[英]Why HashMap method returns null object reference?
我試圖制作一個HashMap
方法來獲取SQLite數據庫數據,但是當我調用該方法時,它返回的null
引用使我的Android應用程序停止工作。
這是我的代碼:
public HashMap<String, String> getUserDetails(){
HashMap<String,String> user = new HashMap<String,String>();
String selectQuery = "SELECT * FROM " + TABLE_LOGIN;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
cursor.moveToFirst();
if(cursor.getCount() > 0){
user.put("name", cursor.getString(1));
user.put("position", cursor.getString(2));
user.put("level", cursor.getString(3));
user.put("email", cursor.getString(4));
user.put("uid", cursor.getString(5));
user.put("created_at", cursor.getString(6));
}
cursor.close();
db.close();
return user;
}
這就是我如何在其他類中調用方法
DatabaseHandler db = new DatabaseHandler(getApplicationContext());
HashMap<String,String> userDetail= db.getUserDetails();
int userLevel = Integer.parseInt(userDetail.get("level").toString());
無論如何,我使用教程參考來做到這一點並與我自己的需求融合。
如果用戶存在於數據庫中,則應返回user
對象,否則返回null
並檢查該user
是否為null
public HashMap<String, String> getUserDetails(){
HashMap<String,String> user = null;
String selectQuery = "SELECT * FROM " + TABLE_LOGIN;
try {
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
if (cursor != null){
cursor.moveToFirst();
if(cursor.getCount() > 0){
user = new HashMap<String,String>();
user.put("name", cursor.getString(1));
user.put("position", cursor.getString(2));
user.put("level", cursor.getString(3));
user.put("email", cursor.getString(4));
user.put("uid", cursor.getString(5));
user.put("created_at", cursor.getString(6));
}
}
} finally {
cursor.close();
db.close();
}
return user;
}
然后
DatabaseHandler db = new DatabaseHandler(getApplicationContext());
HashMap<String,String> userDetail= db.getUserDetails();
if (userDetail != null) {
String level = userDetail.get("level");
if (level != null){
try {
int userLevel = Integer.parseInt(level);
} catch (Exception e){
e.printStackTrace();
}
}
}
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