I'm creating a Java swing GUI and I have formatted a JPanel to use a GridLayout. I need to access a specific "box" (i.e. specific coordinate) of the grid, but I cannot see a way to do so.
How can I do this?
You shouldn't depend on GUI code (the View) to give you information about program data (the model). The best solution would be to "know" which component is where from the start--maybe you should have a data structure (2D array?) that holds the components and is updated whenever something's added to the grid.
If you want a quick and very-dirty fix, though, you could start playing games with JPanel.getComponentAt(). This requires pixel coordinates, though, so you'd need to do some reverse-engineering to figure out how much space a given grid square takes up. The space between grid squares is given by your GridLayout object. This is not recommended whatsoever though. I'm just including it in the interest of completeness (and since it's a more literal response to your question).
In GridLayout, "The container is divided into equal-sized rectangles." You can add an empty, transparent component in places you want to appear empty, e.g. new JLabel(""). See also GridBagLayout and Using Layout Managers.
Related
This is perhaps more of a whine than a question, and I'm aware there's a workaround to the problem described in this post. But I have a situation where I have to add components to a GridLayout, possibly enlarging the grid as I go; but the components don't get created and inserted in a nice neat order; and I don't know when I'm done being handed components to insert into the grid. In other words, in a 3x3 grid I might get handed a component to put at (0,2) and then another at (1,0) and then one at (0,0). And then I might get one at (5,2) and need to enlarge the grid. And then I might get told to replace the line at (0,0) with something else.
I understand that there's no way to say "put a component at x, y". I get that I'm going to have to build a 2D array to hold my components and then empty and refill the grid from the array, each time it changes, which is going to be quite often in several large grids, so I'd rather not. I get that life is like that and the language is the language and who am I to question why.
But I'm really curious. This seems like the most basic of operations for a grid to support. Not having it feels like I'm working with a spreadsheet that only lets you enter values in order from left to right - it's simple madness.
I haven't taken apart the source code for GridLayout, but any naive understanding of how it "must work" makes me think add(component, row, col) should be trivial to implement. It must not be, because GridLayout isn't exactly new and I can't believe I'm the first to think random access to a grid is a good idea. So it must be really hard. But why?
I realize understanding why the internals of GridLayout can't support this, doesn't solve any real problems, except the problem of me unable to stop thinking about how fundamentally weird the restriction is. In the end I'm going to end up with a parallel array, or messing with the more complex GridBagLayout, unless someone knows a better way. But I just want to know why I have to.
Why not approach the problem from a different angle:
Create your grid using GridLayout
Fill the grid with empty JPanels
JPanels that each uses a BorderLayout
Keep these JPanels where they are
But swap the JPanels that they display within them in each of their BorderLayout.CENTER positions
Alternatively, you could have them use a CardLayout, but the effect would be the same
I'm trying to re-purpose an existing Java AWT (stand alone) application to run on dedicated, single-purpose hardware (think a kiosk in a museum that also controls hardware behind the scenes) and my presumption that if I simply set the layout manager on my main panel to null I'd be able to lay out items using something like Rectangle(starting x, starting y, x-width, y-height) or perhaps another similar method to position things, has proven false! So, I'm more lost than I thought I would be!
Here are a few excerpts:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
[...]
public class myGUI extends JFrame
{
JPanel MainPanel = new JPanel();
JMenuBar Menu = new JMenuBar();
int MaxWidth = 1920;
int MaxHeight = 1080;
Dimension FullScreen = new Dimension(MaxHeight, MaxWidth);
Rectangle recHZbar = new Rectangle(0, 32, MaxWidth, 4);
[...]
MainPanel.setLayout(null);
MainPanel.setPreferredSize(FullScreen);
MainPanel.setEnabled(true);
MainPanel.setBackground(LightBlue);
There are all manner of components totaling around a hundred or so and it makes no sense to present them here. Suffice to say that I'm trying to eliminate what were stand-alone frames and instead present all the data around the edges of a very large screen and then manage the center space of the screen separately with key data, hopefully able to use visibility to switch what the user sees (instead of panes / panels), since in many cases there's a lot of commonality.
I thought that by setting the layout manager to null I would then be able to position components on MainPanel using something like this horizontal bar with a message embedded in it:
JLabel HorizontalBar = new JLabel();
HorizontalBar.setBackground(DarkBlue);
HorizontalBar.setFont(new java.awt.Font("Dialog", 0, 10));
HorizontalBar.setForeground(LightBlue);
HorizontalBar.setPreferredSize(dimMxW10pt);
HorizontalBar.setOpaque(true);
HorizontalBar.setHorizontalTextPosition(SwingConstants.CENTER);
HorizontalBar.setText(HZBarTxt);
HorizontalBar.setBounds(recHZbar);
MainPanel.add(HorizontalBar, null);
... And this, of course, works, BUT, when I tried to position this horizontal bar (via setBounds(rectangle)), it's apparent that the coordinates are based off of the bottom of the JMenuBar I added earlier, and NOT from the upper left corner of the screen! This has me rather concerned! (I presume the next bar will be based on the space below the first one, etc?!) Am I correct in thinking I've got a layout manager I didn't (explicitly) ask for? (If so, how do I avoid it?)
I'm hoping I'm overlooking something simple to be able to do positioning myself without having to go through too much work. If I can't just pick where I want things to be on the screen, I'm going to be in trouble on this project! I'm hoping to avoid lots of little panels and such. I need to create irregular columns and so forth. I know I can do the math to lay things out how I want, and I'm loathe to trust a layout manager to get it right, especially since the testing on the actual production hardware is very hard, and if the layout manager is different, it'll mean trouble. I may well be I'm overlooking the right layout manager - the "do it yourself layout manager", perhaps? - but I don't see how "GridLayout" is going to work for me, at least, not easily. So I'm hoping to learn how to do my own layout as simply and directly as possible (which is what I thought I was already doing).
TIA.
It turns out that my original assumption that the call to setLayout(null) hadn't worked was itself mistaken, and that's a good thing!
Given MY requirements, I made the exactly correct choice of NOT using a window manager at all. Yes, it can easily be seen from the comments to the question that many people think it's foolhearty or even stupid to NOT use a window manager, but in my case I made the EXACTLY right choice, and here's why:
THIS PROJECT'S circumstances are one of the rare cases for "doing it yourself", and, indeed, if I'd used a window manager it would NOT have worked out _AT_ALL!_ ...at least not in the time I had available.
A brief review of the use-case for this project
This was for dedicated hardware control and, indeed, it could not run in production in any place but a very singular installation of specialized hardware that the Java code is providing a user-interface for. Further, it won't have any internet connection, ever, and will never be upgraded. There's ZERO concern over either operating system or other software upgrade - it just cannot happen. As it has a singular fixed running environment, there's no concern over font-change handling or anything like that.
The Application Design; WHY A Layout Manager Would Screw It Up
I chose to use one frame, "undecorated" so that if fills the entire display, like this:
This fills a 1090 X 1920 display completely, so IDK how well it will go here.
I created a JFrame that serves as a backdrop for the whole thing. Within it, I first created a menu bar, followed by a heading / title bar, and for these things, a layout manager could have done a great job, of course, but that's the end of the easy part.
I created a right and left column of necessarily different widths and then a section at the bottom just by placing the items using item.setBounds(X, Y, W, H). I used variables for the values, and used them to create standard row & column positions, widths and heights. This provided for easy shifting from the standard in places that required it; I'd just use a different set of variables (using a naming convention I invented to keep it easy). I'd imagine that you COULD have used a layout manager for this part, but it would have been tedious and it's not at all clear it would have been any less work. In particular, how do you get the two vertical columns do be where you want them? You'd have to create separate inset panes / panels for each differently formatted region within each column - and even the bottom rows! You'd have to get them to stack or space just right, too. Then there are those vertical and horizontal bars - how'd you do that?
Vitally, I left room for an inset panel in the center, of which there are a VERY large number (!!) way more than are apparent from what you can see in the sample image. They're JPanels, only one of which is visible here, of course. And this is where a layout manager would completely fall on its face. Good UI design keeps things consistent and so users can know where to expect to find various things. And on the various panels, there are things that are common among some panels and different on others with DIFFERENT commonality, and there are yet more panels that cross with commonality between different sets of panes, yet few of the panels are really full enough that the common layout manager packing algorithms could handle; Various items are - and need to be - in what may appear to be non-standard positions for various reasons, so using a layout manager would have required filling up the panes with lots of sub-panels and such so that each of the various layout managers could do their jobs properly. By NOT using a layout manager, and thereby being free to just exactly specify the different positioning of the components when looking at different inset panes, I was able to VERY SIMPLY just use panel.add(item) syntax to move items between panes and keep the position exactly. Further, because of the same top position of the outer panel and the inner ones, getting rows exactly right was a cinch!
This was hands-down the easiest approach. I would have been fighting the damned layout manager all along the way. ...DO NOT BE AFRAID TO SKIP A LAYOUT MANAGER AND DO IT YOURSELF, just be prepared to do the whole job yourself. If you're up to that task, and if you have a fixed-use-case situation like I had, it's not so bad at all, and it might even be the only practical way for some tasks.
I've been looking around for a way to do this. I found some code to change the order of strings in a list, but i want to add buttons and such on each panel so that wouldn't work...
You may want to take a look at the docking frameworks. For example, Docking Frames has a good example of a chess board - basically, you can "dock" pieces on the chess board squares which server as the drop targets. Just launch the demonstration via the provided jnlp and then pick the Chess demonstration in the list on the left to see how it works. Here's a screenshoot of it:
You can see that each of the squares is a docking tile (i.e. a draggable object).
In your case, instead of 8x8 of squares, you can have Nx1 to simulate a one-column list instead of a table.
Use a JList. Look into the dragging behavior for the reordering ability.
See How to Use Lists for more details.
We're integrating Draw2D/GEF into an application, and are encountering an issue with the standard layouts provided.
We have a collection (say 100) of elements that need to be displayed in a grid-like fashion. We implemented our view using a GraphViewer, and applied a GridLayoutAlgorithm.
This works almost as we'd like it to, but the one stipulation we haven't been able to meet is that each node must be of a constant, defined size. Say, 50x50 pixels. The current GridLayoutAlgorithm we're using resizes the nodes so that they all fit in the window. If our window is small, the 100 elements become minuscule. We would instead like them to fill the width, then wrap to multiple rows, with a vertical scrollbar.
For the life of me, I can't find a simple, straightforward way to accomplish this.
Kind of a bummer answer, but I just ended up writing my own subclass of a GridLayoutAlgorithm and did a bunch of the math by hand. Frustrating that this wasn't included out-of-the-box, but it works fine.
How would I go about writing my own scrollbar using standard Java 2D.
I really don't want to use swing, and I've already made up my own component parts for everything else such as buttons etc.
I'm not really looking for code, rather the math involved in the event changes and the drawing.
Why on earth would you want to write your own java GUI toolkit? You already have the choice of Swing and SWT, can you really do better than these two teams?
If you've already written the rest of the toolkit, I don't understand why the scrollbar would stump you. Without knowing anything about your event system, or how your custom components are structured, it's impossible to give much advise. I don't see this being particularly maths intensive - just maintain the height of the scrollable component, and the view it's in, and the scrollbar size should match the proportion of the component that is visible. The position of the scrollbar should match which part of the component is visible (this will have to be scaled). Specifically, what do you want to know?
Java is now open. I'd go look at the source for the Swing and/or SWT as they are already implemented. The math seems fairly straight forward. You have a Bar and a Container. To simplify we will only discuss length (the dimension in which the scrollbar moves). The container is of a certain length. The bar is of a length that is equal to or less than the container. It is useful to define the center and the two endpoints of the scrollbar. You can have the scrollbar start at 0 at the top and 1 at the bottom or 0 at the top and 100 at the bottom with the important part being defining your scrollbar in the same manner. Then you can check the endpoints for collision with the edge to stop the bar from moving. If the mouse is held down with the cursor over the coordinates inside the bar, the bar starts caring about where the cursor is and will paint the scrollbar and whatever the scrollbar is ultimately supposed to be affecting. So, you would take the page to be affected and map it to 0 and 1 * the scale in pixels of the scrollbar. Then you get to worry about the arrows at either end and how big of a jump each click is and dealing with mousedown events etc.etc. Use what is given don't reinvent the wheel.
While not Java2D, this straightforward code snippet might help:
http://processing.org/learning/topics/scrollbar.html