Hey there, let's break down why your custom widget plugin works smoothly in Qt Designer but crashes your app right after compiling. Here are the most likely culprits and actionable fixes to try:

• Match Build Modes Explicitly
  Qt’s debug and release environments are strictly isolated—mixing them is a top cause of silent crashes. Double-check:

  • Your main app, custom plugin, and widget library are all built in the same mode (Debug/Release).
  • Debug versions of Qt libraries have a d suffix (e.g., Qt5Widgetsd.dll on Windows), so your plugin must link against these for Debug builds, and non-suffixed libraries for Release.
  • The plugin’s output file uses the correct mode suffix too (e.g., mycustomplugind.dll for Debug).

• Fix Plugin Deployment Paths
  Qt needs clear directions to find your plugin at runtime. Try these steps:

  • Place your plugin in the standard Qt widget plugin directory: <app-exe-folder>/plugins/widgets.
  • Alternatively, add the plugin’s directory to the library path early in your main() function:

    QCoreApplication::addLibraryPath(QCoreApplication::applicationDirPath() + "/plugins");
    

  • Confirm the plugin file exists in the expected path for your active build mode (Debug vs Release).

• Remove Designer-Specific Code
  Qt Designer provides a unique environment that your main app doesn’t have. Scan your plugin/widget code for:

  • Uses of QDesignerFormEditorInterface or other QtDesigner module classes outside the plugin’s Designer initialization logic—these will crash the main app.
  • Constructor logic that assumes it’s running inside Designer (e.g., loading resources only available in the Designer context).

• Debug the Exact Crash Site
  Since the app terminates immediately, use Debug mode to get precise context:

  • In Qt Creator, switch to the Debug build configuration and start debugging.
  • When the crash hits, check the call stack to pinpoint where it fails—this will tell you if it’s during plugin loading, widget instantiation, or static initialization.
  • Set a breakpoint at the start of main() and step through code until the crash occurs to narrow down the issue.

• Validate Dependencies
  Missing or mismatched dependencies often cause silent crashes. Use system tools to verify links:

  • Windows: Run dumpbin /dependents <plugin-path>.dll to list required libraries. Ensure all are present in the app’s directory or system PATH.
  • Linux: Use ldd <plugin-path>.so to check shared library dependencies.
  • macOS: Run otool -L <plugin-path>.dylib to verify linked frameworks.

内容的提问来源于stack exchange，提问作者Nicholas Johnson