.NestedScrollView>



.
看看您的代码，我猜错误在于您首先使用空列表设置适配器，然后在
FindCallback
中将项目添加到列表中，但从未告诉列表重新呈现项目

您是否检查了设置适配器时列表是否已填充？因为您的查询是在后台运行的，所以有可能在查询完成之前执行以下几行


studentidAdapter=new StudentIdAdapter(studentidarraylist);
recycleerviewDetails.setAdapter(studentidAdapter);


为了实现你想做的事，我想你应该打电话


studentidAdapter=new StudentIdAdapter(studentidarraylist);
recycleerviewDetails.setAdapter(studentidAdapter);
studentidAdapter.notifyDataSetChanged();



在FindCallback中，当您确定列表已填充时。
因此，我在代码中做了以下更改

AdminShowStudentId.java


     package com.example.Aphexams;

     import android.content.Intent;
     import android.os.Bundle;
     import android.app.Activity;
     import android.support.v7.widget.GridLayoutManager;
     import android.support.v7.widget.RecyclerView;
     import android.util.Log;
     import android.view.View;
     import android.widget.Adapter;
     import android.widget.Spinner;
     import android.widget.SpinnerAdapter;
     import android.widget.Toast;

     import com.parse.FindCallback;
     import com.parse.GetCallback;
     import com.parse.ParseException;
     import com.parse.ParseObject;
     import com.parse.ParseQuery;
     import com.parse.ParseQueryAdapter;

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

     //import app.android.project.com.olexam.R;



     public class AdminShowStudentId extends Activity {

    private RecyclerView recycleerviewDetails;
    private RecyclerView.LayoutManager layoutManager;
    private StudentIdAdapter studentidAdapter;
    private ArrayList<StudentId> studentidarraylist;
    private boolean notComplete = true;
    private String studId;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_admin_show_student_id);
      final StudentId studentId=new StudentId();
        studentidarraylist=new ArrayList<StudentId>();

            if(notComplete) {


                ParseQuery<ParseObject> query = ParseQuery.getQuery("studAuth");

                query.findInBackground(new FindCallback<ParseObject>() {
                    @Override
                    public void done(List<ParseObject> objects, ParseException e) {
                        if (e == null) {
                            for (ParseObject object : objects) {
                                String studentid = (String) object.get("StudUserName");
                                studentId.setStudentId(studentid);
                                studentidarraylist.add(studentId);


                            }
                            //is it fetching or not

                        } else {
                            Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_SHORT).show();
                        }

                    }
                });
                notComplete=false;
            }


        recycleerviewDetails=(RecyclerView)findViewById(R.id.studentidrecyclerview);
        if (recycleerviewDetails != null)
        {
            recycleerviewDetails.setHasFixedSize(true);
        }

        /*fetching data from the database*/
        studentidAdapter=new StudentIdAdapter(studentidarraylist);
        recycleerviewDetails.setAdapter(studentidAdapter);
        studentidAdapter.notifyDataSetChanged();
        layoutManager=new GridLayoutManager(this,1);
        recycleerviewDetails.setLayoutManager(layoutManager);


        recycleerviewDetails.addOnItemTouchListener(new RecyclerViewListener(AdminShowStudentId.this,new RecyclerViewListener.OnItemClickListener() {
            @Override
            public void onItemClick(View view, int position) {
                studId=studentidarraylist.get(position).getStudentId();
                Intent i=new Intent(AdminShowStudentId.this,ViewStudent.class);
                i.putExtra("studId",studId);
            }
        }));








       }
  }



package com.example.Aphexams;

/**
 * Created by HP on 24-05-2018.
 */

public class StudentId {
    private String StudentId;

    public String getStudentId() {
        return StudentId;
    }

    public void setStudentId(String studentId) {
        StudentId = studentId;
    }
}



As suggested by Thiago Loddi

public class AdminShowStudentId extends Activity {

private RecyclerView recycleerviewDetails;
private RecyclerView.LayoutManager layoutManager;
private StudentIdAdapter studentidAdapter;
private ArrayList<StudentId> studentidarraylist;
private boolean notComplete = true;
private String studId;

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

    recycleerviewDetails=(RecyclerView)findViewById(R.id.studentidrecyclerview);
    if (recycleerviewDetails != null)
    {
        recycleerviewDetails.setHasFixedSize(true);
    }
    layoutManager=new GridLayoutManager(this,1);
    recycleerviewDetails.setLayoutManager(layoutManager);

    studentidarraylist=new ArrayList<StudentId>();

        if(notComplete) {


            ParseQuery<ParseObject> query = ParseQuery.getQuery("studAuth");

            query.findInBackground(new FindCallback<ParseObject>() {
                @Override
                public void done(List<ParseObject> objects, ParseException e) {
                    if (e == null) {

                        for(int i=0;i<objects.size();i++)
                        {
                            String studentidstring = (String) objects.get(i).get("StudUserName");
                            StudentId studentId=new StudentId();
                            studentId.setStudentId(studentidstring);
                            studentidarraylist.add(studentId);
                        }
                        //Now the arraylist is populated!
                        for(int i=0;i<studentidarraylist.size();i++)
                        {
                            Toast.makeText(AdminShowStudentId.this,studentidarraylist.get(i).getStudentId() + "  "+i, Toast.LENGTH_SHORT).show();

                        }
                        studentidAdapter=new StudentIdAdapter(studentidarraylist);
                        recycleerviewDetails.setAdapter(studentidAdapter);
                        studentidAdapter.notifyDataSetChanged();

                        recycleerviewDetails.addOnItemTouchListener(new RecyclerViewListener(AdminShowStudentId.this,new RecyclerViewListener.OnItemClickListener() {
                            @Override
                            public void onItemClick(View view, int position) {
                                studId=studentidarraylist.get(position).getStudentId();
                                Intent i=new Intent(AdminShowStudentId.this,ViewStudent.class);
                                i.putExtra("studId",studId);
                                startActivity(i);
                            }
                        }));

                    } else {
                        Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_SHORT).show();
                    }

                }
            });

            notComplete=false;

        }



}


Thiago Loddi建议的

公共类AdminShowStudentId扩展活动{
私人RecyclerView RecyclerViewDetails；
private RecyclerView.LayoutManager LayoutManager；
私人学生公寓；
私立ArrayList学生名单；
私有布尔值notComplete=true；
私有字符串studId；
@凌驾
创建时受保护的void（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
setContentView（R.layout.activity\u admin\u show\u student\u id）；
RecycleViewDetails=（RecyclerView）findViewById（R.id.StudentidRecycleView）；
如果（RecyclerViewDetails！=null）
{
RecyclierViewDetails.setHasFixedSize（true）；
}
layoutManager=新的GridLayoutManager（这个，1）；
setLayoutManager（layoutManager）；
studentidarraylist=new ArrayList（）；
如果（未完成）{
ParseQuery=ParseQuery.getQuery（“studAuth”）；
findInBackground（新的FindCallback（）{
@凌驾
公共void done（列出对象，parsee异常）{
如果（e==null）{

对于（inti=0；它在Thiago Loddi上有很多漏洞……你的建议帮助我消除了这个漏洞。