无法使用光标成功检索数据库中的微调器选定项目文本以填充我应用程序中的联系人列表项目(Can't successfully retrieve Spinner selected item tex

无法使用光标成功检索数据库中的微调器选定项目文本以填充我应用程序中的联系人列表项目(Can't successfully retrieve Spinner selected item text from database to fill contact list item in my app using cursor)

我的应用程序有一个血液捐赠者登记屏幕，血型字段是一个微调。我将所有的施主信息保存在SQLite数据库中。现在我需要检索它，并显示一个列表，显示所有注册的献血者与他们的血型。

我怎样才能做到这一点？

下面我附上了我的所有代码。主要的问题出现在RegisterActivity.java和DonorList.java中。

RegisterActivity.java

import android.content.Intent; import android.os.Bundle; import android.support.v7.app.AppCompatActivity; import android.util.Log; import android.view.View; import android.widget.ArrayAdapter; import android.widget.Button; import android.widget.EditText; import android.widget.Spinner; import android.widget.Toast; public class RegisterActivity extends AppCompatActivity { EditText edtname, edtnumber; Spinner spblood; Button btnregister, btnlist; public static SQLiteHelper sqLiteHelper; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_register); init(); Spinner spinner = findViewById(R.id.blood_selector); // Create an ArrayAdapter using the string array and a default spinner layout ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this, R.array.blood_type, android.R.layout.simple_spinner_item); // Specify the layout to use when the list of choices appears adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); // Apply the adapter to the spinner spinner.setAdapter(adapter); sqLiteHelper = new SQLiteHelper(this, "Donors.sqlite", null, 1); sqLiteHelper.queryData("CREATE TABLE IF NOT EXISTS DONORS (Id INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR, number VARCHAR, blood VARCHAR)"); btnregister.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { try { sqLiteHelper.insertData( edtname.getText().toString().trim(), edtnumber.getText().toString().trim(), spblood ); } catch (Exception e) { e.printStackTrace(); } } }); btnlist.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent intent = new Intent(RegisterActivity.this, DonorList.class); startActivity(intent); } }); } private void init() { edtname = findViewById(R.id.name_input); edtnumber = findViewById(R.id.numberinput); spblood = findViewById(R.id.blood_selector); btnregister = findViewById(R.id.register_button); btnlist = findViewById(R.id.list_button); } }

DonorList.java

import android.database.Cursor; import android.os.Bundle; import android.support.annotation.Nullable; import android.support.v7.app.AppCompatActivity; import android.widget.ListView; import android.widget.Spinner; import java.util.ArrayList; public class DonorList extends AppCompatActivity { ListView listView; ArrayList<Donor> list; DonorListAdapter adapter = null; @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); listView = (ListView) findViewById(R.id.contacts_list); list = new ArrayList<>(); adapter = new DonorListAdapter(this, R.layout.activity_main, list); listView.setAdapter(adapter); Cursor cursor = RegisterActivity.sqLiteHelper.getData("SELECT * FROM DONORS"); list.clear(); while (cursor.moveToNext()) { String name = cursor.getString(1); String number = cursor.getString(2); String blood = cursor.getString(3); list.add(new Donor(name, number, blood)); } adapter.notifyDataSetChanged(); } }

Donor.java

import android.widget.Spinner; public class Donor { private String name; private String number; private Spinner blood; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getNumber() { return number; } public void setNumber(String number) { this.number = number; } public Spinner getBlood() { return blood; } public void setBlood(Spinner blood) { this.blood = blood; } public Donor(String name, String number, Spinner blood) { this.name = name; this.number = number; this.blood = blood; } }

SQLiteHelper.java

import android.content.Context; import android.database.Cursor; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.database.sqlite.SQLiteStatement; import android.widget.Spinner; public class SQLiteHelper extends SQLiteOpenHelper { public SQLiteHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) { super(context, name, factory, version); } public void queryData(String sql) { SQLiteDatabase database = getWritableDatabase(); database.execSQL(sql); } public void insertData(String name, String number, Spinner blood) { SQLiteDatabase database = getWritableDatabase(); String sql = "INSERT INTO DONORS (name, number, blood) values (?, ?, ?)"; SQLiteStatement statement = database.compileStatement(sql); statement.clearBindings(); statement.bindString(1, name); statement.bindString(2, number); statement.bindString(3, blood.getSelectedItem().toString()); statement.executeInsert(); } public Cursor getData(String sql) { SQLiteDatabase database = getReadableDatabase(); return database.rawQuery(sql, null); } }

DonorListAdapter.java

import android.content.Context; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.TextView; import java.util.ArrayList; public class DonorListAdapter extends BaseAdapter { private Context context; private int layout; private ArrayList<Donor> donorList; public DonorListAdapter(Context context, int layout, ArrayList<Donor> donorList) { this.context = context; this.layout = layout; this.donorList = donorList; } @Override public int getCount() { return donorList.size(); } @Override public Object getItem(int position) { return donorList.get(position); } @Override public long getItemId(int position) { return position; } private class ViewHolder { TextView txtname, txtnumber, txtblood; } @Override public View getView(int position, View convertView, ViewGroup parent) { View row = convertView; ViewHolder holder = new ViewHolder(); if (row == null) { LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); if (inflater != null) { row = inflater.inflate(layout, null); } if (row != null) { holder.txtname = row.findViewById(R.id.name_input); } if (row != null) { holder.txtnumber = row.findViewById(R.id.numberinput); } if (row != null) { holder.txtblood = (TextView) row.findViewById(R.id.blood_selector); } if (row != null) { row.setTag(holder); } } else { holder = (ViewHolder) row.getTag(); } Donor donor = donorList.get(position); holder.txtname.setText(donor.getName()); holder.txtnumber.setText(donor.getNumber()); holder.txtblood.setText(donor.getBlood().toString()); return row; } }

activity_main.xml中

activity_register.xml

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent"> <EditText android:id="@+id/name_input" android:layout_width="match_parent" android:layout_height="wrap_content" android:hint="@string/person_name" android:ems="10" android:inputType="textCapWords" android:layout_marginBottom="5sp" /> <EditText android:id="@+id/numberinput" android:layout_width="match_parent" android:layout_height="wrap_content" android:hint="@string/hint" android:ems="10" android:inputType="phone" android:layout_marginBottom="5sp" /> <TextView android:id="@+id/blood" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="@string/blood_type" android:layout_marginBottom="10sp"/> <Spinner android:id="@+id/blood_selector" android:layout_width="match_parent" android:layout_height="wrap_content" android:entries="@array/blood_type" android:prompt="@string/blood_select" android:layout_marginBottom="5sp"/> <Button android:id="@+id/register_button" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/register" /> <Button android:id="@+id/list_button" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/show_donors" /> </LinearLayout>

contact_item.xml

<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"> <TextView android:id="@+id/contact_name" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/contact_name" android:textSize="22sp"/> <TextView android:id="@+id/contact_number" android:layout_width="match_parent" android:layout_height="match_parent" android:textAppearance="?android:textAppearanceSmall" android:text="@string/contact_number" android:layout_alignParentTop="true" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" android:layout_marginLeft="29sp" android:layout_marginStart="29sp" android:layout_marginTop="31sp" /> <TextView android:id="@+id/contact_blood" android:layout_width="match_parent" android:layout_height="match_parent" android:textAppearance="?android:textAppearanceMedium" android:text="@string/blood_type" android:layout_alignParentTop="true" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" android:layout_marginLeft="300sp" android:layout_marginStart="300sp" android:layout_marginTop="30sp"/> </RelativeLayout>

My app has a registration screen for blood donors and the blood type field is a spinner. I save all the donor information in an SQLite database. Now I need to retrieve it and show it for a list showing all the registered blood donors with their blood types.

How can I do that?

I've attached all my code below. The main problems appear in RegisterActivity.java and DonorList.java.

RegisterActivity.java

import android.content.Intent; import android.os.Bundle; import android.support.v7.app.AppCompatActivity; import android.util.Log; import android.view.View; import android.widget.ArrayAdapter; import android.widget.Button; import android.widget.EditText; import android.widget.Spinner; import android.widget.Toast; public class RegisterActivity extends AppCompatActivity { EditText edtname, edtnumber; Spinner spblood; Button btnregister, btnlist; public static SQLiteHelper sqLiteHelper; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_register); init(); Spinner spinner = findViewById(R.id.blood_selector); // Create an ArrayAdapter using the string array and a default spinner layout ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this, R.array.blood_type, android.R.layout.simple_spinner_item); // Specify the layout to use when the list of choices appears adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); // Apply the adapter to the spinner spinner.setAdapter(adapter); sqLiteHelper = new SQLiteHelper(this, "Donors.sqlite", null, 1); sqLiteHelper.queryData("CREATE TABLE IF NOT EXISTS DONORS (Id INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR, number VARCHAR, blood VARCHAR)"); btnregister.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { try { sqLiteHelper.insertData( edtname.getText().toString().trim(), edtnumber.getText().toString().trim(), spblood ); } catch (Exception e) { e.printStackTrace(); } } }); btnlist.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent intent = new Intent(RegisterActivity.this, DonorList.class); startActivity(intent); } }); } private void init() { edtname = findViewById(R.id.name_input); edtnumber = findViewById(R.id.numberinput); spblood = findViewById(R.id.blood_selector); btnregister = findViewById(R.id.register_button); btnlist = findViewById(R.id.list_button); } }

DonorList.java

import android.database.Cursor; import android.os.Bundle; import android.support.annotation.Nullable; import android.support.v7.app.AppCompatActivity; import android.widget.ListView; import android.widget.Spinner; import java.util.ArrayList; public class DonorList extends AppCompatActivity { ListView listView; ArrayList<Donor> list; DonorListAdapter adapter = null; @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); listView = (ListView) findViewById(R.id.contacts_list); list = new ArrayList<>(); adapter = new DonorListAdapter(this, R.layout.activity_main, list); listView.setAdapter(adapter); Cursor cursor = RegisterActivity.sqLiteHelper.getData("SELECT * FROM DONORS"); list.clear(); while (cursor.moveToNext()) { String name = cursor.getString(1); String number = cursor.getString(2); String blood = cursor.getString(3); list.add(new Donor(name, number, blood)); } adapter.notifyDataSetChanged(); } }

Donor.java

import android.widget.Spinner; public class Donor { private String name; private String number; private Spinner blood; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getNumber() { return number; } public void setNumber(String number) { this.number = number; } public Spinner getBlood() { return blood; } public void setBlood(Spinner blood) { this.blood = blood; } public Donor(String name, String number, Spinner blood) { this.name = name; this.number = number; this.blood = blood; } }

SQLiteHelper.java

import android.content.Context; import android.database.Cursor; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.database.sqlite.SQLiteStatement; import android.widget.Spinner; public class SQLiteHelper extends SQLiteOpenHelper { public SQLiteHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) { super(context, name, factory, version); } public void queryData(String sql) { SQLiteDatabase database = getWritableDatabase(); database.execSQL(sql); } public void insertData(String name, String number, Spinner blood) { SQLiteDatabase database = getWritableDatabase(); String sql = "INSERT INTO DONORS (name, number, blood) values (?, ?, ?)"; SQLiteStatement statement = database.compileStatement(sql); statement.clearBindings(); statement.bindString(1, name); statement.bindString(2, number); statement.bindString(3, blood.getSelectedItem().toString()); statement.executeInsert(); } public Cursor getData(String sql) { SQLiteDatabase database = getReadableDatabase(); return database.rawQuery(sql, null); } }

DonorListAdapter.java

import android.content.Context; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.TextView; import java.util.ArrayList; public class DonorListAdapter extends BaseAdapter { private Context context; private int layout; private ArrayList<Donor> donorList; public DonorListAdapter(Context context, int layout, ArrayList<Donor> donorList) { this.context = context; this.layout = layout; this.donorList = donorList; } @Override public int getCount() { return donorList.size(); } @Override public Object getItem(int position) { return donorList.get(position); } @Override public long getItemId(int position) { return position; } private class ViewHolder { TextView txtname, txtnumber, txtblood; } @Override public View getView(int position, View convertView, ViewGroup parent) { View row = convertView; ViewHolder holder = new ViewHolder(); if (row == null) { LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); if (inflater != null) { row = inflater.inflate(layout, null); } if (row != null) { holder.txtname = row.findViewById(R.id.name_input); } if (row != null) { holder.txtnumber = row.findViewById(R.id.numberinput); } if (row != null) { holder.txtblood = (TextView) row.findViewById(R.id.blood_selector); } if (row != null) { row.setTag(holder); } } else { holder = (ViewHolder) row.getTag(); } Donor donor = donorList.get(position); holder.txtname.setText(donor.getName()); holder.txtnumber.setText(donor.getNumber()); holder.txtblood.setText(donor.getBlood().toString()); return row; } }

activity_main.xml

activity_register.xml

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent"> <EditText android:id="@+id/name_input" android:layout_width="match_parent" android:layout_height="wrap_content" android:hint="@string/person_name" android:ems="10" android:inputType="textCapWords" android:layout_marginBottom="5sp" /> <EditText android:id="@+id/numberinput" android:layout_width="match_parent" android:layout_height="wrap_content" android:hint="@string/hint" android:ems="10" android:inputType="phone" android:layout_marginBottom="5sp" /> <TextView android:id="@+id/blood" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="@string/blood_type" android:layout_marginBottom="10sp"/> <Spinner android:id="@+id/blood_selector" android:layout_width="match_parent" android:layout_height="wrap_content" android:entries="@array/blood_type" android:prompt="@string/blood_select" android:layout_marginBottom="5sp"/> <Button android:id="@+id/register_button" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/register" /> <Button android:id="@+id/list_button" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/show_donors" /> </LinearLayout>

contact_item.xml

<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"> <TextView android:id="@+id/contact_name" android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/contact_name" android:textSize="22sp"/> <TextView android:id="@+id/contact_number" android:layout_width="match_parent" android:layout_height="match_parent" android:textAppearance="?android:textAppearanceSmall" android:text="@string/contact_number" android:layout_alignParentTop="true" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" android:layout_marginLeft="29sp" android:layout_marginStart="29sp" android:layout_marginTop="31sp" /> <TextView android:id="@+id/contact_blood" android:layout_width="match_parent" android:layout_height="match_parent" android:textAppearance="?android:textAppearanceMedium" android:text="@string/blood_type" android:layout_alignParentTop="true" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" android:layout_marginLeft="300sp" android:layout_marginStart="300sp" android:layout_marginTop="30sp"/> </RelativeLayout>

最满意答案

你的班级Donor似乎有一个Spinner类型的场血。我将类型更改为String因为数据类不应该包含任何View s：

public class Donor { private String name; private String number; private String blood; // Getters and Setters here... public Donor(String name, String number, String blood) { this.name = name; this.number = number; this.blood = blood; } }

SQLiteHelper应该有一个静态的getInstance()方法，这样可以避免将它作为RegisterActivity的静态字段。另外，我认为数据库设置应该被封装。该Activity不需要知道有关数据库实施的任何信息。所以我将DDL移动到SQLiteHelper的onCreate()并删除了queryData() 。出于同样的原因，我将getData(String sql)更改为getDonors() 。最后， insertData()应该将数据作为参数而不是View 。所以不应该通过Spinner而是选定的项目的价值。

我的SQLiteHelper.java版本：

public class SQLiteHelper extends SQLiteOpenHelper{ private static SQLiteHelper sqliteHelper; private static String dbName = "Donors.sqlite"; private static int version = 1; private static final String CREATE_TABLE_DONORS = "CREATE TABLE IF NOT EXISTS DONORS (Id INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR, number VARCHAR, blood VARCHAR)"; /** * We use the application Context under the hood because this helps to avoid Exceptions * @param ctx */ private SQLiteHelper(Context ctx){ super(ctx.getApplicationContext(), dbName, null, version); } /** * SQLiteHelper as a Singleton * @param ctx any Context * @return x */ public static SQLiteHelper getInstance(Context ctx) { if(sqliteHelper == null){ sqliteHelper = new SQLiteHelper(ctx); } return sqliteHelper; } @Override public void onCreate(SQLiteDatabase db) { db.execSQL(CREATE_TABLE_DONORS); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { // necessary if you have a new database version } public void insertData(String name, String number, String blood) { SQLiteDatabase database = getWritableDatabase(); String sql = "INSERT INTO DONORS (name, number, blood) values (?, ?, ?)"; SQLiteStatement statement = database.compileStatement(sql); statement.clearBindings(); statement.bindString(1, name); statement.bindString(2, number); statement.bindString(3, blood); statement.executeInsert(); } public Cursor getDonors() { String sql = "SELECT * FROM DONORS"; SQLiteDatabase database = getReadableDatabase(); return database.rawQuery(sql, null); } }

更新的RegisterActivity.java（注意，我摆脱了局部变量微调器 ，只使用了spblood ）：

public class RegisterActivity extends AppCompatActivity { private EditText edtname, edtnumber; private Spinner spblood; private Button btnregister, btnlist; private SQLiteHelper sqLiteHelper; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_register); init(); ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this, R.array.blood_type, android.R.layout.simple_spinner_item); adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); spblood.setAdapter(adapter); sqLiteHelper = SQLiteHelper.getInstance(this); btnregister.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { try { sqLiteHelper.insertData( edtname.getText().toString().trim(), edtnumber.getText().toString().trim(), spblood.getSelectedItem().toString() ); } catch (Exception e) { e.printStackTrace(); } } }); btnlist.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent intent = new Intent(RegisterActivity.this, DonorList.class); startActivity(intent); } }); } private void init() { edtname = findViewById(R.id.name_input); edtnumber = findViewById(R.id.numberinput); spblood = findViewById(R.id.blood_selector); btnregister = findViewById(R.id.register_button); btnlist = findViewById(R.id.list_button); } }

对DonorList和适配器的更改归因于我对SQLiteHelper和Donor所做的更改。除此之外，您需要将列表行的资源ID传递给适配器的构造函数，而不是活动布局的资源ID。同样，列表行中TextView的R.id ....值必须与contact_item.xml中的值匹配

DonorList.java

public class DonorList extends AppCompatActivity { private ListView listView; private ArrayList<Donor> list; private DonorListAdapter adapter = null; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); listView = (ListView) findViewById(R.id.contacts_list); list = new ArrayList<>(); adapter = new DonorListAdapter(this, R.layout.contact_item, list); listView.setAdapter(adapter); Cursor cursor = SQLiteHelper.getInstance(this).getDonors(); list.clear(); while (cursor.moveToNext()) { String name = cursor.getString(1); String number = cursor.getString(2); String blood = cursor.getString(3); list.add(new Donor(name, number, blood)); } adapter.notifyDataSetChanged(); } }

最后，适配器：

public class DonorListAdapter extends BaseAdapter { private Context context; private int layout; private ArrayList<Donor> donorList; public DonorListAdapter(Context context, int layout, ArrayList<Donor> donorList) { this.context = context; this.layout = layout; this.donorList = donorList; } @Override public int getCount() { return donorList.size(); } @Override public Object getItem(int position) { return donorList.get(position); } @Override public long getItemId(int position) { return position; } private class ViewHolder { TextView txtname, txtnumber, txtblood; } @Override public View getView(int position, View convertView, ViewGroup parent) { View row = convertView; if (row == null) { ViewHolder holder = new ViewHolder(); row = LayoutInflater.from(context).inflate(layout, null); holder.txtname = (TextView)row.findViewById(R.id.contact_name); holder.txtnumber = (TextView)row.findViewById(R.id.contact_number); holder.txtblood = (TextView) row.findViewById(R.id.contact_blood); row.setTag(holder); } ViewHolder viewHolder = (ViewHolder) row.getTag(); Donor donor = donorList.get(position); viewHolder.txtname.setText(donor.getName()); viewHolder.txtnumber.setText(donor.getNumber()); viewHolder.txtblood.setText(donor.getBlood()); return row; } }

请享用！

Your class Donor seems to have a field blood of type Spinner. I changed the type to String because a data class should not contain any Views:

public class Donor { private String name; private String number; private String blood; // Getters and Setters here... public Donor(String name, String number, String blood) { this.name = name; this.number = number; this.blood = blood; } }

The SQLiteHelper should have a static getInstance() method so you can avoid having it as a static field in RegisterActivity. Also, I think that the database setup should be encapsulated. The Activity does not need to know anything about the database implementation. So I moved the DDL to the SQLiteHelper's onCreate() and dropped queryData(). For the same reason, I changed getData(String sql) to getDonors(). Lastly, insertData() should take data as parameters not Views. So one should not pass the Spinner but the selected item's value.

My version of SQLiteHelper.java:

public class SQLiteHelper extends SQLiteOpenHelper{ private static SQLiteHelper sqliteHelper; private static String dbName = "Donors.sqlite"; private static int version = 1; private static final String CREATE_TABLE_DONORS = "CREATE TABLE IF NOT EXISTS DONORS (Id INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR, number VARCHAR, blood VARCHAR)"; /** * We use the application Context under the hood because this helps to avoid Exceptions * @param ctx */ private SQLiteHelper(Context ctx){ super(ctx.getApplicationContext(), dbName, null, version); } /** * SQLiteHelper as a Singleton * @param ctx any Context * @return x */ public static SQLiteHelper getInstance(Context ctx) { if(sqliteHelper == null){ sqliteHelper = new SQLiteHelper(ctx); } return sqliteHelper; } @Override public void onCreate(SQLiteDatabase db) { db.execSQL(CREATE_TABLE_DONORS); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { // necessary if you have a new database version } public void insertData(String name, String number, String blood) { SQLiteDatabase database = getWritableDatabase(); String sql = "INSERT INTO DONORS (name, number, blood) values (?, ?, ?)"; SQLiteStatement statement = database.compileStatement(sql); statement.clearBindings(); statement.bindString(1, name); statement.bindString(2, number); statement.bindString(3, blood); statement.executeInsert(); } public Cursor getDonors() { String sql = "SELECT * FROM DONORS"; SQLiteDatabase database = getReadableDatabase(); return database.rawQuery(sql, null); } }

The updated RegisterActivity.java (note that I got rid of the local variable spinner and only used spblood):

public class RegisterActivity extends AppCompatActivity { private EditText edtname, edtnumber; private Spinner spblood; private Button btnregister, btnlist; private SQLiteHelper sqLiteHelper; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_register); init(); ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this, R.array.blood_type, android.R.layout.simple_spinner_item); adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); spblood.setAdapter(adapter); sqLiteHelper = SQLiteHelper.getInstance(this); btnregister.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { try { sqLiteHelper.insertData( edtname.getText().toString().trim(), edtnumber.getText().toString().trim(), spblood.getSelectedItem().toString() ); } catch (Exception e) { e.printStackTrace(); } } }); btnlist.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent intent = new Intent(RegisterActivity.this, DonorList.class); startActivity(intent); } }); } private void init() { edtname = findViewById(R.id.name_input); edtnumber = findViewById(R.id.numberinput); spblood = findViewById(R.id.blood_selector); btnregister = findViewById(R.id.register_button); btnlist = findViewById(R.id.list_button); } }

The changes to DonorList and the Adapter are due to the changes I made to SQLiteHelper and Donor. In addition to that, you need to pass the resource id of the list row to the Adapter's Constructor not the resource id of the Activity's layout. Similarly, the R.id.... values for the TextViews in the list row have to match those in contact_item.xml

DonorList.java

public class DonorList extends AppCompatActivity { private ListView listView; private ArrayList<Donor> list; private DonorListAdapter adapter = null; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); listView = (ListView) findViewById(R.id.contacts_list); list = new ArrayList<>(); adapter = new DonorListAdapter(this, R.layout.contact_item, list); listView.setAdapter(adapter); Cursor cursor = SQLiteHelper.getInstance(this).getDonors(); list.clear(); while (cursor.moveToNext()) { String name = cursor.getString(1); String number = cursor.getString(2); String blood = cursor.getString(3); list.add(new Donor(name, number, blood)); } adapter.notifyDataSetChanged(); } }

And finally, the Adapter:

public class DonorListAdapter extends BaseAdapter { private Context context; private int layout; private ArrayList<Donor> donorList; public DonorListAdapter(Context context, int layout, ArrayList<Donor> donorList) { this.context = context; this.layout = layout; this.donorList = donorList; } @Override public int getCount() { return donorList.size(); } @Override public Object getItem(int position) { return donorList.get(position); } @Override public long getItemId(int position) { return position; } private class ViewHolder { TextView txtname, txtnumber, txtblood; } @Override public View getView(int position, View convertView, ViewGroup parent) { View row = convertView; if (row == null) { ViewHolder holder = new ViewHolder(); row = LayoutInflater.from(context).inflate(layout, null); holder.txtname = (TextView)row.findViewById(R.id.contact_name); holder.txtnumber = (TextView)row.findViewById(R.id.contact_number); holder.txtblood = (TextView) row.findViewById(R.id.contact_blood); row.setTag(holder); } ViewHolder viewHolder = (ViewHolder) row.getTag(); Donor donor = donorList.get(position); viewHolder.txtname.setText(donor.getName()); viewHolder.txtnumber.setText(donor.getNumber()); viewHolder.txtblood.setText(donor.getBlood()); return row; } }

Enjoy!

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