Drawable.Callback 学习

今天抽空动手学习了一下Drawable这个东东从内心里一直有点惧怕动画效果所以决定把基础打好以不变应万变
重点看了Drawable.callback这个接口因为我一直不明白这个接口到底是干什么实际开发中有什么用看下都有谁实现了这个接口基本上全部是view级别的
drawable类上面的注释说 drawable代表可绘制的对象不接受事件只是draw
也就是说他只管画东西别的什么也不管
自定以drawable的时候要重写 ondraw 方法我写了个动画的例子


public class ShapeDrawable extends Drawable implements Animatable {

    private final Paint mPaint;
    private ValueAnimator mValueAnimator;

    public ShapeDrawable() {
        mPaint = new Paint();
        mPaint.setStyle(Paint.Style.FILL);
        mPaint.setColor(Color.BLUE);
    }

    @Override
    public void draw(@NonNull Canvas canvas) {
        canvas.drawColor(Color.MAGENTA);
        canvas.save();
        canvas.translate(mPosition, 0);
        canvas.drawCircle(200, 200, 100, mPaint);
        canvas.restore();
    }

    @Override
    public void setAlpha(int alpha) {

    }

    @Override
    public void setColorFilter(@Nullable ColorFilter colorFilter) {

    }

    @Override
    public int getOpacity() {
        return PixelFormat.TRANSLUCENT;
    }

    int mPosition = 0;

    public void setPosition(int position) {
        this.mPosition = position;
        this.invalidateSelf();
    }

    @Override
    public void start() {

        if (mValueAnimator != null) {
            mValueAnimator.cancel();
        }
        mValueAnimator = ValueAnimator.ofInt(0, 400);
        mValueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                int animatedValue = (int) animation.getAnimatedValue();
                setPosition(animatedValue);
            }
        });
        mValueAnimator.setDuration(2000);
        mValueAnimator.start();

    }

    @Override
    public void stop() {
        if (mValueAnimator != null) {
            mValueAnimator.cancel();
        }
    }

    @Override
    public boolean isRunning() {
        if (mValueAnimator != null) {
            return mValueAnimator.isRunning();
        }
        return false;
    }
}


public class ShapeActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_shape);
        final View imageView = findViewById(R.id.shape_view);
        final ShapeDrawable background = new ShapeDrawable();
        background.setBounds(new Rect(0, 0, 900, 900));
        imageView.setBackground(background);
        imageView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                background.start();
            }
        });

        background.setCallback(new Drawable.Callback() {
            @Override
            public void invalidateDrawable(@NonNull Drawable who) {
                Log.e("ShapeActivity", "invalidateDrawable: ");
                imageView.invalidate();
            }

            @Override
            public void scheduleDrawable(@NonNull Drawable who, @NonNull Runnable what, long when) {
                Log.e("ShapeActivity", "scheduleDrawable: ");
            }

            @Override
            public void unscheduleDrawable(@NonNull Drawable who, @NonNull Runnable what) {
                Log.e("ShapeActivity", "unscheduleDrawable: ");
            }
        });


    }
}

常用套路是修改drawable的自定义属性后调用invalidateSelf() 方法重绘修改了属性后自然是要重新绘制才能看到效果其实没有上面的setcallback 也有效果因为view默认实现了callback 并且在invalidateDrawable 方法里面调用了view的invalidate方法如果你直接自己设置了callback 什么也不处理反而看不到效果了由此可见callbcak的作用就是把具体怎么引起刷新的功能抛出去如果这时你再自己手动调用imageView.invalidate(); 像我上面那样做就又看到效果了😄
所以callback接口的实现就是具体的刷新逻辑我觉得一般不需要自己实现callback 因为view默认已经实现了根本不用我们多做什么可是自己心贱非带想知道这个接口到底咋子用😄

周末愉快

最后编辑于：2019.05.12 14:59:43