Question

我正在创建一个不扩展Activity的java类，在其构造函数中，我想从另一个实例化SQLiteOpenHelper的类中实例化一个对象。问题是，当实例化SQLiteOpenHelper类的对象时，我需要传递当前类的Context，该类不会扩展Activity。我应该将什么参数传递给SQLiteOpenHelper。

的实例

SQLiteOpenHelper的构造函数：

public class MPLDataBase extends SQLiteOpenHelper {

private static final int DATABASE_VERSION = 2;
private static final String DATABASE_NAME = "MPL.db";
private static final String MPL_TABLE_NAME = "MPLData";

public MPLDataBase(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);

}

实例化SQLiteOpenHelper的类： 这是一个NON_ACTIVITY类

public class NotifyArrayAdapter {

private MPLDataBase mplOpenHelperDB = null;
private SQLiteDatabase sqliteDB = null;
private int itemClickedPos;

public NotifyArrayAdapter() {
    mplOpenHelperDB = new MPLDataBase(WHAT_SHOULD_I_PASS_HERE);
}

NotifyArrayAdapterClass

public class NotifyArrayAdapter {

private MPLDataBase mplOpenHelperDB = null;
private SQLiteDatabase sqliteDB = null;
private int itemClickedPos;

public NotifyArrayAdapter(Context context) {
    if (this.mplOpenHelperDB == null) {
        this.mplOpenHelperDB = new MPLDataBase(context);
    }
    if (this.sqliteDB == null) {
        this.sqliteDB = mplOpenHelperDB.getWritableDatabase();
    }

}
public void deleteAtPos(int pos) {
    if(! this.sqliteDB.isOpen()) {
        this.sqliteDB = mplOpenHelperDB.getWritableDatabase();
    }
    this.itemClickedPos = pos;
    int [] dbIDs = this.mplOpenHelperDB.getIDs();
    mplOpenHelperDB.deleteRow(dbIDs[this.itemClickedPos]);
}

public void deleteAllDBRows() {
    if(! this.sqliteDB.isOpen()) {
        this.sqliteDB = mplOpenHelperDB.getWritableDatabase();
    }
    mplOpenHelperDB.deleteALLRows();
}

}

Answer 1

您需要将当前context传递给MPLDataBase构造函数

 public NotifyArrayAdapter(Context con) {
  mplOpenHelperDB = new MPLDataBase(con);
 }

就像你从任何Activity那样打电话给

 NotifyArrayAdapter notifyarrayAdapter = new NotifyArrayAdapter(yourActivity.This);

就像你从任何Fargment那样打电话给

 NotifyArrayAdapter notifyarrayAdapter = new NotifyArrayAdapter(getActivity());

如何从非活动类实例化活动类的对象？

1 个答案: