Building a gesture driven interface with draggable elements.
- Mobile Architecture Basics: Model View Presenter
- Touch-Draggable Views
- Beginner Level Java
- Android: Views and Layouts
- Android: Basic Layout XML design
- Proposal
- Model View Presenter Architecture
- Touch Draggable Views
- Hold and Change Button redesign
- Selectable Dice
- Change and Hold Buttons
In part 2, I mentioned that scrolling through a dice list is not so user friendly. So to make the interface feel more natural, I will change the dice roll area from a ListView into a graphical Layout modeling a physical dice board where the player can place the dice anywhere on the board.
- Refactor into MVP
- Swap in new DiceRollLayout
- Draggable Dice
- Custom ImageView : DiceView
- Capturing Touch Event Handling
- Hold and Change buttons
- Selectable/Unselect Dice
- Hold Button
- Change Button
All I'm doing in this tutorial is replacing the area occupied by the @+id/dice_list ListView element with a graphical dice board layout. Ideally, I wouldn't have to touch any code unrelated to rendering dice. But as it stands, I'd need to delete the DiceAdapter, add/remove Layout components, and rewrite the MainActivity class.
Instead of jumping into the code and rewriting MainActivity, I'm first going to reorganize my code and add some structure. This first task falls into the broad category of Software Architecture. A common approach to architecting mobile apps is Model-View-Presenter.
- Model
- Encapsulates Domain specific non-UI Logic, Data Sources
- In this case, the model layer object consists of the list of dice and logic around dice such as roll, add, and remove.
- View
- Encapsulates UI, visual elements (Views, Layouts and Buttons) and user interactions(Activity)
- For many apps, most of the code base falls into this category. Any Android specific UI components such Views, Layouts, and Activities fall into this category.
- Presenter
- Coordinates UI changes and Model changes.
- This is where the tire meets the road. The Presenter translates the UI events into model changes and translates model changes into UI events.
Image By Google - http://www.gwtproject.org/articles/testing_methodologies_using_gwt.html, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=34271902
I create a MainView interface to encapsulate UI updates and implement it with MainActivity. The intent for this is to avoid references to Android UI elements from the Presenter layer.
public interface MainView {
void updateDiceCount(int totalDice, int blankDice, int magDice, int starDice);
void rollDice(int diceIndex);
void refreshAdapter();
}
The Presenter layer is responsible for coordinating UI changes with Model changes. In this case, the model is only a list of dice so I will not have a formal interface separating Presenter and Model layers.
public class MainPresenter {
private static final int MAX_DICE_COUNT = 25;
List<Dice> diceList = new ArrayList<>();
private MainView mainView;
private int countDice(Dice.Face type) {
int count =0;
for(Dice dice : diceList) {
if(dice.diceVal == type) {
count++;
}
}
return count;
}
public void setView(MainView mainView) {
this.mainView = mainView;
}
public void addButtonClicked() {
if(diceList.size()<MAX_DICE_COUNT) {
diceList.add(new Dice());
mainView.refreshAdapter();
mainView.updateDiceCount(diceList.size(), countDice(Dice.Face.BLANK), countDice(Dice.Face.MAGNIFY), countDice(Dice.Face.STAR));
}
}
public void removeButtonClicked() {
if(!diceList.isEmpty()) {
diceList.remove(diceList.size() - 1);
mainView.refreshAdapter();
mainView.updateDiceCount(diceList.size(), countDice(Dice.Face.BLANK), countDice(Dice.Face.MAGNIFY), countDice(Dice.Face.STAR));
}
}
public void rollButtonClicked() {
for(int index=0;index<diceList.size();index++) {
Dice dice = diceList.get(index);
if(!dice.hold) {
dice.roll();
mainView.rollDice(index);
}
}
mainView.refreshAdapter();
}
public void changeButtonClicked(int diceIndex) {
Dice dice = diceList.get(diceIndex);
dice.nextValue();
mainView.refreshAdapter();
mainView.updateDiceCount(diceList.size(), countDice(Dice.Face.BLANK), countDice(Dice.Face.MAGNIFY), countDice(Dice.Face.STAR));
}
public void holdButtonClick(int diceIndex) {
Dice dice = diceList.get(diceIndex);
dice.toggleHold();
mainView.refreshAdapter();
mainView.updateDiceCount(diceList.size(), countDice(Dice.Face.BLANK), countDice(Dice.Face.MAGNIFY), countDice(Dice.Face.STAR));
}
public List<Dice> getDiceList() {
return diceList;
}
}
public class MainActivity extends AppCompatActivity implements MainView {
...
MainPresenter presenter;
...
@Override
protected void onCreate(Bundle savedInstanceState) {
...
//Presenter
presenter = new MainPresenter();
presenter.setView(this);
...
}
@Override
public void rollDice(int diceIndex) {
//roll all dice that are not being held
View diceRowView = listView.getChildAt(diceIndex);
if (diceRowView != null) {
ImageView diceView = diceRowView.findViewById(R.id.dice_icon);
int rotation = randomRotation();
int duration = randomDuration();
RotateAnimation rotate = new RotateAnimation(
0, rotation,
Animation.RELATIVE_TO_SELF, CENTER,
Animation.RELATIVE_TO_SELF, CENTER
);
rotate.setFillAfter(true);
rotate.setFillEnabled(true);
rotate.setDuration(duration);
rotate.setInterpolator(new DecelerateInterpolator());
diceView.startAnimation(rotate);
}
}
@Override
public void refreshAdapter() {
this.diceAdapter.notifyDataSetChanged();
}
@Override
public void updateDiceCount(int totalDice, int blankDice, int magDice, int starDice) {
totalCount.setText(Integer.toString(totalDice));
blankCount.setText(Integer.toString(blankDice));
magCount.setText(Integer.toString(magDice));
starCount.setText(Integer.toString(starDice));
}
public void onClickAddButton(View view) {
presenter.addButtonClicked();
}
public void onClickRemoveButton(View view) {
presenter.removeButtonClicked();
}
public void onClickRollButton(View view) {
presenter.rollButtonClicked();
}
}
An organized codebase is easier to maintain then a disorganized one. I would liken this to organizing one's living space. Functionally, there may be difference between organized code and disorganized code in terms of what the app does, much like a disorganized space is still livable. But when problems arise or when one wants to change something, fixing an organized codebase is much easier. So to answer the question, if you anticipate changes in the future, organizing code is a good idea.
There are multiple architecting paradigms available to follow including MVVM or MVC. At the end of the day, these are tools that the industry has a whole have adopted to make engineering life easier. If you'd like to propose your own organization, that's perfectly reasonable!
First, I'll swap in my new design. This includes replacing the listview with my custom layout and adding 2 buttons. One for change and one for hold dice.
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<farsight.solutions.tutorial.diceroller.DiceRollLayout
android:id="@+id/dice_canvas"
android:layout_height="0dp"
android:layout_width="0dp"
app:layout_constraintBottom_toTopOf="@id/dice_summary"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent">
</farsight.solutions.tutorial.diceroller.DiceRollLayout>
<Button
android:id="@+id/hold_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hold"
android:onClick="onClickHoldButton"
app:layout_constraintBottom_toBottomOf="@id/dice_canvas"
app:layout_constraintHorizontal_bias="0.945"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.949" />
<Button
android:id="@+id/change_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Change"
android:onClick="onClickChangeButton"
app:layout_constraintBottom_toBottomOf="@id/dice_canvas"
app:layout_constraintHorizontal_bias="0.945"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.799" />
<LinearLayout
android:id="@+id/dice_summary"
android:layout_width="match_parent"
android:layout_height="@dimen/control_bar_line_height"
android:orientation="horizontal"
android:weightSum="4"
app:layout_constraintBottom_toTopOf="@id/button_bar"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="@id/dice_canvas">
<LinearLayout
android:layout_height="match_parent"
android:layout_width="0dp"
android:layout_weight="1"
android:orientation="horizontal">
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="@dimen/dice_padding"
android:layout_gravity = "center"
android:src="@drawable/star"/>
<TextView
android:id="@+id/star_count"
android:layout_gravity="center"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="count"
/>
</LinearLayout>
<LinearLayout
android:layout_height="match_parent"
android:layout_width="0dp"
android:layout_weight="1"
android:orientation="horizontal">
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:padding="@dimen/dice_padding"
android:src="@drawable/magnifying_glass"/>
<TextView
android:id="@+id/mag_count"
android:layout_gravity="center"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="count"
/>
</LinearLayout>
<LinearLayout
android:layout_height="match_parent"
android:layout_width="0dp"
android:layout_weight="1"
android:orientation="horizontal">
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity = "center"
android:padding="@dimen/dice_padding"
android:src="@drawable/blank_dice"/>
<TextView
android:id="@+id/blank_count"
android:layout_gravity="center"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="count"
/>
</LinearLayout>
<LinearLayout
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="match_parent"
android:orientation="horizontal">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="@string/total_label"
/>
<TextView
android:id="@+id/total_count"
android:layout_gravity="center"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="count"/>
</LinearLayout>
</LinearLayout>
<LinearLayout
android:id="@+id/button_bar"
android:layout_weight="1"
android:layout_width="match_parent"
android:layout_height="@dimen/control_bar_line_height"
android:orientation="horizontal"
android:weightSum="3"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="@id/dice_summary">
<Button
android:id="@+id/add_dice_button"
android:layout_gravity = "center"
android:layout_weight="1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/add_button_label"
android:onClick="onClickAddButton"/>
<Button
android:id="@+id/rem_dice_button"
android:layout_gravity = "center"
android:layout_weight="1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/rem_button_label"
android:onClick="onClickRemoveButton"/>
<Button
android:id="@+id/roll_dice_button"
android:layout_weight="1"
android:layout_gravity = "center"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/roll_button_label"
android:onClick="onClickRollButton"/>
</LinearLayout>
</android.support.constraint.ConstraintLayout>
To capture gestures for the draggable dice, I attach an OnTouchListener to the custom DiceView. OnTouchListener offers several callback methods to detect gestures. What I'll need for the draggable dice feature is touch down and touch move. A summary of the Gesture framework can be found here.
Previously, I represented the dice with ImageView. Now that the Dice will have some custom behavior, the I'm creating a new DiceView class.
public class DiceView extends ImageView {
public DiceView(Context context) {
this(context, null);
}
public DiceView(Context context, @Nullable AttributeSet attrs) {
this(context, attrs, 0);
}
public DiceView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
public void refreshDiceFace(Dice.Face face, Boolean hold) {
switch (face) {
case BLANK:
setImageResource(R.drawable.blank_dice);
break;
case MAGNIFY:
setImageResource(R.drawable.magnifying_glass);
break;
case STAR:
setImageResource(R.drawable.star);
break;
}
}
}
Android Views have a bunch of different constructors because Views can be instantiated a couple different ways. The main two are xml instantiation (when views are defined in the layout xml), and programmatic. The 3 arg and 4 arg constructor are relevant for views that take into account themes and style.
The DiceView's encapsulating Layout determines the position in the Layout. The Layouts that support X/Y positions are RelativeLayout and AbsoluteLayout. For this app, I will extend RelativeLayout. This custom layout has 1 method updateDicePositions. updateDicePositions essentially syncs the DiceView on the board with the Dice in my model. If there are extra DiceView on the board, remove them. If there the diceBoard has fewer dice than the dicelist, add. Aind finally, when I add Dice, I add a the onTouchListener. The logic for updating the dice position is to capture the dice position when the user starts the touch gesture. As the user moves his finger around the board, update the diceView position.
public class DiceRollLayout extends RelativeLayout {
final static String TAG = DiceRollLayout.class.getName();
public DiceRollLayout(Context context) {
super(context);
}
public DiceRollLayout(Context context, AttributeSet attrs) {
super(context, attrs);
}
public DiceRollLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
public void updateDicePositions(List <Dice> diceList) {
int diceCount = diceList.size();
//remove dice
while (diceCount < getChildCount()) {
this.removeViewAt(getChildCount() - 1);
}
//add dice
while (getChildCount() < diceCount) {
final int index = getChildCount();
//initial layout parameters
DiceRollLayout.LayoutParams layoutParams = new DiceRollLayout.LayoutParams(
RelativeLayout.LayoutParams.WRAP_CONTENT,
RelativeLayout.LayoutParams.WRAP_CONTENT
);
int diceViewSize = getResources().getDimensionPixelSize(R.dimen.dice_size);
layoutParams.setMarginStart((index%5) * diceViewSize );
layoutParams.topMargin = ((index/5) * diceViewSize );
//initialize DiceView
DiceView diceView = new DiceView(getContext(), null, 0);
diceView.setLayoutParams(layoutParams);
diceView.setBorderColor(ContextCompat.getColor(getContext(), R.color.diceSelectionBorderColor));
diceView.setBorderOverlay(true);
diceView.setBorderWidth(0);
//touch drag listener
diceView.setOnTouchListener(new View.OnTouchListener() {
RelativeLayout.LayoutParams parms;
float dx=0,dy=0,x=0,y=0;
@Override
public boolean onTouch(View view, MotionEvent event) {
switch(event.getAction())
{
case MotionEvent.ACTION_DOWN :
{
parms = (RelativeLayout.LayoutParams) view.getLayoutParams();
dx = event.getRawX() - parms.leftMargin;
dy = event.getRawY() - parms.topMargin;
}
break;
case MotionEvent.ACTION_MOVE :
{
x = event.getRawX();
y = event.getRawY();
parms.leftMargin = (int) (x-dx);
parms.topMargin = (int) (y-dy);
view.setLayoutParams(parms);
}
break;
case MotionEvent.ACTION_UP :
{
((MainActivity)getContext()).onReleaseDiceView(index);
}
break;
}
return true;
}
});
this.addView(diceView);
}
//refresh dice face
for (int i = 0; i < getChildCount(); i++) {
DiceView diceView = (DiceView) getChildAt(i);
diceView.refreshDiceFace(diceList.get(i).diceVal, diceList.get(i).hold);
}
}
}
First, AbsoluteLayout has been deprecated. To explain a bit about that, AbsoluteLayout offered a way to position things by pixel position. The problem is that Android devices cover a very large range of device dimensions and pixel density. Pixel positioning is not a very reliable way position views into a layout.
After removing the Dice rows, the app loses those Hold and Change buttons. To address this, I'm going add a state variable to the presenter that keeps track of which dice has been selected. The hold or change buttons triggers on the selected dice. If there are no dice selected, the buttons should be greyed out. And finally, I'll need to add a visual cue to indicate which dice has been selected. To do this, i'm going to borrow an open source CircleImageView from hdodenhof@github. What this custom image view offers is a circle shaped imageview with borders. The visual cue i'm looking for is just a circle around the dice.
Visual cue for selected dice
public class DiceView extends CircleImageView {
...
public void highlight() {
this.setBorderWidth(6);
}
public void unhighlight() {
this.setBorderWidth(0);
}
}
Adding touch events to trigger select/deselect dice
public class DiceRollLayout extends RelativeLayout {
...
public void updateDicePositions(List <Dice> diceList) {
...
while (getChildCount() < diceCount) {
...
//touch drag listener
diceView.setOnTouchListener(new View.OnTouchListener() {
RelativeLayout.LayoutParams parms;
float dx=0,dy=0,x=0,y=0;
@Override
public boolean onTouch(View view, MotionEvent event) {
switch(event.getAction())
{
...
case MotionEvent.ACTION_UP :
{
((MainActivity)getContext()).onReleaseDiceView(index);
}
break;
}
return true;
}
});
this.addView(diceView);
}
...
}
@Override
protected void onAttachedToWindow() {
super.onAttachedToWindow();
this.setOnTouchListener(new OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_UP: {
((MainActivity)getContext()).onTouchUpLayout();
}
break;
}
return true;
}
});
}
...
}