记使用Android SQLite遇到的小问题

之前一直是遇到activity需要保存数据就直接使用SQLite就好，但是有一天突然发现，我需要在其中一个Activity里访问另一个Activity建立的SQLiteDatabase，从而引出了该文。

查了很多资料，大多数都是说，使用单例模式建立继承SQLiteOpenHelper的类，然后使用静态方法（一般取名getInstance）来获得。自己亲自尝试了，发现总是不对，于是找了一种更简便更懒的方法（直接用文件位置引用数据库）：

SettingActivity.java

db = openOrCreateDatabase("callon_set_pump", Context.MODE_PRIVATE, null);
if(tabbleIsExist("table1")){
DatabaseHelper dbHelper = new DatabaseHelper(SettingActivity.this, "callon_set_pump");
SQLiteDatabase db = dbHelper.getReadableDatabase();
Cursor cursor = db.query("table1", new String[]{"id","name"}, "id=?", new String[]{"1"}, null, null, null);
while(cursor.moveToNext()){
String name = cursor.getString(cursor.getColumnIndex("name"));
//add your code here
}
cursor = db.query("table1", new String[]{"id","name"}, "id=?", new String[]{"2"}, null, null, null);
while(cursor.moveToNext()){
String name = cursor.getString(cursor.getColumnIndex("name"));
//add your code here
}
cursor = db.query("table1", new String[]{"id","name"}, "id=?", new String[]{"3"}, null, null, null);
while(cursor.moveToNext()){
String name = cursor.getString(cursor.getColumnIndex("name"));
//add your code here
}
cursor = db.query("table1", new String[]{"id","name"}, "id=?", new String[]{"4"}, null, null, null);
while(cursor.moveToNext()){
String name = cursor.getString(cursor.getColumnIndex("name"));
//add your code here
}
cursor = db.query("table1", new String[]{"id","name"}, "id=?", new String[]{"5"}, null, null, null);
while(cursor.moveToNext()){
String name = cursor.getString(cursor.getColumnIndex("name"));
//add your code here
}

}
else {
db.execSQL("CREATE TABLE table1(id int,name varchar(20))");
ContentValues values = new ContentValues();
values.put("id", 1);
values.put("name", "5000");
db.insert("table1", null, values);
values = new ContentValues();
values.put("id", 2);
values.put("name", "1000");
db.insert("table1", null, values);
values = new ContentValues();
values.put("id", 3);
values.put("name", "3");
db.insert("table1", null, values);
values = new ContentValues();
values.put("id", 4);
values.put("name", "3");
db.insert("table1", null, values);
values = new ContentValues();
values.put("id", 5);
values.put("name", "NONE");
db.insert("table1", null, values);
//add your code here
}

上述类建立了一个数据库callon_set_pump，在另一个类中使用的话，

PageActivity.java

db_set = SQLiteDatabase.openOrCreateDatabase("data/data/com.autopump.callon.nenu/databases/callon_set_pump",null);
Cursor cursor = db_set.query("table1", new String[]{"id","name"}, "id=?", new String[]{"1"}, null, null, null);
while(cursor.moveToNext()){
String name = cursor.getString(cursor.getColumnIndex("name"));
System.out.println("name is :"+ name);
}

关于tabbleIsExist方法，它是用来检测是否存在该数据库的，如果存在重复创建会出现异常的哦～

private boolean tabbleIsExist(String tableName){
boolean result = false;
if(tableName == null){
return false;
}
SQLiteDatabase db = null;
DatabaseHelper dbHelper = new DatabaseHelper(SettingActivity.this, "callon_set_pump");
Cursor cursor = null;
try {
db = dbHelper.getReadableDatabase();
String sql = "select count(*) as c from Sqlite_master where type ='table' and name ='"+tableName.trim()+"' ";
cursor = db.rawQuery(sql, null);
if(cursor.moveToNext()){
int count = cursor.getInt(0);
if(count>0){
result = true;
}
}