Doodlz App Android How to Program ©1992-2013 by Pearson Education, Inc. All Rights Reserved

Doodlz AppAndroid How to Program

©1992-2013 by Pearson Education, Inc. All Rights

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Test Drive the Doodlz app©1992-2013 by Pearson Education, Inc. All Rights

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Technologies Overview• No Android 3.0+ features in this app, but we

specify in the manifest that we target 3.0SDK, so we get 3.0’s look-and-feel▫Holographic theme

• Use SensorManager to Listen for Accelerometer Events▫Detects movement of device▫User will shake device to erase drawing▫Other sensors: gravity, gyroscope, light, linear

acceleration, magnetic field, pressure, proximity, rotation vector and temperature

▫To listen for sensor events, you et a reference to system’s SensorManager service

▫Classes and interfaces for processing sensor events are in package android.hardware


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Technologies Overview•Create Custom Dialogs

▫AlertDialogs display only simple Strings and Buttons

▫Class Dialog displays custom GUIs (eg SeekBars)

•AtomicBoolean▫Sensor events are handled in separate

thread of excution from GUI events so possible shake event handler could try to

display confirmation dialog, when another dialog is on screen

▫AtomicBoolean manages a Boolean in a thread-safe manner, so it can be accessed by multiple threads


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Technologies Overview•Custom Colors

▫Specify alpha, red, green, blue components of colors using SeekBars in a Dialog

▫Class Color provides methods for assembling a color and for obtaining components values from a Color

•Drawing Lines and Paths▫Drawing on a bitmap here▫Associating a canvas with a bitmap, use

Canvas to draw on the Bitmap (which can be displayed and saved)


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Technologies Overview•Processing Touch events

▫Touch, Drag, or Lift with one or more fingers▫Information for each finger stored in Path

object Consists of line segments

▫Using View method onTouchEvent which receives a MotionEvent Need type of touch event and ID of finger

•Saving Drawing to device’s Gallery▫ContentResolver enables app to read and

store data▫Uses OutputStream


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Technologies Overview•Using Toasts to display a message for a

short time▫Used to display minor error messages or

informational messages briefly▫Used in this app to let user know image

was successfully saved to the gallery


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Building the App’s GUI and Resource Files•Ensure Build Target is Android 2.3.3•Min SDK Version: 8•In AndroidManifest.xml, set

android:targetSdkVersion attribute to “11”, which represents Android 3.0 SDK▫So will run on 2.3.3, but if device is a

Tablet, it will have the holographic theme seen on tablets

•Delete and replace main.xml▫Only component is custom View class,

DoodleView


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Added manually to main.xml


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Maximum value of SeekBar is 255


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LinearLayout has white background and contains a View to display the current drawing color.

The white enables the color to display accurately when the user makes the color semitransparent with alphaSeekBar.


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Displays sample line in current width and current color.

Building the AppTwo classes

•Doodlz (the Activity subclass)▫Provides the app’s menu, dialogs and

accelerometer event handling

•DoodleView (View subclass)▫Processes user’s touches and draws the

corresponding lines


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App’s Java program structure©1992-2013 by Pearson Education, Inc. All Rights

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onCreate

+enableAccer

onPause

+disableAccer

registerListener

onSensorChanged

+clear

Builder positive Button onClick

onCreateOptionsMenu

onOptionsItemSelected

showColorDialog showLineWidthDialog

+setDrawingColor+saveImage +getDrawingColor

colorSeekBar.onProgressChanged

setColorButtonListeneronClick

+getLineWidth +setLineWidth

App’s Java program structure©1992-2013 by Pearson Education, Inc. All Rights

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onCreate

onOptionsItemSelected

showLineWidthDialog

+clear +setDrawingColor+saveImage +getDrawingColor +getLineWidth +setLineWidth

widthSeekBar.onProgressChanged

setLineWidthListeneronClick

DoodleView – subclass of View©1992-2013 by Pearson Education, Inc. All Rights

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+clear

+setDrawingColor+saveImage

+getDrawingColor +getLineWidth

+setLineWidth

DoodleView onSizeChanged onDraw onTouchEvent

+touchStarted +touchEnded +touchMoved


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Note: Do NOT need redColorSeekBarChanged and blueColorSeekBarChanged, etc.


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Reserved.Paint is like a “paint brush” - it has a color, style, size, etc.


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DoodleView’s size not determined until it’s inflated and added to Doodlz activity’s View hiearchy; therefore cannot determine size of drawing Bitmap in onCreate.


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System automatically determines when the View’s onDraw method should be called.


Reserved.Not index of the finger, but the index at which finger’s information is located in this MotionEvent object.

Index of finger

New finger: first finger

New finger: others

Removed finger


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Draw lines


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Reserved.Contains touch info for multiple moves on screen if they occur at same time


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Some devices sensitive enough to generate MotionEvent even if user attempts to hold finger motionless

Adding geometric quadratic Bezier curve


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Saving Image

•Possible image won’t appear in Gallery until device scans for new media

•In AVD’s development tools, touch MediaScanner option, then the new image will appear in the Gallery


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Wrap up•Enabled a pre-Android 3.0 device to use

Android 3.0’s holographic user interface components

•Processed sensor events (accelerator) by register SensorEventListener with SensorManager service

•Displayed custom dialogs with complex GUIs•Used thread-safe AtomicBoolean to prevent

multiple dialogs from displaying•Created custom colors•Drew onto Bitmaps using Canvas objects•Saved Bitmap as an image to Gallery


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Wrap up•Stored information on each finger drag in

a Path object•Overrode onTouchEvent and used the

MotionEvent parameter to get type of touch event and ID of finger that generated it

•Got an OutputStream from a ContentResolver

•Used a Toast to display a brief message – be able to write code to do this on Quiz


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Documents

Doodlz App Android How to Program ©1992-2013 by Pearson Education, Inc. All Rights Reserved