Android自定义View、ViewgroupAndroid开发经验谈Android开发

手撸一个物体下落的控件,实现雪花飘落效果

2018-12-26  本文已影响21人  饮水思源为名

效果图:

圣诞登录页.gif

参考文章:

Android自定义View——从零开始实现雪花飘落效果
感谢原文作者,不仅实现了效果,并且写得非常详细,还做了优化。笔者参考原文作者的源码,做了一点修改,实现了效果并加入了项目中。不过都大同小异,下面笔者会将学习和制作中的难点和注意点分享给大家。

提炼与分享:

1. 如何实现简单的物体下落:

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        if(fallObjects.size()>0){
            for (int i=0;i<fallObjects.size();i++) {
                //然后进行绘制
                fallObjects.get(i).drawObject(canvas);
            }
            // 隔一段时间重绘一次, 动画效果
            getHandler().postDelayed(runnable, intervalTime);
        }
    }
    private Runnable runnable = new Runnable() {
        @Override
        public void run() {
            invalidate();
        }
    };
    public void drawObject(Canvas canvas){
        moveObject();
        canvas.drawBitmap(bitmap,presentX,presentY,null);
    }
    private void moveObject(){
        moveX();
        moveY();
        if(presentY>parentHeight || presentX<-bitmap.getWidth() || presentX>parentWidth+bitmap.getWidth()){
            reset();
        }
    }
    private void moveY(){
        presentY += presentSpeed;
    }
    private void moveX(){
        presentX += defaultWindSpeed * Math.sin(angle);
        if(isAngleChange){
            angle += (float) (random.nextBoolean()?-1:1) * Math.random() * 0.0025;
        }
    }
    private void reset(){
        presentY = -objectHeight;
        randomSpeed();
        randomWind();//记得重置一下初始角度,不然雪花会越下越少(因为角度累加会让雪花越下越偏)
    }

  首先是Y轴控制竖直下落,初始的Y轴坐标是通过屏幕高度取随机值-屏幕高度来确定的。这样物体会从不同的位置下落,在相同速度的情况下,也能在不同的时间进入屏幕。
  然后是X轴,正常的雪花肯定不是竖直下落,也不是折线下落,而是弧形,View中采用的sin函数的-Pi到Pi之间的值绘制弧形。x轴的初始位置通过对屏幕宽度做随机值确定。
  最后在物体到底屏幕底部,或者超过屏幕左右边界时,重置物体(reset方法)。需要重置的是y轴的点,以及物体的速度,当然还有我们模拟的风力,后面会单独说。

2. 为什么要使用Builder建造者模式

  其实原文已经讲得很仔细了,我们物体会有大量的参数和对应的行为方法,为了提高代码的可读性,我们将物体提取出来,作为一个单独的类。而大量的参数采用普通的构造方法去构造,实在是不知道,传入的参数究竟代表什么。而建造者模式能够解决这个问题。

        FallObject.Builder builder = new FallObject.Builder(getResources().getDrawable(R.drawable.snowflake));
        FallObject fallObject = builder
                .setSpeed(8,true)
                .setSize(80,80,true)
                .setWind(5,true)
                .build();
        //初始化一个雪球样式的fallObject
        ((FallingView)findViewById(R.id.fallingView)).addFallObject(fallObject,60);//添加60个雪球对象

  在这个项目中,我们将所有与下落物体相关的方法和属性全部封装在FallObject中,并且提供Builder内部类实例化。而我们的View则仅仅需要作为一个画布,提供添加下落对象的方法,重复的绘制物体即可。至于绘制的对象是要下落还是要旋转,都与View没有关系了。

3. 绘制图片并且控制其大小

  绘制图片在View中是有提供方法的:canvas.drawBitmap(bitmap,presentX,presentY,null);从方法中可以看到,我们需要的是bitmap的图片,那么,我们在修改图片大小之前,还需要先将drawable转化为bitmap。

    /**
     * drawable图片资源转bitmap
     * @param drawable
     * @return
     */
    public static Bitmap drawableToBitmap(Drawable drawable) {
        Bitmap bitmap = Bitmap.createBitmap(
                drawable.getIntrinsicWidth(),
                drawable.getIntrinsicHeight(),
                drawable.getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB_8888
                        : Bitmap.Config.RGB_565);
        Canvas canvas = new Canvas(bitmap);
        drawable.setBounds(0, 0, drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight());
        drawable.draw(canvas);
        return bitmap;
    }

  上面是drawable转化为bitmap的代码,简单来讲就是Bitmap的采用的是工厂模式创建一个bitmap空对象,然后通过drawable将图片图像画在bitmap对象中。

    /**
     * 改变bitmap的大小
     * @param bitmap 目标bitmap
     * @param newW 目标宽度-
     * @param newH 目标高度
     * @return
     */
    public static Bitmap changeBitmapSize(Bitmap bitmap, int newW, int newH) {
        int oldW = bitmap.getWidth();
        int oldH = bitmap.getHeight();
        // 计算缩放比例
        float scaleWidth = ((float) newW) / oldW;
        float scaleHeight = ((float) newH) / oldH;
        // 取得想要缩放的matrix参数
        Matrix matrix = new Matrix();
        matrix.postScale(scaleWidth, scaleHeight);
        // 得到新的图片
        bitmap = Bitmap.createBitmap(bitmap, 0, 0, oldW, oldH, matrix, true);
        return bitmap;
    }

  上面是改变图片显示大小的方法。就是直接对bitmap的缩放操作返回新的bitmao对象。需要注意的是为了保证不失帧,新的宽高度需要按原大小等比例缩放。

4. 如何引入风的概念

    /**
     * 随机风的风向和风力大小比例,即随机物体初始下落角度
     */
    private void randomWind(){
        if(isAngleChange){
            angle = (float) ((random.nextBoolean()?-1:1) * Math.random() * initWindLevel /50);
        }else {
            angle = (float) initWindLevel /50;
        }
        //限制angle的最大最小值
        if(angle>HALF_PI){
            angle = HALF_PI;
        }else if(angle<-HALF_PI){
            angle = -HALF_PI;
        }
    }

  正常情况下,我们的雪花不会是直线下落的,而是有轻微的弧度飘落,我们通过改变X轴的方式来实现水平位移,但是为了保证位移的平滑,我们采用了sin正弦函数计算x轴的值,采用-π/2到π/2的弧线值作为函数的角度。这个曲线值是[-1,1],可以实现雪花自由的左右弧线移动。initWindLevel是我们模拟的风力,风力值越大,雪花飘落的弧度就越大。

源码:

画布View:

package com.wusy.wusylibrary.view.FallingView;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewTreeObserver;

import java.util.ArrayList;
import java.util.List;

/**
 * Created by XIAO RONG on 2018/12/24.
 */

public class FallingView extends View {

    private Context mContext;
    private AttributeSet mAttrs;

    private int viewWidth;
    private int viewHeight;

    private static final int defaultWidth = 600;//默认宽度
    private static final int defaultHeight = 1000;//默认高度
    private static final int intervalTime = 10;//重绘间隔时间

    private List<FallObject> fallObjects;

    public FallingView(Context context) {
        super(context);
        mContext = context;
        init();
    }

    public FallingView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        mContext = context;
        mAttrs = attrs;
        init();
    }

    private void init(){
        fallObjects = new ArrayList<>();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int height = measureSize(defaultHeight, heightMeasureSpec);
        int width = measureSize(defaultWidth, widthMeasureSpec);
        setMeasuredDimension(width, height);

        viewWidth = width;
        viewHeight = height;
    }

    private int measureSize(int defaultSize,int measureSpec) {
        int result = defaultSize;
        int specMode = MeasureSpec.getMode(measureSpec);
        int specSize = MeasureSpec.getSize(measureSpec);

        if (specMode == MeasureSpec.EXACTLY) {
            result = specSize;
        } else if (specMode == MeasureSpec.AT_MOST) {
            result = Math.min(result, specSize);
        }
        return result;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        if(fallObjects.size()>0){
            for (int i=0;i<fallObjects.size();i++) {
                //然后进行绘制
                fallObjects.get(i).drawObject(canvas);
            }
            // 隔一段时间重绘一次, 动画效果
            getHandler().postDelayed(runnable, intervalTime);
        }
    }

    // 重绘线程
    private Runnable runnable = new Runnable() {
        @Override
        public void run() {
            invalidate();
        }
    };
    /**
     * 向View添加下落物体对象
     * @param fallObject 下落物体对象
     * @param num
     * view.getViewTreeObserver().addOnPreDrawListener(opdl)
     * 此方法在视图绘制前会被调用,测量结束,客户获取到一些数据。再计算一些动态宽高时可以使用。
     * 调用一次后需要注销这个监听,否则会阻塞ui线程。
     */
    public void addFallObject(final FallObject fallObject, final int num) {
        getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
            @Override
            public boolean onPreDraw() {
                getViewTreeObserver().removeOnPreDrawListener(this);
                for (int i = 0; i < num; i++) {
                    FallObject newFallObject = new FallObject(fallObject.builder,viewWidth,viewHeight);
                    fallObjects.add(newFallObject);
                }
                invalidate();
                return true;
            }
        });
    }
}

下落物体类:

package com.wusy.wusylibrary.view.FallingView;

import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.PixelFormat;
import android.graphics.drawable.Drawable;

import java.util.Random;

public class FallObject {
    private int initX;
    private int initY;
    private Random random;
    private int parentWidth;//父容器宽度
    private int parentHeight;//父容器高度
    private float objectWidth;//下落物体宽度
    private float objectHeight;//下落物体高度

    public int initWindLevel;//初始风力等级
    private float angle;//下落物体角度
    private boolean isAngleChange;//下落物体角度是否改变
    private static final int defaultWindLevel = 0;//默认风力等级
    private static final int defaultWindSpeed = 10;//默认单位风速
    private static final float HALF_PI = (float) Math.PI / 2;//π/2

    public float initSpeed;//初始下降速度
    public float presentSpeed;//当前下降速度


    public float presentX;//当前位置X坐标
    public float presentY;//当前位置Y坐标

    private boolean isSpeedRandom;//物体初始下降速度比例是否随机
    private boolean isSizeRandom;//物体初始大小比例是否随机

    private Bitmap bitmap;
    public Builder builder;

    private static final int defaultSpeed = 10;//默认下降速度

    public FallObject(Builder builder, int parentWidth, int parentHeight){
        random = new Random();
        this.parentWidth = parentWidth;
        this.parentHeight = parentHeight;
        initX = random.nextInt(parentWidth);//随机物体的X坐标
        initY = random.nextInt(parentHeight)- parentHeight;//随机物体的Y坐标,并让物体一开始从屏幕顶部下落
        presentX = initX;
        presentY = initY;
        this.builder = builder;
        isSpeedRandom = builder.isSpeedRandom;
        isSizeRandom = builder.isSizeRandom;
        isAngleChange=builder.isAngleChange;
        initWindLevel=builder.initWindLevel;
        randomSpeed();
        randomSize();
    }

    private FallObject(Builder builder) {
        this.builder = builder;
        initSpeed = builder.initSpeed;
        bitmap = builder.bitmap;
        isSpeedRandom = builder.isSpeedRandom;
        isSizeRandom = builder.isSizeRandom;
        isAngleChange=builder.isAngleChange;
        initWindLevel=builder.initWindLevel;
    }
    /**
     * 绘制物体对象
     * @param canvas
     */
    public void drawObject(Canvas canvas){
        moveObject();
        canvas.drawBitmap(bitmap,presentX,presentY,null);
    }

    /**
     * 移动物体对象
     */
    private void moveObject(){
        moveX();
        moveY();
        if(presentY>parentHeight || presentX<-bitmap.getWidth() || presentX>parentWidth+bitmap.getWidth()){
            reset();
        }
    }

    /**
     * Y轴上的移动逻辑
     */
    private void moveY(){
        presentY += presentSpeed;
    }
    private void moveX(){
        presentX += defaultWindSpeed * Math.sin(angle);
        if(isAngleChange){
            angle += (float) (random.nextBoolean()?-1:1) * Math.random() * 0.0025;
        }
    }
    /**
     * 重置object位置
     */
    private void reset(){
        presentY = -objectHeight;
        randomSpeed();
        randomWind();//记得重置一下初始角度,不然雪花会越下越少(因为角度累加会让雪花越下越偏)
    }
    /**
     * 随机风的风向和风力大小比例,即随机物体初始下落角度
     */
    private void randomWind(){
        if(isAngleChange){
            angle = (float) ((random.nextBoolean()?-1:1) * Math.random() * initWindLevel /50);
        }else {
            angle = (float) initWindLevel /50;
        }
        //限制angle的最大最小值
        if(angle>HALF_PI){
            angle = HALF_PI;
        }else if(angle<-HALF_PI){
            angle = -HALF_PI;
        }
    }
    /**
     * 随机物体初始下落速度
     */
    private void randomSpeed(){
        if(isSpeedRandom){
            initSpeed = (float)((random.nextInt(3)+1)*0.1+1)* builder.initSpeed;
        }else {
            initSpeed = builder.initSpeed;
        }
        presentSpeed = initSpeed;
    }

    /**
     * 随机物体初始大小比例
     */
    private void randomSize(){
        if(isSizeRandom){
            float r = (random.nextInt(10)+1)*0.1f;
            float rW = r * builder.bitmap.getWidth();
            float rH = r * builder.bitmap.getHeight();
            bitmap = changeBitmapSize(builder.bitmap,(int)rW,(int)rH);
        }else {
            bitmap = builder.bitmap;
        }
        objectWidth = bitmap.getWidth();
        objectHeight = bitmap.getHeight();
    }
    /**
     * 改变bitmap的大小
     * @param bitmap 目标bitmap
     * @param newW 目标宽度-
     * @param newH 目标高度
     * @return
     */
    public static Bitmap changeBitmapSize(Bitmap bitmap, int newW, int newH) {
        int oldW = bitmap.getWidth();
        int oldH = bitmap.getHeight();
        // 计算缩放比例
        float scaleWidth = ((float) newW) / oldW;
        float scaleHeight = ((float) newH) / oldH;
        // 取得想要缩放的matrix参数
        Matrix matrix = new Matrix();
        matrix.postScale(scaleWidth, scaleHeight);
        // 得到新的图片
        bitmap = Bitmap.createBitmap(bitmap, 0, 0, oldW, oldH, matrix, true);
        return bitmap;
    }
    /**
     * drawable图片资源转bitmap
     * @param drawable
     * @return
     */
    public static Bitmap drawableToBitmap(Drawable drawable) {
        Bitmap bitmap = Bitmap.createBitmap(
                drawable.getIntrinsicWidth(),
                drawable.getIntrinsicHeight(),
                drawable.getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB_8888
                        : Bitmap.Config.RGB_565);
        Canvas canvas = new Canvas(bitmap);
        drawable.setBounds(0, 0, drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight());
        drawable.draw(canvas);
        return bitmap;
    }

    public static final class Builder {
        private float initSpeed;
        private Bitmap bitmap;
        private boolean isSpeedRandom;
        private boolean isSizeRandom;
        private int initWindLevel;//下落物体角度
        private boolean isAngleChange;//下落物体角度是否改变
        public Builder(Bitmap bitmap) {
            this.initSpeed = defaultSpeed;
            this.bitmap = bitmap;
        }
        public Builder(Drawable drawable) {
            this.initSpeed = defaultSpeed;
            this.bitmap = drawableToBitmap(drawable);
        }

        /**
         * 设置物体的初始下落速度
         * @param level
         * @param isAngleChange 物体初始下降速度比例是否随机
         * @return
         */
        public Builder setWind(int level,boolean isAngleChange) {
            this.initWindLevel  = level;
            this.isAngleChange = isAngleChange;
            return this;
        }
        /**
         * 设置物体的初始下落速度
         * @param speed
         * @return
         */
        public Builder setSpeed(float speed) {
            this.initSpeed = speed;
            return this;
        }
        /**
         * 设置物体的初始下落速度
         * @param speed
         * @param isRandomSpeed 物体初始下降速度比例是否随机
         * @return
         */
        public Builder setSpeed(float speed,boolean isRandomSpeed) {
            this.initSpeed = speed;
            this.isSpeedRandom = isRandomSpeed;
            return this;
        }
        /**
         * 设置下落物体的大小
         * @param w
         * @param h
         * @return
         */
        public Builder setSize(int w, int h){
            this.bitmap = changeBitmapSize(this.bitmap,w,h);
            return this;
        }
        /**
         * 设置物体大小
         * @param w
         * @param h
         * @param isRandomSize 物体初始大小比例是否随机
         * @return
         */
        public Builder setSize(int w, int h, boolean isRandomSize){
            this.bitmap = changeBitmapSize(this.bitmap,w,h);
            this.isSizeRandom = isRandomSize;
            return this;
        }

        /**
         * 构建FallObject
         * @return
         */
        public FallObject build() {
            return new FallObject(this);
        }

    }
}

在用户在xml中使用,Activity中实例化:

  FallObject.Builder builder = new FallObject.Builder(getResources().getDrawable(R.drawable.snowflake));
        FallObject fallObject = builder
                .setSpeed(8,true)
                .setSize(80,80,true)
                .setWind(5,true)
                .build();
        //初始化一个雪球样式的fallObject
        ((FallingView)findViewById(R.id.fallingView)).addFallObject(fallObject,60);//添加50个雪球对象
 <com.wusy.wusylibrary.view.FallingView.FallingView
            android:id="@+id/fallingView"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
上一篇下一篇

猜你喜欢

热点阅读