為了加強對自定義 View 的認知以及開發能力，我計劃這段時間陸續來完成幾個難度從易到難的自定義 View，並簡單的寫幾篇部落格來進行介紹，所有的程式碼也都會開源，也希望讀者能給個 star 哈 GitHub 地址：github.com/leavesC/Cus… 也可以下載 Apk 來體驗下：www.pgyer.com/CustomView
先看下效果圖：
一、思路解析
可以看出來這是一個具有“彈性”效果的小球，小球加速下落，減速上升，小球在碰到水平線的時候，水平線會被下壓一定距離，在小球被彈起時，水平線會有一個上下回彈的“黏性”效果
設計這樣一個自定義View的步驟可以分為以下幾步：
- 繪製一條水平線
- 在最高點繪製一個紅色小球，X座標居於水平線中間
- 通過 ValueAnimator 提供的加速插值器 AccelerateInterpolator 來逐漸增大小球的 Y 座標，使之加速下落
- 當小球觸碰到水平線的同時，通過改變貝塞爾曲線的控制點座標，使得水平線和小球一直保持接觸狀態，即繪製出一條符合條件的曲線
- 當小球落到最低點時，通過減速插值器 DecelerateInterpolator 來逐漸減小小球的 Y 座標，使之減速上升
- 當小球被反彈超出水平線一定高度內，水平線依然和小球保持接觸
- 當小球離開水平線後，改變貝塞爾曲線的控制點來繪製出水平線的上下回彈效果
二、程式碼解析
上述過程中需要一直改變兩個點的座標系，即小球和貝塞爾曲線的控制點
private static class Point {
private float x;
private float y;
private float radius;
}
//小球
private Point ballPoint;
//貝塞爾曲線控制點
private Point controlPoint;
複製程式碼根據View的寬高大小，以一定的比例來計算小球最高點座標、最低點座標，水平線的起始點座標這些引數值
private float lineY;
private float lineXLeft;
private float lineXRight;
//小球最高點Y座標
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;
//小球最低點Y座標
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();
}
複製程式碼在 ValueAnimator 中動態改變小球和貝塞爾曲線的控制點這兩個點的座標系
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();
//減速上升
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) { //還處於水平線以下
controlPoint.y = lineY + 2 * (ballPoint.y + ballPoint.radius - lineY);
} else {
//小球總的要上升的距離
float tempY = lineY - pointYMin;
//小球最低點距離水平線的距離，即小球已上升的距離
float distance = lineY - ballPoint.y - ballPoint.radius;
//上升比例
float percentage = distance / tempY;
if (percentage <= 0.2) { //線從水平線升高到最高點
controlPoint.y = lineY + 2 * (ballPoint.y + ballPoint.radius - lineY);
} else if (percentage <= 0.28) { //線從最高點降落到水平線
controlPoint.y = lineY - (distance - tempY * 0.2f);
} else if (percentage <= 0.34) { //線從水平線降落到最低點
controlPoint.y = lineY + (distance - tempY * 0.28f);
} else if (percentage <= 0.39) { //線從最低點升高到水平線
controlPoint.y = lineY - (distance - tempY * 0.34f);
} else {
controlPoint.y = lineY;
}
}
invalidate();
}
});
upAnimator.addListener(new AnimatorListenerAdapter() {
@Override
public void onAnimationEnd(Animator animation) {
startDownAnimator();
}
});
}
複製程式碼然後繪製出每一個動畫值所呈現的畫面即可
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);
}
複製程式碼總的程式碼是這樣的
/**
* 作者：leavesC
* 時間：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;
//貝塞爾曲線控制點
private Point controlPoint;
private ValueAnimator downAnimator;
private ValueAnimator upAnimator;
private float lineY;
private float lineXLeft;
private float lineXRight;
//小球最高點Y座標
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;
//小球最低點Y座標
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();
//減速上升
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) { //還處於水平線以下
controlPoint.y = lineY + 2 * (ballPoint.y + ballPoint.radius - lineY);
} else {
//小球總的要上升的距離
float tempY = lineY - pointYMin;
//小球最低點距離水平線的距離，即小球已上升的距離
float distance = lineY - ballPoint.y - ballPoint.radius;
//上升比例
float percentage = distance / tempY;
if (percentage <= 0.2) { //線從水平線升高到最高點
controlPoint.y = lineY + 2 * (ballPoint.y + ballPoint.radius - lineY);
} else if (percentage <= 0.28) { //線從最高點降落到水平線
controlPoint.y = lineY - (distance - tempY * 0.2f);
} else if (percentage <= 0.34) { //線從水平線降落到最低點
controlPoint.y = lineY + (distance - tempY * 0.28f);
} else if (percentage <= 0.39) { //線從最低點升高到水平線
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();
}
}
}
複製程式碼