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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<meta content="App Inventor for Android" name="description" />
<meta content="Android, Blocks App Inventor, Mobile, Phone, IDE" name="keywords" />
<title>
Basic Components - App Inventor for Android
</title>
<link href="/static/images/appinventor-16.png" rel="SHORTCUT ICON" type="image/ico" />
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<script src="http://www.google.com/js/gweb/analytics/autotrack.js">
</script>
<script>
var tracker = new gweb.analytics.AutoTrack({
profile: 'UA-5856106-2'
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</script>
<script language = "JavaScript" src="/static/scripts/HeaderAndFooter.js"></script>
<style>
img.c3 {border-width:0}
code.c2 {font-style: italic}
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</style>
</head>
<body>
<script language = "JavaScript">createHeader('<div id="navigation-breadcrumb"> <a href="/learn/">Learn</a> > <a href="/learn/reference/">Reference</a> > Basic > ');</script><br>
<div id="aiac">
<div class="main-container">
<div class="customhr customhr-gray">
</div>
<div class="content">
<div class="content-body">
<div class="learn-page">
<h1>
Basic Components
</h1>
<h2>
Table of Contents
</h2>
<ul>
<li>
<a href="#Button">
Button
</a>
</li>
<li>
<a href="#Canvas">
Canvas
</a>
</li>
<li>
<a href="#CheckBox">
CheckBox
</a>
</li>
<li>
<a href="#Clock">
Clock
</a>
</li>
<li>
<a href="#Image">
Image
</a>
</li>
<li>
<a href="#Label">
Label
</a>
</li>
<li>
<a href="#ListPicker">
ListPicker
</a>
</li>
<li>
<a href="#PasswordTextBox">
PasswordTextBox
</a>
</li>
<li>
<a href="#Screen">
Screen
</a>
</li>
<li>
<a href="#TextBox">
TextBox
</a>
</li>
<li>
<a href="#TinyDB">
TinyDB
</a>
</li>
</ul>
<h2 id="Button">
Button
</h2>
<img alt="" src="images/button.png" />
<p>
Buttons are components that users touch to perform some action in your app.
</p>
<p>
Buttons detect when users tap them. Many aspects of a button's appearance can be
changed. You can use the
<code>
Enabled
</code>
property to choose whether a button
can be tapped.
</p>
<h3>
Properties
</h3>
<dl>
<dt>
<code>
BackgroundColor
</code>
</dt>
<dd>
Color for button background.
</dd>
<dt>
<code>
Enabled
</code>
</dt>
<dd>
If set, user can tap button to cause action.
</dd>
<dt>
<code>
FontBold
</code>
</dt>
<dd>
If set, button text is displayed in bold.
</dd>
<dt>
<code>
FontItalic
</code>
</dt>
<dd>
If set, button text is displayed in italics.
</dd>
<dt>
<code>
FontSize
</code>
</dt>
<dd>
Point size for button text.
</dd>
<dt>
<code>
FontTypeface
</code>
</dt>
<dd>
Font family for button text.
</dd>
<dt>
<code>
Height
</code>
</dt>
<dd>
Button height (y-size).
</dd>
<dt>
<code>
Width
</code>
</dt>
<dd>
Button width (x-size).
</dd>
<dt>
<code>
Image
</code>
</dt>
<dd>
Image to display on button.
</dd>
<dt>
<code>
Text
</code>
</dt>
<dd>
Text to display on button.
</dd>
<dt>
<code>
TextAlignment
</code>
</dt>
<dd>
Left, center, or right.
</dd>
<dt>
<code>
TextColor
</code>
</dt>
<dd>
Color for button text.
</dd>
</dl>
<h3>
Events
</h3>
<dl>
<dt>
<code>
Click()
</code>
</dt>
<dd>
User tapped and released the button.
</dd>
<dt>
<code>
GotFocus()
</code>
</dt>
<dd>
Button became the focused component.
</dd>
<dt>
<code>
LostFocus()
</code>
</dt>
<dd>
Button stopped being the focused component.
</dd>
</dl>
<h2 id="Canvas">
Canvas
</h2>
<img alt="" src="images/canvas.png" />
<p>
A two-dimensional touch-sensitive rectangular panel on which drawing can be done
and sprites can be moved.
</p>
<p>
The
<code>
BackgroundColor
</code>
,
<code>
PaintColor
</code>
,
<code>
BackgroundImage
</code>
,
<code>
Width
</code>
, and
<code>
Height
</code>
of the
Canvas can be set in either the Designer or in the Blocks Editor. The
<code>
Width
</code>
and
<code>
Height
</code>
are measured in pixels and must be
positive.
</p>
<p>
Any location on the Canvas can be specified as a pair of (X, Y) values, where
</p>
<ul>
<li>
X is the number of pixels away from the left edge of the Canvas
</li>
<li>
Y is the number of pixels away from the top edge of the Canvas
</li>
</ul>
<p>
There are events to tell when and where a Canvas has been touched or a
<code>
Sprite
</code>
(
<code>
ImageSprite
</code>
or
<code>
Ball
</code>
) has been
dragged. There are also methods for drawing points, lines, and circles.
</p>
<h3>
Properties
</h3>
<dl>
<dt>
<code>
BackgroundColor
</code>
</dt>
<dd>
The color of the canvas background.
</dd>
<dt>
<code>
BackgroundImage
</code>
</dt>
<dd>
The name of a file containing the background image for the canvas
</dd>
<dt>
<code>
Height
</code>
</dt>
<dt>
<code>
LineWidth
</code>
</dt>
<dd>
The width of lines drawn on the canvas.
</dd>
<dt>
<code>
PaintColor
</code>
</dt>
<dd>
The color in which lines are drawn
</dd>
<dt>
<code>
Visible
</code>
</dt>
<dd>
Whether the component is visible
</dd>
<dt>
<code>
Width
</code>
</dt>
</dl>
<h3>
Events
</h3>
<dl>
<dt>
<code>
Dragged(number startX, number startY, number prevX, number prevY, number
currentX, number currentY, boolean draggedSprite)
</code>
</dt>
<dd>
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.
</dd>
<dt>
<code>
Flung(number startX, number startY, number xSpeed, number ySpeed)
</code>
</dt>
<dd>
When the user performs a fling (quick swipe) on the screen. Provides the (x, y)
position of the start of the fling, relative to the upper left of the
canvas. Also provides the x velocity and y velocity of the fling.
</dd>
<dt>
<code>
TouchDown(number x, number y)
</code>
</dt>
<dd>
When the user starts touching the canvas (putting finger down for the first time).
Provides the (x,y) position of the touch relative to the upper-left
corner of the canvas.
</dd>
<dt>
<code>
Touched(number x, number y, boolean touchedSprite)
</code>
</dt>
<dd>
When the user touches a canvas, providing the (x, y) position of the touch
relative to the upper left corner of the canvas. The value "touchedSprite" is
true if a sprite was also in this position.
</dd>
<dt>
<code>
TouchUp(number x, number y)
</code>
</dt>
<dd>
When the user stops touching the canvas (lifting his/her finger up). Provides
the (x, y) position of the touch relative to the upper left corner
of the canvas.
</dd>
</dl>
<h3>
Methods
</h3>
<dl>
<dt>
<code>
Clear()
</code>
</dt>
<dd>
Clears the canvas, without removing the background image, if one was provided.
</dd>
<dt>
<code>
DrawCircle(number x, number y, number r)
</code>
</dt>
<dd>
Draws a circle (filled in) at the given coordinates on the canvas, with the given
radius.
</dd>
<dt>
<code>
DrawLine(number x1, number y1, number x2, number y2)
</code>
</dt>
<dd>
Draws a line between the given coordinates on the canvas.
</dd>
<dt>
<code>
DrawPoint(number x, number y)
</code>
</dt>
<dd>
Draws a point at the given coordinates on the canvas.
</dd>
<dt>
<code>
Save()
</code>
</dt>
<dd>
Saves a picture of this Canvas to the device's external storage and returns the
full path name of the saved file. If an error occurs the Screen's
<code>
ErrorOccurred
</code>
event will be called.
</dd>
<dt>
<code>
SaveAs(text filename)
</code>
</dt>
<dd>
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). Returns the full path name of the saved
file.
</dd>
</dl>
<h2 id="CheckBox">
CheckBox
</h2>
<img alt="" src="images/checkbox.png" />
<p>
Check box components can detect user taps and can change their boolean state in
response.
</p>
<p>
A check box component raises an event when the user taps it. There are many
properties affecting its appearance that can be set in the Designer or Blocks
Editor.
</p>
<h3>
Properties
</h3>
<dl>
<dt>
<code>
BackgroundColor
</code>
</dt>
<dd>
Color for check box background.
</dd>
<dt>
<code>
Checked
</code>
</dt>
<dd>
True if the box is checked, false otherwise.
</dd>
<dt>
<code>
Enabled
</code>
</dt>
<dd>
If set, user can tap check box to cause action.
</dd>
<dt>
<code>
Height
</code>
</dt>
<dd>
Check box height (y-size).
</dd>
<dt>
<code>
Width
</code>
</dt>
<dd>
Check box width (x-size).
</dd>
<dt>
<code>
Text
</code>
</dt>
<dd>
Text to display on check box.
</dd>
<dt>
<code>
TextColor
</code>
</dt>
<dd>
Color for check box text.
</dd>
<dt>
<code>
Visible
</code>
</dt>
<dd>
If set, check box is visible.
</dd>
</dl>
<h3>
Events
</h3>
<dl>
<dt>
<code>
Click()
</code>
</dt>
<dd>
User tapped and released check box.
</dd>
<dt>
<code>
GotFocus()
</code>
</dt>
<dd>
Check box became the focused component.
</dd>
<dt>
<code>
LostFocus()
</code>
</dt>
<dd>
Check box stopped being the focused component.
</dd>
</dl>
<h2 id="Clock">
Clock
</h2>
<img alt="" src="images/clock.png" />
<p>
Use a clock component to create a timer that signals events at regular intervals.
The clock component also does various conversions and manipulations with time
units.
</p>
<p>
One use of the clock component is a a
<em>
timer
</em>
: set the timer interval, and
the timer will fire repeatedly at the interval, signalling a timer event.
</p>
<p>
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
<em>
instant
</em>
. The clock's
<code>
Now
</code>
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.
</p>
<h3>
Properties
</h3>
<dl>
<dt>
<code>
TimerInterval
</code>
</dt>
<dd>
timer interval in milliseconds
</dd>
<dt>
<code>
TimerEnabled
</code>
</dt>
<dd>
If true, then the timer will fire
</dd>
<dt>
<code>
TimerAlwaysFires
</code>
</dt>
<dd>
if true, the timer will fire even if the application is not showing on the screen
</dd>
</dl>
<h3>
Events
</h3>
<dl>
<dt>
<code>
Timer()
</code>
</dt>
<dd>
This event is signaled when the timer fires
</dd>
</dl>
<h3>
Methods
</h3>
<dl>
<dt>
<code>
SystemTime()
</code>
</dt>
<dd>
The phone's internal time in milliseconds
</dd>
<dt>
<code>
Now()
</code>
</dt>
<dd>
The instant in time read from phone's clock
</dd>
<dt>
<code>
MakeInstant(Text from)
</code>
</dt>
<dd>
Make an instant specified by MM/DD/YYYY hh:mm:ss or MM/DD/YYYY or hh:mm.
</dd>
<dt>
<code>
MakeInstantFromMillis(Number millis)
</code>
</dt>
<dd>
Make an instant specified by time in milliseconds
</dd>
<dt>
<code>
GetMillis(instant)
</code>
</dt>
<dd>
The instant in time measured as milliseconds since 1970
</dd>
<dt>
<code>
AddSeconds(instant, Number seconds)
</code>
</dt>
<dd>
An instant in time some number of seconds after the given instant
</dd>
<dt>
<code>
AddMinutes(instant, Number minutes)
</code>
</dt>
<dd>
An instant in time some number of minutes after the given instant
</dd>
<dt>
<code>
AddHours(instant, Number hours)
</code>
</dt>
<dd>
An instant in time some number of hours after the given instant
</dd>
<dt>
<code>
AddDays(instant, Number days)
</code>
</dt>
<dd>
An instant in time some number of days after the given instant
</dd>
<dt>
<code>
AddWeeks(instant, Number weeks)
</code>
</dt>
<dd>
An instant in time some number of weeks after the given instant
</dd>
<dt>
<code>
AddMonths(instant, Number months)
</code>
</dt>
<dd>
An instant in time some number of months after the given instant
</dd>
<dt>
<code>
AddYears(instant, Number years)
</code>
</dt>
<dd>
An instant in time some number of years after the given instant
</dd>
<dt>
<code>
Duration(Calendar start, Calendar end)
</code>
</dt>
<dd>
Milliseconds between instants
</dd>
<dt>
<code>
Second(Calendar instant)
</code>
</dt>
<dd>
The second of the minute
</dd>
<dt>
<code>
Minute(Calendar instant)
</code>
</dt>
<dd>
The minute of the hour
</dd>
<dt>
<code>
Hour(Calendar instant)
</code>
</dt>
<dd>
The hour of the day
</dd>
<dt>
<code>
DayOfMonth(Calendar instant)
</code>
</dt>
<dd>
The day of the month,a number from 1 to 31
</dd>
<dt>
<code>
Weekday(Calendar instant)
</code>
</dt>
<dd>
The day of the week. a number from 1 (Sunday) to 7 (Saturday)
</dd>
<dt>
<code>
WeekdayName(Calendar instant)
</code>
</dt>
<dd>
The name of the day of the week
</dd>
<dt>
<code>
Month(Calendar instant)
</code>
</dt>
<dd>
The month of the year, a number from 1 to 12)
</dd>
<dt>
<code>
MonthName(Calendar instant)
</code>
</dt>
<dd>
The name of the month
</dd>
<dt>
<code>
Year(Calendar instant)
</code>
</dt>
<dd>
The year
</dd>
<dt>
<code>
FormatDateTime(Calendar instant)
</code>
</dt>
<dd>
Text describing the date and time of an instant
</dd>
<dt>
<code>
FormatDate(Calendar instant)
</code>
</dt>
<dd>
Text describing the date of an instant
</dd>
<dt>
<code>
FormatTime(Calendar instant)
</code>
</dt>
<dd>
Text describing time time of an instant
</dd>
</dl>
<h2 id="Image">
Image
</h2>
<img alt="" src="images/image.png" width="100" />
<p>
You use image components to represent images that users select and manipulate.
</p>
<p>
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.
</p>
<h3>
Properties
</h3>
<dl>
<dt>
<code>
Picture
</code>
</dt>
<dd>
Picture displayed by this image.
</dd>
<dt>
<code>
Visible
</code>
</dt>
<dd>
If true, image is displayed.
</dd>
<dt>
<code>
Height
</code>
</dt>
<dd>
Image height (y-size).
</dd>
<dt>
<code>
Width
</code>
</dt>
<dd>
Image width (x-size).
</dd>
</dl>
<h2 id="Label">
Label
</h2>
<img alt="" src="images/label.png" />
<p>
Labels are components used to show text.
</p>
<p>
A label displays text which is specified by the
<code>
Text
</code>
property. Other
properties, all of which can be set in the Designer or Blocks Editor, control the
appearance and placement of the text.
</p>
<h3>
Properties
</h3>
<dl>
<dt>
<code>
BackgroundColor
</code>
</dt>
<dd>
Color for label background.
</dd>
<dt>
<code>
FontBold
</code>
</dt>
<dd>
If set, label text is displayed in bold.
</dd>
<dt>
<code>
FontItalic
</code>
</dt>
<dd>
If set, label text is displayed in italics.
</dd>
<dt>
<code>
FontSize
</code>
</dt>
<dd>
Point size for label text.
</dd>
<dt>
<code>
FontTypeface
</code>
</dt>
<dd>
Font family for label text.
</dd>
<dt>
<code>
Height
</code>
</dt>
<dd>
Label height (y-size).
</dd>
<dt>
<code>
Width
</code>
</dt>
<dd>
Label width (x-size).
</dd>