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I described the basics of creating a bouncing ball animation earlier and mentioned that “image sprites” are similar to the bouncing ball graphic, but provide a way to specify your own image for the ball. To introduce a bit about images in App Inventor, we took a quick look at using the phone’s camera.
This tutorial starts with the original bouncing ball program and then modifies it to use an Image Sprite instead of a ball. Be sure to read the bouncing ball and camera tutorials first!
Previous:
The ImageSprite component is almost identical to the ball component!
Continue reading Using ImageSprites for animated App Inventor graphics
A frequent search topic on this blog is how to use lists. “Lists” are a way of storing a collection of data in App Inventor programs. Many other programming languages provide a number of methods for storing collections of data including arrays, records, even lists, and even something called “collections” (imagine that!)
App Inventor provides Lists, plus you can also use components like the TinyDB.
For a detailed description of using Lists, please refer to Chapter 8 – Introduction to Lists in my e-book “App Inventor 2: Tutorial”, available for $2.99 from Amazon. I hope to make this text available in additional e-reader formats during November.
In an earlier post, I mentioned that ImageSprites use images – and suggested I do a tutorial on images so here is a first look at using images in App Inventor 2.
For this tutorial, we create a very simple app that uses the camera to take a picture, or we can fetch a selected photo from the phone’s photo gallery. Either way, the image that is obtained is displayed on the screen.
First, create a simple user interface. To set this up, I used the VerticalArrangement layout and then added a button, an ImagePicker and an Image on to the Viewer:
The Image component is located in the User Interface section of the Palette, in the Designer.
The ImagePicker is located in the Media section of the Palette. Drag each to the Viewer window.
You also need to drag a Camera component to the Viewer; the Camera is also located in the Media section. Note that the Camera is an invisible component and will appear below your app’s user interface screen, as shown above.
After renaming the components, we should have a set of components like this:
For the Image1 component, the Properties look like:
Note that the text box field named Picture has the name of a .jpg image file entered into, in this example. Sorry for the ugly gibberish filename – I just grabbed a photo off of my own Flickr page, saved to my hard drive and then uploaded to App Inventor.
To upload a photo from your computer to the Image1 control, click on the Picture field – this displays a prompt:
The prompt shows the full name of the image I have already uploaded, and this file is already highlighted. Or, click on Upload File … at bottom to select and upload your own .jpg image file.
This uploaded .jpg becomes the default image initially displayed in the program. If you want, you could leave this blank but having something to show on screen makes the program a bit more interesting and helps the user to see where photos will be displayed.
The Blocks
Taking a photo is absurdly easy. When the button for taking a photo (btnTakePhoto) is clicked on (or rather, pressed with your finger), the Click event is raised – and all this event handled need do is call the camera’s TakePicture method:
Once the camera completes taking the picture, the AfterPicture event occurs. This is where we fetch the image (hover your mouse over the pink “image” within the AfterPicture block and select “get image”). Assign the image that was just taken (the get image) to the Picture property of the Image1 control. This copies the photo that was just taken, and displays it on screen.
We could stop here, but let’s take a look at grabbing a picture from the photo gallery on the phone. To implement this, we use ImagePicker. The ImagePicker is a control that displays the photo gallery, let’s you select an image from the photo gallery, and then returns that selected image to the app.
The ImagePicker displayed in the Designer is effectively a button that contains its own event handler for the Click event. Pressing the ImagePicker button on the main screen automatically enters the gallery where you select your photo. When the selection is complete, the ImagePicker’s AfterPicking event is raised and we add a tiny bit of code to process the image, merely copying the “Selection” property of the ImagePicker control (renamed here as impgSelectPhoto) to the Image control on screen to display the selected photo.
Running the App
When activating the camera, take a photo and wait a moment – you should see a “checkmark” at the bottom of the screen after the photo is processed. Tap the checkmark icon to signify you are done and you should be returned to the app and the photo you took should be displayed.
When selecting a photo from the gallery, wait for the gallery to appear, scroll through and select a photo. Tap the photo and wait for a moment – and control should return to the app and the selected photo will appear on the screen.
Note – if you have more than one photo gallery app registered on your phone (I have 3 such apps), Android will prompt you as to which of the gallery apps you wish to use.
There are additional features that are not shown here. For example, if your phone has a front facing and back facing camera, its possible to switch between the cameras.
SOURCE CODE
Source code is available in the MIT App Inventor Gallery –> here
This is for advanced software developers only: MIT App Inventor Sources. That’s the actual source code that makes App Inventor work behind the scenes – from the browser based editor to the server side support to the AI Companion. It’s all there.
MIT has made the source code for App Inventor publicly available. At a minimum, you need to be proficient in Java, Javascript, and have familiarity with various web techniques, such as JSON. Exploring this source code is not for the neophyte.
With access to the source code it is possible to host App Inventor on your own server and it is possible to develop your own App Inventor components (this also requires making a custom version of AI Companion).
Again, this is for advanced software developers.
App Inventor 2 provides easy to use features for creating games. These features have proven popular for introducing programming concepts to students in K-12, especially at the elementary and middle school level. While our focus is oriented towards practical applications rather than games, we can have a little fun too!
The purpose of the sample app in this blog post is to illustrate the basic programming concepts of a bouncing ball animation.
The “Game”
Well, its not much of a game! To keep the programming simple, all this does is enable a ball to bounce around on the screen, to change its heading or trajectory, and to make it travel faster or slower. When the ball hits the edge of the screen, it rebounds in an appropriate direction. Here’s the user interface as seen on the smart phone:
Press the Start button to make the ball start moving; press Stop to end the movement.
To change the speed of movement press the Faster or Slower buttons. Pretty easy?
To change the trajectory, you may enter a heading value in degrees, in the field next to the Set heading button, and then press the Set heading button.
Continue reading How to create a bouncing ball animation in App Inventor 2