这是从class User < ActiveRecord::Base
# as parent
has_many: student_relations, foreign_key: :parent_id, class_name: "ParentStudent"
has_many: students, through: :student_relations, source: :student
# as student
has_many: parent_relations, foreign_key: :student_id, class_name: "ParentStudent"
has_many: parents, through: :parent_relations, source: :parent
end
class ParentStudent < ActiveRecord::Base
belongs_to :student, foreign_key: "student_id", class_name: "User"
belongs_to :parent, foreign_key: "parent_id", class_name: "User"
end
获取表格 RECORD 的代码。在SQLiteDatebase出现问题时，它总是抛出try block。我在这里尝试的只是将表“RECORD”的每一行转换为字符串并将其添加到SQLiteException，然后将数组连接到ArrayList，最后使用{{1显示数组。
ArrayAdapter这是我的datebaseHelper的代码：
ListView package com.example.tommy.stop_watch_real;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.CursorAdapter;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import android.widget.Toast;
import java.util.ArrayList;
public class RecordList extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_record_list);
ListView temp = (ListView) findViewById(R.id.recordList);
ArrayList<String> arrayList = new ArrayList<String>();
ArrayAdapter<String> adapter;
**try {
SQLiteOpenHelper dataBaseHelper = new DataBaseHelper(this);
SQLiteDatabase db = dataBaseHelper.getReadableDatabase();
Cursor cursor = db.query("RECORD", new String[] {"_id, DATE, MINUTES"}, null, null,null,null,null);
while (cursor.moveToFirst()){
String id = Integer.toString(cursor.getInt(0));
String date = cursor.getString(1);
String minutes = Integer.toString(cursor.getInt(2));
String finalValue = id + "|" + date + "|" + minutes;
arrayList.add(finalValue);
}
adapter=new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1,
arrayList);
temp.setAdapter(adapter);
cursor.close();
db.close();}**
catch (SQLiteException e) {
Toast.makeText(RecordList.this, "Database not available", Toast.LENGTH_LONG).show();
}
}
}
始终显示，意味着class DataBaseHelper extends SQLiteOpenHelper {
private static final String DB_NAME = "Record"; // name of the database
private static final int DB_VERSION = 1; //Version
DataBaseHelper (Context context){
super(context, DB_NAME, null, DB_VERSION);
}
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE RECORD ("
+ "_id INTEGER PRIMARY KEY AUTOINCERMENT, "
+ "DATE STRING," //careful
+ "MINUTES INTEGER" + ");"
);
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
//no need to worry about this yet.
}
}
出现问题。我刚刚开始一周前的android开发，我不知道我的代码出了什么问题。如果你能给我一些指导，那就太好了。
提前谢谢你。
答案 0 :(得分：1)
这部分对我来说似乎不对。
while (cursor.moveToFirst()){
String id = Integer.toString(cursor.getInt(0));
String date = cursor.getString(1);
String minutes = Integer.toString(cursor.getInt(2));
String finalValue = id + "|" + date + "|" + minutes;
arrayList.add(finalValue);
}
我不确定您要实现的目标，但从数据库获取数据的正确方法如下：
cursor.moveToFirst()
while (cursor.isAfterLast()){
String id = Integer.toString(cursor.getInt(0));
String date = cursor.getString(1);
String minutes = Integer.toString(cursor.getInt(2));
String finalValue = id + "|" + date + "|" + minutes;
arrayList.add(finalValue);
}