Question

我有一个关于在android中的SQLite数据库表中插入默认值的问题。我有一个DBHandler（显然）负责创建数据库，表和执行CRUD查询。

但我似乎无法弄清楚的是，如何在表格中插入默认值。首先，我尝试使用以下方法在我的DBHandler中插入默认值：

// Write settings to db
public void addSetting(String key, String value) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(SETTING_KEY, key);
    values.put(SETTING_VALUE, value);
    db.insert(TABLE_APP_SETTINGS, null, values);
    db.close();
}

使用onCreate（）方法调用它：

@Override
public void onCreate(SQLiteDatabase db) {
    // creating tables
    db.execSQL(DATABASE_CREATE);
    db.execSQL(CREATE_TABLE_SETTINGS);

    // insert default values
    this.addSetting("access_admin_fingers", "2");
}

但由于某种原因，这导致应用程序崩溃，给我以下LogCat消息：

02-18 09:43:52.050: W/dalvikvm(14297): threadid=1: thread exiting with uncaught exception (group=0x41f3d930)
02-18 09:43:52.060: E/AndroidRuntime(14297): FATAL EXCEPTION: main
02-18 09:43:52.060: E/AndroidRuntime(14297): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.customerratingsystem/com.customerratingsystem.AdminActivity}: java.lang.IllegalStateException: getDatabase called recursively
02-18 09:43:52.060: E/AndroidRuntime(14297):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at android.app.ActivityThread.access$600(ActivityThread.java:141)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at android.os.Handler.dispatchMessage(Handler.java:99)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at android.os.Looper.loop(Looper.java:137)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at android.app.ActivityThread.main(ActivityThread.java:5041)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at java.lang.reflect.Method.invokeNative(Native Method)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at java.lang.reflect.Method.invoke(Method.java:511)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:817)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:584)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at dalvik.system.NativeStart.main(Native Method)
02-18 09:43:52.060: E/AndroidRuntime(14297): Caused by: java.lang.IllegalStateException: getDatabase called recursively
02-18 09:43:52.060: E/AndroidRuntime(14297):    at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:204)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at com.db.DBHandler.addSetting(DBHandler.java:69)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at com.db.DBHandler.onCreate(DBHandler.java:51)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:252)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at com.db.DBHandler.getSetting(DBHandler.java:83)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at com.customerratingsystem.AdminActivity.onCreate(AdminActivity.java:28)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at android.app.Activity.performCreate(Activity.java:5104)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
02-18 09:43:52.060: E/AndroidRuntime(14297):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)

然后我尝试通过从我的UI调用addSetting方法来插入这个“默认值”，如下所示：

db = new DBHandler(getApplicationContext());
db.addSetting("access_admin_fingers", "2");

哪个有效！但我的问题是：为什么我无法在DBHandler中使用此方法？

另外，在Android SQLite数据库中插入默认值的探测器是什么？

Answer 1

您已在SQLiteDatabase中拥有onCreate()个对象。您可以更改方法以获取SQLiteDatabase参数：

public void addSetting(SQLiteDatabase db, String key, String value) {
    ContentValues values = new ContentValues();
    values.put(SETTING_KEY, key);
    values.put(SETTING_VALUE, value);
    db.insert(TABLE_APP_SETTINGS, null, values);
}

并称之为：

@Override
public void onCreate(SQLiteDatabase db) {
    // creating tables
    db.execSQL(DATABASE_CREATE);
    db.execSQL(CREATE_TABLE_SETTINGS);

    // insert default values
    this.addSetting(db, "access_admin_fingers", "2");
}

Answer 2

有很多方法。您可以通过调用DB本身来访问DBHelper课程{/ 1}}，如下所示：

SQliteDatabase Object

此处，DB为// insert default values db.addSetting("access_admin_fingers", "2");。

或者您可以直接在SQliteDatabase Object方法中运行插入查询。

如何在Android SQLite中插入默认值？

2 个答案: