Question

有人可以帮助我解决我得到的错误吗？我真的无法弄清楚为什么addCategory（）方法被调用两次然后导致“UNIQUE约束失败”问题。非常感谢。代码如下：

public class MainActivity extends ActionBarActivity {
MyDatabase mdb;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
     mdb=new MyDatabase(this);
     mdb.addCategory("hello");
    setContentView(R.layout.activity_main);

}

和在Mydatabase中

public class MyDatabase extends SQLiteOpenHelper {

private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "Event24";
public MyDatabase(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}


@Override
public void onCreate(SQLiteDatabase db) {
    String CREATE_CATEGORY_TABLE = "CREATE TABLE if not exists test2 
(     " +
            " _id INTEGER PRIMARY KEY AUTOINCREMENT, " +
            " categorys TEXT UNIQUE)" ;
      db.execSQL(CREATE_CATEGORY_TABLE);

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int  
newVersion) {
    db.execSQL("DROP TABLE IF EXISTS events");
    // create fresh books table
    this.onCreate(db);
}

public void addCategory(String name){
    Log.e("mydatabase","addCategory");
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues cv = new ContentValues();
    cv.put("categorys", name);
    db.insert("test2", // table
            null,  //nullColumnHack
            cv); // key/value -> keys = column names/ values = 
  column values
    db.close();

}

}

，错误如下：

  05-22 09:50:34.672    1884-1884/com.example.julia.testactivitydatabase E/mydatabase﹕ addCategory
  05-22 09:50:53.135    1884-1884/com.example.julia.testactivitydatabase E/mydatabase﹕ addCategory
  05-22 09:50:53.137    1884-1884/com.example.julia.testactivitydatabase E/SQLiteLog﹕ (2067) abort at 12 in [INSERT INTO test2(categorys) VALUES (?)]: UNIQUE constraint failed: test2.categorys
  05-22 09:50:53.137    1884-1884/com.example.julia.testactivitydatabase E/SQLiteDatabase﹕ Error inserting categorys=hello
android.database.sqlite.SQLiteConstraintException: UNIQUE constraint failed: test2.categorys (code 2067)
        at android.database.sqlite.SQLiteConnection.nativeExecuteForLastInsertedRowId(Native Method)
        at android.database.sqlite.SQLiteConnection.executeForLastInsertedRowId(SQLiteConnection.java:782)
        at android.database.sqlite.SQLiteSession.executeForLastInsertedRowId(SQLiteSession.java:788)
        at android.database.sqlite.SQLiteStatement.executeInsert(SQLiteStatement.java:86)
        at android.database.sqlite.SQLiteDatabase.insertWithOnConflict(SQLiteDatabase.java:1471)
        at android.database.sqlite.SQLiteDatabase.insert(SQLiteDatabase.java:1341)
        at com.example.julia.testactivitydatabase.MyDatabase.addCategory(MyDatabase.java:54)
        at com.example.julia.testactivitydatabase.MainActivity.onCreate(MainActivity.java:23)
        at android.app.Activity.performCreate(Activity.java:5933)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
        at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3912)
        at android.app.ActivityThread.access$900(ActivityThread.java:144)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1284)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5221)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

Answer 1

每次启动应用程序或旋转屏幕时都会执行Activity.onCreate。此调用用于创建用户界面，而不是处理数据库初始化。这意味着它将被召唤两次但不会多次。

如果您需要设置一些预先存在的类别ONCE，请在MyDatabase.onCreate方法中执行此操作。

至于＆＃34;为什么叫两次＆＃34; - 在那里放一个日志。在单个应用程序启动中，没有必要连续两次调用它。如果您启动应用程序一次，将创建数据库行。如果你第二次启动它，即使onCreate在第二次启动期间被调用一次（应该如此），DB也会从之前的启动中获得这个固定的唯一记录。毕竟，DB的目的是在发布之间持久化信息。

Android数据库方法被调用了两次

1 个答案: