如何在JNI方法中正确调用NSOpenPanel并在主线程运行？

我对Objective-C和JNI不熟悉，JNI类仅能部分执行，以下是我的尝试：

代码文件 #

Open.java（最小复现代码） #

这是大型Java Swing应用的最小复现代码，目的是替代难用的java.awt.FileDialog或功能有限的javax.swing.JFileChooser，实现更美观完善的打开文件对话框：

import java.awt.event.*;
import javax.swing.*;
public class Open extends JFrame {
   public Open () {
      getContentPane().add(new JButton(new AbstractAction() {
         public void actionPerformed (ActionEvent e) {
            try {
               NativeOpenFileDialog.run();
            } catch (Throwable ex) {
               System.err.println(ex.getMessage());
            }
         }
      }));
      pack();
      setVisible(true);
   }
   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() { new Open(); }
      });
   }
}

NativeOpenFileDialog.java（JNI桥接类） #

import javax.swing.*;

public class NativeOpenFileDialog {
   static {
       System.loadLibrary("natopndlg");
   };
   public static native void run ();
   public static void main (String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() { NativeOpenFileDialog.run(); }
      });

   }
}

NativeOpenFileDialog.m（Objective-C实现） #

#import <Cocoa/Cocoa.h>

#include <jni.h>
#include "NativeOpenFileDialog.h"

JNIEXPORT void JNICALL Java_NativeOpenFileDialog_run (JNIEnv *thisEnv, jclass jcls) {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSOpenPanel *panel = [NSOpenPanel openPanel];
    [panel setCanChooseFiles:YES];
    [panel setCanChooseDirectories:YES];
    [panel setAllowsMultipleSelection:YES];
    if ([panel runModal] != NSModalResponseOK)
        NSLog(@"User did not press OK");
    [pool release];
}

Makefile（Xcode 15.2环境） #

SDK = /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk

Open.class: Open.java NativeOpenFileDialog.java NativeOpenFileDialog.m
    javac -h . NativeOpenFileDialog.java
    javac Open.java
    gcc -dynamiclib -o libnatopndlg.dylib -framework Cocoa -isysroot $(SDK) -I $(JAVA_HOME)/include -I $(JAVA_HOME)/include/darwin -fobjc-exceptions -std=c99 NativeOpenFileDialog.m

执行步骤与异常 #

执行make编译后，运行命令：

java Open

点击按钮时抛出异常：

NSInternalInconsistencyException', reason: 'NSWindow should only be instantiated on the main thread!

问题分析与思路 #

这个异常是合理的，因为Cocoa的UI组件必须在主线程（UI线程）上创建。我认为需要确保NSOpenPanel在主线程打开，并且作为JFrame的子窗口，这至少需要实现一个Java函数来获取JFrame对应的NSWindow实例。

内容的提问来源于stack exchange，提问作者Jeff Holt