哪种效率更高-先设置滤色器，然后设置位图，还是先设置位图，然后再设置滤色器？

Question

我正在动态放大许多图像视图，每个图像视图都有不同的滤色镜。

有时应用会变得笨拙，UI开始粘滞。我做了一些研究，现在我正在后台线程中加载位图。

但是，我的问题是，先将位图设置为图像视图，然后再设置滤色器会更有效，还是先设置颜色滤镜然后再设置位图？

Answer 1

tl：dr

首先设置颜色滤镜可为您节省一个applyColorMode和一个无效方法Call。当您没有设置colorMod且在这种情况下onDraw调用也不太昂贵时，“应用颜色模式”不会执行任何操作，因此实际上没有任何区别。

ImageView的Releavant源代码

如果您首先致电设置彩色滤光片，则会发生这种情况：

首先，图像视图调用setColorFilter（ColorFilter cf）

 public void setColorFilter(ColorFilter cf) {
        if (mColorFilter != cf) {
            mColorFilter = cf;
            mHasColorFilter = true;
            mColorMod = true;
            applyColorMod();
            invalidate();
        }
    }

这将应用ColorMod，然后使其无效

  private void applyColorMod() {
        // Only mutate and apply when modifications have occurred. This should
        // not reset the mColorMod flag, since these filters need to be
        // re-applied if the Drawable is changed.
        if (mDrawable != null && mColorMod) {
            mDrawable = mDrawable.mutate();
            if (mHasColorFilter) {
                mDrawable.setColorFilter(mColorFilter);
            }
            mDrawable.setXfermode(mXfermode);
            mDrawable.setAlpha(mAlpha * mViewAlphaScale >> 8);
        }
    }

现在您设置imageBitmap

@android.view.RemotableViewMethod
public void setImageBitmap(Bitmap bm) {
    // Hacky fix to force setImageDrawable to do a full setImageDrawable
    // instead of doing an object reference comparison
    mDrawable = null;
    if (mRecycleableBitmapDrawable == null) {
        mRecycleableBitmapDrawable = new BitmapDrawable(mContext.getResources(), bm);
    } else {
        mRecycleableBitmapDrawable.setBitmap(bm);
    }
    setImageDrawable(mRecycleableBitmapDrawable);
}

这将调用setImageDrawable

public void setImageDrawable(@Nullable Drawable drawable) {
    if (mDrawable != drawable) {
        mResource = 0;
        mUri = null;
        final int oldWidth = mDrawableWidth;
        final int oldHeight = mDrawableHeight;
        updateDrawable(drawable);
        if (oldWidth != mDrawableWidth || oldHeight != mDrawableHeight) {
            requestLayout();
        }
        invalidate();
    }
}

在无效之前调用updateDrawable：

  @UnsupportedAppUsage
    private void updateDrawable(Drawable d) {
        if (d != mRecycleableBitmapDrawable && mRecycleableBitmapDrawable != null) {
            mRecycleableBitmapDrawable.setBitmap(null);
        }
        boolean sameDrawable = false;
        if (mDrawable != null) {
            sameDrawable = mDrawable == d;
            mDrawable.setCallback(null);
            unscheduleDrawable(mDrawable);
            if (!sCompatDrawableVisibilityDispatch && !sameDrawable && isAttachedToWindow()) {
                mDrawable.setVisible(false, false);
            }
        }
        mDrawable = d;
        if (d != null) {
            d.setCallback(this);
            d.setLayoutDirection(getLayoutDirection());
            if (d.isStateful()) {
                d.setState(getDrawableState());
            }
            if (!sameDrawable || sCompatDrawableVisibilityDispatch) {
                final boolean visible = sCompatDrawableVisibilityDispatch
                        ? getVisibility() == VISIBLE
                        : isAttachedToWindow() && getWindowVisibility() == VISIBLE && isShown();
                d.setVisible(visible, true);
            }
            d.setLevel(mLevel);
            mDrawableWidth = d.getIntrinsicWidth();
            mDrawableHeight = d.getIntrinsicHeight();
            applyImageTint();
            applyColorMod();
            configureBounds();
        } else {
            mDrawableWidth = mDrawableHeight = -1;
        }
    }