我正在尝试运行此代码：
for(int i=1; i <= 48; i++) { insertdiary("", ""); }
在MyDBhelper文件中创建数据库时：
...
@Override
public void onCreate(SQLiteDatabase db) {
Log.v("MyDBhelper onCreate","Creating all the tables");
try {
db.execSQL(CREATE_TABLE);
for(int i=1; i <= 48; i++) { insertdiary("", ""); }
}
catch(SQLiteException ex) {
Log.v("Create table exception", ex.getMessage());
}
}
...
但由于某种原因，循环不会创建新行。我认为这可能是因为数据库已经存在且代码未启动。我可能错了，这可能是由于其他原因造成的。无论如何，知道如何删除和重新创建我的数据库会很棒。更新数据库版本并不会冻结我的应用程序。
编辑---------------------------------------------- -----------------------------------------
这是带有新代码的MyDBhelper文件：
package com.cookbook.data;
import android.content.ContentValues;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class MyDBhelper extends SQLiteOpenHelper{
private SQLiteDatabase db;
private static final String CREATE_TABLE="create table "+
Constants.TABLE_NAME+" ("+
Constants.KEY_ID+" integer primary key autoincrement, "+
Constants.TITLE_NAME+" text not null, "+
Constants.CONTENT_NAME+" text not null, "+
Constants.DATE_NAME+" long);";
// database initialization
public MyDBhelper(Context context, String name, CursorFactory factory,
int version) {
super(context, name, factory, version);
}
public void drop() {
drop tables diaries;
}
@Override
public void onCreate(SQLiteDatabase db) {
Log.v("MyDBhelper onCreate","Creating all the tables");
try {
db.execSQL(CREATE_TABLE);
for(int i=1; i <= 48; i++) { insertdiary("", ""); }
}
catch(SQLiteException ex) {
Log.v("Create table exception", ex.getMessage());
}
}
// Saves a diary entry to the database as name-value pairs in ContentValues instance
// then passes the data to the SQLitedatabase instance to do an insert
public long insertdiary(String title, String content)
{
try{
ContentValues newTaskValue = new ContentValues();
newTaskValue.put(Constants.TITLE_NAME, title);
newTaskValue.put(Constants.CONTENT_NAME, content);
newTaskValue.put(Constants.DATE_NAME, java.lang.System.currentTimeMillis());
return db.insert(Constants.TABLE_NAME, null, newTaskValue);
} catch(SQLiteException ex) {
Log.v("Insert into database exception caught",
ex.getMessage());
return -1;
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,
int newVersion) {
Log.w("TaskDBAdapter", "Upgrading from version "+oldVersion
+" to "+newVersion
+", which will destroy all old data");
db.execSQL("drop table if exists "+Constants.TABLE_NAME);
onCreate(db);
}
}
编辑---------------------------------------------- --------------------------------------- Constants.java
package com.cookbook.data;
public class Constants {
public static final String DATABASE_NAME="datastorage";
public static final int DATABASE_VERSION=1;
public static final String TABLE_NAME="diaries";
public static final String TITLE_NAME="title";
public static final String CONTENT_NAME="content";
public static final String DATE_NAME="recorddate";
public static final String KEY_ID="_id";
public static final String TABLE_ROW="row_id";
}
编辑---------------------------------------------- --------------------------- LogCat
04-11 12:31:24.379: I/ActivityThread(8459): Pub com.example.classorganizer: com.example.classorganizer.DiaryContentProvider
04-11 12:31:24.509: V/MyDBhelper onCreate(8459): Creating all the tables
04-11 12:31:24.529: W/dalvikvm(8459): threadid=1: thread exiting with uncaught exception (group=0x40018578)
04-11 12:31:24.539: E/AndroidRuntime(8459): FATAL EXCEPTION: main
04-11 12:31:24.539: E/AndroidRuntime(8459): java.lang.RuntimeException: Unable to get provider com.example.classorganizer.DiaryContentProvider: java.lang.IllegalStateException: getWritableDatabase called recursively
04-11 12:31:24.539: E/AndroidRuntime(8459): at android.app.ActivityThread.installProvider(ActivityThread.java:3561)
04-11 12:31:24.539: E/AndroidRuntime(8459): at android.app.ActivityThread.installContentProviders(ActivityThread.java:3313)
04-11 12:31:24.539: E/AndroidRuntime(8459): at android.app.ActivityThread.handleBindApplication(ActivityThread.java:3269)
04-11 12:31:24.539: E/AndroidRuntime(8459): at android.app.ActivityThread.access$2200(ActivityThread.java:117)
04-11 12:31:24.539: E/AndroidRuntime(8459): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:973)
04-11 12:31:24.539: E/AndroidRuntime(8459): at android.os.Handler.dispatchMessage(Handler.java:99)
04-11 12:31:24.539: E/AndroidRuntime(8459): at android.os.Looper.loop(Looper.java:130)
04-11 12:31:24.539: E/AndroidRuntime(8459): at android.app.ActivityThread.main(ActivityThread.java:3687)
04-11 12:31:24.539: E/AndroidRuntime(8459): at java.lang.reflect.Method.invokeNative(Native Method)
04-11 12:31:24.539: E/AndroidRuntime(8459): at java.lang.reflect.Method.invoke(Method.java:507)
04-11 12:31:24.539: E/AndroidRuntime(8459): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
04-11 12:31:24.539: E/AndroidRuntime(8459): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
04-11 12:31:24.539: E/AndroidRuntime(8459): at dalvik.system.NativeStart.main(Native Method)
04-11 12:31:24.539: E/AndroidRuntime(8459): Caused by: java.lang.IllegalStateException: getWritableDatabase called recursively
04-11 12:31:24.539: E/AndroidRuntime(8459): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:101)
04-11 12:31:24.539: E/AndroidRuntime(8459): at com.cookbook.data.MyDBhelper.insertdiary(MyDBhelper.java:62)
04-11 12:31:24.539: E/AndroidRuntime(8459): at com.cookbook.data.MyDBhelper.onCreate(MyDBhelper.java:45)
04-11 12:31:24.539: E/AndroidRuntime(8459): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:126)
04-11 12:31:24.539: E/AndroidRuntime(8459): at com.cookbook.data.MyDB.open(MyDB.java:39)
04-11 12:31:24.539: E/AndroidRuntime(8459): at com.example.classorganizer.DiaryContentProvider.onCreate(DiaryContentProvider.java:36)
04-11 12:31:24.539: E/AndroidRuntime(8459): at android.content.ContentProvider.attachInfo(ContentProvider.java:840)
04-11 12:31:24.539: E/AndroidRuntime(8459): at android.app.ActivityThread.installProvider(ActivityThread.java:3558)
04-11 12:31:24.539: E/AndroidRuntime(8459): ... 12 more
编辑---------------------------------------------- -------------------------------------- MyDB.class
package com.cookbook.data;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.util.Log;
public class MyDB {
private SQLiteDatabase db;
private final Context context;
private final MyDBhelper dbhelper;
// Initializes MyDBHelper instance
public MyDB(Context c){
context = c;
dbhelper = new MyDBhelper(context, Constants.DATABASE_NAME, null,
Constants.DATABASE_VERSION);
}
// Closes the database connection
public void close()
{
db.close();
}
// Initializes a SQLiteDatabase instance using MyDBhelper
public void open() throws SQLiteException
{
try {
db = dbhelper.getWritableDatabase();
} catch(SQLiteException ex) {
Log.v("Open database exception caught", ex.getMessage());
db = dbhelper.getReadableDatabase();
}
}
// updates a diary entry (existing row)
public boolean updateDiaryEntry(String title, long rowId)
{
ContentValues newValue = new ContentValues();
newValue.put(Constants.TITLE_NAME, title);
return db.update(Constants.TABLE_NAME, newValue, Constants.KEY_ID + "=" + rowId, null)>0;
}
// Reads the diary entries from database, saves them in a Cursor class and returns it from the method
public Cursor getdiaries()
{
Cursor c = db.query(Constants.TABLE_NAME, null, null,
null, null, null, null);
return c;
}
}
编辑---------------------------------------------- -------------------------------------- 新错误logcat
04-11 13:26:55.699: I/ActivityThread(9752): Pub com.example.classorganizer: com.example.classorganizer.DiaryContentProvider
04-11 13:26:55.809: V/MyDBhelper onCreate(9752): Creating all the tables
04-11 13:26:55.839: W/dalvikvm(9752): threadid=1: thread exiting with uncaught exception (group=0x40018578)
04-11 13:26:55.859: E/AndroidRuntime(9752): FATAL EXCEPTION: main
04-11 13:26:55.859: E/AndroidRuntime(9752): java.lang.RuntimeException: Unable to get provider com.example.classorganizer.DiaryContentProvider: java.lang.IllegalStateException: getWritableDatabase called recursively
04-11 13:26:55.859: E/AndroidRuntime(9752): at android.app.ActivityThread.installProvider(ActivityThread.java:3561)
04-11 13:26:55.859: E/AndroidRuntime(9752): at android.app.ActivityThread.installContentProviders(ActivityThread.java:3313)
04-11 13:26:55.859: E/AndroidRuntime(9752): at android.app.ActivityThread.handleBindApplication(ActivityThread.java:3269)
04-11 13:26:55.859: E/AndroidRuntime(9752): at android.app.ActivityThread.access$2200(ActivityThread.java:117)
04-11 13:26:55.859: E/AndroidRuntime(9752): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:973)
04-11 13:26:55.859: E/AndroidRuntime(9752): at android.os.Handler.dispatchMessage(Handler.java:99)
04-11 13:26:55.859: E/AndroidRuntime(9752): at android.os.Looper.loop(Looper.java:130)
04-11 13:26:55.859: E/AndroidRuntime(9752): at android.app.ActivityThread.main(ActivityThread.java:3687)
04-11 13:26:55.859: E/AndroidRuntime(9752): at java.lang.reflect.Method.invokeNative(Native Method)
04-11 13:26:55.859: E/AndroidRuntime(9752): at java.lang.reflect.Method.invoke(Method.java:507)
04-11 13:26:55.859: E/AndroidRuntime(9752): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
04-11 13:26:55.859: E/AndroidRuntime(9752): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
04-11 13:26:55.859: E/AndroidRuntime(9752): at dalvik.system.NativeStart.main(Native Method)
04-11 13:26:55.859: E/AndroidRuntime(9752): Caused by: java.lang.IllegalStateException: getWritableDatabase called recursively
04-11 13:26:55.859: E/AndroidRuntime(9752): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:101)
04-11 13:26:55.859: E/AndroidRuntime(9752): at com.cookbook.data.MyDBhelper.insertdiary(MyDBhelper.java:64)
04-11 13:26:55.859: E/AndroidRuntime(9752): at com.cookbook.data.MyDBhelper.onCreate(MyDBhelper.java:47)
04-11 13:26:55.859: E/AndroidRuntime(9752): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:126)
04-11 13:26:55.859: E/AndroidRuntime(9752): at com.cookbook.data.MyDB.open(MyDB.java:39)
04-11 13:26:55.859: E/AndroidRuntime(9752): at com.example.classorganizer.DiaryContentProvider.onCreate(DiaryContentProvider.java:36)
04-11 13:26:55.859: E/AndroidRuntime(9752): at android.content.ContentProvider.attachInfo(ContentProvider.java:840)
04-11 13:26:55.859: E/AndroidRuntime(9752): at android.app.ActivityThread.installProvider(ActivityThread.java:3558)
04-11 13:26:55.859: E/AndroidRuntime(9752): ... 12 more
答案 0 :(得分：0)
您可以按照以下方式删除您的表格，
public void dropTable()
{
SQLiteDatabase db = this.getWritableDatabase();
db.execSQL ( "drop table diaries" );
}
上述方法也会删除您的表格和数据。但是如果您不想删除表并且只想删除记录，那么您可以尝试以下方法，
public void deleteData( String tableName )
{
SQLiteDatabase db = this.getWritableDatabase();
db.execSQL ( "truncate table " + tableName );
// db.execSQL ( "delete from " + tableName ); Using delete query
}