Visual Studio 2019: iOS Simulator stays blank

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Today, I wanted to continue one of my current app projects, when I was suddenly hampered by a strange behavior of my iOS simulator. Usually I’m used to clicking „Start Debugging“, and everything works like a charm. But today all that I got was a blank iOS simulator Window:

As I said above, I’m usually used to it working like a charm, so it was surely strange.

At first, I was thinking about any changes that I might have made to any of the two systems, since the last time it worked (which was just about 12 hours before). I came to the conclusion, that neither on my Windows PC, nor on my Mac there were any recent changes (no Updates, no system changes, nothing).

Next, I did the obvious: Restarted the Mac, restarted my PC, checked for Updates, all the usual things. But still: The iOS simulator was broken.

At this moment I need to admit, that my knowledge about native iOS development under macOS it pretty much zero, so I didn’t have much of a clue about what to do on the macOS side.

Investigating the problem

Even without knowing things under macOS too well, I came up with a very basic, fundamental question: “Does the simulator run, if I directly run it on the Mac?”

This led me to another, also very fundamental question:

“Where can I run the simulators under macOS?”

Luckily that wasn’t too hard to find out. I just fired up Xcode and found the solution quickly:

  1. I opened Xcode
  2. In the top menu, I selected “Xcode -> Open Developer Tool -> Simulator”
  3. Shortly after that, I was presented with an iPhone shaped iOS simulator. But surprise: It was also blank!
  1. I switched to a different simulator (e.g. File -> Open Device -> iOS 13.5 -> iPhone 8). The iPhone 8 is one of my usual simulators used in Visual Studio, so I wanted to try that out. But still: Just a blank window… =/
  2. I starred at the two dark simulators, while thinking about what to do next. But then, suddenly, after 2-3 minutes: The apple icon appeared inside the emulator windows. A few seconds later, I was presented with the colorful iOS UI.
The Simulator staying dark even under macOS.
The Simulator staying dark even under macOS.

  1. And it got even better: The simulator windows in my Visual Studio also immediately came back to live. My problem was miraculously fixed. Phew….
The iOS Simulator suddenly came to life!
The iOS Simulator suddenly came to life!

I was happy that the problem could be fixed so easily, although I was wondering how it came into being in the first place. It was also strange that before, not even a reboot of both, the Mac and my PC, could fix it. The problem never recurred since then.

Summary

The solution was quite easy in the end: Switch to the Mac, open up Xcode, run a Simulator from there and wait 2-3 minutes.

This experience was a little strange, and quite esoteric to solve. I hope by documenting this I can help someone who may stumble over the same problem in the future.

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