注册活动有问题

Question

我能否第二眼看到这一点。我试图写一个注册活动，它一直在崩溃我。我从昨晚起就一直在挣扎。谁能指出我做错了什么？

这是活动代码

package mw.technology.app.ribbit;

import android.app.Activity;
import android.app.AlertDialog;
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;

public class SignUpActivity extends Activity {

    protected EditText mUsername;
    protected EditText mPassword;
    protected EditText mEmail;
    protected Button mSignUpButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_sign_up);

        mUsername = (EditText)findViewById(R.id.usernameField);
        mPassword = (EditText)findViewById(R.id.passwordField);
        mEmail = (EditText)findViewById(R.id.emailField);
        mSignUpButton = (Button)findViewById(R.id.signupButton);
        mSignUpButton.setOnClickListener(new View.OnClickListener() {


            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                String username = mUsername.getText().toString();
                String password = mPassword.getText().toString();
                String email = mEmail.getText().toString();

                username = username.trim();
                password = password.trim();
                email = email.trim();

                if (username.isEmpty() || password.isEmpty() || email.isEmpty()) {
                    AlertDialog.Builder builder = new AlertDialog.Builder(SignUpActivity.this);
                    builder.setMessage(R.string.signup_error_message)
                        .setTitle(R.string.signup_error_tittle)
                        .setPositiveButton(android.R.string.ok, null);
                    AlertDialog dialog = builder.create();
                    dialog.show();
                }
                else {
                    // create the new user!
                }


            }
        });


    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.sign_up, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_sign_up,
                    container, false);
            return rootView;
        }
    }

}

这是布局代码

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="mw.technology.app.ribbit.SignUpActivity"
    tools:ignore="MergeRootFrame" >

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingBottom="@dimen/activity_vertical_margin"
        android:paddingLeft="@dimen/activity_horizontal_margin"
        android:paddingRight="@dimen/activity_horizontal_margin"
        android:paddingTop="@dimen/activity_vertical_margin" >

        <EditText
            android:id="@+id/userName"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            android:layout_alignParentTop="true"
            android:ems="10"
            android:hint="@string/username_hint" >

            <requestFocus />
        </EditText>

        <EditText
            android:id="@+id/password"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            android:layout_below="@+id/userName"
            android:ems="10"
            android:hint="@string/password_hint"
            android:inputType="textPassword" />

        <EditText
            android:id="@+id/emailField"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            android:layout_below="@+id/password"
            android:ems="10"
            android:hint="@string/email_hint"
            android:inputType="textEmailAddress" />

        <Button
            android:id="@+id/signupButton"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            android:layout_below="@+id/emailField"
            android:text="@string/sign_up_button_label" />

    </RelativeLayout>

</FrameLayout>

提前致谢，我为当前的无能为力而道。

有什么想法吗？