字符串无法解析或不是字段？

Question

基本上我有一个登录和注册的解析代码。我正在处理这个tutorial。我有：

LoginSignupActivity.java

package com.androidbegin.parselogintutorial; 

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

import com.parse.LogInCallback; 
import com.parse.ParseException; 
import com.parse.ParseUser; 
import com.parse.SignUpCallback; 

public class LoginSignupActivity extends Activity { 
// Declare Variables 
Button loginbutton; 
Button signup; 
String usernametxt; 
String passwordtxt; 
EditText password; 
EditText username; 

/** Called when the activity is first created. */ 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    // Get the view from main.xml 
    setContentView(R.layout.main); 
    // Locate EditTexts in main.xml 
    username = (EditText) findViewById(R.id.username); 
    password = (EditText) findViewById(R.id.password); 

    // Locate Buttons in main.xml 
    loginbutton = (Button) findViewById(R.id.login); 
    signup = (Button) findViewById(R.id.signup); 

    // Login Button Click Listener 
    loginbutton.setOnClickListener(new OnClickListener() { 

     public void onClick(View arg0) { 
      // Retrieve the text entered from the EditText 
      usernametxt = username.getText().toString(); 
      passwordtxt = password.getText().toString(); 

      // Send data to Parse.com for verification 
      ParseUser.logInInBackground(usernametxt, passwordtxt, 
        new LogInCallback() { 
         public void done(ParseUser user, ParseException e) { 
          if (user != null) { 
           // If user exist and authenticated, send user to Welcome.class 
           Intent intent = new Intent(
             LoginSignupActivity.this, 
             Welcome.class); 
           startActivity(intent); 
           Toast.makeText(getApplicationContext(), 
             "Successfully Logged in", 
             Toast.LENGTH_LONG).show(); 
           finish(); 
          } else { 
           Toast.makeText(
             getApplicationContext(), 
             "No such user exist, please signup", 
             Toast.LENGTH_LONG).show(); 
          } 
         } 
        }); 
     } 
    }); 
    // Sign up Button Click Listener 
    signup.setOnClickListener(new OnClickListener() { 

     public void onClick(View arg0) { 
      // Retrieve the text entered from the EditText 
      usernametxt = username.getText().toString(); 
      passwordtxt = password.getText().toString(); 

      // Force user to fill up the form 
      if (usernametxt.equals("") && passwordtxt.equals("")) { 
       Toast.makeText(getApplicationContext(), 
         "Please complete the sign up form", 
         Toast.LENGTH_LONG).show(); 

      } else { 
       // Save new user data into Parse.com Data Storage 
       ParseUser user = new ParseUser(); 
       user.setUsername(usernametxt); 
       user.setPassword(passwordtxt); 
       user.signUpInBackground(new SignUpCallback() { 
        public void done(ParseException e) { 
         if (e == null) { 
          // Show a simple Toast message upon successful registration 
          Toast.makeText(getApplicationContext(), 
            "Successfully Signed up, please log in.", 
            Toast.LENGTH_LONG).show(); 
         } else { 
          Toast.makeText(getApplicationContext(), 
            "Sign up Error", Toast.LENGTH_LONG) 
            .show(); 
         } 
        } 
       }); 
      } 

     } 
    }); 

} 
} 

而且我loginsignup.xml：

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    android:orientation="vertical" 
    android:padding="10dip" > 

    <TextView 
     android:id="@+id/txtusername" 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:text="@string/Username" /> 

    <EditText 
     android:id="@+id/username" 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:layout_below="@+id/txtusername" 
     android:inputType="text" /> 

    <TextView 
     android:id="@+id/txtpassword" 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:layout_below="@+id/username" 
     android:text="@string/Password" /> 

    <EditText 
     android:id="@+id/password" 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:layout_below="@+id/txtpassword" 
     android:inputType="textPassword" /> 

    <Button 
     android:id="@+id/login" 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:layout_below="@+id/password" 
     android:text="@string/LoginBtn" /> 

    <Button 
     android:id="@+id/signup" 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:layout_below="@+id/login" 
     android:text="@string/SignupBtn" /> 

</RelativeLayout> 

当我尝试运行它，我得到 “字符串不能得到解决，或者不是一个领域。” （字符串用作占位符）。我对Android开发很神奇。任何帮助都会很棒。

Answer 1

相反OF-

setContentView(R.layout.main); 

写这个 -

setContentView(R.layout.loginsignup); 

Answer 2

尝试清除您的项目。

如果您有任何第三方库项目，请将其移除。

添加构建您的Android v4库的路径。

然后再次清除您的项目。