In the below example I have created Display spinner in Popup Window. Here I have created a popup.xml layout. In popup layot i have added TextView, ImageView, Spinner and button. And in activity_main.xml layout I have added a button to open spinner popup window. See the below code it will clearly described you to make Spinner in Popup window.

Step(1)-main.xml layout-

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="http://android-er.blogspot.com/"
        android:textStyle="bold"
        android:layout_gravity="center_horizontal"
        android:autoLink="web" />

    <Button
        android:id="@+id/openpopup"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"

        android:text="Hello Click here" />

</LinearLayout>

Step(2)-Create a new layout-popup.xml-

<?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:background="@android:color/background_light"
    android:orientation="vertical" >

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="1dp"
        android:background="@android:color/darker_gray"
        android:orientation="vertical" >
        >

        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="20dp"
            android:orientation="vertical" >

            <TextView
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:text="Select your comapny"
                android:textSize="25dp"
               />

            <ImageView
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:src="@drawable/images" />

            <Spinner
                android:id="@+id/popupspinner"
                android:spinnerMode="dialog"
                android:layout_width="fill_parent"
                android:layout_height="wrap_content" />

            <Button
                android:id="@+id/dismiss"
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:text="Dismiss" />
        </LinearLayout>
    </LinearLayout>

</LinearLayout>

Step(3)-MainActivity-

public class MainActivity extends Activity {

    String[] Company = {"Apple","Genpack","Microsoft","HP","HCL","Ericsson"};

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

        final Button btnOpenPopup = (Button) findViewById(R.id.openpopup);
        btnOpenPopup.setOnClickListener(new Button.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                LayoutInflater layoutInflater =
                        (LayoutInflater)getBaseContext()
                                .getSystemService(LAYOUT_INFLATER_SERVICE);
                View popupView = layoutInflater.inflate(R.layout.popup, null);
                final PopupWindow popupWindow = new PopupWindow(
                        popupView, LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);

                Button btnDismiss = (Button)popupView.findViewById(R.id.dismiss);

                Spinner popupSpinner = (Spinner)popupView.findViewById(R.id.popupspinner);

                ArrayAdapter<String> adapter =
                        new ArrayAdapter<String>(MainActivity.this,
                                android.R.layout.simple_spinner_item, Company);
                adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
                popupSpinner.setAdapter(adapter);

                btnDismiss.setOnClickListener(new Button.OnClickListener(){

                    @Override
                    public void onClick(View v) {
                        popupWindow.dismiss();
                    }});

                popupWindow.showAsDropDown(btnOpenPopup, 50, -30);
            }

        });
    }

}