手撸一个物体下落的控件,实现雪花飘落效果
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" />