安卓版落叶特效-canvas篇（一）

自定义View，代码如下:

package net.cloudelevator.anim;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Handler;
import android.os.Message;
import android.util.AttributeSet;
import android.view.View;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import java.util.ArrayList;
import java.util.List
public class MyCanvas extends View {
    Paint paint;
    Paint tpaint;
    private int[] list = new int[192];
    Handler handler = new Handler() {
        @Override
        public void handleMessage(@NonNull Message msg) {
            switch (msg.what) {
                case 1:
                    postInvalidate();
                    handler.sendEmptyMessageDelayed(1, 0);
                    break;
            }
        }
    };

    public MyCanvas(Context context) {
        super(context);
        for (int i = 0; i < 192; i++) {
            list[i] = 1;
        }
        for (int j = 0; j < 100; j++) {
            for (int i = 0; i < list.length; i++) {
                if (list[i] > 758 + Math.random() * 1e4) {
                    list[i] = 0;
                } else {
                    list[i] = list[i] + 10;
                }
            }
        }
        handler.sendEmptyMessageDelayed(1, 0);
    }

    public MyCanvas(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        for (int i = 0; i < 192; i++) {
            list[i] = 1;
        }
        for (int j = 0; j < 100; j++) {
            for (int i = 0; i < list.length; i++) {
                if (list[i] > 758 + Math.random() * 1e4) {
                    list[i] = 0;
                } else {
                    list[i] = list[i] + 10;
                }
            }
        }
        handler.sendEmptyMessageDelayed(1, 0);
    }

    public MyCanvas(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        for (int i = 0; i < 192; i++) {
            list[i] = 1;
        }
        for (int j = 0; j < 100; j++) {
            for (int i = 0; i < list.length; i++) {
                if (list[i] > 758 + Math.random() * 1e4) {
                    list[i] = 0;
                } else {
                    list[i] = list[i] + 10;
                }
            }
        }
        handler.sendEmptyMessageDelayed(1, 0);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        paint = new Paint();
        tpaint = new Paint();
        tpaint.setColor(Color.WHITE);
        paint.setStrokeWidth(0);
        Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.bg);
        canvas.drawBitmap(bitmap, 0, 0, paint);
        for (int i = 0; i < list.length; i++) {
            canvas.drawText("\uD83C\uDF42", i * 50, list[i], tpaint);
            if (list[i] > 758 + Math.random() * 1e4) {
                list[i] = 0;
            } else {
                list[i] = list[i] + 10;
            }
        }
    }
}