Google Alphabetic Scroll
<p>I've seen the following example in the Android API:</p>

<pre><code>    /*
    * Copyright (C) 2007 The Android Open Source Project
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *      http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    package com.example.android.apis.view;

    import com.example.android.apis.R;

    import android.app.ListActivity;
    import android.content.Context;
    import android.graphics.PixelFormat;
    import android.os.Bundle;
    import android.os.Handler;
    import android.view.View;
    import android.view.LayoutInflater;
    import android.view.WindowManager;
    import android.view.WindowManager.LayoutParams;
    import android.widget.AbsListView;
    import android.widget.ArrayAdapter;
    import android.widget.ListView;
    import android.widget.TextView;

/**
 * Another variation of the list of cheeses. In this case, we use
 * {@link AbsListView#setOnScrollListener(AbsListView.OnScrollListener) 
 * AbsListView#setOnItemScrollListener(AbsListView.OnItemScrollListener)} to display the
 * first letter of the visible range of cheeses.
 */
public class List9 extends ListActivity implements ListView.OnScrollListener {

    private final class RemoveWindow implements Runnable {
        public void run() {
            removeWindow();
        }
    }

    private RemoveWindow mRemoveWindow = new RemoveWindow();
    Handler mHandler = new Handler();
    private WindowManager mWindowManager;
    private TextView mDialogText;
    private boolean mShowing;
    private boolean mReady;
    private char mPrevLetter = Character.MIN_VALUE;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mWindowManager = (WindowManager)getSystemService(Context.WINDOW_SERVICE);

        // Use an existing ListAdapter that will map an array
        // of strings to TextViews
        setListAdapter(new ArrayAdapter&lt;String&gt;(this,
                android.R.layout.simple_list_item_1, mStrings));

        getListView().setOnScrollListener(this);

        LayoutInflater inflate = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        mDialogText = (TextView) inflate.inflate(R.layout.list_position, null);
        mDialogText.setVisibility(View.INVISIBLE);

        mHandler.post(new Runnable() {

            public void run() {
                mReady = true;
                WindowManager.LayoutParams lp = new WindowManager.LayoutParams(
                        LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT,
                        WindowManager.LayoutParams.TYPE_APPLICATION,
                        WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE
                                | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
                        PixelFormat.TRANSLUCENT);
                mWindowManager.addView(mDialogText, lp);
            }});
    }

    @Override
    protected void onResume() {
        super.onResume();
        mReady = true;
    }


    @Override
    protected void onPause() {
        super.onPause();
        removeWindow();
        mReady = false;
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        mWindowManager.removeView(mDialogText);
        mReady = false;
    }




    public void onScroll(AbsListView view, int firstVisibleItem,
            int visibleItemCount, int totalItemCount) {
        if (mReady) {
            char firstLetter = mStrings[firstVisibleItem].charAt(0);

            if (!mShowing &amp;&amp; firstLetter != mPrevLetter) {

                mShowing = true;
                mDialogText.setVisibility(View.VISIBLE);
            }
            mDialogText.setText(((Character)firstLetter).toString());
            mHandler.removeCallbacks(mRemoveWindow);
            mHandler.postDelayed(mRemoveWindow, 3000);
            mPrevLetter = firstLetter;
        }
    }


    public void onScrollStateChanged(AbsListView view, int scrollState) {
    }


    private void removeWindow() {
        if (mShowing) {
            mShowing = false;
            mDialogText.setVisibility(View.INVISIBLE);
        }
    }

    private String[] mStrings = Cheeses.sCheeseStrings;
    }
</code></pre>

<p>Does anyone know how to make the window showing the current letter appear only when the user is scrolling? At the moment it is taking at least 3-4 seconds to disappear when the activity has started.</p>
