如何將數據庫中的值顯示到列表視圖中

Question

應用程序的目標：

1. 允許用戶將客戶添加到數據庫（完成）
2. 允許用戶從數據庫中檢索所有客戶，並將其顯示在列表視圖中（幫助）。

用戶可以輸入名字和姓氏，此信息將存儲到本地數據庫中。 我能夠檢索信息並在logcat中看到它，但是當我嘗試使用listview在應用程序中顯示信息時，它會使我的應用程序崩潰。 我提供了代碼和崩潰日志的副本。

另外要添加的一件事是，我為listview創建了一個自定義布局。 我已經提供了以下所有代碼，因此，如果您在任何地方都感到困惑，請問一下，我會相應地更新或回復。

我只想一旦用戶單擊“列表”，就可以在列表視圖中列出數據庫中的值

碼：

MainActivity.java

    package bluwyreinc.mangecontacts;

    import android.content.Intent;
    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    import android.util.Log;
    import android.view.View;
    import android.widget.Button;

    import java.util.List;

    public class MainActivity extends AppCompatActivity {

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

        final DatabaseHandler databasehandler = new DatabaseHandler(this);

        Button add = (Button)findViewById(R.id.button);
        Button list = (Button)findViewById(R.id.button2);

        add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent add = new Intent(MainActivity.this, AddClient.class);
                startActivity(add);
            }
        });

        list.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                Intent list = new Intent(MainActivity.this, ListActivity.class);
                startActivity(list);
            }
        });

    }
}

activity_main.xml

    <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" tools:context="bluwyreinc.mangecontacts.MainActivity">


    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="96dp"
        android:text="add" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignEnd="@+id/button"
        android:layout_below="@+id/button"
        android:layout_marginTop="14dp"
        android:text="list" />
</RelativeLayout>

AddClient.java

package bluwyreinc.mangecontacts;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class AddClient extends AppCompatActivity {

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

        final DatabaseHandler databaseHandler = new DatabaseHandler(this);

        Button submit = (Button)findViewById(R.id.submit);
        final EditText firstName = (EditText)findViewById(R.id.fname);
        final EditText lastName = (EditText)findViewById(R.id.lname);

        submit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                String fn = firstName.getText().toString();
                String ln = lastName.getText().toString();
                Log.d("Insert: ", "Inserting ..");
                databaseHandler.addContact(new Contact(ln, fn));
                Toast.makeText(AddClient.this, fn+".."+ln, Toast.LENGTH_SHORT).show();
            }
        });




    }
}

activity_add_client.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="bluwyreinc.mangecontacts.AddClient">

    <EditText
        android:id="@+id/fname"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="57dp"
        android:ems="10"
        android:hint="first"
        android:inputType="textPersonName"
        tools:layout_editor_absoluteX="85dp"
        tools:layout_editor_absoluteY="58dp" />

    <EditText
        android:id="@+id/lname"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignStart="@+id/fname"
        android:layout_below="@+id/fname"
        android:layout_marginTop="18dp"
        android:ems="10"
        android:hint="last"
        android:inputType="textPersonName" />

    <Button
        android:id="@+id/submit"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignEnd="@+id/lname"
        android:layout_alignStart="@+id/lname"
        android:layout_below="@+id/lname"
        android:layout_marginTop="27dp"
        android:text="Submit" />
</RelativeLayout>

ListActivity.java

package bluwyreinc.mangecontacts;

import android.database.Cursor;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;

import java.util.List;

public class ListActivity extends AppCompatActivity {

    DatabaseHandler databaseHandler = new DatabaseHandler(this);

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


        Button list = (Button)findViewById(R.id.list);

        list.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                populateListView();
                Log.d("Reading: ", "Reading all contacts..");
                List<Contact> contacts = databaseHandler.getAllContacts();

                for (Contact cn : contacts) {
                    String log = "Id: " + cn.getID() + " ,First Name: " + cn.getName() + " , Last Name: " + cn.getPhoneNumber();
                    // Writing Contacts to log
                    Log.d("Name: ", log);
                }
            }
        });
    }

    private void populateListView(){
//Cursor cursor = (Cursor) databaseHandler.getAllContacts();
Cursor cursor = databaseHandler.getAllContactsCursor();
String[] fromFieldFirstLastNames = new String[]{databaseHandler.KEY_FNAME, databaseHandler.KEY_LNAME};
int[] toViewIDs = new int[]{R.id.firstnamelist,R.id.lastnamelist};
SimpleCursorAdapter simpleCursorAdapter;
simpleCursorAdapter = new SimpleCursorAdapter(getBaseContext(),R.layout.listviewlayout, cursor, fromFieldFirstLastNames,toViewIDs,0);

ListView myList = (ListView)findViewById(R.id.listviewclients);
myList.setAdapter(simpleCursorAdapter);

}}

activity_list.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="bluwyreinc.mangecontacts.ListActivity">


    <Button
        android:id="@+id/list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="18dp"
        android:text="List" />

    <ListView
        android:id="@+id/listviewclients"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@+id/list"
        android:layout_alignParentStart="true"
        android:layout_marginTop="14dp" />
</RelativeLayout>

listview的自定義布局... listviewlayout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/firstnamelist"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingRight="20dp"
        android:text="TextView" />

    <TextView
        android:id="@+id/lastnamelist"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TextView" />
</LinearLayout>

以下兩個是類。

數據庫處理程序

      package bluwyreinc.mangecontacts;

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

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

public class DatabaseHandler extends SQLiteOpenHelper {

    // All Static variables
    // Database Version
    private static final int DATABASE_VERSION = 1;

    // Database Name
    private static final String DATABASE_NAME = "contactsManager";

    // Contacts table name
    String TABLE_CONTACTS = "contacts";

    // Contacts Table Columns names
    String KEY_ID = "id";
    String KEY_FNAME = "fname";
    String KEY_LNAME = "lname";

    public DatabaseHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    // Creating Tables
    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
                + KEY_ID + " INTEGER PRIMARY KEY," + KEY_FNAME + " TEXT,"
                + KEY_LNAME + " TEXT" + ")";
        db.execSQL(CREATE_CONTACTS_TABLE);
    }

    // Upgrading database
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);

        // Create tables again
        onCreate(db);
    }

    /**
     * All CRUD(Create, Read, Update, Delete) Operations
     */

    // Adding new contact
    void addContact(Contact contact) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_FNAME, contact.getName()); // Contact Name
        values.put(KEY_LNAME, contact.getPhoneNumber()); // Contact Phone

        // Inserting Row
        db.insert(TABLE_CONTACTS, null, values);
        db.close(); // Closing database connection
    }

    // Getting single contact
    Contact getContact(int id) {
        SQLiteDatabase db = this.getReadableDatabase();

        Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID,
                        KEY_FNAME, KEY_LNAME }, KEY_ID + "=?",
                new String[] { String.valueOf(id) }, null, null, null, null);
        if (cursor != null)
            cursor.moveToFirst();

        Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
                cursor.getString(1), cursor.getString(2));
        // return contact
        return contact;
    }

    // Getting All Contacts

    public List<Contact> getAllContacts() {
        List<Contact> contactList = new ArrayList<Contact>();

        Cursor cursor = getAllContactsCursor();

        // looping through all rows and adding to list
        if (cursor.moveToFirst()) {
            do {
                Contact contact = new Contact();
                contact.setID(Integer.parseInt(cursor.getString(0)));
                contact.setName(cursor.getString(1));
                contact.setPhoneNumber(cursor.getString(2));
                // Adding contact to list
                contactList.add(contact);
            } while (cursor.moveToNext());
        }

        // return contact list
        return contactList;
    }


    // Updating single contact
    public int updateContact(Contact contact) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_FNAME, contact.getName());
        values.put(KEY_LNAME, contact.getPhoneNumber());

        // updating row
        return db.update(TABLE_CONTACTS, values, KEY_ID + " = ?",
                new String[] { String.valueOf(contact.getID()) });
    }

    // Deleting single contact
    public void deleteContact(Contact contact) {
        SQLiteDatabase db = this.getWritableDatabase();
        db.delete(TABLE_CONTACTS, KEY_ID + " = ?",
                new String[] { String.valueOf(contact.getID()) });
        db.close();
    }


    // Getting contacts Count
    public int getContactsCount() {
        String countQuery = "SELECT  * FROM " + TABLE_CONTACTS;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(countQuery, null);
        cursor.close();

        // return count
        return cursor.getCount();
    }

    public Cursor getAllContactsCursor() {
        // Select All Query
        String selectQuery = "SELECT  * FROM " + TABLE_CONTACTS;
        SQLiteDatabase db = this.getWritableDatabase();
        return db.rawQuery(selectQuery, null);
    }

}

Contact.java

     package bluwyreinc.mangecontacts;

        public class Contact {

            //private variables
            int _id;
            String _fname;
            String _lname;

            // Empty constructor
            public Contact(){

            }
            // constructor
            public Contact(int id, String name, String _lname){
                this._id = id;
                this._fname = name;
                this._lname = _lname;
            }

            // constructor
            public Contact(String name, String _lname){
                this._fname = name;
                this._lname = _lname;
            }
            // getting ID
            public int getID(){
                return this._id;
            }

            // setting id
            public void setID(int id){
                this._id = id;
            }

            // getting name
            public String getName(){
                return this._fname;
            }

            // setting name
            public void setName(String name){
                this._fname = name;
            }

            // getting phone number
            public String getPhoneNumber(){
                return this._lname;
            }

            // setting phone number
            public void setPhoneNumber(String phone_number){
                this._lname = phone_number;
            }
        }

LOGCAT（已更新）

01-05 12:22:56.556 18492-18492/bluwyreinc.mangecontacts E/AndroidRuntime: FATAL EXCEPTION: main
                                                                          Process: bluwyreinc.mangecontacts, PID: 18492
                                                                          java.lang.IllegalArgumentException: column '_id' does not exist
                                                                              at android.database.AbstractCursor.getColumnIndexOrThrow(AbstractCursor.java:333)
                                                                              at android.widget.CursorAdapter.init(CursorAdapter.java:180)
                                                                              at android.widget.CursorAdapter.<init>(CursorAdapter.java:157)
                                                                              at android.widget.ResourceCursorAdapter.<init>(ResourceCursorAdapter.java:96)
                                                                              at android.widget.SimpleCursorAdapter.<init>(SimpleCursorAdapter.java:104)
                                                                              at bluwyreinc.mangecontacts.ListActivity.populateListView(ListActivity.java:48)
                                                                              at bluwyreinc.mangecontacts.ListActivity.access$000(ListActivity.java:14)
                                                                              at bluwyreinc.mangecontacts.ListActivity$1.onClick(ListActivity.java:29)
                                                                              at android.view.View.performClick(View.java:6308)
                                                                              at android.widget.TextView.performClick(TextView.java:11202)
                                                                              at android.view.View$PerformClick.run(View.java:23969)
                                                                              at android.os.Handler.handleCallback(Handler.java:751)
                                                                              at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                              at android.os.Looper.loop(Looper.java:154)
                                                                              at android.app.ActivityThread.main(ActivityThread.java:6823)
                                                                              at java.lang.reflect.Method.invoke(Native Method)
                                                                              at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1563)
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1451)
01-05 12:22:56.560 3104-3122/? W/ActivityManager:   Force finishing activity bluwyreinc.mangecontacts/.ListActivity

Answer 1

創建一個新版本的databaseHandler.getAllContacts() ：

public Cursor getAllContactsCursor() {
    // Select All Query
    String selectQuery = "SELECT  * FROM " + TABLE_CONTACTS;
    SQLiteDatabase db = this.getWritableDatabase();
    return db.rawQuery(selectQuery, null);
}

然后在ListActivity.java的第43行調用該方法。

private void populateListView(){
Cursor cursor = databaseHandler.getAllContactsCursor();
...
}

然后，您可以修改databaseHandler.getAllContacts()以使用新方法。

public List<Contact> getAllContacts() {
    List<Contact> contactList = new ArrayList<Contact>();

    Cursor cursor = getAllContactsCursor();

    // looping through all rows and adding to list
    if (cursor.moveToFirst()) {
        do {
            Contact contact = new Contact();
            contact.setID(Integer.parseInt(cursor.getString(0)));
            contact.setName(cursor.getString(1));
            contact.setPhoneNumber(cursor.getString(2));
            // Adding contact to list
            contactList.add(contact);
        } while (cursor.moveToNext());
    }

    // return contact list
    return contactList;
}