根据类型生成表格元素，并带有覆盖

Question

With a few applications I'm building, I could use the ability to generate dynamic forms for filling in arbitrary lists of variables. For example, when running a Lua script that reads in an arbitrary file format, the script may need unique information to decode that format (eg separating character for a CSV). Essentially, I want something similar to Unity 's inspector.

I have a HashMap that maps a Class to a Handler :

private interface Handler {
    Control handle(GridPane grid, Integer row);
}

private static final HashMap<Class, Handler> FormInputs =
        new HashMap<Class, Handler>() {
    {
        // String
        put(String.class, (grid, row) -> CreateStringInput(grid, row));

        // Integer
        put(int.class, (grid, row) -> CreateIntegerInput(grid, row));
        put(Integer.class, (grid, row) -> CreateIntegerInput(grid, row));

        // Float
        put(float.class, (grid, row) -> CreateFloatInput(grid, row));

        // Directory
        put(Path.class, (grid, row) -> CreateFileInput(grid, row));
        put(File.class, (grid, row) -> CreateFileInput(grid, row));

    }
};

When the form is created, it uses getFields() to get the list of fields from the passed Class , and when the form is constructed, it creates a simple GridPane and fills it with labels and controls.

In theory, this should work fine, but I noticed with the Path class that the class does not always line up with its intended use. A Path may point to a file or a directory, which require different settings for the browsing dialog. Similarly, a String may be used for any number of things, and may need certain validation.

What would be the most friendly approach for overriding the type check and explicitly stating which form input to use? I looked into using Decorators, but those seem to be for extending existing functions of the decorated object, whereas I want to imbue them with extra information.

edit: For further context, I would like to be able to do things like Unity's [Range()] decorator, whereby numeric classes become represented by a slider between the min and max values.

edit 2: To clarify and simplify: The Form class generates an automatic form based on a class. For example, passing it the following class

public class TestClass {
    public boolean bool1;
    public Boolean bool2;
    public String string1;
    public String string2;
    public Integer int1;
    public int int2;
    public Path path1;
    public File file1;
}

results in the following form:

I want to be able to indicate, in the class, which fields should be handled differently. Ideally I also want this to work by passing in an array of mixed variables, and I want to be able to define a custom schema, like can be done with Unity and custom inspectors.

Answer 1

The best method I have come up with involves a bit of rearranging. It only works automatically for custom classes, but it allows for some customisation after initialisation.

First, write a public interface for custom classes to implement that allows them to define a custom list of controls:

public interface FormLayout {
    List<Input> getLayout();
}

Then, in the constructor, instead of initialising a list of fields, check if the object defines its own layout:

public Form (Object objRef) {
    Field[] fields = objRef.getClass().getFields();
    if(objRef instanceof Form.FormLayout) {
        inputs = ((FormLayout) objRef).getLayout();
    }
    else {
        inputs = new ArrayList<>();
        for (int i = 0; i < fields.length; i++) {
            inputs.add(new Input(fields[i].getName(), FormInputs.get(fields[i].getType())));
        }
    }
}

Now you have a list of defined inputs that can be manipulated before constructing the form, and the ability to define a custom layout for a class.

Further work will need to be done to handle associating an input with a field so the user input actually makes its way to the right variable, but this seems to be the most reasonable approach.