应用程序的目标：
用户可以输入名字和姓氏，此信息将存储到本地数据库中。我能够检索信息并在我的logcat中看到它，但是当我尝试使用listview在应用程序中显示信息时，它会崩溃我的应用程序。我提供了我的代码和崩溃logcat的副本。
还要添加一件事，我为listview创建了自定义布局。我已经提供了下面的所有代码，所以如果您在任何地方感到困惑，请询问，我会相应地更新或回复。
我希望用户点击＆＃34;列表＆＃34;
后，列表视图中会列出数据库中的值 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);
}
});
}
}
<?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>
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();
}
});
}
}
<?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>
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);
} }
<?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>
<?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>
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);
}
}
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;
}
}
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
答案 0 :(得分：0)
创建databaseHandler.getAllContacts()的新版本：
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行调用该方法。
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;
}