I'm a new to java and android. I was working on my own app but I'm having a problem in passing a method from Activity A to Activity B.
Here is what I did :
ActivityA has Demo() method.
public class ActivityA extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
protected void demo() {
// Do something
}
}
I created the below class to access the method of ActivityA to ActivityB:
public class External {
private ActivityA activitya;
private static External instance = null;
public External(ActivityA activitya) {
this.activitya = activitya;
}
static public External getInstance(ActivityA activitya) {
if (instance == null) {
instance = new MyntraExternal(activitya);
return instance;
} else {
return instance;
}
}
}
Now how can I proceed further? I'm having lots of problem in getting the method which is in ActivityA from ActivityB.
Please anybody help.
Edit :
ActivityB is my launcher class and I want some access from ActivityA's method in ActivityB. What to do ?
Since you are new to Android, I will tell you it's a bad practice call methods from Activity A to B or vice versa, you can pass parameters from one activity to another using intents and bundles and if you need to pass parameters from the second activity to the first you need to use the override method onActivityResults
Here are some usefull link about passing parameters from one activity to another:
https://www.dev2qa.com/passing-data-between-activities-android-tutorial/
In this link you can see a example of how things work.
Hope it helps.
--EDIT (if you need to call a function from B to A in case you want to change something in A upon creation this is the best and simplest way to do it):
In Activity B:
Intent intent = new Intent(this, ActivityA.class);
intent.putExtra("Work","doJump");
startActivity(intent);
In Activity A:
onCreate:
String extra = getIntent().getStringExtra("Work");
if(extra != null && extra.equals("doJump")){
jump();
}
make that method public and static and then access it using class name. e.g. In your 2nd activity, use ActivityB.demo()
Try using startActivityForResult
To start activity B from activity A
startActivityForResult(intent, SOME_CODE)
And to be called back on result you will need to add the following code the also in activity A
override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
super.onActivityResult(requestCode, resultCode, data)
when(code){
SOME_CODE -> if (resultCode == Activity.RESULT_OK) doSomething()
}
}
To tell Activity A to call the method, in activity B you can say:
setResult(Activity.RESULT_OK)
finish()
After B is finished, onActivityResult in A will be executed
To go back to A without executing the "doSomething()" method,
setResult(Activity.RESULT_CANCELED)
finish()
Please try this way
public class ActivityA extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void demo() {
// Do something
}
}
public class ActivityB extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ActivityA activityA = new ActivityA(); // create object
activityA.demo(); //
}
}
Related
So There are 3 activities A, B and C.
From Activity A, I go to activity B in activity B, I perform some tasks and I go to Activity C from Activity B.
I activity C, I have a button and some data, when I click the button I should update text in activity A. Is there a best way to do it?
edit: I do not want to go to back, when I click the button in activity C, but the text present in the activity a should be updated, later when I reach the activity a I should see the changes.
I think, you should create a separate class that you will share between your activities A, B and C. The class should has a field, which will store text for your TextView in activity A. And there is a good variant to use Observer pattern (rxJava or custom decision).
Example:
SharedStateModel is used to save state for ActivityA.
That decision is not very clear, because it breaks dependency inversion rule so I recommend you to use Dagger 2 to inject SharedStateModel into ActivityA and ActivityC and manage its component's lifecycle like I describe in comments to SharedStateModeClass.
/*
Let's make that state-class a local singleton - you create it in onCreate of ActivityA and
further it can be destroyed in onDestroy of ActivityA.
*/
public class SharedStateModel {
private PublishSubject<String> stateListener = PublishSubject.create();
private String viewState;
private static SharedStateModel instance;
private SharedStateModel() {
}
public void setViewState(String viewState) {
this.viewState = viewState;
stateListener.onNext(viewState);
}
public PublishSubject<String> getStateListener() {
return stateListener;
}
public void destroyViewState() {
instance = null;
}
public static SharedStateModel getInstance() {
if (instance != null) {
return instance;
} else {
instance = new SharedStateModel();
return instance;
}
}
}
public class ActivityA extends AppCompatActivity {
#BindView(R.id.textView)
private TextView textView;
private SharedStateModel sharedStateModel;
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ButterKnife.bind(this);
sharedStateModel = SharedStateModel.getInstance();
sharedStateModel.getStateListener().subscribe(
textViewState -> textView.setText(textViewState));
}
#Override
protected void onDestroy() {
super.onDestroy();
sharedStateModel.destroyViewState();
}
}
public class ActivityC extends AppCompatActivity {
#BindView(R.id.button)
private Button button;
/*
Let's assume that you want to send a message from EditText in ActivityC
*/
#BindView(R.id.editText)
private EditText editText;
private SharedStateModel sharedStateModel;
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ButterKnife.bind(this);
sharedStateModel = SharedStateModel.getInstance();
button.setOnClickListener(view -> sharedStateModel.setViewState(
String.valueOf(editText.getText().toString())));
}
}
And I want to recommend you good guides from Eugene Matsyuk if you want to learn Dagger 2.
2 way
when you leaving activity C and going to activity A, pass the value from activity C to A just like you are going to a new activity. then set the text view.
Pass your textView object from activity A activity B, then activity B to activity C. in activity C just setText normally with the textview object you bring from activity A to activity C.
When I need a callback from Activity B back to Activity A I usually make the reference variable in Activity B 'static'. I realize that if the user rotates the device the Life Cycle methods will remove my reference.
Is this the only drawback and is there a better way to register without a static reference. Is it better to simply put all data in the Application class ? - Thank you.
public class MainActivity extends Activity implements InterfaceMainActivityTwo {
static Main2Activity main2Activity;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
main2Activity = new Main2Activity();
main2Activity.setDataListener(this);
}
#Override
public void getDataMainActivityTwo(String string) {
tvTextData.setText(string);
}
}
public class Main2Activity extends Activity {
static InterfaceMainActivityTwo mGetDataInterface;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
}
public void getDataSaveBtn(View v) {
if (mGetDataInterface != null)
mGetDataInterface.getDataMainActivityTwo(fullName);
else
Toast.makeText(this, "IS NULL.INTERFACE NOT INITIALIZED !!!!", Toast.LENGTH_SHORT).show();
}
/////////// interface setup
interface InterfaceMainActivityTwo {
void getDataMainActivityTwo(String string);
}
public void setDataListener(InterfaceMainActivityTwo listener) {
this.mGetDataInterface = listener;
}
}
You should never need a callback between two activities. You're doing something wrong if you do. If you need to pass data from A to B, pass it in the bundle. If you need to pass it back from B to A, use startActivityForResult and pass it in the result. If you need to share data between many activities, it should be held in some globally accessible data structure, either in memory or on disk.
There are two Activities..
1. Open SecondActivity from MainActivity
2. When event comes into MainActivity, call testMethod of SecondActivity
But how to do call this testMethod?
public class MainActivity extends Activity implements someListener {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//Launch SecondActivity here!!
Intent intent = new Intent();
intent.setClass(MainActivity.this, SecondActivity.class);
startActivityForResult(intent, ID_PlayerActivity);
}
//trigger by JNI, it's in the other thread, not main thread.
void onEventCome() {
//How to call testMethod() in SecondActivity?
}
}
public class SecondActivity extends Activity {
void testMethod() {
//execute something...
}
}
If you open the SecondActivity, your MainActivity becomes inactive. I don't believe it is a good idea to call some activity method from other inactive/stopped activity.
I suggest to use observer pattern. Create a global long-lived object like EventProducer and register all activities as observer. So your EventProducer can inform all Activities about new event.
Example:
public class SecondActivity extends Activity implements MyEventListener {
#Override
public void onResume(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
EventProducer.instance().register(this);
}
#Override
public void onPause(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
EventProducer.instance().unregister(this);
}
void testMethod(){
//just doit
}
#Override
void onMyEventCome() {
testMethod();
}
}
First you need an event aware listener that will capture such an event happening. Your class seems ill equipped to do so.
Since you have a valid question, here goes:
void onEventCome() {
SecondActivity secondActivity = new SecondActivity();
secondActivity.testMethod();
}
There are many ways.
For eg:
Create the method as static and use class name and call it.
public static void onEventCome() {
}
In MainActivity:
MainActivity.onEventCome();
This is one method. Another method is create an object for MainActivity.
public void onEventCome() {
}
MainActivity main;
main = new MainActivity();
main.onEventCome();
You don't have a content view for your second activity. If you don't need to see the operation happen, you could remove your
Intent intent = new Intent();
intent.setClass(MainActivity.this, SecondActivity.class);
startActivityForResult(intent, ID_PlayerActivity);
remove extends Activity in SecondActivity and add a constructor public SecondActivity(Context context) and invoke the test method from your first activity like #Dragan example:
void onEventCome() {
SecondActivity secondActivity = new SecondActivity(MainActivity.this);
secondActivity.testMethod();
}
guys, I'm pretty new to java android programming (that's the first app I'm making) and I have this question:
How can i refresh my Main Activity from another activity, which is called from the Main one?
I would also appreciate if you give me some examples, because I'm still not very orientated...
You can use startActivityForResult() for that purpose, instead of context.startActivity() call context.startActivityForResult() and then set result in launched activity before finishing it.
Here is the documentation for Context.startActivityForResult()
Sample code:
// Activity A
public class ActivityA extends Activity {
private static final int REQUEST_CODE_ACTIVITY_B_FOR_RESULT = 1; // or other int value
// sample code which starts Activity B
private void onSomeButtonClick() {
Intent intent = new Intent(this, ActivityB.class);
startActivityForResult(intent, REQUEST_CODE_ACTIVITY_B_FOR_RESULT);
}
// this method will be called when started activity finished
// and returned some result of its work
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent resultData) {
super.onActivityResult(requestCode, resultCode, resultData);
if (requestCode == REQUEST_CODE_ACTIVITY_B_FOR_RESULT) {
if (resultCode == RESULT_OK) {
// handle result ok and resultData here
} else {
// handle result canceled or other resultCode and its resultData here
}
}
}
}
// Activity B
public class ActivityB extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setResult(RESULT_CANCELED); // by default result of starting activity is negative
}
// some code which doing some action and setting result as ok
private void doSomething() {
Intent resultData = new Intent();
resultData.putExtra("SOME_EXTRA", "did it"); // or other result data
setResult(RESULT_OK, resultData);
finish(); // finishing this activity, result code and result data will be accessible in previous activity
}
}
How to call main activity from the sub activity. Use an interface.
1. Creata a public interface in the sub-activity
public class MapSettings extends DialogFragment implements
OnCheckedChangeListener {
public interface BestRidesSettingsDialogListener {
void onMapSettingsChange(int mapType);
}
2. Implement the interface in the main activity note right click on errors and select add imports add reference add unimplemented methods.
public class KmlReader extends ActionBarActivity implements
BestRidesSettingsDialogListener {
3. when the sub activity starts in the sub activity cast getActivity to the public interface
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// the activity may be null if this is called without implementing the
// BestRidesSettingsDialogListener (The settings object saves the
// setting so the
// call back may not be needed.
activity = (BestRidesSettingsDialogListener) getActivity();
4. Then in the sub activity when a button is clicked or some event happens call through to the interface method.
#Override
public void onCheckedChanged(RadioGroup rg, int checkId) {
// TODO Auto-generated method stub
int mapType = 0;
switch (checkId) {
case R.id.RDORoad:
mapType = GoogleMap.MAP_TYPE_NORMAL;
break;
case R.id.RDOHybrid:
mapType = GoogleMap.MAP_TYPE_HYBRID;
break;
case R.id.RDOSatelite:
mapType = GoogleMap.MAP_TYPE_SATELLITE;
break;
case R.id.RDOTerrain:
mapType = GoogleMap.MAP_TYPE_TERRAIN;
break;
}
// run the activity onchange
// if the activity is null there is no listener to take action on the
// settings
if (activity != null) {
activity.onMapSettingsChange(mapType);
}
5. if you've filled in the unimplemented methods stubs in your main activity your executing code directly in the main activity from the sub activity.
#Override
public void onMapSettingsChange(int mapType) {
if (mMap != null) {
mMap.setMapType(mapType);
}
}
sidebar for comments: The interface has always been my favorite part of java. You might call it a listener or a call back. Just right click on the errors and select add reference, add unimplemented methods there really are not too many keystrokes to do this. The interface is perhaps the easiest way to coordinate a team effort on making the next big thing.
I have two Activities A and B. B has a method searchDevices. I want to access that method from A 's onCreate method. How can I do it with Intent?
I tried this :
public void onCreate(Bundle savedInstanceState)
{
try{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
MY_UUID= UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
//Function enbling Bluetooth
enableBluetooth();
///Function to initialize components
init();
//Calling AvailableDevices class's method searchDevice to get AvailableDevices
Intent intent=new Intent(this,AvailableDevices.class);
int x=10;
intent.putExtra("A", x);
}catch(Exception e){Toast.makeText(getApplicationContext(), e.toString(), Toast.LENGTH_LONG).show();}
}
You can also create a base activity that both ActivityA and ActivityB extends and put searchDevices() method in it.
For ex:
public class BaseActivity extends Activity{
public void searchDevices(){
}
}
public class ActivityB extends BaseActivity{
onCreate..
{
...
searchDevices();
}
}
public class ActivityA extends BaseActivity{
onCreate..
{
...
searchDevices();
}
}
if ActivityA is in a class called class1 make a method in class1 like this
public static void method1(){
}
then in activity 2 call the method by doing this ActivityA.method1()
Why don't use StartActivityForResult.
As per my understanding You can start AvailableDevices Activity for result with Intent having extra data and call searchDevice to get AvailableDevices and return the result to calling Activity.
[Edit]
In Class A
//Calling AvailableDevices class's method searchDevice to get AvailableDevices
Intent intent=new Intent(this,AvailableDevices.class);
int x=10;
intent.putExtra("A", x);
startActivityForResult(intent , searchDevicesRequestCode); //searchDevicesRequestCode = 100
Also override onActivityResult()
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
// Check which request we're responding to
if (requestCode == searchDevicesRequestCode) {
// Make sure the request was successful
if (resultCode == RESULT_OK) {
// Manipulate searchDevicesResult from Intent data
}
}
}
In Class B
#override
onCreate()
{
//call searchDevices()
String result = searchDevices(); // save result to send in any form
// Create intent to deliver some kind of result data
Intent intentResult = new Intent("RESULT_ACTION");
intentResult.putExtra("key",result);
setResult(Activity.RESULT_OK, intentResult);
finish();
}