最近在做公司新產品的設計，想到下雪效果設計加入到專案應該挺不錯的，所以我們想將這個設計理念加入到我們的產品中。

下面是效果圖：

沒擷取動態圖

XML 程式碼：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_snow"
android:layout_width=
 
"match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:background="#f221f5"
tools
 
:context="com.dzz.android191_ui_touch.SnowActivity">
    <FrameLayout
android:layout_width="match_parent"
android:layout_height="match_parent" >

       <com.dzz.android191_ui_touch.SnowView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="10dp"
 
/>
    </FrameLayout>

</RelativeLayout>

Java程式碼

  新建一個activity  SnowView

package com.dzz.android191_ui_touch;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

/**
 * Created by ASUS on 2017-01-18.
 */
public class SnowView extends View {
    private static final int NUM_SNOWFLAKES = 100;
    private static final int DELAY = 5;

    private SnowFlake[] snowflakes;

    public SnowView(Context context) {
        super(context);
    }

    public SnowView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public SnowView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    protected void resize(int width, int height) {
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(Color.WHITE);
        paint.setStyle(Paint.Style.FILL);
        snowflakes = new SnowFlake[NUM_SNOWFLAKES];
        for (int i = 0; i < NUM_SNOWFLAKES; i++) {
            snowflakes[i] = SnowFlake.create(width, height, paint);
        }
    }

    @Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        if (w != oldw || h != oldh) {
            resize(w, h);
        }
    }

    @Override
protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        for (SnowFlake snowFlake : snowflakes) {
            snowFlake.draw(canvas);
        }
        getHandler().postDelayed(runnable, DELAY);
    }

    private Runnable runnable = new Runnable() {
        @Override
public void run() {
            invalidate();
        }
    };
}

 還要 新建一個activity  SnowFlake

package com.dzz.android191_ui_touch;

import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Point;


/**
 * Created by ASUS on 2017-01-18.
 */
public class SnowFlake {
    // 雪花的角度
private static final float ANGE_RANGE = 0.1f; // 角度範圍
private static final float HALF_ANGLE_RANGE = ANGE_RANGE / 2f; // 一般的角度
private static final float HALF_PI = (float) Math.PI / 2f; // 半PI
private static final float ANGLE_SEED = 25f; // 角度隨機種子
private static final float ANGLE_DIVISOR = 10000f;
    // 雪花的移動速度
private static final float INCREMENT_LOWER = 2f;
    private static final float INCREMENT_UPPER = 4f;

    // 雪花的大小
private static final float FLAKE_SIZE_LOWER = 7f;
    private static final float FLAKE_SIZE_UPPER = 20f;

    private final RandomGenerator mRandom; // 隨機控制器
private final Point mPosition; // 雪花位置
private float mAngle; // 角度
private final float mIncrement; // 雪花的速度
private final float mFlakeSize; // 雪花的大小
private final Paint mPaint; // 畫筆
private SnowFlake(RandomGenerator random, Point position, float angle, float increment, float flakeSize, Paint paint) {
        mRandom = random;
        mPosition = position;
        mIncrement = increment;
        mFlakeSize = flakeSize;
        mPaint = paint;
        mAngle = angle;
    }

    public static SnowFlake create(int width, int height, Paint paint) {
        RandomGenerator random = new RandomGenerator();
        int x = random.getRandom(width);
        int y = random.getRandom(height);
        Point position = new Point(x, y);
        float angle = random.getRandom(ANGLE_SEED) / ANGLE_SEED * ANGE_RANGE + HALF_PI - HALF_ANGLE_RANGE;
        float increment = random.getRandom(INCREMENT_LOWER, INCREMENT_UPPER);
        float flakeSize = random.getRandom(FLAKE_SIZE_LOWER, FLAKE_SIZE_UPPER);
        return new SnowFlake(random, position, angle, increment, flakeSize, paint);
    }

    // 繪製雪花
public void draw(Canvas canvas) {
        int width = canvas.getWidth();
        int height = canvas.getHeight();
        move(width, height);
        canvas.drawCircle(mPosition.x, mPosition.y, mFlakeSize, mPaint);
    }

    // 移動雪花
private void move(int width, int height) {
        //x水平方向，那麼需要晃動，主要設定這個值就可以，現在取消晃動了
        //如果 mPosition.x不加上後面那個值，就不會晃動了
double x = mPosition.x + (mIncrement * Math.cos(mAngle));
        //y是豎直方向，就是下落
double y = mPosition.y + (mIncrement * Math.sin(mAngle));

        mAngle += mRandom.getRandom(-ANGLE_SEED, ANGLE_SEED) / ANGLE_DIVISOR;
        //這個是設定雪花位置，如果在很短時間內重新整理一次，就是連起來的動畫效果
mPosition.set((int) x, (int) y);

        // 移除螢幕, 重新開始
if (!isInside(width, height)) {
            // 重置雪花
reset(width);
        }
    }

    // 判斷是否在其中
private boolean isInside(int width, int height) {
        int x = mPosition.x;
        int y = mPosition.y;
        return x > mFlakeSize -5 && x + mFlakeSize <= width && y >= -mFlakeSize - 1 && y - mFlakeSize < height;
    }

    // 重置雪花
private void reset(int width) {
        mPosition.x = mRandom.getRandom(width);
        mPosition.y = (int) (-mFlakeSize - 1); // 最上面
mAngle = mRandom.getRandom(ANGLE_SEED) / ANGLE_SEED * ANGE_RANGE + HALF_PI - HALF_ANGLE_RANGE;
    }
}