为了加强对自定义 View 的认知以及开发能力，我计划这段时间陆续来完成几个难度从易到难的自定义 View，并简单的写几篇博客来进行介绍，所有的代码也都会开源，也希望读者能给个 star 哈
GitHub 地址：https://github.com/leavesC/CustomView
也可以下载 Apk 来体验下：https://www.pgyer.com/CustomView
先看下效果图：
一、思路解析
可以看出来这是一个具有“弹性”效果的小球，小球加速下落，减速上升，小球在碰到水平线的时候，水平线会被下压一定距离，在小球被弹起时，水平线会有一个上下回弹的“黏性”效果
设计这样一个自定义View的步骤可以分为以下几步：
- 绘制一条水平线
- 在最高点绘制一个红色小球，X坐标居于水平线中间
- 通过 ValueAnimator 提供的加速插值器 AccelerateInterpolator 来逐渐增大小球的 Y 坐标，使之加速下落
- 当小球触碰到水平线的同时，通过改变贝塞尔曲线的控制点坐标，使得水平线和小球一直保持接触状态，即绘制出一条符合条件的曲线
- 当小球落到最低点时，通过减速插值器 DecelerateInterpolator 来逐渐减小小球的 Y 坐标，使之减速上升
- 当小球被反弹超出水平线一定高度内，水平线依然和小球保持接触
- 当小球离开水平线后，改变贝塞尔曲线的控制点来绘制出水平线的上下回弹效果
二、代码解析
上述过程中需要一直改变两个点的坐标系，即小球和贝塞尔曲线的控制点
private static class Point {
private float x;
private float y;
private float radius;
}
//小球
private Point ballPoint;
//贝塞尔曲线控制点
private Point controlPoint;
根据View的宽高大小，以一定的比例来计算小球最高点坐标、最低点坐标，水平线的起始点坐标这些参数值
private float lineY;
private float lineXLeft;
private float lineXRight;
//小球最高点Y坐标
private float pointYMin;
@Override
protected void onSizeChanged(int contentWidth, int contentHeight, int oldW, int oldH) {
super.onSizeChanged(contentWidth, contentHeight, oldW, oldH);
lineY = contentHeight * 0.5f;
lineXLeft = contentWidth * 0.15f;
lineXRight = contentWidth * 0.85f;
//小球最低点Y坐标
float pointYMax = contentHeight * 0.55f;
pointYMin = contentHeight * 0.22f;
ballPoint.x = contentWidth * 0.5F;
ballPoint.radius = 26;
ballPoint.y = pointYMin;
controlPoint.x = ballPoint.x;
long speed = 1800;
downAnimator.setFloatValues(pointYMin, pointYMax);
upAnimator.setFloatValues(pointYMax, pointYMin);
downAnimator.setDuration(speed);
upAnimator.setDuration((long) (0.8 * speed));
start();
}
在 ValueAnimator 中动态改变小球和贝塞尔曲线的控制点这两个点的坐标系
private void initAnimator() {
downAnimator = new ValueAnimator();
//加速下降
downAnimator.setInterpolator(new AccelerateInterpolator());
downAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
ballPoint.y = (float) animation.getAnimatedValue();
if (ballPoint.y + ballPoint.radius <= lineY) {
controlPoint.y = lineY;
} else {
controlPoint.y = lineY + 2 * (ballPoint.y + ballPoint.radius - lineY);
}
invalidate();
}
});
downAnimator.addListener(new AnimatorListenerAdapter() {
@Override
public void onAnimationEnd(Animator animation) {
startUpAnimator();
}
});
upAnimator = new ValueAnimator();
//减速上升
upAnimator.setInterpolator(new DecelerateInterpolator());
upAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
ballPoint.y = (float) animation.getAnimatedValue();
if (ballPoint.y + ballPoint.radius >= lineY) { //还处于水平线以下
controlPoint.y = lineY + 2 * (ballPoint.y + ballPoint.radius - lineY);
} else {
//小球总的要上升的距离
float tempY = lineY - pointYMin;
//小球最低点距离水平线的距离，即小球已上升的距离
float distance = lineY - ballPoint.y - ballPoint.radius;
//上升比例
float percentage = distance / tempY;
if (percentage <= 0.2) { //线从水平线升高到最高点
controlPoint.y = lineY + 2 * (ballPoint.y + ballPoint.radius - lineY);
} else if (percentage <= 0.28) { //线从最高点降落到水平线
controlPoint.y = lineY - (distance - tempY * 0.2f);
} else if (percentage <= 0.34) { //线从水平线降落到最低点
controlPoint.y = lineY + (distance - tempY * 0.28f);
} else if (percentage <= 0.39) { //线从最低点升高到水平线
controlPoint.y = lineY - (distance - tempY * 0.34f);
} else {
controlPoint.y = lineY;
}
}
invalidate();
}
});
upAnimator.addListener(new AnimatorListenerAdapter() {
@Override
public void onAnimationEnd(Animator animation) {
startDownAnimator();
}
});
}
然后绘制出每一个动画值所呈现的画面即可
private Path path = new Path();
@Override
protected void onDraw(Canvas canvas) {
paint.setColor(Color.WHITE);
paint.setStrokeWidth(8f);
path.reset();
path.moveTo(lineXLeft, lineY);
path.quadTo(controlPoint.x, controlPoint.y, lineXRight, lineY);
paint.setStyle(Paint.Style.STROKE);
canvas.drawPath(path, paint);
paint.setStyle(Paint.Style.FILL);
canvas.drawCircle(lineXLeft, lineY, 16, paint);
canvas.drawCircle(lineXRight, lineY, 16, paint);
paint.setColor(Color.parseColor("#f7584d"));
paint.setStrokeWidth(0f);
canvas.drawCircle(ballPoint.x, ballPoint.y, ballPoint.radius, paint);
}
总的代码是这样的
/**
* 作者：leavesC
* 时间：2019/5/1 23:04
* 描述：
* GitHub：https://github.com/leavesC
* Blog：https://www.jianshu.com/u/9df45b87cfdf
*/
public class PointBeatView extends BaseView {
private static class Point {
private float x;
private float y;
private float radius;
}
//小球
private Point ballPoint;
//贝塞尔曲线控制点
private Point controlPoint;
private ValueAnimator downAnimator;
private ValueAnimator upAnimator;
private float lineY;
private float lineXLeft;
private float lineXRight;
//小球最高点Y坐标
private float pointYMin;
private Paint paint;
public PointBeatView(Context context) {
this(context, null);
}
public PointBeatView(Context context, @Nullable AttributeSet attrs) {
this(context, attrs, 0);
}
public PointBeatView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
ballPoint = new Point();
controlPoint = new Point();
initPaint();
initAnimator();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int width = getSize(widthMeasureSpec, getResources().getDisplayMetrics().widthPixels);
int height = getSize(heightMeasureSpec, getResources().getDisplayMetrics().heightPixels);
setMeasuredDimension(width, height);
}
private void initPaint() {
paint = new Paint();
paint.setAntiAlias(true);
paint.setDither(true);
}
@Override
protected void onSizeChanged(int contentWidth, int contentHeight, int oldW, int oldH) {
super.onSizeChanged(contentWidth, contentHeight, oldW, oldH);
lineY = contentHeight * 0.5f;
lineXLeft = contentWidth * 0.15f;
lineXRight = contentWidth * 0.85f;
//小球最低点Y坐标
float pointYMax = contentHeight * 0.55f;
pointYMin = contentHeight * 0.22f;
ballPoint.x = contentWidth * 0.5F;
ballPoint.radius = 26;
ballPoint.y = pointYMin;
controlPoint.x = ballPoint.x;
long speed = 1800;
downAnimator.setFloatValues(pointYMin, pointYMax);
upAnimator.setFloatValues(pointYMax, pointYMin);
downAnimator.setDuration(speed);
upAnimator.setDuration((long) (0.8 * speed));
start();
}
private Path path = new Path();
@Override
protected void onDraw(Canvas canvas) {
paint.setColor(Color.WHITE);
paint.setStrokeWidth(8f);
path.reset();
path.moveTo(lineXLeft, lineY);
path.quadTo(controlPoint.x, controlPoint.y, lineXRight, lineY);
paint.setStyle(Paint.Style.STROKE);
canvas.drawPath(path, paint);
paint.setStyle(Paint.Style.FILL);
canvas.drawCircle(lineXLeft, lineY, 16, paint);
canvas.drawCircle(lineXRight, lineY, 16, paint);
paint.setColor(Color.parseColor("#f7584d"));
paint.setStrokeWidth(0f);
canvas.drawCircle(ballPoint.x, ballPoint.y, ballPoint.radius, paint);
}
private void initAnimator() {
downAnimator = new ValueAnimator();
//加速下降
downAnimator.setInterpolator(new AccelerateInterpolator());
downAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
ballPoint.y = (float) animation.getAnimatedValue();
if (ballPoint.y + ballPoint.radius <= lineY) {
controlPoint.y = lineY;
} else {
controlPoint.y = lineY + 2 * (ballPoint.y + ballPoint.radius - lineY);
}
invalidate();
}
});
downAnimator.addListener(new AnimatorListenerAdapter() {
@Override
public void onAnimationEnd(Animator animation) {
startUpAnimator();
}
});
upAnimator = new ValueAnimator();
//减速上升
upAnimator.setInterpolator(new DecelerateInterpolator());
upAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
ballPoint.y = (float) animation.getAnimatedValue();
if (ballPoint.y + ballPoint.radius >= lineY) { //还处于水平线以下
controlPoint.y = lineY + 2 * (ballPoint.y + ballPoint.radius - lineY);
} else {
//小球总的要上升的距离
float tempY = lineY - pointYMin;
//小球最低点距离水平线的距离，即小球已上升的距离
float distance = lineY - ballPoint.y - ballPoint.radius;
//上升比例
float percentage = distance / tempY;
if (percentage <= 0.2) { //线从水平线升高到最高点
controlPoint.y = lineY + 2 * (ballPoint.y + ballPoint.radius - lineY);
} else if (percentage <= 0.28) { //线从最高点降落到水平线
controlPoint.y = lineY - (distance - tempY * 0.2f);
} else if (percentage <= 0.34) { //线从水平线降落到最低点
controlPoint.y = lineY + (distance - tempY * 0.28f);
} else if (percentage <= 0.39) { //线从最低点升高到水平线
controlPoint.y = lineY - (distance - tempY * 0.34f);
} else {
controlPoint.y = lineY;
}
}
invalidate();
}
});
upAnimator.addListener(new AnimatorListenerAdapter() {
@Override
public void onAnimationEnd(Animator animation) {
startDownAnimator();
}
});
}
@Override
protected void onDetachedFromWindow() {
super.onDetachedFromWindow();
stop();
}
@Override
protected void onVisibilityChanged(@NonNull View changedView, int visibility) {
super.onVisibilityChanged(changedView, visibility);
switch (visibility) {
case View.VISIBLE: {
start();
break;
}
case View.INVISIBLE:
case View.GONE: {
stop();
break;
}
}
Log.e(TAG, "onVisibilityChanged: " + visibility);
}
public void start() {
startDownAnimator();
}
public void stop() {
stopDownAnimator();
stopUpAnimator();
}
private void startDownAnimator() {
if (downAnimator != null && downAnimator.getValues() != null && downAnimator.getValues().length > 0 && !downAnimator.isRunning()) {
downAnimator.start();
}
}
private void stopDownAnimator() {
if (downAnimator != null && downAnimator.isRunning()) {
downAnimator.cancel();
}
}
private void startUpAnimator() {
if (upAnimator != null && upAnimator.getValues() != null && upAnimator.getValues().length > 0 && !upAnimator.isRunning()) {
upAnimator.start();
}
}
private void stopUpAnimator() {
if (upAnimator != null && upAnimator.isRunning()) {
upAnimator.cancel();
}
}
}
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