java - 从控制台获取输入后，FileDialog 不显示

Question

当我想在从控制台获得一些输入后打开文件对话框时，它失败了。请参阅下面的代码。当我第一次调用 openFileDialog 然后 chooseOption 时，它工作正常。有人知道这是怎么可能的吗？

public class SomeClass
{
int choice = 2;
Scanner keyboard;
String filter = "*.xml";

public void mainMenu() {
    keyboard = new Scanner(System.in);      
    choice = ChooseOption();    
    FileDialog loadDialog = openFileDialog("Choose file", filter);

    useInfo(loadDialog);
}

public int ChooseOption() {
    System.out.println("Make your choice: \n"
                        + "0) option A \n"
                        + "1) option B");

    try {
        choice = keyboard.nextInt();
    } catch(Exception e) {          
        System.out.println("Invalid input, try again.\n");
        ChooseOption();
    }
    return choice;
}

public FileDialog openFileDialog(String title, String filter) {
    System.out.println("Which file you want to use? \n");       

    FileDialog loadDialog = new FileDialog(new Frame(), title , FileDialog.LOAD);
    loadDialog.setFile(filter);
    //loadDialog.pack();
    loadDialog.setVisible(true);    

    return loadDialog;      
}

public void useInfo(FileDialog loadDialog) {
    if( loadDialog == null || loadDialog.getFile() == null ) {
        useDefaultFile();
        doSomthing();
    } else {
        doSomthingElse();
    }
}

}

Answer 1

FileDialog 显示为 frame，但它可能位于其他 Activity 窗口后面。