问题

升级28后，FloatingActionButton显示异常，图片非常小

原因

SDK28，初始化逻辑：

 public FloatingActionButton(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        this.shadowPadding = new Rect();
        this.touchArea = new Rect();
        TypedArray a = ThemeEnforcement.obtainStyledAttributes(context, attrs, styleable.FloatingActionButton, defStyleAttr, style.Widget_Design_FloatingActionButton, new int[0]);
        this.backgroundTint = MaterialResources.getColorStateList(context, a, styleable.FloatingActionButton_backgroundTint);
        this.backgroundTintMode = ViewUtils.parseTintMode(a.getInt(styleable.FloatingActionButton_backgroundTintMode, -1), (Mode)null);
        this.rippleColor = MaterialResources.getColorStateList(context, a, styleable.FloatingActionButton_rippleColor);
        this.size = a.getInt(styleable.FloatingActionButton_fabSize, -1);
        this.customSize = a.getDimensionPixelSize(styleable.FloatingActionButton_fabCustomSize, 0);
        this.borderWidth = a.getDimensionPixelSize(styleable.FloatingActionButton_borderWidth, 0);
        float elevation = a.getDimension(styleable.FloatingActionButton_elevation, 0.0F);
        float hoveredFocusedTranslationZ = a.getDimension(styleable.FloatingActionButton_hoveredFocusedTranslationZ, 0.0F);
        float pressedTranslationZ = a.getDimension(styleable.FloatingActionButton_pressedTranslationZ, 0.0F);
        this.compatPadding = a.getBoolean(styleable.FloatingActionButton_useCompatPadding, false);
        this.maxImageSize = a.getDimensionPixelSize(styleable.FloatingActionButton_maxImageSize, 0);
        MotionSpec showMotionSpec = MotionSpec.createFromAttribute(context, a, styleable.FloatingActionButton_showMotionSpec);
        MotionSpec hideMotionSpec = MotionSpec.createFromAttribute(context, a, styleable.FloatingActionButton_hideMotionSpec);
        a.recycle();
        this.imageHelper = new AppCompatImageHelper(this);
        this.imageHelper.loadFromAttributes(attrs, defStyleAttr);
        this.expandableWidgetHelper = new ExpandableWidgetHelper(this);
        this.getImpl().setBackgroundDrawable(this.backgroundTint, this.backgroundTintMode, this.rippleColor, this.borderWidth);
        this.getImpl().setElevation(elevation);
        this.getImpl().setHoveredFocusedTranslationZ(hoveredFocusedTranslationZ);
        this.getImpl().setPressedTranslationZ(pressedTranslationZ);
        this.getImpl().setMaxImageSize(this.maxImageSize);
        this.getImpl().setShowMotionSpec(showMotionSpec);
        this.getImpl().setHideMotionSpec(hideMotionSpec);
        this.setScaleType(ScaleType.MATRIX);
    }

SDK26，初始化逻辑：

    public FloatingActionButton(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        ThemeUtils.checkAppCompatTheme(context);

        TypedArray a = context.obtainStyledAttributes(attrs,
                R.styleable.FloatingActionButton, defStyleAttr,
                R.style.Widget_Design_FloatingActionButton);
        mBackgroundTint = a.getColorStateList(R.styleable.FloatingActionButton_backgroundTint);
        mBackgroundTintMode = ViewUtils.parseTintMode(a.getInt(
                R.styleable.FloatingActionButton_backgroundTintMode, -1), null);
        mRippleColor = a.getColor(R.styleable.FloatingActionButton_rippleColor, 0);
        mSize = a.getInt(R.styleable.FloatingActionButton_fabSize, SIZE_AUTO);
        mBorderWidth = a.getDimensionPixelSize(R.styleable.FloatingActionButton_borderWidth, 0);
        final float elevation = a.getDimension(R.styleable.FloatingActionButton_elevation, 0f);
        final float pressedTranslationZ = a.getDimension(
                R.styleable.FloatingActionButton_pressedTranslationZ, 0f);
        mCompatPadding = a.getBoolean(R.styleable.FloatingActionButton_useCompatPadding, false);
        a.recycle();

        mImageHelper = new AppCompatImageHelper(this);
        mImageHelper.loadFromAttributes(attrs, defStyleAttr);

        mMaxImageSize = (int) getResources().getDimension(R.dimen.design_fab_image_size);

        getImpl().setBackgroundDrawable(mBackgroundTint, mBackgroundTintMode,
                mRippleColor, mBorderWidth);
        getImpl().setElevation(elevation);
        getImpl().setPressedTranslationZ(pressedTranslationZ);
    }

对比一下，就找到了出问题的地方，如下：

this.setScaleType(ScaleType.MATRIX);

解决

xml中设置scaleType已经失效，只能在代码中重置了。

原：

android:scaleType="center"

修改为：

fab.setScaleType(ImageView.ScaleType.CENTER);