Social Icons

Basic

Basic Components

App Inventor Classic • App Inventor Classic • FOR APP INVENTOR 2 CLICK HERE• App Inventor Classic • App Inventor Classic

Table of Contents

Button

Buttons are components that users touch to perform some action in your app.

Buttons detect when users tap them. Many aspects of a button's appearance can be changed. You can use the Enabled property to choose whether a button can be tapped.

Properties

BackgroundColor
Color for button background.
Enabled
If set, user can tap button to cause action.
FontBold
If set, button text is displayed in bold.
FontItalic
If set, button text is displayed in italics.
FontSize
Point size for button text.
FontTypeface
Font family for button text.
Height
Button height (y-size).
Width
Button width (x-size).
Image
Image to display on button.
Shape (designer only)
Specifies the button's shape (default, rounded, rectangular, oval). The shape will not be visible if an Image is being displayed.
ShowFeedback
Specifies if a visual feedback should be shown for a button that has an image as background.
Text
Text to display on button.
TextAlignment
Left, center, or right.
TextColor
Color for button text.
Visible
Specifies whether the component should be visible on the screen. Value is true if the component is showing and false if hidden.

Events

Click()
Indicates a user has clicked on the button.
GotFocus()
Indicates the cursor moved over the button so it is now possible
to click it.
LongClick()
Indicates a user has long clicked on the button.
LostFocus()
Indicates the cursor moved away from the button so it is now no
longer possible to click it.

Methods

none

Canvas

A two-dimensional touch-sensitive rectangular panel on which drawing can be done and sprites can be moved.

The BackgroundColor , PaintColor , BackgroundImage , Width, and Height of the Canvas can be set in either the Designer or in the Blocks Editor. The Width and Height are measured in pixels and must be positive.

Any location on the Canvas can be specified as a pair of (X, Y) values, where

  • X is the number of pixels away from the left edge of the Canvas
  • Y is the number of pixels away from the top edge of the Canvas

There are events to tell when and where a Canvas has been touched or a Sprite ( ImageSprite or Ball ) has been dragged. There are also methods for drawing points, lines, and circles.

Properties

BackgroundColor
The color of the canvas background.
BackgroundImage
The name of a file containing the background image for the canvas
FontSize
The font size of text drawn on the canvas.
Height
LineWidth
The width of lines drawn on the canvas.
PaintColor
The color in which lines are drawn
TextAlignment (designer only)
Visible
Specifies whether the component should be visible on the screen. Value is true if the component is showing and false if hidden.
Width

Events

Dragged(number startX, number startY, number prevX, number prevY, number currentX, number currentY, boolean draggedSprite)
When the user does a drag from one point (prevX, prevY) to
another (x, y). The pair (startX, startY) indicates where the
user first touched the screen, and "draggedSprite" indicates whether a
sprite is being dragged.
Flung(number x, number y, number speed, number heading, number xvel, number yvel, boolean flungSprite)
When a fling gesture (quick swipe) is made on the canvas: provides
the (x,y) position of the start of the fling, relative to the upper
left of the canvas. Also provides the speed (pixels per millisecond) and heading
(0-360 degrees) of the fling, as well as the x velocity and y velocity
components of the fling's vector. The value "flungSprite" is true if a sprite
was located near the the starting point of the fling gesture.
TouchDown(number x, number y)
When the user begins touching the canvas (places finger on canvas and
leaves it there): provides the (x,y) position of the touch, relative
to the upper left of the canvas
TouchUp(number x, number y)
When the user stops touching the canvas (lifts finger after a
TouchDown event): provides the (x,y) position of the touch, relative
to the upper left of the canvas
Touched(number x, number y, boolean touchedSprite)
When the user touches the canvas and then immediately lifts finger: provides
the (x,y) position of the touch, relative to the upper left of the canvas. TouchedSprite
is true if the same touch also touched a sprite, and false otherwise.

Methods

Clear()
Clears anything drawn on this Canvas but not any background color or image.
DrawCircle(number x, number y, number r)
Draws a circle (filled in) at the given coordinates on the canvas, with the
given radius.
DrawLine(number x1, number y1, number x2, number y2)
Draws a line between the given coordinates on the canvas.
DrawPoint(number x, number y)
Draws a point at the given coordinates on the canvas.
DrawText(text text, number x, number y)
Draws the specified text relative to the specified coordinates using the values of the FontSize and TextAlignment properties.
DrawTextAtAngle(text text, number x, number y, number angle)
Draws the specified text starting at the specified coordinates at the specified angle using the values of the FontSize and TextAlignment properties.
number GetBackgroundPixelColor(number x, number y)
Gets the color of the specified point. This includes the background and any drawn points, lines, or circles but not sprites.
number GetPixelColor(number x, number y)
Gets the color of the specified point.
text Save()
Saves a picture of this Canvas to the device's external storage.
If an error occurs, the Screen's ErrorOccurred event will be called.
text SaveAs(text fileName)
Saves a picture of this Canvas to the device's external storage in the file
named fileName. fileName must end with one of ".jpg", ".jpeg", or ".png"
(which determines the file type: JPEG, or PNG).
SetBackgroundPixelColor(number x, number y, number color)
Sets the color of the specified point. This differs from DrawPoint by having an argument for color.

CheckBox

Check box components can detect user taps and can change their boolean state in response.

A check box component raises an even when the user taps it. There are many properties affecting its appearance that can be set in the Designer or Blocks Editor.

Properties

BackgroundColor
Color for check box background.
Checked
True if the box is checked, false otherwise.
Enabled
If set, user can tap check box to cause action.
FontBold (designer only)
FontItalic (designer only)
FontSize
FontTypeface (designer only)
Height
Check box height (y-size).
Text
Text to display on check box.
TextColor
Color for check box text.
Visible
If set, check box is visible.
Width
Check box width (x-size).

Events

Changed()
User tapped and released check box.
GotFocus()
Check box became the focused component.
LostFocus()
Check box stopped being the focused component.

Methods

none

Clock

Use a clock component to create a time that signals events at regular intervals. The clock component also dies various conversions and manipulations with time units.

One use of the clock component is a timer: set the time interval, and the timer will fire repeatedly at the interval, signalling a timer event.

A second use of the clock component is to manipulate time, and express time in various units. The internal time format used by the clock is called an instant. The clock's Now method returns the current time as an instant. The clock provides methods to manipulate instants, for example, return an instant that is several seconds, or months, or years from the given instant. It also provides methods to show the second, minute, hour, day, …, corresponding to a given instant.

Properties

TimerAlwaysFires
If true, the timer will fire even if the application is not showing on the screen
TimerEnabled
If true, then the timer will fire
TimerInterval
Timer interval in milliseconds

Events

Timer()
This event is signaled when the timer fired

Methods

InstantInTime AddDays(InstantInTime instant, number days)
An instant in time some days after the argument
InstantInTime AddHours(InstantInTime instant, number hours)
An instant in time some hours after the argument
InstantInTime AddMinutes(InstantInTime instant, number minutes)
An instant in time some minutes after the argument
InstantInTime AddMonths(InstantInTime instant, number months)
An instant in time some months after the argument
InstantInTime AddSeconds(InstantInTime instant, number seconds)
An instant in time some seconds after the argument
InstantInTime AddWeeks(InstantInTime instant, number weeks)
An instant in time some weeks after the argument
InstantInTime AddYears(InstantInTime instant, number years)
An instant in time some years after the argument
number DayOfMonth(InstantInTime instant)
The day of the month
number Duration(InstantInTime start, InstantInTime end)
Milliseconds between instants
text FormatDate(InstantInTime instant)
Text describing the date of an instant
text FormatDateTime(InstantInTime instant)
Text describing the date and time of an instant
text FormatTime(InstantInTime instant)
Text describing time time of an instant
number GetMillis(InstantInTime instant)
The instant in time measured as milliseconds since 1970.
number Hour(InstantInTime instant)
The hour of the day
InstantInTime MakeInstant(text from)
An instant specified by MM/DD/YYYY hh:mm:ss or MM/DD/YYYY or hh:mm
InstantInTime MakeInstantFromMillis(number millis)
An instant in time specified by the milliseconds since 1970.
number Minute(InstantInTime instant)
The minute of the hour
number Month(InstantInTime instant)
The month of the year, a number from 1 to 12)
text MonthName(InstantInTime instant)
The name of the month
InstantInTime Now()
The instant in time read from phone's clock
number Second(InstantInTime instant)
The second of the minute
number SystemTime()
The phone's internal time in milliseconds
number Weekday(InstantInTime instant)
The day of the week. a number from 1 (Sunday) to 7 (Saturday)
text WeekdayName(InstantInTime instant)
The name of the day of the week
number Year(InstantInTime instant)
The year

Image

You use image components to represent images that users select and manipulate.

An image component displays an image. You can specify the picture to display and other aspects of the image's appearance in the Designer or in the Blocks Editor.

Properties

Animation
Height
Image height (y-size).
Picture
Picture displayed by this image.
Visible
If true, image is displayed.
Width
Image width (x-size).

Events

none

Methods

none

Label

Labels are components used to show text.

A label displays text which is specified by the Text property. Other properties, all of which can be set in the Designer or Blocks Editor, control the appearance and placement of the text.

Events

none

Methods

none

ListPicker

Users tap a list picker component to select one item from a list of text strings.

When a user taps a list picker, it displays a list of text items for the user to choose from. The text items can be specified through the Designer or Blocks Editor by setting the ElementsFromString property to their comma-separated concatenation (for example, choice 1, choice 2, choice 3) or by setting the Elements property to a List in the Blocks Editor.

Other properties, including TextAlignment and BackgroundColor, affect the appearance of the button and whether it can be tapped (Enabled).

Properties

Selection
Selected list element.
Items
Comma-separated list of items to display in component.
ElementsFromString
(Description to come.)
BackgroundColor
Color for list picker background.
FontBold
If set, list picker text is displayed in bold.
FontItalic
If set, list picker text is displayed in italics.
FontSize
Point size for list picker text.
FontTypeface
Font family for list picker text.
Height
List picker height (y-size).
Width
List picker width (x-size).
Text
Title text to display on list picker.
TextAlignment
Left, center, or right.
TextColor
Color for list picker text.
Visible
If set, list picker is visible.

Events

AfterPicking()
User selected an item from the list picker.
BeforePicking()
User has tapped the list picker but hasn't yet selected an item.
GotFocus()
List picker became the focused component.
LostFocus()
List picker is no longer the focused component.

Methods

Open()
Opens the picker, as though the user clicked on it.

PasswordTextBox

Users enter passwords in a password text box component, which hides the text that has been typed in it.

A password text box is the same as the ordinary TextBox component, except that it does not display the characters typed by the user.

You can get or set the value of the text in the box with the Text property. If Text is blank, you can use the Hint property to provide the user with a suggestion of what to type. The Hint appears as faint text in the box.

Password text box components are usually used with a button component. The user taps the button after entering text.

Properties

BackgroundColor
Color for text box background.
Enabled
If set, user can enter a password in the box.
FontBold
If set, text is displayed in bold.
FontItalic
If set, text is displayed in italics.
FontSize
Point size for text.
FontTypeface
Font family for text.
Height
Box height (y-size).
Width
Box width (x-size).
Text
The text in the input box, which can be set by the programmer in the Designer or Blocks Editor, or it can be entered by the user (unless the Enabled property is false).
TextAlignment
Left, center, or right.
TextColor
Color for text.
Visible
Specifies whether the component should be visible on the screen. Value is true if the component is showing and false if hidden.
Hint
Password hint.

Events

GotFocus()
Box became the focused component.
LostFocus()
Box is no longer the focused component.

Methods

none

Screen

The screen does not appear in the palette like other components, but it comes automatically with the project. Each project starts with one screen, named Screen1. This name cannot be changed. More screens can be added.

Properties

AlignHorizontal
A number that encodes how contents of the screen are aligned horizontally. The choices are: 1 = left aligned, 2 = horizontally centered, 3 = right aligned.
AlignVertical
A number that encodes how the contents of the arrangement are aligned vertically. The choices are: 1 = aligned at the top, 2 = vertically centered, 3 = aligned at the bottom. Vertical alignment has no effect if the screen is scrollable.
BackgroundColor
Color for screen background.
BackgroundImage
An image that forms the screen's background.
Height
Screen height (y-size).
Icon
An image to be used as the icon for the installed application on the phone. This should be a PNG or a JPG image; 48x48 is a good size. Warning: Specifying images other than PNG or JPG, for example GIF or .ico files, may prevent App Inventor from being able to package the application.
ScreenOrientation
The requested screen orientation. Commonly used values are "unspecified", "landscape", "portrait", "sensor", and "user".
Scrollable
This is set by a checkbox in the designer. When checked, there will be a vertical scrollbar on the screen, and the height of the application can exceed the physical height of the device. When unchecked, the application height is constrained to the height of the device.
VersionCode (designer only - main screen only)
VersionName (designer only - main screen only)
Title
Title for the screen (text). This will appear at the upper left of the phone when the application runs. A natural choice for the title is the title of the App, but you could make it something else, or even change it while the app is running.
Width
Screen width (x-size).

Events

BackPressed()
Device back button pressed.
Initialize()
Signaled when the application starts. It can be used setting initial values and performing other setup operations.
ErrorOccurred(component component, text functionName, number errorNumber, text message)
Signaled when an error occurs. The ErrorOccurred event is currently used for a small set of errors including:
  • Errors that occur in the LEGO MINDSTORMS Nxt* components
  • Errors that occur in the Bluetooth components
  • Errors that occur in the Twitter component
  • Errors that occur in the SoundRecorder component
  • ActivityStarter - when StartActivity is called, but there is no activity that corresponds to the activity properties.
  • LocationSensor - when LatitudeFromAddress or LongitudeFromAddress fails
  • Player - when setting the Source property fails
  • Sound - when setting the Source property fails or when the Play function fails
  • VideoPlayer - when setting the Source property fails

For those errors, the system will show a notification by default, with an error number and a message. You can use this event handler to prescribe an error behavior different than the default, by testing errorNumber and taking the appropriate action.

OtherScreenClosed(text otherScreenName, any result)
Event raised when another screen has closed and control has returned to this screen.
ScreenOrientationChanged()
Screen orientation changed

Methods

CloseScreenAnimation(text animType)
Sets the animation for closing current screen and returning to the previous screen. Valid options are default, fade, zoom, slidehorizontal, slidevertical, and none
OpenScreenAnimation(text animType)
Sets the animation for switching to another screen. Valid options are default, fade, zoom, slidehorizontal, slidevertical, and none

Slider

A Slider is a progress bar that adds a draggable thumb. You can touch the thumb and drag left or right to set the slider thumb position. As the Slider thumb is dragged, it will trigger the PositionChanged event, reporting the position of the Slider thumb. The reported position of the Slider thumb can be used to dynamically update another component attribute, such as the font size of a TextBox or the radius of a Ball.

Properties

ColorLeft
The color of slider to the left of the thumb.
ColorRight
The color of slider to the left of the thumb.
MaxValue
Sets the maximum value of slider. Changing the maximum value also resets Thumbposition to be halfway between the minimum and the (new) maximum. If the new maximum is less than the current minimum, then minimum and maximum will both be set to this value. Setting MaxValue resets the thumb position to halfway between MinValue and MaxValue and signals the PositionChanged event.
MinValue
Sets the minimum value of slider. Changing the minimum value also resets Thumbposition to be halfway between the (new) minimum and the maximum. If the new minimum is greater than the current maximum, then minimum and maximum will both be set to this value. Setting MinValue resets the thumb position to halfway between MinValue and MaxValue and signals the PositionChanged event.
ThumbPosition
Sets the position of the slider thumb. If this value is greater than MaxValue, then it will be set to same value as MaxValue. If this value is less than MinValue, then it will be set to same value as MinValue.
Visible
Specifies whether the component should be visible on the screen. Value is true if the component is showing and false if hidden.
Width

Events

PositionChanged(number thumbPosition)
Indicates that position of the slider thumb has changed.

Methods

none

TextBox

Users enter text in a text box component.

The initial or user-entered text value in a text box component is in the Text property. If Text is blank, you can use the Hint property to provide the user with a suggestion of what to type. The Hint appears as faint text in the box.

The MultiLine property determines if the text can have more than one line. For a single line text box, the keyboard will close automatically when the user presses the Done key. To close the keyboard for multiline text boxes, the app should use the HideKeyboard method or rely on the user to press the Back key.

The NumbersOnly property restricts the keyboard to accept numeric input only.

Other properties affect the appearance of the text box (TextAlignment, BackgroundColor, etc.) and whether it can be used (Enabled).

Text boxes are usually used with the Button component, with the user clicking on the button when text entry is complete.

If the text entered by the user should not be displayed, use PasswordTextBox instead.

Properties

BackgroundColor
The background color of the input box. You can choose a color by name in the Designer or in the Blocks Editor. The default background color is 'default' (shaded 3-D look).
Enabled
Whether the user can enter text into this input box. By default, this is true.
FontBold(designer only)
Whether the font for the text should be bold. By default, it is not.
FontItalic(designer only)
Whether the text should appear in italics. By default, it does not.
FontSize
The font size for the text. By default, it is 14.0 points.
FontTypeface(designer only)
The font for the text. The value can be changed in the Designer.
Height
Hint
Text that should appear faintly in the input box to provide a hint as to what the user should enter. This can only be seen if the Text property is empty.
MultiLine
If true, then this text box accepts multiple lines of input, which are entered using the return key. For single line text boxes there is a Done key instead of a return key, and pressing Done hides the keyboard. The app should call the HideKeyboard method to hide the keyboard for a mutiline text box.
NumbersOnly
If true, then this text box accepts only numbers as keyboard input. Numbers can include a decimal point and an optional leading minus sign. This applies to keyboard input only. Even if NumbersOnly is true, you can use [set Text to] to enter any text at all.
Text
The text in the input box, which can be set by the programmer in the Designer or Blocks Editor, or it can be entered by the user (unless the Enabled property is false).
TextAlignment (designer only)
Whether the text should be left justified, centered, or right justified. By default, text is left justified.
TextColor
The color for the text. You can choose a color by name in the Designer or in the Blocks Editor. The default text color is black.
Visible
Whether the component is visible
Width

Events

GotFocus()
Event raised when this component is selected for input, such as by the user touching it.
LostFocus()
Event raised when this component is no longer selected for input, such as if the user touches a different text box.

Methods

HideKeyboard()
Hide the keyboard. Only multiline text boxes need this. Single line text boxes close the keyboard when the users presses the Done key.

TinyDB

Use a TinyDB component to store data that will be available each time the app runs.

TinyDB is a non-visible component.

Apps created with App Inventor are initialized each time they run. If an app sets the value of a variable and the user then quits the app, the value of that variable will not be remembered the next time the app is run. TinyDB is a persistent data store for the app, that is, the data stored there will be available each time the app is run. An example might be a game that saved the high score, and retrieved it each time the game is played.

Data items are stored under tags. To store a data item, you specify the tag it should be stored under. Subsequently, you can retrieve the data item that was stored under a given tag. If there is no value stored under a tag, then the value returned is the empty text. Consequently, to see if a tag has a value stored under it, test whether the return value is equal to the empty text (i.e., a text box with no text filled in).

There is only one data store per app. If you have multiple TinyDB components, they will use the same data store. To get the effect of separate stores, use different keys. Also each app has its own data store. You cannot use TinyDB to pass data between two different apps on the phone.

Tutorials

The Make Quiz tutorial on using TinyDB will demonstrate how to use this component. Also, there is a video screencast describing a simple NoteTaking app using TinyDB.

Properties

none

Events

none

Methods

StoreValue(text tag, valueToStore)
Store the value under the given tag. The tag must be a text string; the value can be a string or a list.
GetValue(text tag)
Gets the value that was stored under the given tag. If no value was stored, returns the empty text.
Note: To clear out the data base for an app, go on the phone under Settings → Applications → Manage Applications, the pick the app, and press "Clear Data".

The data in TinyDB is persistent only when you have packaged and downloading your app. If you are developing connected to the phone, and you restart the Appinventor application, or if you disconnect and reconnect the phone, then the data base will start fresh. This is a case where the application is not merely being stopped and restarted; it is being removed from the phone and then reloaded.