AlertDialog自定义控件

package nbe.sense7.vinci.custom.alertdialog;
import android.app.Activity;
import android.app.AlertDialog;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.Window;
import android.widget.Button;
import android.widget.ImageButton;
public class CustomAlertDialogActivity extends Activity {
    /** Called when the activity is first created. */
    private Button button;
自定义对话框布局文件custom_alertdialog.xml：

<?xml version="1.0" encoding="UTF-8" ?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="wrap_content"
    android:layout_width="wrap_content"
    android:layout_margin="15dp"
    android:gravity="center_horizontal"
    android:orientation="horizontal"
    android:background="@drawable/dialog_bg">
    
    <!-- enter button -->
    <ImageButton 
        android:id="@+id/enter_btn"
        android:layout_height="wrap_content"
        android:layout_width="wrap_content"