我正在尝试使用 SQLite 做一个 Android 应用程序，但是当我尝试在我的智能手机上启动我的应用程序时，它会出现一个白屏并崩溃。
所以我查看了 LogCat，它显示了这个错误：
04-18 01:33:32.186: E/AndroidRuntime(26741): FATAL EXCEPTION: main
04-18 01:33:32.186: E/AndroidRuntime(26741): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.sqliteexample/database.MySQLiteHelper}: java.lang.InstantiationException: can't instantiate class database.MySQLiteHelper; no empty constructor
04-18 01:33:32.186: E/AndroidRuntime(26741): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2034)
04-18 01:33:32.186: E/AndroidRuntime(26741): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
04-18 01:33:32.186: E/AndroidRuntime(26741): at android.app.ActivityThread.access$700(ActivityThread.java:140)
04-18 01:33:32.186: E/AndroidRuntime(26741): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
04-18 01:33:32.186: E/AndroidRuntime(26741): at android.os.Handler.dispatchMessage(Handler.java:99)
04-18 01:33:32.186: E/AndroidRuntime(26741): at android.os.Looper.loop(Looper.java:137)
04-18 01:33:32.186: E/AndroidRuntime(26741): at android.app.ActivityThread.main(ActivityThread.java:4921)
04-18 01:33:32.186: E/AndroidRuntime(26741): at java.lang.reflect.Method.invokeNative(Native Method)
04-18 01:33:32.186: E/AndroidRuntime(26741): at java.lang.reflect.Method.invoke(Method.java:511)
04-18 01:33:32.186: E/AndroidRuntime(26741): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
04-18 01:33:32.186: E/AndroidRuntime(26741): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
04-18 01:33:32.186: E/AndroidRuntime(26741): at dalvik.system.NativeStart.main(Native Method)
04-18 01:33:32.186: E/AndroidRuntime(26741): Caused by: java.lang.InstantiationException: can't instantiate class database.MySQLiteHelper; no empty constructor
04-18 01:33:32.186: E/AndroidRuntime(26741): at java.lang.Class.newInstanceImpl(Native Method)
04-18 01:33:32.186: E/AndroidRuntime(26741): at java.lang.Class.newInstance(Class.java:1319)
04-18 01:33:32.186: E/AndroidRuntime(26741): at android.app.Instrumentation.newActivity(Instrumentation.java:1068)
04-18 01:33:32.186: E/AndroidRuntime(26741): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2025)
04-18 01:33:32.186: E/AndroidRuntime(26741): ... 11 more
这是 MySQLiteHelper 类：
package database;
import android.util.Log;
import android.annotation.SuppressLint;
import android.content.Context;
import android.database.DatabaseErrorHandler;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
@SuppressLint("NewApi")
public class MySQLiteHelper extends SQLiteOpenHelper {
public static final String TABLE_COMMENTS = "comments";
public static final String COLUMN_ID = "_id";
public static final String COLUMN_COMMENT = "comment";
private static final String DATABASE_NAME = "commments.db";
private static final int DATABASE_VERSION = 1;
// Database creation sql statement
private static final String DATABASE_CREATE = "create table "
+ TABLE_COMMENTS + "(" + COLUMN_ID
+ " integer primary key autoincrement, " + COLUMN_COMMENT
+ " text not null);";
public MySQLiteHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase database) {
database.execSQL(DATABASE_CREATE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w(MySQLiteHelper.class.getName(),
"Upgrading database from version " + oldVersion + " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS " + TABLE_COMMENTS);
onCreate(db);
}
}
这是 TestDatabaseActivity 类：
package activity;
import java.util.List;
import java.util.Random;
import model.Comment;
import dao.CommentsDataSource;
import android.app.ListActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import com.example.sqliteexample.R;
public class TestDatabaseActivity extends ListActivity {
private CommentsDataSource datasource;
public TestDatabaseActivity(){
super();
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my_sqlite_helper);
datasource = new CommentsDataSource(this);
datasource.open();
List<Comment> values = datasource.getAllComments();
// Use the SimpleCursorAdapter to show the
// elements in a ListView
ArrayAdapter<Comment> adapter = new ArrayAdapter<Comment>(this,
android.R.layout.simple_list_item_1, values);
setListAdapter(adapter);
}
// Will be called via the onClick attribute
// of the buttons in main.xml
public void onClick(View view) {
@SuppressWarnings("unchecked")
ArrayAdapter<Comment> adapter = (ArrayAdapter<Comment>) getListAdapter();
Comment comment = null;
switch (view.getId()) {
case R.id.add:
String[] comments = new String[] { "Cool", "Very nice", "Hate it" };
int nextInt = new Random().nextInt(3);
// Save the new comment to the database
comment = datasource.createComment(comments[nextInt]);
adapter.add(comment);
break;
case R.id.delete:
if (getListAdapter().getCount() > 0) {
comment = (Comment) getListAdapter().getItem(0);
datasource.deleteComment(comment);
adapter.remove(comment);
}
break;
}
adapter.notifyDataSetChanged();
}
@Override
protected void onResume() {
datasource.open();
super.onResume();
}
@Override
protected void onPause() {
datasource.close();
super.onPause();
}
}
评论数据源类：
import java.util.ArrayList;
import java.util.List;
import database.MySQLiteHelper;
import model.Comment;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
public class CommentsDataSource {
private SQLiteDatabase database;
private MySQLiteHelper dbHelper;
private String[] allColumns = { MySQLiteHelper.COLUMN_ID,
MySQLiteHelper.COLUMN_COMMENT };
public CommentsDataSource(Context context) {
dbHelper = new MySQLiteHelper(context);
}
public void open() throws SQLException {
database = dbHelper.getWritableDatabase();
}
public void close() {
dbHelper.close();
}
public Comment createComment(String comment) {
ContentValues values = new ContentValues();
values.put(MySQLiteHelper.COLUMN_COMMENT, comment);
long insertId = database.insert(MySQLiteHelper.TABLE_COMMENTS, null,
values);
Cursor cursor = database.query(MySQLiteHelper.TABLE_COMMENTS,
allColumns, MySQLiteHelper.COLUMN_ID + " = " + insertId, null,
null, null, null);
cursor.moveToFirst();
Comment newComment = cursorToComment(cursor);
cursor.close();
return newComment;
}
public void deleteComment(Comment comment) {
long id = comment.getId();
System.out.println("Comment deleted with id: " + id);
database.delete(MySQLiteHelper.TABLE_COMMENTS, MySQLiteHelper.COLUMN_ID
+ " = " + id, null);
}
public List<Comment> getAllComments() {
List<Comment> comments = new ArrayList<Comment>();
Cursor cursor = database.query(MySQLiteHelper.TABLE_COMMENTS,
allColumns, null, null, null, null, null);
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
Comment comment = cursorToComment(cursor);
comments.add(comment);
cursor.moveToNext();
}
// Make sure to close the cursor
cursor.close();
return comments;
}
private Comment cursorToComment(Cursor cursor) {
Comment comment = new Comment();
comment.setId(cursor.getLong(0));
comment.setComment(cursor.getString(1));
return comment;
}
}
我已经找到了java.lang.InstantiationException: can't instantiate class database.MySQLiteHelper; no empty constructor，但我不知道如何修复它..