Drawable + Animatable实现动画

看看效果

Demo效果图

总体的实现思路

• 用一个View（ImageView）容器来呈现动画
• 给ImageView设置一个Drawable（在这个drawable里面实现所有的绘制逻辑）
• 实现动画的效果的核心就是，当ImageView调用Drawable的draw（系统自动调用）方法的时候再次调用ImageView的重绘方法就实现了动画效果了

看看这个demo的实现

• 重写了一个ImageView仅仅就是为了设置一个Drawable，不用重写也可以。

public class LoadingView extends ImageView{

    public LoadingView(Context context) {
        super(context);
        setImageDrawable(new LoadingDrawable(this));
    }

    public LoadingView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        setImageDrawable(new LoadingDrawable(this));
    }

    public LoadingView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        setImageDrawable(new LoadingDrawable(this));
    }

}

• 核心就是这个LoadingDrawable，直接看draw方法吧

    @Override
    public void draw(@NonNull Canvas canvas) {
        //默认从左到右
        int width = canvas.getWidth();
        int height = canvas.getHeight();
        int centerX = width / 2;
        int centerY = height / 2;
        //canvas.drawCircle(centerX,centerY,width / 2 - 8,paint);
        for(int i=0;i < lineModels.size();i++){
            drawLine(canvas,lineModels.get(i));
        }
        //updatedata
        contannier.invalidate();
    }


    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    private void drawLine(Canvas canvas, LineModel lineModel){
        int width = canvas.getWidth() / 2;
        int height = canvas.getHeight() / 2;
        paint.setColor(lineModel.color);
        canvas.drawArc(
                width - lineModel.raudis - strokeWidth,height - lineModel.raudis - strokeWidth,
                width + lineModel.raudis + strokeWidth,height + lineModel.raudis + strokeWidth,
                lineModel.start,lineModel.end,
                false,paint
        );
        lineModel.updata();
    }

- 这里的**drawLine**就是具体的绘制过程，并且在绘制完成之后更新了下次需要绘制的各种信息
- 绘制完成之后调用了 **ImageView**的**invalidate**方法进行循环绘制

实现思路来自

[==↓ ] https://github.com/81813780/AVLoadingIndicatorView

[== ↑] https://github.com/tyrantgit/ExplosionField

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