为何调整MaterialToolbar的AdaptiveIconDrawable图标大小无效？

直接修改AdaptiveIconDrawable的bounds无效，是因为MaterialToolbar在渲染Logo时，会根据自身的布局逻辑重新计算尺寸，忽略手动设置的bounds。以下是几种可行的解决方法：

方法一：自定义Drawable包裹原Logo，重写固有尺寸 #

创建一个自定义Drawable，包裹原AdaptiveIconDrawable，通过重写getIntrinsicWidth和getIntrinsicHeight来控制显示尺寸：

public class ScaledDrawable extends DrawableWrapper {
    private final float scaleFactor;

    public ScaledDrawable(Drawable drawable, float scaleFactor) {
        super(drawable);
        this.scaleFactor = scaleFactor;
    }

    @Override
    public int getIntrinsicWidth() {
        return (int) (super.getIntrinsicWidth() * scaleFactor);
    }

    @Override
    public int getIntrinsicHeight() {
        return (int) (super.getIntrinsicHeight() * scaleFactor);
    }
}

在Activity中使用：

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
    AdaptiveIconDrawable originalLogo = (AdaptiveIconDrawable) _toolbar.getLogo();
    // 缩小到原尺寸的1/4
    ScaledDrawable scaledLogo = new ScaledDrawable(originalLogo, 0.25f);
    _toolbar.setLogo(scaledLogo);
}

方法二：直接调整Logo对应的ImageView尺寸 #

MaterialToolbar提供getLogoView()方法（需Material Components库版本足够新），可直接获取Logo的ImageView并设置宽高：

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
    ImageView logoView = _toolbar.getLogoView();
    if (logoView != null) {
        ViewGroup.LayoutParams params = logoView.getLayoutParams();
        // 示例：设置为40dp对应的像素值
        int size = (int) getResources().getDimension(R.dimen.logo_size);
        params.width = size;
        params.height = size;
        logoView.setLayoutParams(params);
    }
}

若getLogoView()不可用，可遍历Toolbar子View找到Logo对应的ImageView：

private ImageView findLogoView(Toolbar toolbar) {
    for (int i = 0; i < toolbar.getChildCount(); i++) {
        View child = toolbar.getChildAt(i);
        if (child instanceof ImageView && child.getContentDescription().equals(toolbar.getLogoDescription())) {
            return (ImageView) child;
        }
    }
    return null;
}

方法三：将Logo转为Bitmap后缩小 #

把原AdaptiveIconDrawable转换成Bitmap，缩小后再转成Drawable设置给Toolbar：

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
    AdaptiveIconDrawable originalLogo = (AdaptiveIconDrawable) _toolbar.getLogo();
    Bitmap originalBitmap = drawableToBitmap(originalLogo);
    // 缩小到原尺寸的1/4
    Bitmap scaledBitmap = Bitmap.createScaledBitmap(originalBitmap, 
            originalBitmap.getWidth() / 4, originalBitmap.getHeight() / 4, true);
    _toolbar.setLogo(new BitmapDrawable(getResources(), scaledBitmap));
    originalBitmap.recycle();
}

// 辅助方法：Drawable转Bitmap
private Bitmap drawableToBitmap(Drawable drawable) {
    if (drawable instanceof BitmapDrawable) {
        return ((BitmapDrawable) drawable).getBitmap();
    }
    Bitmap bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(), 
            drawable.getIntrinsicHeight(), Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(bitmap);
    drawable.setBounds(0, 0, canvas.getWidth(), canvas.getHeight());
    drawable.draw(canvas);
    return bitmap;
}

内容的提问来源于stack exchange，提问作者Hong