The sprite editor won't let me slice

thank you!

It worked for me thanks :)

While this might not be a solution for every cases, there are 2 things that must be always remembered with the Slice tool in the Sprite Editor.

1) The alpha/opacity value of 1 pixel in every slices minus 1 has to be higher than 0. This is a bit hard to explain, but when you're using the slice tool, you got to make sure there's a visible pixel (meaning its alpha/transparency value isn't 0) in each slices between each empty slices. This means that, when you're using the Slicing tool, you can't have 2 slices in either 2 rows or 2 columns next to each other that has no visible pixels. For example, if you try to slice an image that has a series of characters and end up with 1 row or 1 column with 2 following empty spaces, the slicing tool might skip the remaining of that row and/or column. A solution to this is to create a texture holder filled with 1 color, slice the picture in Unity and then open the picture and copy/paste (with pixel precision) the actual content you want. Once the Slices are done, there are no problem with empty spaces/tiles.

2) The Slices might be hard to see the Sprite Editor menu until you select them and they aren't visible in the Project folder in Unity until you apply the change in the Sprite Editor menu. If you only enter the slicing parameter, press "Slice" and nothing is happening, it might be because the color of the slices edge is white and it's really slim and hard to see. I usually switch the between Color mode and Alpha mode to check if the slice are alright. (The button right from the Apply button in the Sprite Editor menu). If you close the Sprite Editor after slicing without pressing the Apply, the change won't be saved. This might seem simple and stupid, but it's a possibility. A bit like changes on textures, if you don't hit "Apply" in the Sprite Editor menu, no change will occur.