运行Xamarin空白应用报错：请选择有效设备（VS 2015环境）

Hey there, I’m sorry you’ve been stuck on this frustrating issue for 5 days—since you’re working with a blank project, we can rule out custom code problems entirely, which narrows things down nicely. Let’s walk through some targeted fixes that might resolve this:

• Verify your Android Virtual Device (AVD) is actually functional
  Even if you’ve selected the Nexus One with Android 7.1 in the dropdown, the virtual device might not be properly configured or able to start. Open the Android Device Manager in VS2015, find your Nexus One AVD, and click the "Play" button to launch it manually. Wait for it to fully boot (this can take a minute or two) then try running your project again. If the AVD fails to start, delete it and create a new one with the same specs—sometimes AVD config files get corrupted unexpectedly.

• Double-check project-target SDK compatibility
  Ensure your project’s target Android version matches the AVD’s OS version. Right-click your Android project → Properties → Application tab. Confirm the "Compile using Android version (Target Framework)" is set to Android 7.1 (Nougat) or a version that’s compatible with your AVD. Mismatched versions can cause VS to reject the selected device even if it shows up in the dropdown.

• Reset ADB (Android Debug Bridge) service
  ADB can sometimes get stuck in a broken state that blocks device detection. Open a command prompt as Administrator, navigate to your Android SDK’s platform-tools folder (usually something like C:\Users\[YourUsername]\AppData\Local\Android\Sdk\platform-tools), and run these commands:

  adb kill-server
  adb start-server
  

  Close and re-open VS2015 after doing this, then try running your project again.

• Repair your Visual Studio 2015 installation
  Corrupted VS or Xamarin components are a common culprit with older VS versions like 2015. Open the Control Panel → Programs and Features, find Microsoft Visual Studio 2015, right-click it, and select Change. Choose the Repair option and let the process complete. This will fix any missing or damaged Xamarin-related files that might be causing the device recognition issue.

• Check Android SDK Build Tools installation
  Missing build tools can prevent VS from properly communicating with the AVD. Open the Android SDK Manager in VS2015, go to the SDK Tools tab, and make sure the build tools version corresponding to Android 7.1 is installed. Look for "Android SDK Build Tools 25.x.x" (since Android 7.1 uses SDK level 25) and check the box if it’s missing, then click Apply Changes to install.

If none of these steps work, since you’re open to TeamViewer assistance, you could also check for conflicts with other software (like antivirus blocking ADB processes) or verify your user account has full read/write permissions to the Android SDK and VS project folders. But let’s start with the steps above first—they’re the most likely fixes for this specific error.

内容的提问来源于stack exchange，提问作者Adnan Khan