LoanCalculator Phase 1, Iteration 1

Create an Android Project

- On Eclipse, click File->New->Other->Anroid Project
- Create a new Android Project with the following …

• Project name= LoanCalculator
• Target= Android 1.5
• Application name= LoanCalculator
• Package name=com.androidfun.loancalculator
• [checked] Create Activity = LoanCalculatorActivity
• Min SDK Version = 3

- Verify the project by selecting the “LoanCalculator” folder, right mouse click and select “Run as …”->Android Application. You shall see the emulator and the Hello world message from Eclipse generated code.

Create the LoanCalculator GUI

- Android UI components can be created declaratively by XML or programmatically inside the code. For now, we are using XML. The main.xml (i.e. LoanCalculator/res/layout/main.xml) defines the UI for LoanCalculatorActivity.

public class LoanCalculatorActivity extends Activity {
/** Called when the activity is first created. */
@Override public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main); }
}

- The content view of the LoanCalculatorActivity is sourced from the main.xml in ./res/layout folder by calling setContentView(...)

- We would like to have a Calculator view looks like the diagram below.


- Layout management in main.xml. The view has a vertical stack of rows of widget. The vertical stack is declared as the outer <Linearlayout> element with anroid:orientation="vertical". Each row of widgets is a <Linearlayout> element with anroid:orientation="horizaontal".

- In main.xml, we use:

• <Textview> for label
• <Edittext> for text entry field
• <Spinner> for drop down selection
• <Button> for button

Listing of main.xml available in http://mobile.k1computing.com/android/download/LoanCalculator_1_1/res/layout/main.xml

Note the two Android attributes in the view declaration elements.

• android:id="@+id/annualRate" declares the ID of the widget, the widget can be referenced in Java by (EditText)findViewById(R.id.annualRate);

• android:text="@string/annualRate" reference the string value in res/values/strings.xml

Listing of strings.xml available in http://mobile.k1computing.com/android/download/LoanCalculator_1_1/res/values/strings.xml

Java classes

We create two Java classes ...

• LoanCalculator.java - A POJO domain object that encapsulates the loan calculator formula
• LoanCalculatorActivity - Subclasses from Android's Activity class, the controller that links the GUI and the LoanCalculator domain object.

Listing of LoanCalculator.java
Listing of LoanCalculatorActivity.java

LoanCalculator class walk through

onCreate() - Look up the widget declared in main.xml, create and register event listeners for buttons and initialize the default valus in the view.


public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mCalculator=new LoanCalculator();
mPrincipalText=(EditText)findViewById(R.id.principal);
mAnnualRateText=(EditText)findViewById(R.id.annualRate);
mYears=(EditText)findViewById(R.id.years);
mPmt=(TextView)findViewById(R.id.pmt);
addCalcPmtListener();
addAmortizationListener();
addGetRatesListener();
initPeriodsSpinner();
populateView();
}




initPeriodsSpinner() - Example of populating the selections with values from resource file (i.e. array.xml) to a Spinner widget.



private void initPeriodsSpinner(){
mPeriodsSpinner=(Spinner)findViewById(R.id.periods);
ArrayAdapter adapter = ArrayAdapter.createFromResource(
this, R.array.periods, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
mPeriodsSpinner.setAdapter(adapter);
mPeriodsSpinner.setSelection(0);
}





addCalcPmtListener() - Example of creating an event listener for a button.



private void addCalcPmtListener(){
Button calcPmtButton=(Button)findViewById(R.id.b_calcPmt);
calcPmtButton.setOnClickListener(
new View.OnClickListener(){
public void onClick(View view){
mCalculator.setPrincipal(Double.parseDouble(mPrincipalText.getText().toString()));
mCalculator.setAnnualRate(Double.parseDouble(mAnnualRateText.getText().toString()));
mCalculator.setPeriodsPerYear(getSelectedPeriods());
mCalculator.setYears(Integer.parseInt(mYears.getText().toString().trim()));
populateView();
setResult(RESULT_OK);
}
}
);
}





populateView() - Populating the value to the widgets from a domain object.



private void populateView(){
mPrincipalText.setText(""+mCalculator.getPrincipal());
mAnnualRateText.setText(""+mCalculator.getAnnualRate());
mYears.setText(""+mCalculator.getYears());
mPmt.setText(""+mCalculator.computePayment());
}






DOWNLOAD the LoanCalculator Eclipse project (LoanCalculator_1_1.zip)