I am trying to access the activity on which my Imageview is, so I can use the URL of an Image of type SVG and display it to the user using the GlideToVectorYou library.
GlideToVectorYou.justLoadImage(activity, IMAGE_URI, targetImageView)
But when I try to get access to the activity using R.layout.activityname, a syntax error appears.
this is the code that I'm using
Uri myurl = Uri.parse(match.getFlag());
GlideToVectorYou.justLoadImage(R.layout.item_basketball, myurl, iv_location);
Thank you!
R.layout.item_basketball is just an integer ID for your activity layout - not the activity instance itself. If you want the activity in your adapter you would need to pass it in when you construct the adapter and save it as a class member (example below), or check if your adapter base class already can provide it via getActivity() or getContext() or a similar method.
class MyAdapter(private val activity: Activity) : BaseAdapter() {
fun someMethod() {
// then you can access "activity" in your adapter methods
GlideToVectorYou.justLoadImage(activity, IMAGE_URI, targetImageView)
}
}
and when you create it in your Activity, you would just do something like this
val adapter = MyAdapter(this)
You need a activity reference. R.layout.somethinghere is the layout reference.
On your adapter constructor add a activity parameter and use it inside the adapter.
If you call adapter constructor from an activity, just pass "this" as parameter. If call from a fragment, use "requireActivity" (if using kotlin) or analogous method (getActivity, for example) if using Java
Good evening,
I am new at Android App development. I have a project where I receive data from multiple sensors which are connected an instrument.
At this time, I can select any sensor and stream its data using AudioTrack. The streaming is from a service and this service is bound to the MainActivity instance. A single sensor data is streamed at the time. This is working as expected.
Now, I want to plot (using MPAndroidChart) the data for each sensor in its own chart. In the activity_main layout, I added a ViewPager2 element, and Fragments are instantiated by the PagerAdapter::CreateFragment(int position) method.
My class model is as follow (based on a ViewPager2 example):
public class MainActivity extends AppCompatActivity
public class PagerAdapter extends FragmentStateAdapter
public class ChannelFragment extends Fragment
public class SensorViewModel extends ViewModel
I tested the visualisation of the plots in the Fragments using mock data (and a different colour background). The mock data was generated in ChannelFragment::onCreateView() method. This also works, though the mock data is the same for all fragments/charts, but different background colour for each fragment.
In a live test, I also proved to myself that I process changing the visible fragment correctly. I associate each fragment to a specific sensor and the streaming data changes as the visible fragment changes. This is done from MainActivity using ViewPager2.OnPageChangeCallback onPageSelected(position)
I am able to set the sensor data to the SensorViewModel and trigger a notification when calling postValue() from SensorViewModel.
The SensorViewModel contains the following declaration
private MutableLiveData<float[][]> sensorLiveData = new MutableLiveData<>();
and is created in MainActivity::onCreate(Bundle savedInstanceState)
// Create a ViewModel to hold the audio (sensor) data. This view model is used to communicate
// with the UI, graphically display the audio data for example
sensorViewModel = new ViewModelProvider(this).get(SensorViewModel.class);
The code for the observer is defined as a ChannelFragment method and listed as
#Override
public void onViewCreated(#NonNull View view, Bundle savedInstanceState)
{
super.onViewCreated(view, savedInstanceState);
sensorViewModel = new ViewModelProvider(requireActivity()).get(SensorViewModel.class);
sensorViewModel.getSampleData().observe(requireActivity(), new Observer<float[][]>() {
#Override
public void onChanged(#Nullable float[][] sampleData)
{
// Update the sample data graphical representation
Log.d(TAG, String.format("ChannelFragment; onChanged() sampleData length : %d, size: %d",
sampleData.length, sampleData[0].length));
addEntry(sampleData);
}
});
And the log statement reports
ChannelFragment: ChannelFragment; onChanged() sampleData length : 8, size: 170
I am stuck as to update the correct chart (correct ChannelFragment) with its corresponding sensor data.
How to a plot sampleData[0][] in Fragment at position 0, sampleData1 in Fragment at position 1, and so forth?
Calls to ChannelFragment.getId() always returns 0, though I am able to access other attributes such as title when different fragments become visible.
I also modified the SensorVIewModel as suggested by Tiago Redaelli. The new declaration:
private HashMap<Integer, MutableLiveData<ArrayList<Float>>> sensorLiveData = new HashMap<>();
where the key identifies the sensor/fragment the MutableLiveData belongs to. However, the example does not explain how to set (inject?) the ViewModel (and MutableLiveData value) to the ChannelFragment. In the example, the method setViewModel() is implemented but call is not shown.
Using this new ViewModel definition, how do I associate each HashMap values with their corresponding Fragment (who is calling setViewModel() ? What I am missing?
Thanks in advance
Daniel
Just a quick update. I was trying to create a complicated solution to my issue, including looking at ViewModel factory for example.
In my solution, I simply call setViewModel() (mentioned above) using the position/index value passed as argument when creating an instance of ChannelFragment.
This appears to be working.
I have an activity that contains a number of fragments. Each fragment has a viewModel scoped to its lifetime with some logic inside. The host activity has a viewModel too, including some code to show a popup-style message.
I want my fragment viewModels to be able to post messages to this popup. However, how could I access the activity-viewModel from inside one of my fragment-viewModels?
I'll write some exemplary Kotlin code, but the question is not specific to Kotlin since it's more of an architectural issue.
class MyActivityViewModel {
...
popupMessage = MutableLiveData<String>("") // is observed by my activity
fun postMessage(text: String) {
popupMessage.value = text
}
}
class MyFragmentAViewModel {
...
fun someFunctionA() {
// want to call ActivityViewModel's postMessage from here
}
}
class MyFragmentBViewModel {
...
fun someFunctionB() {
// want to call ActivityViewModel's postMessage from here too
}
}
I can't easily call ViewModelProvider since I'd rather not keep a reference to an Activity in my viewModel. The only direct option I see is to pass the activity-viewModel to the fragment-viewModels through the constructor or an init() method. That should be safe since the parent viewModel's lifetime should exceed the fragment viewModels' lifetime. I think.
Still, that solution rubs me the wrong way.
Are there any other alternatives? Or perhaps an entirely different approach to the issue?
Here's the thought of a greenhorn:
Can't you tell the activity that your fragment wants to use its method?
If you
Make an interface with a method a la "fragmentAWantsToUsePostMessage" in your fragment
Implement the interface in the activity, so that every time fragmentAWantsToUsePostMessage is called, the activity calls postMessage
Get a reference to the implementation of the interface in your fragment
Use that reference when the fragment needs to call "post message"
Shouldn't that work? Or is that against your "not keeping a reference"?
As I said: I'm new to all of this, so I might be completely wrong.
I can see that there's a post on medium that might be relevant: How to Communicate between Fragment and Activity
This question is mostly to solicit opinions on the best way to handle my app. I have three fragments being handled by one activity. Fragment A has one clickable element the photo and Fragment B has 4 clickable elements the buttons. The other fragment just displays details when the photo is clicked. I am using ActionBarSherlock.
The forward and back buttons need to change the photo to the next or previous poses, respectively. I could keep the photo and the buttons in the same fragment, but wanted to keep them separate in case I wanted to rearrange them in a tablet.
I need some advice - should I combine Fragments A and B? If not, I will need to figure out how to implement an interface for 3 clickable items.
I considered using Roboguice, but I am already extending using SherlockFragmentActivity so that's a no go. I saw mention of Otto, but I didn't see good tutorials on how to include in a project. What do you think best design practice should be?
I also need help figuring out how to communicate between a fragment and an activity. I'd like to keep some data "global" in the application, like the pose id. Is there some example code I can see besides the stock android developer's information? That is not all that helpful.
BTW, I'm already storing all the information about each pose in a SQLite database. That's the easy part.
The easiest way to communicate between your activity and fragments is using interfaces. The idea is basically to define an interface inside a given fragment A and let the activity implement that interface.
Once it has implemented that interface, you could do anything you want in the method it overrides.
The other important part of the interface is that you have to call the abstract method from your fragment and remember to cast it to your activity. It should catch a ClassCastException if not done correctly.
There is a good tutorial on Simple Developer Blog on how to do exactly this kind of thing.
I hope this was helpful to you!
The suggested method for communicating between fragments is to use callbacks\listeners that are managed by your main Activity.
I think the code on this page is pretty clear:
http://developer.android.com/training/basics/fragments/communicating.html
You can also reference the IO 2012 Schedule app, which is designed to be a de-facto reference app. It can be found here:
http://code.google.com/p/iosched/
Also, here is a SO question with good info:
How to pass data between fragments
It is implemented by a Callback interface:
First of all, we have to make an interface:
public interface UpdateFrag {
void updatefrag();
}
In the Activity do the following code:
UpdateFrag updatfrag ;
public void updateApi(UpdateFrag listener) {
updatfrag = listener;
}
from the event from where the callback has to fire in the Activity:
updatfrag.updatefrag();
In the Fragment implement the interface in CreateView do the
following code:
((Home)getActivity()).updateApi(new UpdateFrag() {
#Override
public void updatefrag() {
.....your stuff......
}
});
To communicate between an Activity and Fragments, there are several options, but after lots of reading and many experiences, I found out that it could be resumed this way:
Activity wants to communicate with child Fragment => Simply write public methods in your Fragment class, and let the Activity call them
Fragment wants to communicate with the parent Activity => This requires a bit more of work, as the official Android link https://developer.android.com/training/basics/fragments/communicating suggests, it would be a great idea to define an interface that will be implemented by the Activity, and which will establish a contract for any Activity that wants to communicate with that Fragment. For example, if you have FragmentA, which wants to communicate with any activity that includes it, then define the FragmentAInterface which will define what method can the FragmentA call for the activities that decide to use it.
A Fragment wants to communicate with other Fragment => This is the case where you get the most 'complicated' situation. Since you could potentially need to pass data from FragmentA to FragmentB and viceversa, that could lead us to defining 2 interfaces, FragmentAInterface which will be implemented by FragmentB and FragmentAInterface which will be implemented by FragmentA. That will start making things messy. And imagine if you have a few more Fragments on place, and even the parent activity wants to communicate with them. Well, this case is a perfect moment to establish a shared ViewModel for the activity and it's fragments. More info here https://developer.android.com/topic/libraries/architecture/viewmodel . Basically, you need to define a SharedViewModel class, that has all the data you want to share between the activity and the fragments that will be in need of communicating data among them.
The ViewModel case, makes things pretty simpler at the end, since you don't have to add extra logic that makes things dirty in the code and messy. Plus it will allow you to separate the gathering (through calls to an SQLite Database or an API) of data from the Controller (activities and fragments).
I made a annotation library that can do the cast for you. check this out.
https://github.com/zeroarst/callbackfragment/
#CallbackFragment
public class MyFragment extends Fragment {
#Callback
interface FragmentCallback {
void onClickButton(MyFragment fragment);
}
private FragmentCallback mCallback;
#Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.bt1
mCallback.onClickButton(this);
break;
case R.id.bt2
// Because we give mandatory = false so this might be null if not implemented by the host.
if (mCallbackNotForce != null)
mCallbackNotForce.onClickButton(this);
break;
}
}
}
It then generates a subclass of your fragment. And just add it to FragmentManager.
public class MainActivity extends AppCompatActivity implements MyFragment.FragmentCallback {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getSupportFragmentManager().beginTransaction()
.add(R.id.lo_fragm_container, MyFragmentCallbackable.create(), "MY_FRAGM")
.commit();
}
Toast mToast;
#Override
public void onClickButton(MyFragment fragment) {
if (mToast != null)
mToast.cancel();
mToast = Toast.makeText(this, "Callback from " + fragment.getTag(), Toast.LENGTH_SHORT);
mToast.show();
}
}
Google Recommended Method
If you take a look at this page you can see that Google suggests you use the ViewModel to share data between Fragment and Activity.
Add this dependency:
implementation "androidx.activity:activity-ktx:$activity_version"
First, define the ViewModel you are going to use to pass data.
class ItemViewModel : ViewModel() {
private val mutableSelectedItem = MutableLiveData<Item>()
val selectedItem: LiveData<Item> get() = mutableSelectedItem
fun selectItem(item: Item) {
mutableSelectedItem.value = item
}
}
Second, instantiate the ViewModel inside the Activity.
class MainActivity : AppCompatActivity() {
// Using the viewModels() Kotlin property delegate from the activity-ktx
// artifact to retrieve the ViewModel in the activity scope
private val viewModel: ItemViewModel by viewModels()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
viewModel.selectedItem.observe(this, Observer { item ->
// Perform an action with the latest item data
})
}
}
Third, instantiate the ViewModel inside the Fragment.
class ListFragment : Fragment() {
// Using the activityViewModels() Kotlin property delegate from the
// fragment-ktx artifact to retrieve the ViewModel in the activity scope
private val viewModel: ItemViewModel by activityViewModels()
// Called when the item is clicked
fun onItemClicked(item: Item) {
// Set a new item
viewModel.selectItem(item)
}
}
You can now edit this code creating new observers or settings methods.
There are severals ways to communicate between activities, fragments, services etc. The obvious one is to communicate using interfaces. However, it is not a productive way to communicate. You have to implement the listeners etc.
My suggestion is to use an event bus. Event bus is a publish/subscribe pattern implementation.
You can subscribe to events in your activity and then you can post that events in your fragments etc.
Here on my blog post you can find more detail about this pattern and also an example project to show the usage.
I'm not sure I really understood what you want to do, but the suggested way to communicate between fragments is to use callbacks with the Activity, never directly between fragments. See here http://developer.android.com/training/basics/fragments/communicating.html
You can create declare a public interface with a function declaration in the fragment and implement the interface in the activity. Then you can call the function from the fragment.
I am using Intents to communicate actions back to the main activity. The main activity is listening to these by overriding onNewIntent(Intent intent). The main activity translates these actions to the corresponding fragments for example.
So you can do something like this:
public class MainActivity extends Activity {
public static final String INTENT_ACTION_SHOW_FOO = "show_foo";
public static final String INTENT_ACTION_SHOW_BAR = "show_bar";
#Override
protected void onNewIntent(Intent intent) {
routeIntent(intent);
}
private void routeIntent(Intent intent) {
String action = intent.getAction();
if (action != null) {
switch (action) {
case INTENT_ACTION_SHOW_FOO:
// for example show the corresponding fragment
loadFragment(FooFragment);
break;
case INTENT_ACTION_SHOW_BAR:
loadFragment(BarFragment);
break;
}
}
}
Then inside any fragment to show the foo fragment:
Intent intent = new Intent(context, MainActivity.class);
intent.setAction(INTENT_ACTION_SHOW_FOO);
// Prevent activity to be re-instantiated if it is already running.
// Instead, the onNewEvent() is triggered
intent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP | Intent.FLAG_ACTIVITY_CLEAR_TOP);
getContext().startActivity(intent);
There is the latest techniques to communicate fragment to activity without any interface follow the steps
Step 1- Add the dependency in gradle
implementation 'androidx.fragment:fragment:1.3.0-rc01'
I have a class that is handling a database in my Android app. When the database changes, I'd like to update the fragment displaying the information from the frogment. My approach has been to give the fragment a tag and then find the fragment with the following code:
FragmentManager manager = getFragmentManager();
Fragment fragment = manager.findFragmentByTag("Schedule");
if (fragment instanceof ScheduleFragment){
ScheduleFragment fr = (ScheduleFragment)fragment;
fr.scheduleUpdated();
}
However, as long as my database class is not an extension of Fragment, the compiler refuses to recognise getFragmentManager(). To me it makes no sense to extend Fragment, as the database class is no fragment, but a simple helper class to manage the database. Is it possible to get a reference to my fragment without extending Fragment? Or is this bad practice and should be done in another way?
Also, is it possible to get a reference to the fragment from a static method?
try using a localBroadcast manager. when database changes laumch a Broadcast intent. registere this in "Schedule" Fragment and you can handle the database changes.
Refer to this link for more about LocalBroadcast Manager
how to use LocalBroadcastManager?
http://www.vogella.com/tutorials/AndroidBroadcastReceiver/article.html