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# 10 RETARGETING THROUGH PICK-AND-DROP

You now know quite a few ways of re-targeting a Development Window to a "development object" -- a class or a feature -- but haven't yet seen one of the most important: "Pick-and-Drop", which lets you pick a development object that you have spotted anywhere in the display, and retarget the current tool, or another, to it.

## Trying Pick-and-Drop

We restart from the last state, with a Development Window target to feature forth of class LIST . The next figure shows the whole window; it should be exactly what you see as a result of the last operations. We'll use the Ancestor versions view of the Feature Tab.

If for some reason the window doesn't look like the next figure, it's easy to reconstruct it: make sure both the Cluster tree and the Feature tree are visible (if not, click the corresponding buttons as detailed here); target the tool to class LIST ; target further to its feature forth by clicking that feature name in the Feature tree; make sure both the top-right Editing Tool and the bottom-right Context Tool are visible; in the Context Tool, select the Feature Tab and its Descendant versions format.

In the Context Tool near the bottom right, there is an entry that reads

    	ARRAYED_CIRCULAR forth

referring to the version of feature forth in class ARRAYED_CIRCULAR . Let's assume you want to see what that version actually is. It suffices to retarget the tool to it. Of course you could type or copy-paste the class name ARRAYED_CIRCULAR in the Class field at the top of the window, and the feature name forth in the adjacent Feature field. But this is too much work; after all, you have just seen a reference to the feature, through its name as it appears in the Descendant version format, so it's natural to use it directly from the graphical interface.

As we've seen before, you could control-right-click on the feature name at the place where it appears; this would create a new Development Window targeted to forth from ARRAYED_CIRCULAR . But you don't necessarily want a new window. Instead you can use Pick-and-Drop to retarget the current window.

Here is how it works. Position the cursor on the desired feature reference: the word forth in the line forth ARRAYED_CIRCULAR . Right-click, that is to say click the rightmost mouse button, and release the button immediately. That's right: you use a simple click, and do not maintain the button down.

Now move the mouse a trifle, without pressing any button :

The cursor has changed into a new shape, a cross representing the type of development object that you have picked, a feature. For a class, as you may have guessed, it would be a small ellipse ("bubble"). Each kind of development object that you may create and manipulate during your work with EiffelStudio has its distinctive icon.

The display reflects that you have " picked " the feature forth . Now you can drop it at any appropriate place to retarget the corresponding tool. In fact you can drop it right where it is, in the Context Tool of the current Development tool. To drop, just right-click again. (That is to say, as before, press the rightmost mouse button and release it immediately.) This achieves a "drop", and retargets the Development Window to the chosen feature, forth from ARRAYED_CIRCULAR . The retargeting affects both the Editing Tool and the Context Tool (assuming the Link Content View option is selected on the toolbar, see below "Isolating the context" for more information), which keeps its current view ( Descendant versions in the Feature Tab). We'll see shortly how to give them separate targets if that's preferred.

## How Pick-and-Drop works

The Pick-and-Drop mechanism is very simple. It consists of three steps:

- Pick step: find the development object you want to pick, right-click it, release the mouse button.
- Move step: move the mouse to the desired drop point, without pressing any button.
- Drop step: right-click (again releasing the button immediately) at the drop position.

During the Move step, you can at any time cancel the whole operation simply through a left-click.

The Move step is actually optional: if the current position is a valid drop target, as explained next, you can drop immediately after the pick without moving the mouse.

## Pebbles, holes, drop targets and type compatibility

The Pick-and-Drop mechanism relies on the metaphor of pebbles and holes. When you pick a development object, the cursor changes into a "pebble" whose shape represents the type of the development object: cluster, class, feature, run-time object ... You may then drop it into a "hole", which can be a window, a tree view entry, or a hole-shaped icon. This performs the appropriate action such as retargeting a tool.

In the same way that Eiffel is a typed object-oriented language, the Pick-and-Drop mechanism is typed: you can only drop a pebble into a compatible hole. For example you may drop a class pebble into a Development Window, to retarget it to the chosen class.

In Eiffel, type compatibility is not necessarily type identity, but is governed by conformance, based on inheritance and polymorphism: to an entity of type POLYGON , you may assign not only an expression of that same type, but also one of type RECTANGLE , if class RECTANGLE inherits from -- conforms to -- class POLYGON . Similarly, EiffelStudio considers that the development type "feature" conforms to "class"; this means you may drop a feature into a Development Window targeted to a class; this will retarget the tool to the feature's class and the feature itself, with the text of the class scrolled to the position of the feature.

In the Pick-and-Drop example -- for forth of ARRAYED_CIRCULAR -- you did not have to go to a new target: the current window was a valid drop target, so you just dropped right away. In such a case you don't even have to move the mouse; Pick-and-Drop is just a matter of two right-clicks.

This is similar to a double-click, a commonly used interaction technique, but without the stress of the usual double-click, which requires you to wait no more than a specified time -- typically half a second or so -- between the two clicks. With Pick-and-Drop the effect is the same whether the second click follows the first after one tenth of a second or two days.

## Multiple tools

In the previous example we pick-and-dropped a feature to its own tool. You can also pick-and-drop to a different tool.

Try this now. Bring up a new Development Window by choosing the menu entry File --> New window (unless you already have a second Development Window open, in which case you can simply reuse it). Make sure the two Development Window do not overlap too much, so that you can see enough of each. In the first Development Window, pick a class (right-click it). Move the mouse to the Editing Tool of the second Development Tool. Drop the class by right-clicking again. The tool retargets itself to the chosen class.

Many people like to take advantage of this possibility to keep two or more Development Windows open, and pick-and-drop frequently from one to the other when they see a development object of interest and want to know more about it, without losing its original context.

## Clickable formats

A good deal of the power of Pick-and-Drop comes from its connection with the various views of the Context Tool -- Class Views, Feature Views, Diagram View. As was mentioned when we saw these views, all the feature and class names or other graphical representations that appear in these views are clickable ; this means that you can select any of them as the source of a Pick-and-Drop.

As a result, you can quickly traverse a system and get to its essential properties by displaying the information of a class in any of the many available views -- the contract and flat contract of a class, its routines, its attributes, its clients, its ancestors, the ancestor and descendant versions of a feature, and so on -- then wherever you see a feature or class name follow the corresponding link. This proximity-based form of browsing, combined with the other techniques seen earlier, provides considerable help when you are dealing with a large, possibly complex system, and want to master its intricacies, be it for development, testing, debugging, maintenance or revision.

Other places where you can pick development objects include the class bubbles in a Diagram View, and the icons representing classes and features in the Cluster Tree, Feature Tree and Favorites list.

## Semantic consistency

An important property of the pick-and-drop mechanism, shared by its cousin the right-click mechanism, has already been mentioned in this chapter: semantic consistency, which guarantees that the operations you can perform on a class, such as pick-and-drop, only depend on the development object to which you are applying the operation. It doesn't matter where you picked the object -- in any development tool under any view -- and in what form: textual, as a class or feature name; graphical representation, as a class bubble in a Diagram View; or an icon, for example in the Cluster Tree, Feature Tree, Favorites list.

The pebble that you see during the Move step of Pick-and-Drop represents the underlying development object -- such as a class or a feature -- regardless of how you got to it.

## Behind the Pick-and-Drop conventions

Pick-and-Drop works differently from the usual Drag-and-Drop present on many computing platforms. The usual Drag-and-Drop retains a role within EiffelStudio (to move class bubbles around in the Diagram view) and you may of course have to use it for operating system functions such as copying files. But the key EiffelStudio operation is Pick-and-Drop. This technique is motivated by careful consideration of ergonomics and user comfort. In particular:

- Pick-and-Drop is much less stressful. Drag-and-Drop requires you to maintain pressure throughout the move, being careful not to drop on the wrong place. With Pick-and-Drop there is no stress: you click and release; get a drop from your coffee cup if you like (optional step); move the cursor with no pressure from your fingers or on your mind; make sure, at your leisure, to find the right drop place; and right-click again on it. At the end of the day, after many such operations, the stress reduction can make a real difference.
- With Drag-and-Drop, it's easy to lessen the pressure involuntarily and drop on the wrong place. The consequences can be damaging, especially since in such a case you may well not know where you dropped the element; after all, that wasn't intentional. It is possible, for example, to lose files that way. With Pick-and-Drop this is much less likely to happen.
- Pick-and-Drop makes it easy to cancel the operation if you change your mind: just left-click anywhere. With Drag-and-Drop you have to find an invalid place to drop; this may be difficult, or even impossible! (Sometimes pressing the Escape key works, but this is not universal.)

If you are new to EiffelStudio you may find Pick-and-Drop surprising at first. We trust you will join the ranks of EiffelStudio users who consistently rate it among the most convenient features of the environment.

## Isolating the context

In all the examples so far, the Context Tool was targeted to the same target as the enclosing Development Window and its Editing Tool. You can retarget the Context Tool separately, for example by pick-and-dropping a class or feature into it; but the next time you retarget the Development Window as a whole the Context Tool will follow.

This is called linked behavior, meaning that the target if the Context Tool is linked with the target of the enclosing Development Window and Editing Tool. By default the tools are not linked.

This enables you to see, in the same window, information on two different classes, and is called isolating, or unlinking the Context.

The choice between linked and isolated behavior is a matter of taste; let's see how you can change it, so that you can set your own preference.

To change the behavior, choose the menu entry

    View --> Link context tool

After this, the entry will change to View --> Unlink context tool , so that you can later revert to isolated behavior. Under isolation behavior, try pick-and-dropping a class or feature into the top Editing Tool; then pick-and-drop a class or feature into the bottom Context Tool. You will notice that each of these operations retargets the affected tool, but not the other.

## Customizing the view

If you will often alternate between the linked and isolated behaviors, you can use the Link/Isolate button of the top toolbar. This button is not present by default on the toolbar, so this is a good opportunity to take a quick look at the user interface customization mechanism, which you can use later to tailor the interface to the exact form you need. Select

    View --> Toolbars --> Customize standard toolbar

(The adjacent entry is toolbar project Customize which provides complementary capabilities under a similar form.) You see a list of available buttons:

The icons in the list on the right are currently displayed in the toolbar, but not those on the left. Among the latter you see (fourth from the bottom on the left-side list) Link or not the context tool to other components . Select it by clicking; this makes the -> Add button active. Click this button to move the Link/Isolate icon to the list of displayed icons. It becomes the first item of the list, which is fine for the moment. (Later on you can change the order of buttons in the toolbar if you like, by using the Up and Down buttons.) Click OK . The toolbar of your development tool has a new button which you can now use to switch, for the enclosing Development Window, between the isolated and linked behaviors of the Context Tool.

## Context memory

If you start repeatedly retargeting the Context Tool -- especially under "isolated" behavior -- you will notice the following properties:

- In most cases, pick-and-dropping a class to the Context switches the view to the Class Tab, and pick-and-dropping a feature switches to the Feature Tab.
- The view displayed in each case -- for example Ancestors for the Class Tab and Flat for the Feature Tab -- is default view for the corresponding Tab.

## The many paths to retargeting

As a conclusion to this review of Pick-and-Drop let's recapitulate the various ways we've seen for retargeting a whole Development Window or a tool to a class:

How to retarget | Same window/tool, or new? | Where described
Type class name, then Enter, in class field at top-left of tool | Same | "Retargeting by name" in Chapter 6, "Starting To Browse".
Choose class in Cluster tree | Same | "Retargeting from the Cluster Tree" in Chapter 6, "Starting To Browse".
Choose class in Favorites | Same | "Adding to Favorites" in Chapter 6, "Starting To Browse".
"Back" button | Same | "Moving back and forth" in Chapter 6, "Starting To Browse".
"Forth" button | Same | "Moving back and forth" in Chapter 6, "Starting To Browse".
Pick class from history list | Same | "The Target History" in Chapter 6, "Starting To Browse".
Pick-and-drop: right-click on class name or graphical representation found in any tool, then move, then right-click | Existing window/tool (of drop target) | "How Pick-and-Drop works" In Chapter 10, "Retargeting Through Pick-and-Drop.
Control-right-click on class name or graphical representation found in any tool | New | "Starting a new tool" in Chapter 6, "Starting To Browse".

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