Android Development

Front 1

How to instantiate an ImageView in Activity's onCreate() method using Linear Layout class? And set the imageView bounds to match the Drawable's dimention

Back 1

mLinearLayout = new LinearLayout(this);
ImageView i = new ImageView(this);
i.setImageResource(R.drawable.my_image);
i.setAdjustViewBounds(true);
i.setLayoutParams(new Gallery.LayoutParams(LayoutParams.WRAP_CONTENT,
LayoutParams.WRAP_CONTENT));

// Add the ImageView to the layout and set the layout as the content view
mLinearLayout.addView(i);

Front 2

What are the 2 ways to use a resource image?

Back 2

1) use ImageView.setImageResource(R.drawable.my_image)

2) handle image resource as a Drawable object-
Resources res = mContext.getResources();
Drawable myImage = res.getDrawable(R.drawable.my_image);

Front 3

If you plan on reading an image as a bit stream in order to convert it to a bitmap, where should you put your images?

Back 3

in the res/raw/ folder instead, where they will not be optimized.

Front 4

What will happen to Image resources placed in res/drawable/ ?

Back 4

aapt tool will automatically optimized it with lossless image compression during the build process.

Front 5

Write a TransitionDrawable xml for "image_expand.png" and "image_collapse.png"

Back 5

<transition xmlns:android="http://schemas.android.com/apk/res/android">
<item android:drawable="@drawable/image_expand">
<item android:drawable="@drawable/image_collapse">
</transition>

Front 6

How to nstantiate the TransitionDrawable and set it as the content of an ImageView:

Back 6

Resources res = mContext.getResources();
TransitionDrawable transition = (TransitionDrawable)
res.getDrawable(R.drawable.expand_collapse);
ImageView image = (ImageView) findViewById(R.id.toggle_image);
image.setImageDrawable(transition);

Front 7

How to start a transition (name "transition") can be run forward (for 1 second):

Back 7

transition.startTransition(1000);

Front 8

How can a client find the preferred size for some Drawables?

Back 8

the getIntrinsicHeight() and getIntrinsicWidth() methods.

Front 9

Can Drawable receive events or interact with the user?

Back 9

NO.
Unlike a View, a Drawable does not have any facility to receive events or otherwise interact with the user.

Front 10

How can an Animation Drawable know how to call back to it's client?

Back 10

setCallback(Drawable.Callback))

Front 11

What Interface you need to Implement if you want to create an animated drawable that extends Drawable.

Back 11

Drawable.Callback

Front 12

True of False ? If you set a background drawable for a View, then the View will draw it for you before calling back to its onDraw() method?

Back 12

True
Drawing is handled by walking the tree and rendering each view that intersects the invalid region. Because the tree is traversed in-order, this means that parents will draw before (i.e., behind) their children, with siblings drawn in the order they appear in the tree. If you set a background drawable for a View, then the View will draw it for you before calling back to its onDraw() method.

Front 13

Which region of view the framework will not draw?

Back 13

The framework will not draw views that are not in the "invalid region".

Front 14

How to make a view redraw itself?

Back 14

Call Invalidate().
Invalidate the whole view.

Front 15

What method will be called once a view is being invalidated if the view is visible?

Back 15

onDraw(android.graphics.Canvas).
It will be called at some point in the future.
This must be called from a UI thread.

Front 16

Can invalidate() be called from a non-UI thread?

Back 16

No.
This must be called from a UI thread.

Front 17

How to call invalidate from a non-UI thread?

Back 17

postInvalidate().
Cause an invalidate to happen on a subsequent cycle through the event loop. Use this to invalidate the View from a non-UI thread.

Front 18

How to align a button to the bottom of the parent container?

Back 18

android:layout_alignParentBottom="true"

Front 19

What property to use to tell user about the view that doesn't have a textural interface such as image button.

Back 19

android:contentDescription="@string/app_name"

Front 20

Define a style.xml "AppBaseTheme" that extends "android:Theme.Light".

Back 20

<resources>
<style name="AppBaseTheme" parent="android:Theme.Light">
</resources>

Front 21

Define a dimension object "activity_horizontal_margin" in dimens.xml that is 16dp.

Back 21

<resources>
<dimen name="activity_horizontal_margin">16dp</dimen>
</resources>

Front 22

What is an interpolator?

Back 22

An interpolator defines the rate of change of an animation.

This allows the basic animation effects (alpha, scale, translate, rotate) to be accelerated, decelerated, repeated, etc.

Front 23

What is interface does the AccelerateDecelerateInterpolator class inherites from?

Back 23

1) parent - interpolator Interface
2) grandparnet - timeInterpolator Interface

Front 24

How to use a non-default interpolator ?

Back 24

setInterpolator (TimeInterpolator value).

if value is null, it will be a linear interpolation.

Front 25

How to have valueAniamtor instance listens to every updates on every anitmation frame?

Back 25

valueAnimator.addUpdateListener(new AnimatorUpdateListener(){
@Override
public void onAnimationUpdate(ValueAnimator animation) { imageView.setBackgroundColor((Integer) animation.getAnimatedValue());
}
})

Front 26

Explain what can an implementor of the interface "ValueAnimator.AnimatorUpdateListener" do?

Back 26

Implementors of this interface can add themselves as update listeners to an ValueAnimator instance to receive callbacks on every animation frame, after the current frame's values have been calculated for that ValueAnimator.

Front 27

How to get the updated value from the valueAnimator in the onAnimatorUpdate callback on every frame : onAnimationUpdate(ValueAnimator animation)?

Back 27

animation.getAnimatedValue()

Front 28

What interface must be implemented by all classes that wish to support cloning?

Back 28

Clonable

Front 29

What is a field?

Back 29

Simple explanation: A field is an attribute.

Say, you have a class called Student. Think of all the characteristics of this student. Name, Date of Birth, School Name, Student Id etc. Each of this attribute will be a "field" in the class definition. That is the answer for your question.
Additional information: Almost always define fields as private (unless there is a real good reason) and provide accessors (or simply put methods) to set the value or retrieve the value eg: getStudentId() or setStudentId(int newStudentId)

Front 30

What does it mean when we use :
new Interface() means?

Back 30

You can not instantiate the interface, but you can instantiate an implementation of it. It's an anonymous implementation.

you are creating a brand new class that is an anonymous inner class and which inherit (implements) the interface.

It is called an anonymous inner class because it not has a name of its own and it can therefore not be instantiated explicitly without going through the method testMethod() and it can only be referenced through an reference variable with the type Interface.

Front 31

How to animate color object?

Back 31

ValueAnimator anim = ValueAnimator.ofObject(new ArgbEvaluator(), RED, BLUE);

// Definition.
public static ValueAnimator ofObject(TypeEvaluator evaluator, Object... values) {

Front 32

What does a TypeEvaluator do for the targets in an animation.

Back 32

A TypeEvaluator that will be called on each animation frame to
* provide the ncessry interpolation between the Object values to derive the animated
* value.

Front 33

How to assign top padding using a property value >

Back 33

android:paddingTop="@dimen/activity_vertical_margin"

Front 34

Which are the two types animations an animation resource can define?

Back 34

1) Property Animation :
Creates an animation by modifying an object's property values over a set period of time with an Animator.

2) View Animation:
a) Tween animation: Creates an animation by performing a series of transformations on a single image with an "Animation".

b) Frame animation: creates an animation by showing a sequence of images in order with an AnimationDrawable.

Front 35

What is an Animator object?

Back 35

This is the superclass for classes which provide basic support for animations which can be
1) started,
2) ended,
3) and have AnimatorListeners added to them.

Front 36

What are the different value types in ValueAnimator's value type property?

Back 36

android:valueType =
1) intType
2) floatType

The animation framework automatically handles color values.

Front 37

What is the required attributes in <objectAnimator>?

Back 37

1) android:propertyName = "alpha" or "backgroundColor"

2) valueTo:
float, int, or color. Required. The value where the animated property ends. Colors are represented as six digit hexadecimal numbers (for example, #333333).

Front 38

How to set the target object to animate using the object animator whos' property is defined in the android:propertyName inside the objectAnimator tag in the the animation xml"?

Back 38

1) Inflate your animation xml resource by calling loadAnimator()

2) then, call setTarget() to set the target object that contains this property.

Front 39

What is the xml syntax for an AnimatorSet ?

Back 39

<set
android:ordering=["together" | "sequentially"]>

Front 40

What is an animator's file location?

Back 40

res/animator/property_animator.xml:
The filename will be used as the resource ID.

Front 41

What is an animator's resource reference in JAVA?

Back 41

R.animator.property_animator

Front 42

What is an animator's resource reference in XML?

Back 42

@[package:]animator/property_animator

Front 43

What does this mean : android:valueTo="1f" ?

Back 43

toFind

Front 44

What is the Animation class?

Back 44

Abstraction for an Animation that can be applied to Views, Surfaces, or other objects.

Front 45

Android provides two mechanisms that you can use to create simple animations. What are they?

Back 45

1) tweened animation : in which you tell Android to perform a series of simple transformations (position, size, rotation, and so on) to the content of a View;

2) and frame-by-frame animation: which loads a series of Drawable resources one after the other.

Front 46

What can a tweened animation perform on?

Back 46

to the content of a View.

Front 47

How does android perform in the frame-by-frame animation?

Back 47

it loads a series of Drawable resources one after another.

Front 48

Who handles a tweened animation?

Back 48

the package (android.view.animation);

Front 49

Who handles a frame-by-frame animation?

Back 49

AnimationDrawable class

Front 50

What are the steps in adding a fragment to an activity?

Back 50

1) Get reference to the Fragment Manager
2) Begin a fragment transaction
3) Add the fragment
4) Commit the fragment Transaction.

Front 51

How to make sure that the fragments won't get destroyed on configuration changed?

Back 51

Use setRetainInstance(true)

Front 52

Which lifecycle callbacks won't get called on fragment?

Back 52

1) onDestroy()
2) onCreate()

Front 53

How to make sure the old fragment will be saved when returning?

Back 53

addToBackStack(null)

Front 54

How to inflate a layout from a View?

Back 54

view.getLayoutInflator()

Front 55

How to inflate a layout using service?

Back 55

getSystemService(LayoutInflator)

Front 56

Which method must be called to tell the Drawable where it is drawn and how large it should be?

Back 56

setBounds(Rect)

Front 57

How can a client find the preferred size for some Drawables ?

Back 57

getIntrinsicHeight() and getIntrinsicWidth() methods

Front 58

How to know Drawables information about how to frame content that is placed inside of them.

Back 58

getPadding(Rect)

Front 59

Which method allows the client to tell the Drawable in which state it is to be drawn, such as "focused", "selected"?

Back 59

setState(int[])
Some drawables may modify their imagery based on the selected state.

Front 60

Which method allows the client to supply a single continuous controller that can modify the Drawable is displayed, such as a battery level or progress level?

Back 60

setLevel(int)

Front 61

How can a Drawable call back to its client to perform animations ?

Back 61

Call Drawable.Callback interface.

Front 62

Which interface the client should support so that animations will work.

Back 62

via setCallback(Drawable.Callback)

Front 63

What are the simple way to do setCallback(Drawable.Callback) through the system facilities?

Back 63

setBackgroundDrawable(Drawable) and ImageView.

Front 64

What is a ShapeDrawable?

Back 64

A Drawable object that draws primitive shapes. A ShapeDrawable takes a Shape object and manages its presence on the screen. If no Shape is given, then the ShapeDrawable will default to a RectShape.

Front 65

What is a ClipDrawable?

Back 65

A Drawable that clips another Drawable based on this Drawable's current level value. You can control how much the child Drawable gets clipped in width and height based on the level, as well as a gravity to control where it is placed in its overall container. Most often used to implement things like progress bars, by increasing the drawable's level with setLevel().

Front 66

How to hide a child Drawable with ClipDrawable?

Back 66

setLevel(0)

Front 67

How to 100% show a child Drawable with ClipDrawable?

Back 67

setLevel(10000)

Front 68

How to use progress or volume level to very a ClipDrawable's imagery?

Back 68

1) use setLevel(int level)
.

Front 69

If the new level you are supplying in setLevel() causes the appearance of the Drawable to change, then it is responsible for calling which method in order to have itself redrawn?

Back 69

invalidateSelf()

Front 70

What does it mean when the return value from the setLevel() is true ?

Back 70

This change in level has caused the appearance of the Drawable to change (hence requiring an invalidate), otherwise returns false.

Front 71

What is one way we can set the state of the Drawable in a Button?

Back 71

setState ( [state_focused, state_pressed])

Front 72

How to force a Drawable to behave as if it has just become visible.

Back 72

setVisible(bVisible, bRestart=true)

Front 73

How to have the Drawable unscheduled using the current Drawable.Callback?

Back 73

unscheduleSelf (Runnable what)
what The runnable that you no longer want called.

Front 74

How can a Drawable schedule the next frame of it's animation?

Back 74

Drawable.Callback().scheduleDrawable (Drawable who, Runnable what, long when).

An implementation can generally simply call
"postAtTime(Runnable, Object, long)" with the parameters (what, who, when) to perform the scheduling.

Front 75

What is wrong with this code:
public abstract boolean isChanged() {
return smt else...
}

Back 75

abstract methods cannot have a body.

Front 76

How can a Drawable unschedule an action previously scheduled with scheduleDrawable(Drawable, Runnable, long).

Back 76

An implementation can generally simply call removeCallbacks(Runnable, Object) with the parameters (what, who) to unschedule the drawable.

Front 77

Which method is called when the drawable needs to be redrawn?

Back 77

invalidateDrawable (Drawable who)

A view at this point should invalidate itself (or at least the part of itself where the drawable appears).

Front 78

Which type of Drawable manages an array of other Drawables.

Back 78

LayerDrawable

These are drawn in array order, so the element with the largest index will be drawn on top.

Front 79

What are the xml tags used to represent LayerDrawable?

Back 79

<layer-list>
<item/>
<item/>
</layer-list>

Front 80

Which Drawable is used to cross-fade between the first and second layer?

Back 80

TransitionDrawable

Front 81

How to tell TransitionDrawable to start the transition?

Back 81

call startTransition(int).

Front 82

How to tell TransitionDrawable to display just the first layer,

Back 82

call resetTransition().

Front 83

Which type of Drawable lets you assign a number of graphic images to a single Drawable and swap out the visible item by a string ID value?

Back 83

StateListDrawable

Front 84

What are the xml tags used to represent StateListDrawable?

Back 84

<selector>
<item/>
<item/>
</selector>

Front 85

What type of Drawable manages a number of alternate Drawables, each assigned a maximum numerical value. Setting the level value of the object with setLevel(int) will load the image with the next greater or equal value assigned to its max attribute?

Back 85

LevelListDrawable

Front 86

What are the xml tags used to represent LevelListDrawable?

Back 86

<level-list>
<item android:maxLevel="0" android:drawable="@drawable/ic_wifi_signal_1" />

<item/>
</level-list>

Front 87

Where should a <level-list> drawable be saved so that a ImageView can reference it as a drawable?

Back 87

res/drawable/ folder

Front 88

A <level-list> drawable xml was saved in res/drawable/ folder and is ready to be referenced by an ImageView. How will the imageView change it's default image to one of the other levels?

Back 88

Use setImageLevel(int).

Front 89

What type of Drawable which can be used to create frame-by-frame animations, defined by a series of Drawable objects, which can be used as a View object's background.

Back 89

AnimationDrawable

Front 90

What is the simpliest way to create a frame-by-frame animation?

Back 90

1) define the animation in an XML file,
2) placed in the res/drawable/ folder,
3) and set it as the background to a View object.
4) Then, call start() on the AnimationDrawable to run the animation.

Front 91

What are the xml tags used to represent AnimationDrawable?

Back 91

<animation-list>
<item android:drawable="@drawable/wheel0" android:duration="50" />
<item android:drawable="@drawable/wheel1" android:duration="50" />

</animation-list>

Front 92

How to set a background animation on an ImageView?

Back 92

img.setBackgroundResource(R.drawable.spin_animation);

Front 93

How to start a background animation?

Back 93

// Get the background, which has been compiled to an AnimationDrawable object.
AnimationDrawable frameAnimation = (AnimationDrawable) img.getBackground();
// Start the animation (looped playback by default).
frameAnimation.start();