MainActivity.java

package com.example.fadeytextthingy;

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Typeface;
import android.graphics.drawable.ColorDrawable;
import android.os.Bundle;
import android.support.v4.view.ViewCompat;
import android.text.SpannableString;
import android.text.Spanned;
import android.text.TextPaint;
import android.text.style.CharacterStyle;
import android.text.style.UpdateAppearance;
import android.util.AttributeSet;
import android.util.Log;
import android.util.TypedValue;
import android.view.View;
import android.view.ViewDebug.CapturedViewProperty;
import android.view.animation.AnimationUtils;
import android.view.animation.DecelerateInterpolator;
import android.view.animation.Interpolator;
import android.widget.TextView;


public class MainActivity extends Activity
{
	@Override
	protected void onCreate(Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		
		getWindow().setBackgroundDrawable(new ColorDrawable(Color.BLACK));
		
		int padding = (int)(16 * getResources().getDisplayMetrics().density);
		
		final FadeyTextView textView = new FadeyTextView(this);
		textView.setPadding(padding, padding, padding, padding);
		textView.setTextSize(TypedValue.COMPLEX_UNIT_SP, 22.0f);
		textView.setTextColor(Color.GREEN);
		textView.setTypeface(Typeface.MONOSPACE);
		
		setContentView(textView);
		
		textView.setOnClickListener(new View.OnClickListener()
		{
			@Override
			public void onClick(View v)
			{
				textView.setText("Hello World");
			}
		});
	}
	
	private static class FadeyTextView extends TextView
	{
		private Interpolator mInterpolator;
		private long mStart, mDurationPerLetter;
		private boolean mAnimating = false;
		
		private SpannableString mFadeyText;
		private CharSequence mText;
		
		
		public FadeyTextView(Context context)
		{
			super(context);
			initView();
		}
		
		public FadeyTextView(Context context, AttributeSet attrs)
		{
			super(context, attrs);
			initView();
		}
		
		public FadeyTextView(Context context, AttributeSet attrs, int defStyle)
		{
			super(context, attrs, defStyle);
			initView();
		}
		
		private void initView()
		{
			// Set defaults
			mInterpolator = new DecelerateInterpolator();
			mDurationPerLetter = 250;
		}
		
		public void setInterpolator(Interpolator interpolator)
		{
			mInterpolator = interpolator;
		}
		
		public void setDurationPerLetter(long durationPerLetter)
		{
			mDurationPerLetter = durationPerLetter;
		}
		
		@Override
		public void setText(CharSequence text, BufferType type)
		{
			mText = text;
			
			mFadeyText = new SpannableString(text);
			
			FadeyLetterSpan[] letters = mFadeyText.getSpans(0, mFadeyText.length(), FadeyLetterSpan.class);
			for(FadeyLetterSpan letter : letters){
				mFadeyText.removeSpan(letter);
			}
			
			final int length = mFadeyText.length();
			for(int i = 0; i < length; i++){
				mFadeyText.setSpan(new FadeyLetterSpan(), i, i + 1, Spanned.SPAN_INCLUSIVE_EXCLUSIVE);
			}
			
			super.setText(mFadeyText, BufferType.SPANNABLE);
			
			mAnimating = true;
			mStart = AnimationUtils.currentAnimationTimeMillis();
			ViewCompat.postInvalidateOnAnimation(this);
		}
		
		@Override
		@CapturedViewProperty
		public CharSequence getText()
		{
			return mText;
		}
		
		public boolean isAnimating()
		{
			return mAnimating;
		}
		
		@Override
		protected void onDraw(Canvas canvas)
		{
			super.onDraw(canvas);
			
			if(mAnimating){
				long mDelta   = AnimationUtils.currentAnimationTimeMillis() - mStart;
				
				FadeyLetterSpan[] letters = mFadeyText.getSpans(0, mFadeyText.length(), FadeyLetterSpan.class);
				final int length = letters.length;
				for(int i = 0; i < length; i++){
					FadeyLetterSpan letter = letters[i];
					float delta = (float)Math.max(Math.min((mDelta - (i * mDurationPerLetter)), mDurationPerLetter), 0);
					letter.setAlpha(mInterpolator.getInterpolation(delta / (float)mDurationPerLetter));
				}
				if(mDelta < mDurationPerLetter * length){
					ViewCompat.postInvalidateOnAnimation(this);
				}else{
					mAnimating = false;
				}
			}
		}
		
		
		private class FadeyLetterSpan extends CharacterStyle implements UpdateAppearance
		{
			private float mAlpha = 0.0f;
			
			
			public void setAlpha(float alpha)
			{
				mAlpha = Math.max(Math.min(alpha, 1.0f), 0.0f);
			}
			
			@Override
			public void updateDrawState(TextPaint tp)
			{
				int color = ((int)(0xFF * mAlpha) << 24) | (tp.getColor() & 0x00FFFFFF);
				tp.setColor(color);
			}
		}
	}
}