Animating the drawing of a canvas path on Android

Question

I\'d like to animate the drawing of a path, i.e. to have it progressively appear on the screen. I am using the canvas and my best guess so far is to use an ObjectAnimator to

Answer 1

package com.nexoslav.dashlineanimatedcanvasdemo;

import android.animation.ValueAnimator;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.DashPathEffect;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
import android.view.animation.LinearInterpolator;

import androidx.annotation.Nullable;

public class CustomView extends View {
    float[] dashes = {30, 20};
    Paint mPaint;
    private Path mPath;

    private void init() {

        mPaint = new Paint();
        mPaint.setColor(Color.BLACK);
        mPaint.setStrokeWidth(10f);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setPathEffect(new DashPathEffect(dashes, 0));

        mPath = new Path();
        mPath.moveTo(200, 200);
        mPath.lineTo(300, 100);
        mPath.lineTo(400, 400);
        mPath.lineTo(1000, 200);
        mPath.lineTo(1000, 1000);
        mPath.lineTo(200, 400);

        ValueAnimator animation = ValueAnimator.ofInt(0, 100);
        animation.setInterpolator(new LinearInterpolator());
        animation.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator valueAnimator) {
                Log.d("bla", "bla: " + valueAnimator.getAnimatedValue());
                mPaint.setPathEffect(new DashPathEffect(dashes, (Integer) valueAnimator.getAnimatedValue()));
                invalidate();
            }
        });
        animation.setDuration(1000);
        animation.setRepeatMode(ValueAnimator.RESTART);
        animation.setRepeatCount(ValueAnimator.INFINITE);
        animation.start();
    }

    public CustomView(Context context) {
        super(context);
        init();
    }


    public CustomView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public CustomView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

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

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        canvas.drawPath(mPath, mPaint);
    }
}