Android进阶:九、自定义View之手写Loading动效

这是一个很简单的动画效果,使用属性动画即可实现,希望对读者学习动画能达到抛砖引玉的效果

一.自定义动画效果——Loading效果

如上是我们需要做的一个Loading动画。Loading效果是很常见的一种动画,最简单的实现让设计画个动态图即可,或者画个静态图然后使用帧动画也可以实现。但是今天我们用纯代码实现,不用任何图片资源。

《Android进阶:九、自定义View之手写Loading动效》 1.png

《Android进阶:九、自定义View之手写Loading动效》 1.0.gif

大致思路

我们自定义一个View,继承View类,然后画两个不同半径的弧形,转动不同的角度即可实现。

绘制两个不同半径的弧形
首先初始化外圆和内园的Recf();

    private RectF mOuterCircleRectF = new RectF();
    private RectF mInnerCircleRectF = new RectF();

然后在onDraw方法绘制圆弧:

        //获取View的中心
        float centerX = getWidth() / 2;
        float centerY = getHeight() / 2;

        if (lineWidth > centerX) {
            throw new IllegalArgumentException("lineWidth值太大了");
        }
        //外圆半径,因为我们的弧形是有宽度的,所以计算半径的时候应该把这部分减去,不然会有切割的效果
        float outR = centerX - lineWidth;

        //小圆半径
        float inR = outR * 0.6f - lineWidth;
        //设置弧形的距离上下左右的距离,也就是包围园的矩形。
        mOuterCircleRectF.set(centerX - outR, centerY - outR, centerX + outR, centerY + outR);
        mInnerCircleRectF.set(centerX - inR, centerY - inR, centerX + inR, centerY + inR);
        //绘制外圆
        canvas.drawArc(mOuterCircleRectF, mRotateAngle % 360, OUTER_CIRCLE_ANGLE, false, mStrokePaint);
        //绘制内圆
        canvas.drawArc(mInnerCircleRectF, 270 - mRotateAngle % 360, INTER_CIRCLE_ANGLE, false, mStrokePaint);

代码很简单,就像注释一样:

  • 获取整个loadView的宽高,然后计算loadview的中心
  • 利用中心计算外圆和内园的半径,因为圆弧的弧边有宽度,所以应该减去这部分宽度,不然上下左右会有被切割的效果。
  • 在Recf中设置以圆半径为边长的矩形
  • 在画布中以矩形的数据绘制圆弧即可,这里设置了角度,使圆形有缺角,只要不是360度的圆都是有缺角的。

绘制圆的过程应该放在onDraw方法中,这样我们可以不断的重绘,也可以获取view的真实的宽高

当然,我们还需设置一个画笔来画我们的圆

       mStrokePaint = new Paint();
        mStrokePaint.setStyle(Paint.Style.STROKE);
        mStrokePaint.setStrokeWidth(lineWidth);
        mStrokePaint.setColor(color);
        mStrokePaint.setAntiAlias(true);
        mStrokePaint.setStrokeCap(Paint.Cap.ROUND);
        mStrokePaint.setStrokeJoin(Paint.Join.ROUND);

二.设置属性动画

圆弧画好了,然后利用属性动画即可实现动画效果。这里采用的是ValueAnimator,值属性动画,我们可以设置一个值范围,然后让他在这个范围内变化。

     mFloatValueAnimator = ValueAnimator.ofFloat(0.0f, 1.0f);
        mFloatValueAnimator.setRepeatCount(Animation.INFINITE);
        mFloatValueAnimator.setDuration(ANIMATION_DURATION);
        mFloatValueAnimator.setStartDelay(ANIMATION_START_DELAY);
        mFloatValueAnimator.setInterpolator(new AccelerateDecelerateInterpolator());

这个设置很简单,设置值得范围,这是无线循环,设置动画执行的时间,这只动画循环时延迟的时间,设置插值器。

三.弧形动起来

让弧形动起来的原理,就是监听值属性动画的值变化,然后在这个变化的过程中不断的改变弧形的角度,然后让它重绘即可。

我们让我们的loadview实现ValueAnimator.AnimatorUpdateListener接口,然后在onAnimationUpdate监听动画的变化。我们初始化值属性动画的时候设置了值得范围为float型,所以这里可以获取这个变化的值。然后利用这个值可以改变绘制圆的角度大小,再调用重绘方法,即可实现:

    @Override
    public void onAnimationUpdate(ValueAnimator animation) {
        mRotateAngle = 360 * (float)animation.getAnimatedValue();
        invalidate();
    }

整个思路大致就是这样。完整代码如下:

public class LoadingView extends View implements Animatable, ValueAnimator.AnimatorUpdateListener {
    private static final long ANIMATION_START_DELAY = 200;
    private static final long ANIMATION_DURATION = 1000;
    private static final int OUTER_CIRCLE_ANGLE = 270;
    private static final int INTER_CIRCLE_ANGLE = 90;

    private ValueAnimator mFloatValueAnimator;
    private Paint mStrokePaint;
    private RectF mOuterCircleRectF;
    private RectF mInnerCircleRectF;

    private float mRotateAngle;


    public LoadingView (Context context) {
        this(context, null);
    }

    public LoadingView (Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, -1);
    }

    public LoadingView (Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        this(context, attrs, defStyleAttr, -1);
    }

    public LoadingView (Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        initView(context, attrs);
    }

    float lineWidth;

    private void initView(Context context, AttributeSet attrs) {
        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.MyCustomLoadingView);
        lineWidth = typedArray.getFloat(R.styleable.MyCustomLoadingView_lineWidth, 10.0f);
        int color = typedArray.getColor(R.styleable.MyCustomLoadingView_viewColor, context.getColor(R.color.colorAccent));
        typedArray.recycle();
        initAnimators();
        mOuterCircleRectF = new RectF();
        mInnerCircleRectF = new RectF();
        //初始化画笔
        initPaint(lineWidth, color);
        //旋转角度
        mRotateAngle = 0;
    }

    private void initAnimators() {
        mFloatValueAnimator = ValueAnimator.ofFloat(0.0f, 1.0f);
        mFloatValueAnimator.setRepeatCount(Animation.INFINITE);
        mFloatValueAnimator.setDuration(ANIMATION_DURATION);
        mFloatValueAnimator.setStartDelay(ANIMATION_START_DELAY);
        mFloatValueAnimator.setInterpolator(new AccelerateDecelerateInterpolator());
    }

    /**
     * 初始化画笔
     */
    private void initPaint(float lineWidth, int color) {
        mStrokePaint = new Paint();
        mStrokePaint.setStyle(Paint.Style.STROKE);
        mStrokePaint.setStrokeWidth(lineWidth);
        mStrokePaint.setColor(color);
        mStrokePaint.setAntiAlias(true);
        mStrokePaint.setStrokeCap(Paint.Cap.ROUND);
        mStrokePaint.setStrokeJoin(Paint.Join.ROUND);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        float centerX = getWidth() / 2;
        float centerY = getHeight() / 2;

        //最大尺寸
        if (lineWidth > centerX) {
            throw new IllegalArgumentException("lineWidth值太大了");
        }
        float outR = centerX - lineWidth;
        //小圆尺寸
        float inR = outR * 0.6f;
        mOuterCircleRectF.set(centerX - outR, centerY - outR, centerX + outR, centerY + outR);
        mInnerCircleRectF.set(centerX - inR, centerY - inR, centerX + inR, centerY + inR);
        //先保存画板的状态
        canvas.save();
        //外圆
        canvas.drawArc(mOuterCircleRectF, mRotateAngle % 360, OUTER_CIRCLE_ANGLE, false, mStrokePaint);
        //内圆
        canvas.drawArc(mInnerCircleRectF, 270 - mRotateAngle % 360, INTER_CIRCLE_ANGLE, false, mStrokePaint);
        //恢复画板的状态
        canvas.restore();
    }

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        startLoading();
    }

    public void startLoading() {
        start();
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        stopLoading();
    }

    public void stopLoading() {
        stop();
    }

    @Override
    public void onAnimationUpdate(ValueAnimator animation) {
        mRotateAngle = 360 * (float)animation.getAnimatedValue();
        invalidate();
    }

    protected void computeUpdateValue(float animatedValue) {
        mRotateAngle = (int) (360 * animatedValue);
    }

    @Override
    public void start() {
        if (mFloatValueAnimator.isStarted()) {
            return;
        }
        mFloatValueAnimator.addUpdateListener(this);
        mFloatValueAnimator.setRepeatCount(Animation.INFINITE);
        mFloatValueAnimator.setDuration(ANIMATION_DURATION);
        mFloatValueAnimator.start();
    }

    @Override
    public void stop() {
        mFloatValueAnimator.removeAllUpdateListeners();
        mFloatValueAnimator.removeAllListeners();
        mFloatValueAnimator.setRepeatCount(0);
        mFloatValueAnimator.setDuration(0);
        mFloatValueAnimator.end();
    }

    @Override
    public boolean isRunning() {
        return mFloatValueAnimator.isRunning();
    }
}

attr文件代码如下:

    <declare-styleable name="LoadingView">
        <attr name="lineWidth" format="float" />
        <attr name="viewColor" format="color" />
    </declare-styleable>
    原文作者:Android丶SE
    原文地址: https://www.jianshu.com/p/3bf435a84b74
    本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系博主进行删除。
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