Android UI Development: Tips, Tricks, and Techniques

Android UI Development:
Tips, Tricks, and Techniques
Romain Guy
Chet Haase
Android UI Toolkit Team
Google

Android UI Development:
rrific Tips,Tricks, and Techniques
lly Te
Tota
Romain Guy
Chet Haase
Android UI Toolkit Team
Google

Trash Talk
or
Garbage Zero
Avoid creating garbage,
when necessary and possible

Statics as Temporaries
• Instead of a temporary object:
public boolean pointInArea(int x, int y, Area area) {
Point testPoint = new Point(x, y);
return area.intersect(testPoint);
}

• Consider a static instead:
static final Point tmpPoint = new Point();

public boolean pointInArea(int x, int y, Area area) {
tmpPoint.x = x;
tmpPoint.y = y;
return area.intersect(tmpPoint.yPoint);
}

5

AutoBoxing
• Autoboxing creates Objects

float x = 5;
Float y = x;
doSomething(x);

void doSomething(Float z) {}

is equivalent to
float x = 5;
Float y = new Float(x);
doSomething(new Float(x));

void doSomething(Float z) {}

6

De-Autoboxing
• Use primitive types whenever possible
–Avoids Object creation
• Use types you need for the situation
–Avoids autoboxing back and forth

7

Obliterator
• The enhanced for() loop is great
• ... but creates garbage
for (Node node : nodeList) {}

is equivalent to
Iterator iter = nodeList.iterator();
while (iter.hasNext()) {}

• Consider a size check first:
if (nodeList.size() > 0) {
for (Node node : nodeList) {}
}

8

Image is Everything
• Recycle those Bitmaps
–Device resources are limited
• Finalizers will clear them ... eventually
• You might think this would help
// done using this one, clear reference
myBitmap = null;

• But you really want to do this
// done using this one, recycle it
myBitmap.recycle();

• Don’t wait for the finalizer to do the work if you
need that memory now

9

Varargh
• Parameters to varargs method packaged into a
temporary array
void someMethod(float... args) {}

someMethod(5f);

is equivalent to
someMethod(new float[]{5});

10

Gener-ick
• T doesn’t stand for “primitive Type”
public class MyClass<T> {
T myVar;
MyClass<T>(T arg) {
myVar = arg;
}
}

• Generics only deal with Objects; primitive types
get autoboxed
float f;
MyClass<Float> myObject =
new MyClass<Float>(f);

which is equivalent to
MyClass<Float> myObject =
new MyClass<Float>(new Float(f));
11

Tools: Allocation Tracking
• Limit allocations to find problems
int prevLimt = -1;
try {
prevLimit =
Debug.setAllocationLimit(0);
// Do stuff
} finally {
Debug.setAllocationLimit(-1);
}

• Count the allocations being made
Debug.startAllocationCounting();
// do stuff
int allocCount = Debug.getThreadAllocCount();
Debug.stopAllocationCounting);

12

Tools: DDMS
• Visual tool helps track allocations down to the
object/file/line number
• (demo)

13

Watch the Garbage...
But Don’t Be Silly
• As Michael Abrash might have said:
ViewRoot
–“Premature optimization is the Root of all evil”

• Minor garbage is irrelevant in most cases
• But if you have GCs at critical points in your
application, consider Garbage Zero
–Example: animations

14

Tools: hat
• DDMS
• Heap Analysis Tool is used to track down
memory leaks
• adb shell dumpsys meminfo <process>

15

Memory leaks
• Be careful with Context
• Be careful with static fields
• Avoid non-static inner classes
• Use weak references

16

Responsiveness
• Single-threaded UI
• Don’t block the UI thread
– Also called main thread
• AsyncTask
– Worker thread and UI thread messaging
• Handler
– Messaging

18

Overinvalidating
• Only redraw what you must
• (demo)

19

Fewer is better
• Many views
– Slower layout
– Slower drawing
– Slower startup time
• Deep hierarchies
– Memory
– Slow...
– StackOverflowException

20

Layout optimizations
• Custom views
• Custom layouts
• <merge />
• ViewStub
• Compound drawables
• layoutopt

22

ViewStub

<ViewStub
android:id="@+id/stub_import"
android:inflatedId="@+id/panel_import"

android:layout="@layout/progress_overlay"

android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_gravity="bottom" />

25

ViewStub

findViewById(R.id.stub_import).setVisibility(View.VISIBLE);
// or
View importPanel = ((ViewStub)
findViewById(R.id.stub_import)).inflate();

26

<merge/>


<merge xmlns:android="http://schemas.android.com/apk/res/android">

</merge>

28

Compound drawables
<LinearLayout
android:orientation="horizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content">

<ImageView
android:layout_width="wrap_content"
android:src="@drawable/icon" />
<TextView
android:text="@string/hello" />

</LinearLayout>

29

Compound drawables

<TextView
android:text="@string/hello"
android:drawableLeft="@drawable/icon" />

30

ListView

1 public View getView(int position, View convertView, ViewGroup parent) {
2 View item = mInflater.inflate(R.layout.list_item_icon_text, null);

3 ((TextView) item.findViewById(R.id.text)).setText(DATA[position]);
4 ((ImageView) item.findViewById(R.id.icon)).setImageBitmap(
5 (position & 1) == 1 ? mIcon1 : mIcon2);

6 return item;
7 }

32

ListView

2 if (convertView == null) {
3 convertView = mInflater.inflate(R.layout.item, parent, false);
4 }

5 ((TextView) convertView.findViewById(R.id.text)).setText(DATA[position]);
6 ((ImageView) convertView.findViewById(R.id.icon)).setImageBitmap(
7 (position & 1) == 1 ? mIcon1 : mIcon2);

8 return convertView;
9 }

33

ListView

static class ViewHolder {
TextView text;
ImageView icon;
}

34

ListView
2 ViewHolder holder;
3
4 if (convertView == null) {
5 convertView = mInflater.inflate(R.layout.list_item_icon_text,
6 parent, false);
7 holder = new ViewHolder();
8 holder.text = (TextView) convertView.findViewById(R.id.text);
9 holder.icon = (ImageView) convertView.findViewById(R.id.icon);
10
11 convertView.setTag(holder);
12 } else {
13 holder = (ViewHolder) convertView.getTag();
14 }
15
16 holder.text.setText(DATA[position]);
17 holder.icon.setImageBitmap((position & 1) ==? mIcon1 : mIcon2);
18
19 return convertView;
20 }

35

ListView
60.0

50.0

40.0

30.0

20.0

10.0

0
Dumb Correct Fast
List of 10,000 items on NexusOne, Android 2.2
36

Graphics optimizations
• Pre-scale bitmaps
• Use compatible bitmaps
– ARGB_8888 to draw on 32 bits window
• Avoid blending
• Use View drawing caches
– View.setDrawingCacheEnabled(true)
• View.isOpaque()

37

For More Information
• Android developer site
–developer.android.com
• Romain
–@romainguy
–curious-creature.org
• Chet
–@chethaase
–graphics-geek.blogspot.com

38

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