macOS中WKWebView打开文件选择对话框(NSOpenPanel)

在WKWebView的UIDelegate事件中，调起文件选择对话框，并将选取的文件回调回去。

self.webView.UIDelegate = self;

- (void)webView:(WKWebView*)webView runOpenPanelWithParameters:(WKOpenPanelParameters*)parameters initiatedByFrame:(WKFrameInfo*)frame completionHandler:(nonnull void (^)(NSArray * _Nullable))completionHandler {
    NSOpenPanel* panel = [NSOpenPanel openPanel];
    panel.allowsMultipleSelection = parameters.allowsMultipleSelection;
    panel.canChooseDirectories = parameters.allowsDirectories;
    panel.allowedFileTypes = @[@"png", @"jpg", @"BMP", @"TIFF"];//图片类型
    NSModalResponse result = [panel runModal];
    if (result == NSModalResponseOK) {
        completionHandler([panel URLs]);
    }
    else {
        completionHandler(nil);
    }
}