MobAppDev

Getting Results from

Multiple Called Activities

Vladimir Kulyukin

www.vkedco.blogspot.com

Outline

● Review● Coding Lab: Computing Fibonacci & Prime Numbers with

Activities Called by Explicit or Implicit Intents

Review

Caller & Called Activities

● A caller activity is an activity that launches another activity

● A launch may happen with an explicit or an implicit intent

● A called activity is an activity launched by another activity

What Does the Caller Do?● The caller activity must define request codes

● A request code is an integer constant (with a meaningful name!) that specifies a specific type of request (e.g., compute some math function, grayscale an image, retrieve some information from a data source)

● The caller & called activities must share the data keys they use to pass data back and forth via intents

● The caller must call startActivityForResult() to launch a called activity

● The caller must implement onActivityResult() to get the result back from a called activity

startActivityForResult()

● startActivityForResult(Intent intntForCalledAct, int request_code)

● Intent intntForCalledAct is created by the caller

● Intent intntForCalledAct specifies a called activity explicitly or implicitly through some action and passes data to the called activity via a Bundle

● request_code is a constant shared by the caller and the called

● request_code is used by the called activity to figure out what the caller wants it to do

● request_code is used by the caller to get the results back from the child

onActivityForResult()

● onActivityForResult(int request_code, int result_code, Intent data)

● This callback method must be implemented by the caller: it is called when a called activity returns the results to the caller

● request_code is a constant shared by the caller and the called activities

● result_code is a constant specifying whether the computation performed by the called activity was successful or not (e.g., Activity.RESULT_OK or Activity.RESULT_CANCELED)

What Does the Called Activity Do?● The called activity receives an Intent from its caller

● The called activity uses the request code to figure out what needs to be done

● The called activity uses the caller's intent to get specifics on what needs to be done (e.g., input parameters)

● The called activity must create an Intent returnData

● The called activity must perform the required computation

● The called activity must Activity.setResult(result_code, Intent returnData) to return the results back to its caller

Computing Fibonacci & Prime Numbers with Activities Started by

Explicit or Implicit Intents

source code is hereif the link does not work, the full url is

https://github.com/VKEDCO/CallerAndCalledActivities/blob/master/CallerAndCalledActivities.zip

Application Specs● Develop an application that allows the user compute n-th

fibonacci or prime number through activities called by explicit or implicit intents

● The application has three activities: one caller activity (CallerAct) & two called activities (CalledFibonacciNumbersAct & CalledPrimeNumbersAct)

● CallerAct uses startActivityForResult() to call the called activities and onActivityResult() to display returned results

Solution Steps● Design UI● Define Request Codes● Define Data Keys● Define Actions for Implicit Intent Filters● Implement Caller & Called Activities● Test & Debug

Design UI

UI Layout

UI Functionality● Click on “Expl Intent Fibo” uses startActivityForResult() to

call CalledFibonacciNumbersAct by explicit intent to compute 10th fibonacci number

● Click on “Impl Intent Fibo” uses startActivityForResult() to call CalledFibonacciNumbersAct by implicit intent to compute 10th fibonacci number

● Click on “Expl Intent Prime” uses startActivityForResult() to call CalledPrimeNumbersAct by explicit intent to compute 5th prime

● Click on “Impl Intent Prime” uses startActivityForResult() to call CalledPrimeNumbersAct by implicit intent to compute 5th prime

● onActivityResult() is used to toast returned results

Define Request Codes

Request Codes public class StartActivityForResultCallerAct extends Activity

implements OnClickListener {

// request codes

final static int FIBO_REQUEST_CODE = 1;

final static int PRIME_REQUEST_CODE = 2;

…

}

● FIBO_REQUEST_CODE is used in startActivityForResult() to call CalledFibonacciNumbersAct

● PRIME_REQUEST_CODE is used in startActivityForResult() to call CalledPrimeNumbersAct

Define Data Keys

Data Keys for Intent Bundles <string name="fibo_request_key">fibo_request</string>

<string name="fibo_result_key">fibo_result</string>

<string name="prime_request_key">prime_request</string>

<string name="prime_result_key">prime_result</string>

● fibo_request_key is used by the caller CallerAct to pass the parameter to the callee CalledFibonacciNumbersAct

● fibo_result_key is used by the callee CalledFibonacciNumbersAct is return n-th fibonacci number to the caller

● prime_request_key is used by the caller CallerAct to pass the parameter to the callee CalledPrimeNumbersAct

● prime_result_key is used by the callee CalledPrimeNumbersAct to return the return the n-th prime to the caller

Define Actions for Implicit Intent Resolution

Intent Filter Actions for Implicit Intent Resolution

public class StartActivityForResultCallerAct extends Activity

implements OnClickListener {

// implicit intents to launch called activities

final static String COMPUTE_FIBO_ACTION = "org.vkedco.android.mobicom.fibonacci";

final static String COMPUTE_PRIME_ACTION = "org.vkedco.android.mobicom.primes";

…

}

● Action strings are defined in the caller (use meaningful names!)

● These strings must be the same as the ones used in AndroidManifest.xml in the intent filters of the the called activities

Intent Filter Actions in AndroidManifest.xml <activity android:name="org.vkedco.mobicom.android.start_sum_activity_for_result_app.CalledFibonacciNumbersAct" android:label="@string/app_name" > <intent-filter>

<action android:name="org.vkedco.android.mobicom.fibonacci" /> <category android:name="android.intent.category.DEFAULT" /> </intent-filter> </activity> <activity android:name="org.vkedco.mobicom.android.start_sum_activity_for_result_app.CalledPrimeNumbersAct" android:label="@string/app_name" > <intent-filter>

<action android:name="org.vkedco.android.mobicom.primes" /> <category android:name="android.intent.category.DEFAULT" /> </intent-filter> </activity>

Implement Caller & Called Activities

Calling Activities by Explicit Intent public void onClick(View v) { Button clickedButton = (Button) v; int nth; switch ( clickedButton.getId() ) { case R.id.btnExplFibcn: try { nth = Integer.parseInt(mEdTxtFiboN.getText().toString()); } catch (NumberFormatException nfe) { Toast.makeText(getApplicationContext(), nfe.toString(), Toast.LENGTH_LONG).show(); return; } Intent explFiboIntent = new Intent(this, CalledFibonacciNumbersAct.class); exlFiboIntent.putExtra(mRes.getString(R.string.fibo_request_key), nth); startActivityForResult(explFiboIntent, FIBO_REQUEST_CODE); return; // rest of code}

Calling Activities by Implicit Intent public void onClick(View v) { Button clickedButton = (Button) v; int nth; switch ( clickedButton.getId() ) { case R.id.btnImplFibcn: try { nth = Integer.parseInt(mEdTxtFiboN.getText().toString()); } catch (NumberFormatException nfe) { Toast.makeText(getApplicationContext(), nfe.toString(), Toast.LENGTH_LONG).show(); return; } Intent implFiboIntent = new Intent(COMPUTE_FIBO_ACTION); implFiboIntent.putExtra(mRes.getString(R.string.fibo_request_key), nth); startActivityForResult(implFiboIntent, FIBO_REQUEST_CODE); return; // rest of code}

How Called Activities Return Results to Callers// this is onCreate() in CalledFibonacciSumsAct protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Intent requestIntent = this.getIntent(); // get the caller's intent Resources res = this.getResources(); // check if the caller's intent has the required data key if ( requestIntent.hasExtra(res.getString(R.string.fibo_request_key))) { // fibo is the method that computes n-th fibonacci number int rslt = fibo(requestIntent.getIntExtra(res.getString(R.string.fibo_request_key), -1));; if ( rslt == -1 ) { this.setResult(RESULT_CANCELED); this.finish(); // finish and return RESULT_CANCELLED to the caller } else { Intent resultIntent = new Intent(); resultIntent.putExtra(res.getString(R.string.fibo_result_key), rslt); // put the result into the intent under the appropriate data key this.setResult(RESULT_OK, resultIntent); // return intent to the caller with RESULT_OK this.finish(); } } else { this.setResult(RESULT_CANCELED); this.finish(); }}

How Callers Process Returned Results// this is onActivityResult in CallerAct public void onActivityResult(int requestCode, int resultCode, Intent returnedData) {

super.onActivityResult(requestCode, resultCode, returnedData); switch ( requestCode ) { case FIBO_REQUEST_CODE: if ( resultCode == Activity.RESULT_OK ) { if ( returnedData.hasExtra(mRes.getString(R.string.fibo_result_key)) ) { Toast.makeText(this, "Fibo = " + returnedData.getIntExtra(mRes.getString(R.string.fibo_result_key), -1), Toast.LENGTH_LONG).show(); } else { Toast.makeText(this, "Fibo Computation Failure", Toast.LENGTH_LONG).show(); } } return; // cases for other request codes}