Espresso校验LinearLayout背景色报LayerDrawable无法转ColorDrawable错误求助

错误原因 #

• 直接强制将LayerDrawable转为ColorDrawable失败：你为LinearLayout设置的背景是多层叠加的LayerDrawable（通常由layer-list、selector类xml定义生成），不属于ColorDrawable类型，强转直接触发类型转换异常
• 参数类型不匹配：你调用自定义Matcher时传入的是R.drawable类型的Drawable资源ID，而Matcher中比对逻辑是判断颜色值，二者不匹配

修复方案 #

方案1：仅校验背景色（兼容LayerDrawable）

修改后的自定义Matcher如下，可自动适配ColorDrawable和LayerDrawable类型的背景：

public static Matcher<View> withBgColor(final int expectedColorRes) {
    Checks.checkNotNull(expectedColorRes);
    return new BoundedMatcher<View, LinearLayout>(LinearLayout.class) {
        @Override
        public boolean matchesSafely(LinearLayout row) {
            Drawable background = row.getBackground();
            int actualColor;
            if (background instanceof ColorDrawable) {
                actualColor = ((ColorDrawable) background).getColor();
            } else if (background instanceof LayerDrawable) {
                // 若目标色值在LayerDrawable的非第0层，可自行调整索引值
                Drawable targetLayer = ((LayerDrawable) background).getDrawable(0);
                if (!(targetLayer instanceof ColorDrawable)) {
                    return false;
                }
                actualColor = ((ColorDrawable) targetLayer).getColor();
            } else {
                return false;
            }
            int expectedColor = ContextCompat.getColor(row.getContext(), expectedColorRes);
            return expectedColor == actualColor;
        }
        @Override
        public void describeTo(Description description) {
            description.appendText("with background color: ");
            description.appendValue(expectedColorRes);
        }
    };
}

调用时需传入颜色资源ID（R.color.xxx）：

onView(ViewMatchers.withId(R.id.device_linearLayout))
    .check(ViewAssertions.matches(withBgColor(R.color.your_target_color)));

方案2：校验整个背景Drawable

如果你需要直接校验背景是否为指定的Drawable资源，可使用如下Matcher：

public static Matcher<View> withBackgroundDrawable(final int expectedDrawableRes) {
    Checks.checkNotNull(expectedDrawableRes);
    return new BoundedMatcher<View, LinearLayout>(LinearLayout.class) {
        @Override
        public boolean matchesSafely(LinearLayout row) {
            Drawable actualBg = row.getBackground();
            Drawable expectedBg = ContextCompat.getDrawable(row.getContext(), expectedDrawableRes);
            if (actualBg == null || expectedBg == null) return false;
            
            Bitmap actualBitmap = drawableToBitmap(actualBg);
            Bitmap expectedBitmap = drawableToBitmap(expectedBg);
            return actualBitmap.sameAs(expectedBitmap);
        }

        private Bitmap drawableToBitmap(Drawable drawable) {
            if (drawable instanceof BitmapDrawable) {
                return ((BitmapDrawable) drawable).getBitmap();
            }
            Bitmap bitmap = Bitmap.createBitmap(
                Math.max(drawable.getIntrinsicWidth(), 1),
                Math.max(drawable.getIntrinsicHeight(), 1),
                Bitmap.Config.ARGB_8888
            );
            Canvas canvas = new Canvas(bitmap);
            drawable.setBounds(0, 0, canvas.getWidth(), canvas.getHeight());
            drawable.draw(canvas);
            return bitmap;
        }

        @Override
        public void describeTo(Description description) {
            description.appendText("with background drawable: ");
            description.appendValue(expectedDrawableRes);
        }
    };
}

调用时直接传入你当前的Drawable资源ID即可：

onView(ViewMatchers.withId(R.id.device_linearLayout))
    .check(ViewAssertions.matches(withBackgroundDrawable(R.drawable.background_transparent_list)));

内容的提问来源于stack exchange，提问作者mehdi dehghani