如何在注册活动中防止重复输入

Question

我希望当用户在我的应用程序中注册用户名时，如果用户名已被占用，他/她将得到一个表示“用户名已被占用”的敬酒。

我已经在我的数据库中包含了UNIQUE约束，它工作正常，但是在活动本身中我想让用户知道他们正在尝试注册的用户名已经存在。

package com.fullfrontalgames.numberfighter; 

import android.app.Activity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.Toast; 

public class Register extends Activity { 
    EditText UsernameReg, PasswordReg, PasswordConfirm, EmailReg; 

    Button Register; 

    DBAdapter db; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     // TODO Auto-generated method stub 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.register); 

     // get Instance of Database Adapter 
     final DBAdapter db = new DBAdapter(this); 
     db.open(); 

     // Get reference of views. 
     UsernameReg = (EditText)findViewById(R.id.UsernameReg); 
     PasswordReg = (EditText)findViewById(R.id.PasswordReg); 
     EmailReg = (EditText)findViewById(R.id.EmailReg); 
     PasswordConfirm = (EditText)findViewById(R.id.PasswordConfirm); 

     Register = (Button)findViewById(R.id.Register); 
     Register.setOnClickListener(new View.OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       // TODO Auto-generated method stub 
       String Username = UsernameReg.getText().toString(); 
       String Password = PasswordReg.getText().toString(); 
       String PassConfirm = PasswordConfirm.getText().toString(); 
       String Email = EmailReg.getText().toString(); 
       String TakenUsername = db.getData(); 

       // Check if any of the field are vacant. 
       if (Username.equals("") || Password.equals("") || PassConfirm.equals("")) { 
        Toast.makeText(getApplicationContext(), "Field Vacant", Toast.LENGTH_LONG) 
          .show(); 
        return; 
       } 
       // Check if both passwords matches 
       if (!Password.equals(PassConfirm)) { 
        Toast.makeText(getApplicationContext(), "Password does not match", 
          Toast.LENGTH_LONG).show(); 
        return; 
       } 
       if (Username.equals(TakenUsername)) 

       { 
        Toast.makeText(getApplicationContext(), "Username Already Taken", 
          Toast.LENGTH_LONG).show(); 
        return; 
       } else { 
        // Save data in database 
        db.insertPlayer(Username, Password, Email); 
        Toast.makeText(getApplicationContext(), "Account Successfully Created ", 
          Toast.LENGTH_LONG).show(); 
        startActivity(new Intent("com.fullfrontalgames.numberfighter.Login")); 
       } 
      } 

     }); 

    } 

} 

Answer 1

你可以做到这一点

long id = db.insertPlayer(Username, Password, Email); 
if (id == -1) 
{ 
    Toast.makeText(getApplicationContext(), "Username Already Taken", 
         Toast.LENGTH_LONG).show(); 
} 

其中

public long insertPlayer(String Username, String Password, String Email) 
{ 
    ContentValues values = new ContentValues(); 
    values.put("USERNAME", Username); 
    values.put("PASSWORD", Password); 
    values.put("EMAIL", Email); 

    return db.insertWithOnConflict(Table name, null, values, SQLiteDatabase.CONFLICT_IGNORE); 

} 

Answer 2

检查数据库表是否存在用户名。你可以做相反的

if (Username.equals(TakenUsername)) 

      { 
       Toast.makeText(getApplicationContext(), "Username Already Taken", 
         Toast.LENGTH_LONG).show(); 
       return; 
      } else { 
       // Save data in database 
       db.insertPlayer(Username, Password, Email); 
       Toast.makeText(getApplicationContext(), "Account Successfully Created ", 
         Toast.LENGTH_LONG).show(); 
       startActivity(new Intent("com.fullfrontalgames.numberfighter.Login")); 
      } 

以下

Cursor c = db.query(TABLE_NAME, new String[] { USERNAME}, 
     USERNAME+ " ='" + userName + "'", null, null, null, null); 
     if(c.getCount > 0) 
       username taken;;