自定义控件：瀑布流水字母

<RelativeLayout 
    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:background="@android:color/background_light"
    tools:context=".MainActivity" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:text="@string/hello_world"
        android:textColor="@android:color/white" />

    <com.example.empire.HkTextGroup
        android:id="@+id/hk_text"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_marginTop="20dp"
        android:background="@android:color/background_dark" />

</RelativeLayout>

package com.example.empire;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Align;
import android.graphics.Paint.Style;
import android.os.Handler;
import android.util.AttributeSet;
import android.view.View;

public class HkTextGroup extends View {

    private char[] counts = new char[] { 
            'A', 'B', 'C', 'D', 'E', 'F', 'G',
            'H', 'J', 'K', 'L', 'M', 'N', 'O' };

    private Paint paint;
    private Context ctx;
    private Cell[][] cells;
    // 像素值
    private int textSize = 20;

    public HkTextGroup(Context context, AttributeSet attrs) {
        super(context, attrs);
        ctx = context;
        init();
    }

    private void init() {
        paint = new Paint();
        paint.setAntiAlias(true);
        paint.setColor(Color.WHITE);
        paint.setTextSize(textSize);// PX值
        paint.setTextAlign(Align.LEFT);
        paint.setStyle(Style.FILL);

        cells = new Cell[list][row];
        for (int j = 0; j < list; j++) {
            for (int i = 0; i < row; i++) {
                cells[j][i] = new Cell(i, j);
                cells[j][i].alpha = 0;
                cells[j][i].msg = ""
                        + counts[(int) (Math.random() * counts.length)];
            }
        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        Utils.logleo("getWidth()::" + getWidth());
        Utils.logleo("getHeight()::" + getHeight());

        textSize = getWidth() / 10;
        left_bottom = getHeight();
    }

    public float left;
    public float left_bottom;

    private Handler handler = new Handler() {
        public void handleMessage(android.os.Message msg) {
            int flag = msg.what;// 0 -- 10

            for (int j = 0; j < list; j++) {

                for (int i = row - 1; i >= 0; i--) {
                    // 1、如果第一行透明度为0，则有一定机率变为255
                    // 2、如果中间行透明度为0，不做处理
                    // 3、中间行不为0，依次减少一个梯度
                    // 4、我上面的一个是255，那么我也是255,而他亮度减1
                    Cell cell = cells[j][i];

                    if (i == 0) {
                        if (cell.alpha == 0) {
                            if (Math.random() * 10 > 9) {
                                cell.alpha = 255;
                            }
                        } else {
                            cell.alpha = cell.alpha - 25 > 0 ? cell.alpha - 25
                                    : 0;
                        }
                    } else if (i > 0 && i <= row - 1) {
                        if (cells[j][i - 1].alpha == 255) {
                            cell.alpha = 255;
                        } else {
                            cell.alpha = cell.alpha - 25 > 0 ? cell.alpha - 25
                                    : 0;
                        }
                    }
                }
            }
            invalidate();

        };
    };

    private int seed = 0;
    private int stepCount = 11;
    /** 行 */
    private int row = 20;
    /** 列 */
    private int list = 20;

    @Override
    protected void onDraw(Canvas canvas) {

        for (int j = 0; j < list; j++) {
            for (int i = 0; i < row; i++) {
                Cell cell = cells[j][i];
                // 小机率事件，改变内容
                if (Math.random() * 100 > 85) {
                    cell.msg = ""
                            + counts[(int) (Math.random() * counts.length)];
                }
                // 根据透明度确定颜色
                if (cell.alpha == 255) {
                    paint.setColor(Color.WHITE);
                } else {
                    paint.setColor(Color.GREEN);
                }
                // 设置透明度
                paint.setAlpha(cell.alpha);

                // 绘制
                if (cell.alpha != 0) {
                    canvas.drawText(cell.msg, cell.j * 15, (float) (cell.i
                            * textSize * 0.6 + textSize), paint);
                }
            }
        }

        // seed = (seed + 1) % stepCount;
        handler.sendEmptyMessageDelayed(seed, 10);
    }

    private class Cell {
        public Cell(int i, int j) {
            super();
            this.i = i;
            this.j = j;
        }

        /** 行 */
        public int i;
        /** 列 */
        public int j;
        /** 种子 */
        public int seed;
        /** 透明度 */
        public int alpha;
        public String msg;

    }

}

package com.example.empire;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Align;
import android.graphics.Paint.Style;
import android.os.Handler;
import android.util.AttributeSet;
import android.view.View;

public class HkText extends View {

    private char[] counts = new char[] { 
            'A', 'B', 'C', 'D', 'E', 'F', 'G',
            'H', 'J', 'K', 'L', 'M', 'N', 'O' };

    private Paint paint;
    private Context ctx;

    public HkText(Context context, AttributeSet attrs) {
        super(context, attrs);
        ctx = context;
        init();
    }

    /**
     * 像素值
     */
    private int textSize = 20;

    private void init() {
        paint = new Paint();
        paint.setAntiAlias(true);
        paint.setColor(Color.WHITE);
        paint.setTextSize(textSize);// PX值
        paint.setTextAlign(Align.LEFT);
        paint.setStyle(Style.FILL);
    }

    // private float sp2px(int sp){
    // TypedValue.applyDimension(
    // TypedValue.COMPLEX_UNIT_SP, sp, ctx.getResources().getDisplayMetrics());
    //
    // float px = sp * ctx.getResources().getDisplayMetrics().scaledDensity;
    // return px;
    // }
    //
    // private float px2sp(int px){
    // float sp = px / ctx.getResources().getDisplayMetrics().scaledDensity;
    // return sp;
    // }

    @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        Utils.logleo("getWidth()::" + getWidth());
        Utils.logleo("getHeight()::" + getHeight());

        textSize = getWidth() / 10;
    }

    public float left = 150;
    public float left_bottom = 200;

    private Handler handler = new Handler() {
        public void handleMessage(android.os.Message msg) {
            // int flag = msg.what;// 0 -- 10
            // paint.setColor(Color.BLUE);
            invalidate();
        };
    };

    private int seed = 0;
    private int stepCount = 11;

    @Override
    protected void onDraw(Canvas canvas) {
        left = 10;
        left_bottom = 400;
        for (int i = 0; i < 20; i++) {

            int seed_tem = seed;

            int alpha = 255 - (i + seed_tem) * 25;
            paint.setAlpha(alpha);// 0是没有

            canvas.drawText(counts, i % counts.length, 1, left, 
                     left_bottom,paint);
            left_bottom = (float) (left_bottom - textSize * 0.6);
        }
        seed = (seed + 1) % stepCount;
        handler.sendEmptyMessageDelayed(seed, 500);
    }

}

package com.example.empire;
import android.util.Log;

public class Utils {
    public static boolean isShow = true;
    public static void logleo(String msg) {
        if (isShow) {
            Log.i("leo", msg);
        }
    }
}

DEMO下载地址：http://pan.baidu.com/s/1mgkfQh6