Question

我正在尝试在自定义列表视图中实现搜索功能。我使用菜单进行搜索。当我在搜索栏中键入内容时，我的项目因该错误而崩溃。

2019-11-19 18：50：05.762 17072-17072 /？ E / AndroidRuntime：致命例外：主要流程：com.example.medicationmanagementmanagementsystem，PID：17072 java.lang.NullPointerException：尝试在空对象上调用虚拟方法“ java.util.Iterator java.util.ArrayList.iterator（）” 参考在com.example.medicationmanagementsystem.ViewListContents $ 1.onQueryTextChange（ViewListContents.java:72）

我认为该数组的值为null，因此无法显示任何详细信息。任何帮助将不胜感激。

ViewListContents.java


import android.database.Cursor;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.SearchView;
import android.widget.Toast;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.view.MenuItemCompat;

import com.example.medicationmanagementsystem.DAO.DatabaseHelper;

import java.util.ArrayList;

public class ViewListContents extends AppCompatActivity {
  DatabaseHelper myDB;
  ArrayList<Prescription> prescriptionList;
  ListView listView;
  Prescription prescription;
  ArrayList<String> listItem;
  ArrayAdapter adapter;

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

    myDB = new DatabaseHelper(this);
    prescriptionList = new ArrayList<Prescription>();
    Cursor data = myDB.getListContents();
    int numRows = data.getCount();
    if(numRows == 0){
      Toast.makeText(ViewListContents.this, "There is nothing in this database", Toast.LENGTH_LONG).show();
    }
    else {
      while(data.moveToNext()){
        prescription = new Prescription(data.getString(1), data.getString(2), data.getString(3),
                data.getString(4), data.getString(5), data.getString(6), data.getString(7),
                data.getString(8), data.getString(9));
        prescriptionList.add(prescription);
      }
      EightColumn_ListAdapter adapter = new EightColumn_ListAdapter(this,R.layout.prescription_view,prescriptionList);
      listView = (ListView) findViewById(R.id.listview);
      listView.setAdapter(adapter);
    }
  }
//END
  //This code is based on SQLite Database to ListView- Part 4:Search Items- Android Studio Tutorial, KOD Dev, https://www.youtube.com/watch?v=QY-O49a_Ags
  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.menu, menu);

    MenuItem searchItem = menu.findItem(R.id.item_search);
    SearchView searchView = (SearchView) MenuItemCompat.getActionView(searchItem);

    searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
      @Override
      public boolean onQueryTextSubmit(String query) {

        return false;
      }
      @Override
      public boolean onQueryTextChange(String newText) {
        ArrayList<String> listViews = new ArrayList<>();
        for (String prescription : listItem){
          if (prescription.toLowerCase().contains(newText.toLowerCase())){
            listViews.add(prescription);
          }
        }

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(ViewListContents.this,R.layout.prescription_view,listViews);
        listView = (ListView) findViewById(R.id.listview);
        listView.setAdapter(adapter);
        return true;
      }
    });
    return super.onCreateOptionsMenu(menu);
  }
  }

DatabaseHelper.java


package com.example.medicationmanagementsystem.DAO;

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

public class DatabaseHelper extends SQLiteOpenHelper {

    //Create Database
    public static final String DATABASE_NAME = "ManagementSystem.db";
    //Create patient table
    public static final String TABLE_PATIENT = "patient_table";
    public static final String COL_PATIENT_PATIENTID = "PATIENTID";
    public static final String COL_PATIENT_FNAME = "FNAME";
    public static final String COL_PATIENT_SNAME = "SNAME";
    public static final String COL_PATIENT_PPS = "PPS";
    public static final String COL_PATIENT_DOB = "DOB";
    public static final String COL_PATIENT_ADDRESS = "ADDRESS";
    public static final String COL_PATIENT_TYPE = "PATIENTTYPE";
    public static final String COL_PATIENT_MEDCOND = "PATIENTMEDCON";
    public static final String COL_PATIENT_CARINGID = "CARINGID";

    //Create prescription table
    public static final String TABLE_PRESCRIPTION = "prescription_table";
    public static final String COL_PRESCRIPTION_ID = "PRESCRIPTIONID";
    public static final String COL_PRESCRIPTION__PATIENTID = COL_PATIENT_PATIENTID;
    public static final String COL_PRESCRIPTION__DATE = "DATE";
    public static final String COL_PRESCRIPTION__DRUGNAME = "DRUGNAME";
    public static final String COL_PRESCRIPTION__CONCENTRATION = "CONCENTRATION";
    public static final String COL_PRESCRIPTION__DOSAGE = "DOSAGE";
    public static final String COL_PRESCRIPTION__PREPARATION = "PREPARATION";
    public static final String COL_PRESCRIPTION__STARTDATE = "STARTDATE";
    public static final String COL_PRESCRIPTION__ENDDATE = "ENDDATE";
    public static final String COL_PRESCRIPTION__DOCTORID = "DOCTORID";



    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, 1);

    }
    @Override
    public void onCreate (SQLiteDatabase db) {
        String patienttable = "CREATE TABLE " + TABLE_PATIENT + "(PATIENTID INTEGER PRIMARY KEY AUTOINCREMENT, FNAME TEXT, SNAME TEXT, PPS TEXT, DOB TEXT, ADDRESS TEXT, PATIENTTYPE TEXT, PATIENTMEDCON TEXT, CARINGID INTEGER)";
        String prescriptiontable = "CREATE TABLE " + TABLE_PRESCRIPTION + "(PRESCRIPTIONID INTEGER PRIMARY KEY AUTOINCREMENT, PATIENTID INTEGER, DATE TEXT, DRUGNAME TEXT, CONCENTRATION TEXT, DOSAGE TEXT, PREPARATION TEXT, STARTDATE TEXT, ENDDATE TEXT, DOCTORID INTEGER)";
        db.execSQL(patienttable);
        db.execSQL(prescriptiontable);
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS "+ TABLE_PATIENT);
        db.execSQL("DROP TABLE IF EXISTS "+ TABLE_PRESCRIPTION);
        onCreate(db);
    }
    //insert patient data
    public boolean insertPatientData(String fname, String sname, String pps, String dob, String address, String patienttype, String patientmedcon, String caringid) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues1 = new ContentValues();
        contentValues1.put(COL_PATIENT_FNAME, fname);
        contentValues1.put(COL_PATIENT_SNAME, sname);
        contentValues1.put(COL_PATIENT_PPS, pps);
        contentValues1.put(COL_PATIENT_DOB, dob);
        contentValues1.put(COL_PATIENT_ADDRESS, address);
        contentValues1.put(COL_PATIENT_TYPE, patienttype);
        contentValues1.put(COL_PATIENT_MEDCOND,patientmedcon);
        contentValues1.put(COL_PATIENT_CARINGID, caringid);
        long result= db.insert(TABLE_PATIENT,null, contentValues1);
        if (result == 1)
            return false;
        else
            return true;
    }
    //insert prescription data
    public boolean insertData(String patientid, String date, String drugname, String concentration,String dosage, String preparation, String startdate, String enddate, String doctorid) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues2 = new ContentValues();
        contentValues2.put(COL_PRESCRIPTION__PATIENTID, patientid);
        contentValues2.put(COL_PRESCRIPTION__DATE, date);
        contentValues2.put(COL_PRESCRIPTION__DRUGNAME, drugname);
        contentValues2.put(COL_PRESCRIPTION__CONCENTRATION, concentration);
        contentValues2.put(COL_PRESCRIPTION__DOSAGE, dosage);
        contentValues2.put(COL_PRESCRIPTION__PREPARATION, preparation);
        contentValues2.put(COL_PRESCRIPTION__STARTDATE, startdate);
        contentValues2.put(COL_PRESCRIPTION__ENDDATE, enddate);
        contentValues2.put(COL_PRESCRIPTION__DOCTORID, doctorid);
        long result= db.insert(TABLE_PRESCRIPTION,null, contentValues2);
        if (result == 1)
            return false;
        else
            return true;
        //END

    }

    //Coding with mitch tutorial
    public Cursor getListContents() {
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor data = db.rawQuery("SELECT * FROM " + TABLE_PRESCRIPTION, null);
        return data;
    }
    ////This code is based on SQLite Database to ListView- Part 4:Search Items- Android Studio Tutorial, KOD Dev, https://www.youtube.com/watch?v=QY-O49a_Ags

    public Cursor searchPrescriptions(String text) {
        SQLiteDatabase db = this.getReadableDatabase();
        String query = "Select * from " + TABLE_PRESCRIPTION + "WHERE " + COL_PRESCRIPTION__PATIENTID + " Like '%" + text +"%'";
        Cursor data = db.rawQuery(query, null);
        return data;
    }
}

Eight_Column_ListAdapter.java


package com.example.medicationmanagementsystem;
//The code below is based on Adding multiple columns to your ListView, CodingWithMitch, https://www.youtube.com/watch?v=8K-6gdTlGEA, https://www.youtube.com/watch?v=hHQqFGpod14, https://www.youtube.com/watch?v=jpt3Md9aDIQ
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

import java.util.ArrayList;

public class EightColumn_ListAdapter extends ArrayAdapter<Prescription> {

  private LayoutInflater mInflater;
  private ArrayList<Prescription> prescriptions;
  private int mViewResourceId;

  public EightColumn_ListAdapter(Context context, int textViewResourceId, ArrayList<Prescription> prescriptions) {
    super(context, textViewResourceId, prescriptions);
    this.prescriptions = prescriptions;
    mInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    mViewResourceId = textViewResourceId;

  }

  public View getView(int position, View convertView, ViewGroup parents) {
    convertView = mInflater.inflate(mViewResourceId, null);

    Prescription prescription = prescriptions.get(position);

    if (prescription != null) {
      TextView patientID = (TextView) convertView.findViewById(R.id.textpatientID);
      TextView date = (TextView) convertView.findViewById(R.id.textdate);
      TextView drugname = (TextView) convertView.findViewById(R.id.textdrugname);
      TextView concentration = (TextView) convertView.findViewById(R.id.textcontentration);
      TextView dosage = (TextView) convertView.findViewById(R.id.textdosage);
      TextView prep = (TextView) convertView.findViewById(R.id.textprep);
      TextView startdate = (TextView) convertView.findViewById(R.id.textstartdate);
      TextView enddate = (TextView) convertView.findViewById(R.id.textenddate);
      TextView doctorID = (TextView) convertView.findViewById(R.id.textdoctorid);

      if(patientID != null) {
        patientID.setText((prescription.getPatientID()));
      }
      if(date != null) {
        date.setText((prescription.getPresdate()));
      }
      if(drugname != null) {
        drugname.setText((prescription.getDrugname()));
      }
      if(concentration != null) {
        concentration.setText((prescription.getConcentration()));
      }
      if(dosage != null) {
        dosage.setText((prescription.getDosage()));
      }
      if(prep != null) {
        prep.setText((prescription.getPreparation()));
      }
      if(startdate != null) {
        startdate.setText((prescription.getStartdate()));
      }
      if(enddate != null) {
        enddate.setText((prescription.getEnddate()));
      }
      if(doctorID != null) {
        patientID.setText((prescription.getDoctorID()));
      }
    }
    return convertView;
  }
}

Answer 1

您正在尝试阅读名为listItem的列表元素。该列表为空，因为您从未将其设置为其他任何内容。

更改此：

ArrayList<String> listItem;

对此：

ArrayList<String> listItem = new ArrayList<String>();

...或将其放入onCreate()方法中，就像使用prescriptionList一样：

prescriptionList = new ArrayList<Prescription>();
listItem = new ArrayList<String>();

另外，不要命名您的列表listItem，因为它不是项目，而是列表！

我正在尝试将搜索功能实现到自定义列表视图中。我使用搜索功能菜单

1 个答案: