注册并登录无法正常工作

Question

我正在做android应用程序开发和登录模块工作现在我正在尝试注册，如果用户名已存在，则显示用户名已存在并且用户应该登录的消息。

我的代码 //注册

public void addButtonClicked(View view) { 
    LogIn ln = new LogIn(username.getText().toString(), password.getText().toString()); 

    dbHandler.addUser(ln); 
    printDatabase(); 
    Toast.makeText(this, "Saved", Toast.LENGTH_LONG).show(); 
    boolean r = dbHandler.CheckIsDataAlreadyInDBorNot(username.getText().toString()); 
    if (r) { 
     Toast.makeText(this, "Username already exists", Toast.LENGTH_LONG).show(); 
    } 
} 

//用于登录，登录就应该移动到下一个活动，但它不工作

public void buttonClicked() { 
    boolean h = dbHandler.CheckIsDataAlreadyInDBorNot(username.getText().toString()); 
    if (h) { 

     Intent i = new Intent(getApplicationContext(), third.class); 
     startActivity(i); 
    } 

} 

// DB后处理程序代码

 public boolean CheckIsDataAlreadyInDBorNot(String fieldValue) { 
     SQLiteDatabase db = getWritableDatabase(); 
     String Query = "Select * from " + TABLE_LOGIN + " where " + COLUMN_USERNAME + " = " + fieldValue; 
     Cursor cursor = db.rawQuery(Query, null); 
     if(cursor.getCount() == 0){ 
      cursor.close(); 

      return false; 
     } 
     cursor.close(); 
     return true; 
    } 

登录分类信息

public class LogIn { 
private int _id; 
private String _username; 
private String _password; 

public LogIn(){ 
} 

public LogIn(String username,String password){ 
    this._username = username; 
    this._password = password; 

} 

public void set_id(int _id) { 
    this._id = _id; 
} 


public void set_password(String _password) { 
    this._password = _password; 
} 

public int get_id() { 

    return _id; 
} 

public String get_username() { 
    return _username; 
} 

public String get_password() { 
    return _password; 
} 

public void set_username(String _username) { 

    this._username = _username; 
} 

}

Answer 1

我会尽量建议/纠正我认为这是造成问题， 发布您的logcat领域或任何错误都将帮助更多...

1- addButton的逻辑：

你应该检查用户是否已经存在，并根据这个动作 当前你插入一条记录，然后检查它是否存在，因此r将永远是true！

变化的方法如下：我想虽然我认为你应该使用query()

A.你有方法CheckIsDataAlreadyInDBorNot() 在SQL查询错误

public void addButtonClicked(View view) { 

    boolean r = dbHandler.CheckIsDataAlreadyInDBorNot(username.getText().toString()); 
    if (r) { 
     Toast.makeText(this, "Username already exists", Toast.LENGTH_LONG).show(); 
     return; 
    }else{ 
     LogIn ln = new LogIn(username.getText().toString(), password.getText().toString()); 

     dbHandler.addUser(ln); 
     printDatabase(); 
     Toast.makeText(this, "Saved", Toast.LENGTH_LONG).show(); 
    } 
} 

2-修复当前代码：您遗漏了包含该值的单个问题（因为它是字符串）where userName='Smith'

public boolean CheckIsDataAlreadyInDBorNot(String fieldValue) { 
    SQLiteDatabase db = getWritableDatabase(); 
    String Query = "Select * from " + TABLE_LOGIN + " where " + COLUMN_USERNAME + " = '" + fieldValue + "'"; 
    Cursor cursor = db.rawQuery(Query, null); 
    if(cursor.getCount() == 0){ 
     cursor.close(); 

     return false; 
    } 
    cursor.close(); 
    return true; 
} 

B.使用query()：

public boolean CheckIsDataAlreadyInDBorNot(String fieldValue) { 
    SQLiteDatabase db = getWritableDatabase(); 
    Cursor cursor = db.query(TABLE_LOGIN, null, COLUMN_USERNAME+"=?", new String[]{fieldValue}, null, null, null); 
    if(cursor.getCount() == 0){ 
     cursor.close(); 
     return false; 
    } 
    cursor.close(); 
    return true; 
}