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Selecting and Dragging Flash MX Movie Clips

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To use allow the user to interact with your Flash movies, you've got to make your movies act like real computer applications. In this lesson you will begin to learn user interface interaction by creating selectable and dragable movie clips.

See all Sams Teach Yourself on InformIT Design & Creative Media Tutorials.

This chapter is from the book

The most basic actions in most modern computer programs use object selection and dragging to help the user express what he wants to do. If all you do is move files around on your desktop, you are doing a lot of selecting and dragging.

It makes sense, then, to learn how to re-create this functionality in your Flash movies.

In this hour, you will:

  • Learn how to create selectable movie clips

  • See how to allow the user to drag movie clips around the screen

  • Use draggable movie clips to allow the user to make choices

  • Create a simple matching game

Selection

You have already learned how to make buttons that allow the user to click and make an action occur. A different type of user interface element, however, allows the user to select an item on the screen.

The difference is that a user clicks to make a selection, and that movie clip changes its appearance. But nothing else happens. This way, the user can make or change her selections. After that, the user can click another button or perform another action.

We'll use selections as the first step toward learning how to drag and drop movie clips, the goal of this hour.

Button Inside the Movie Clip Method

A movie clip cannot simply react to a mouse click. Unlike a button, it cannot use an on (release) or on (press) handler.

So you have to be tricky. You put a button inside a movie clip. The button can handle the mouse clicks as long as it is big enough to cover the entire movie clip.

The example 08buttoninmc.fla illustrates this. When you look at the movie, you will see that it has a single movie clip on the screen. Inside that movie clip is a single button.

To turn this into a selectable movie clip, we'll have to make this into a multiframe movie clip. The first frame contains the button named Off Button. This button has the following script:

on (release) {
  this.gotoAndStop(2);
}

By referring to this, the button is referencing the movie clip that it is in. Frame 2 of the movie clip contains a similar button named On Button. The difference is that the On Button is a little brighter, indicating that the movie clip has been selected. The script on this movie clip is similar:

on (release) {
  this.gotoAndStop(1);
}

As you might guess, by clicking the button on frame 2, the movie clip goes to frame 1, where the original Off Button is located. By clicking the buttons in the movie clip over and over again, the movie clip goes back and forth between frames 1 and 2.

The only thing left is to place a stop(); command on the first frame of the movie clip. You can go to the example movie 07buttoninmc.fla to try this out.

hitTest Method

You can detect a mouse click in a movie clip without a button. However, this method is a little trickier. After you learn it, though, it is a much cleaner solution.

To detect a mouse click on a movie clip without a button, use the onClipEvent(mouseDown) or onClipEvent(mouseUp) movie clip handlers. For instance, you can place the following script on a movie clip:

onClipEvent (mouseUp) {
  this.gotoAndStop(2);
}

The example movie 08twomcs1.fla contains two instances of the same movie clip with this same script applied to both. Two frames are in the movie clip, each with a different colored circle. A stop(); command is on the first frame of the movie clip.

When you try this movie, you will see right away why the onClipEvent(mouseUp) handler is different from the on(release) handler used on buttons. If you click on one movie clip, they both react.

This is because all movie clips get the mouseUp event sent to them. It is not exclusive to just the movie clip under the cursor.

Determining Which Movie Clip Was Clicked

There is a way to determine which movie clip has been clicked. The hitTest function tests a mouse location with a movie clip to see whether the location is inside the movie clip. So, by modifying the script, we can only send the correct movie clip to its second frame. You can see this one in example 08twomcs2.fla.

onClipEvent (mouseUp) {
  if (this.hitTest(_root._xmouse, _root._ymouse)) {
    this.gotoAndStop(2);
  }
}

The hitTest function can work a variety of different ways. In this case, it is fed the x and y values of the mouse location. It is prefaced with this so that it refers to the current movie clip. When the user clicks anywhere, the onClipEvent (mouseUp) handlers in all the movie clips get triggered. Then, both of the movie clips perform the hitTest test; only one that is under the mouse will test positive and jump to frame 2.

A Selection Script

To change this into a selection script, we have to allow the user to click the movie clip multiple times and change the state of the movie clip from off to on and back to off again.

The script has to determine which state the movie clip is currently in and then send the clip to the other frame. The script can determine the current state by looking at the current frame of the movie clip. This can be done with the aptly named _currentFrame property. This property reads 1 when the movie clip is on the first frame and 2 when it is on the second.

Here is the new script. You can see it in 08twomcs3.fla. This is a complex script because it first tests the location of the mouse and then tests the current frame of the movie clip.

onClipEvent (mouseUp) {
  if (this.hitTest(_root._xmouse, _root._ymouse)) {
    if (this._currentFrame == 1) {
      this.gotoAndStop(2);
    } else {
      this.gotoAndStop(1);
    }
  }
}

Now you have seen two completely different ways of making selectable movie clips. I like the second way better because you don't end up with the extra library symbols of the buttons. The advantage of using buttons, however, is that they can easily contain up, down, and over states, which are sometimes nice for user feedback as users make their choices.

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