Xamarin ClassNotFoundException

Question

我是 Xamarin 的新手，写了一个简单的应用程序，但它显示以下错误

Unhandled Exception:
Java.Lang.ClassNotFoundException: md5c178831cd46fc53bebc42cf953f78ced.SignupActivity 
occurred

我的MainActivity 代码：

using Android.App;
using Android.Widget;
using Android.OS;

namespace AndroidApp1
{
    [Activity(Label = "Hello Xamarin", MainLauncher = true)]
    public class MainActivity : Activity
    {
        private Button loginButton;
        private Button signupButton;
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.Main);
            loginButton = (Button)FindViewById(Resource.Id.login_btn);
            signupButton = (Button)FindViewById(Resource.Id.signup_btn);
            signupButton.Click += delegate
            {
                StartActivity(typeof(SignupActivity));
            };
        }
    }
}

对于SignupActivity：

using System.Text;
using Android.App;
using Android.OS;
using Android.Widget;

namespace AndroidApp1
{
    [Activity(Label = "SignupActivity")]
    public class SignupActivity : Activity
    {
        private EditText nameField;
        private EditText usernameField;
        private EditText passwordField;
        private EditText emailField;
        private Button signup;
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.SignupLayout);
            nameField = (EditText)FindViewById(Resource.Id.name);
            usernameField = (EditText)FindViewById(Resource.Id.username);
            emailField = (EditText)FindViewById(Resource.Id.email);
            passwordField = (EditText)FindViewById(Resource.Id.password);
            signup = (Button)FindViewById(Resource.Id.signup_btn);
            signup.Click += delegate
            {
                StringBuilder sb = new StringBuilder();
                sb.AppendLine(nameField.Text);
                sb.AppendLine(usernameField.Text);
                sb.AppendLine(emailField.Text);
                sb.AppendLine(passwordField.Text);
                Toast.MakeText(this, sb.ToString(), ToastLength.Short).Show();
            };
        }
    }
}

你能告诉我哪里错了吗？谢谢。

编辑： 清单文件

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
          package="AndroidApp1.AndroidApp1" 
          android:versionCode="1" 
          android:versionName="1.0">
  <uses-sdk android:minSdkVersion="21" />
  <application android:allowBackup="true" android:label="@string/app_name">
  </application>
</manifest>

Answer 1

这是一个已知的错误，清理并重新构建通常可以解决它的项目。