Custom AlertBox in Android

in main.xml file:

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

    < Button
        android:id="@+id/button1"
        android:layout_width="120dp"
        android:layout_height="wrap_content"
        android:text="Button" />

< /LinearLayout> 

in dialog.xml :(xml for custom dialog box) :

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

    < ImageView
        android:id="@+id/imageView1"
        android:layout_width="210dp"
        android:layout_height="232dp"
        android:padding="40dp"
        android:src="@drawable/flower" />

    < TextView
        android:id="@+id/textView1"
        android:layout_width="147dp"
        android:layout_height="wrap_content"
        android:text="This is a flower"
        android:textSize="20dp"
        android:layout_marginLeft="10dp"
        android:layout_marginRight="10dp"
        android:layout_marginBottom="10dp"/>

< /LinearLayout> 

in java file:

Button b= (Button) findViewById(R.id.button1);
        b.setOnClickListener(new OnClickListener() {
         @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                Dialog d=new Dialog(CustomdialogActivity.this);
                d.setContentView(R.layout.dialog);
                d.setTitle("This is important");
                d.show();
            }
        });