I'm trying to build an App for Android Lollipop (5.0). There is a login fragment and when i press login button then app automatically crashes. I'm sharing my code and error message please guide me.
BaseActivity.java
public abstract class BaseActivity extends AppCompatActivity {
protected CoreApplication coreApplication;
#Override
protected void onCreate(Bundle savedState) {
super.onCreate(savedState);
coreApplication = (CoreApplication) getApplication();
}
}
BaseAuthenticatedActivity.java
public abstract class BaseAuthenticatedActivity extends BaseActivity {
#Override
protected final void onCreate(Bundle savedState) {
super.onCreate(savedState);
if (!coreApplication.getAuth().getUser().isLoggedIn()) {
startActivity(new Intent(this, LoginActivity.class));
finish();
return;
}
onCoreApplicationCreate(savedState);
}
protected abstract void onCoreApplicationCreate(Bundle savedState);
}
LoginActivity.java
public class LoginActivity extends BaseActivity implements View.OnClickListener, LoginFragment.CallBacks {
private static final int REQUEST_NARROW_LOGIN = 1;
private View loginButton;
#Override
protected void onCreate(Bundle savedState) {
super.onCreate(savedState);
setContentView(R.layout.activity_login);
loginButton = findViewById(R.id.LoginJustChat);
if (loginButton != null) {
loginButton.setOnClickListener(this);
}
}
#Override
public void onClick(View view) {
if (view == loginButton)
startActivityForResult(new Intent(this, LoginNarrowActivity.class), REQUEST_NARROW_LOGIN);
}
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (resultCode != RESULT_OK)
return;
if (requestCode == REQUEST_NARROW_LOGIN) {
finishLogin();
}
}
private void finishLogin() {
startActivity(new Intent(this, MainActivity.class));
finish();
}
#Override
public void onLoggedIn() {
finishLogin();
}
}
LoginNarrowActivity.java
public class LoginNarrowActivity extends BaseActivity implements LoginFragment.CallBacks {
#Override
protected void onCreate(Bundle savedState){
super.onCreate(savedState);
setContentView(R.layout.activity_login_narrow);
}
#Override
public void onLoggedIn() {
setResult(RESULT_OK);
finish();
}
}
MainActivity.java
public class MainActivity extends BaseAuthenticatedActivity {
#Override
protected void onCoreApplicationCreate(Bundle savedState) {
}
}
BaseFragment.java
public abstract class BaseFragment extends Fragment {
protected CoreApplication application;
#Override
public void onCreate(Bundle savedInstance) {
super.onCreate(savedInstance);
application = (CoreApplication) getActivity().getApplication();
}
}
LoginFragment.java
public class LoginFragment extends BaseFragment implements View.OnClickListener {
private Button loginButton;
private CallBacks callBacks;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup root, Bundle savedState) {
View view = inflater.inflate(R.layout.fragment_login, root, false);
loginButton = (Button) view.findViewById(R.id.fragment_login_loginButton);
loginButton.setOnClickListener(this);
return view;
}
#Override
public void onClick(View view) {
if (view == loginButton) {
application.getAuth().getUser().setIsLoggedIn(true);
callBacks.onLoggedIn();
}
}
// because onAttach(Activity activity) is deprecated
#Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof CallBacks) {
callBacks = (CallBacks) context;
} else {
throw new ClassCastException(context.toString()
+ " must implement MyListFragment.OnItemSelectedListener");
}
}
#Override
public void onDetach() {
super.onDetach();
callBacks = null;
}
public interface CallBacks {
void onLoggedIn();
}
}
Error:
java.lang.NullPointerException: Attempt to invoke interface method
'void
com.example.usama.demoapp.fragments.LoginFragment$CallBacks.onLoggedIn()'
on a null object reference
Please guide me with this.
Welcome to Android !
You got a NullPointerException. It's a very common [and lovely; since it's rather easy to debug] exception in Java. Check your LoginFragment. The following method will cause this exception to raise.
#Override
public void onClick(View view) {
if (view == loginButton) {
application.getAuth().getUser().setIsLoggedIn(true);
callBacks.onLoggedIn();
}
}
A couple of notes in order to diagnose this error:
When you declare a class member with initializing it, in this casecallBacks, Java automatically initialize it to null.
Invoking any method on a null reference will result in NPE.
Okay, let's narrow down to your specific case. You declared a class member called callBacks but never initialized it, as well as, I can see no methods that assign something to it. Therefore, that class member always remains null and thereby any subsequent method invocation on it leads us to NPE.
As a solution, you should add a setter method to your LoginFragment class in which you set that callBacks. In other side supply this object where you first create an instance of this fragment.
Update #1
when i pass Activity instead of Context as parameter in onAttach method it works. but i want to know why it is causing the error?
The why is simple. Since your activity already implemented that interface, so passing it to your LoginFragment as context will result in the condition if (context instanceof CallBacks) becoming true. However, passing bare context won't result in establishment of that if statement.
can u please tell me how i can define setter?
It's pretty simple! Just as other regular method, declare a method like this:
public void setOnLoginListener(Callbacks listener){
this.callbacks = listener;
}
Update #2
where i need to define setOnLoginListener method
Inside the LoginFragment class.
and where should i call it
In your main activity where you first instantiate LoginFragment class.
with what parameters?
Your activity, which implements that Java interface.
You can avoid setting onClickListener for the button by having adding android:onClink="login" in your xml file and a function that looks like this in your java file:
public void login(View view) {
application.getAuth().getUser().setIsLoggedIn(true);
callBacks.onLoggedIn();
}
You can try writing a public setter for the callBacks object in LoginFragment and setting it from the activity instead, like this, supposing you defined your fragment in the activity's layout file:
public class LoginNarrowActivity extends BaseActivity implements LoginFragment.CallBacks {
#Override
protected void onCreate(Bundle savedState){
super.onCreate(savedState);
setContentView(R.layout.activity_login_narrow);
LoginFragment loginFragment = (LoginFragment)getSupportFragmentManager().findFragmentById(R.id.your_fragment_id);
loginFragment.setCallBacks(this);
}
Actually the error was here in onAttach(Context context) when i pass Activity like this onAttach(Activity activity) then it worked. But i want to know why it is causing the error? and onAttach(Activity activity) is deprecated in android 5.0
Related
I have troubles on calling the method update from MainActivity class in a the MSG0100 non-activity class
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void update(boolean msg100Preselection){
if(msg100Preselection){
mExpandableListViewAdapter.setSelectedChild(-1);
mExpandableListViewAdapter.notifyDataSetChanged();
}
}
}
And this is my class where i want to call the update method of Mainactivity.
public class MSG0100{
boolean msg100Preselection=false;
pulic void onUpdate(){
msg100Preselection=true;
// Want to call my update method here
MainActivity activity= new MainActivity();
activity.update(msg100Preselection); //<-------- Using mainactiviy object crashes my app.
}
}
What you want is impossible as you dont have a pointer to your main activity.
The following statement is invalid.
MainActivity activity= new MainActivity();
You are not allowed to use the new operator to create an activity. That should be done using an intent.
There are several things you could do:
Move your update method in another class
OR
declare your update method as static and use it like this:
MainActivity.update(msg100Preselection);
Try using a callbackListener :-
In your MSG0100 class
public class MSG0100 {
boolean msg100Preselection = false;
private static OnUpdateListener mListener;
public static setListener(OnUpdateListener mListener) {
this.mListener = mListener;
}
public void onUpdate() {
msg100Preselection = true;
if (mListener != null)
mListener.onUpdate(msg100Preselection);
}
public interface OnUpdateListener()
{
void onUpdate ( boolean msg100Preselection);
}
}
In your MainActivity-
public class MainActivity extends AppCompatActivity, OnUpdateListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
MSG0100.setListener(this)
}
#Override
public void onUpdate(boolean msg100Preselection) {
if (msg100Preselection) {
mExpandableListViewAdapter.setSelectedChild(-1);
mExpandableListViewAdapter.notifyDataSetChanged();
}
}
#Override
protected void onDestroy() {
super.onDestroy();
MSG0100.setListener(null)
}
}
This way you won't have any memory leaks or crashes due to Activity being killed.
I have two Classes "BaseActivity" and "ChildActivity" i.e. ChildActivity inherts BaseActivity.
Question: In my following Code Snippet, whenever i press LEFT BUTTON - it logs me "I am From Child Activity". What would i need to do if i want to call SUPER CLASS functionality by default.
public class BaseActivity extends Activity implements OnClickListener {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
};
protected void configureTitleBar(String title) {
ImageButton imgLeftButton = ((ImageButton) findViewById(R.id.actionBarLeftButton));
imgLeftButton.setOnClickListener(BaseActivity.this);
}
#Override
public void onClick(View v) {
if(v.getId() == R.id.actionBarLeftButton){
printCustomLog("I am From Base");
}
}
}
Child Activity:
public class ChildActivity extends BaseActivity implements OnClickListener{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_child);
configureTitleBar("MyTitle");
}
#Override
public void onClick(View v) {
if(v.getId() == R.id.actionBarLeftButton){
printCustomLog("I am From Child Activity");
}
}
}
If you want to get super class functionality, you can
a) Not Override the onClick() method at all (but I don't think that's what you want)
b) Call super.onClick(v) from onClick() in your child class.
The code in your ChildActivity will then be.
#Override
public void onClick(View v) {
// Check some condition if you want to handle it in Child class
if(condition){
printCustomLog("I am From Child Activity");
}
// Else, as default, call Base class's onClick()
else{
super.onClick(v);
}
}
#Override
public void onClick(View v) {
if (v.getId() == R.id.actionBarLeftButton) {
// here's my work
}
super.onClick(v); // it will call Super's OnClick
}
I want to implement the ...
#Override
public void onBackPressed() {
}
However, I get an error message saying, "Annotations are not allowed here". I need this method to be implemented here. Is there an alternative?
public class supbreh extends Appbreh
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_intent_breh);
if (myBundle != null) {
String name = myBundle.getString("workout");
ShowDetails(name);
}
}
private void ShowAbDetails(String mName) {
if(mName.equals("abs1")){
#Override
public void onBackPressed() { //"Not Allowed here"
}
}
void onBackPressed ()
Called when the activity has detected the user's press of the back
key. The default implementation simply finishes the current activity,
but you can override this to do whatever you want.
In here you can't declare this method inside another method .
Only override it in that one Activity
#Override
public void onBackPressed()
{
super.onBackPressed();
}
FYI
#Override
public void onBackPressed() {
Intent intent = new Intent(IndividualAbsWorkout.this, IndividualAbsWorkout.class);
startActivity(intent);
}
You can override onBackPressed as normal and call the method in ShowAbDetails() method like below.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_intent_breh);
if (myBundle != null) {
String name = myBundle.getString("workout");
ShowDetails(name);
}
}
private void ShowAbDetails(String mName) {
if(mName.equals("abs1")){
onBackPressed();
}
}
#Override
public void onBackPressed() {
// your logic here
}
I need to call an Intent from the onBindViewHolder of the recycler adapter , on a click event from one of the views in the ViewHolder. I am unable to do so directly ..
public void onBindViewHolder(MyAdapter.MyViewHolder viewHolder, int i) {
viewHolder.button.setonClickListener(new View.onClickListener(
#Override
onClick(View v) {
Intent i=new Intent();
i.setAction("Intent.ACTION_CALL");
i.setData(Uri.parse("tel:1234567890"));
startActivity(i);
}
));
}
This did not work. It kept throwing error. I then created a public method in the Activity with the same code. Passed Activity context in the Adapter constructor. Then called the Method as follows from button click event.
((MyActivity)context).makePhoneCall("1234567890");
This did the trick. But i feel there should be a better method of doing this.
As i am primarily from C background, i am not sure.
So my question is there a better or more proper way to do this , according to Java programming conventions.
If you need to call another activity via Intent, you can use any view's Context:
v.getContext().startActivity(i);
I think this is a correct method.
Another way is to implement a listener in the recycleradapter and listen it in the activity.
So in the adapter:
public class RecyclerAdapter .... {
private MyClickListener listener;
public void onBindViewHolder(MyAdapter.MyViewHolder viewHolder, int i) {
viewHolder.button.setonClickListener(new View.onClickListener(
#Override
onClick(View v) {
listener.onClicked(true);
}
));
public void setMyClickListener(MyClickListener listener) {
this.listener = listener;
}
}
//create MyClickListener.class
public interface MyClickListener {
public void onClicked(boolean status);
}
In your Activity:
public class MainActivity ... implements MyClickListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
adapter.setMyClickListener(this);
}
#Override
onClick(boolean status) {
if (status){
Intent i=new Intent();
i.setAction("Intent.ACTION_CALL");
i.setData(Uri.parse("tel:1234567890"));
startActivity(i);
};
}
}
Try this
In your Adapter:
Activity mContext;
public FollowersAdapter(Activity mContext) {
this.mContext = mContext;
}
//And then your click in onBindViewHolder
holder.linear_user.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
System.out.println("linear click>>>>>>>>>>>>");
Intent ToImage = new Intent(mContext, UserData.class);
ToImage.putExtra("user_id", data.get(position).getFollower_id());
mContext.startActivity(ToImage);
}
});
I have service, which gets data from API and sends this data to BroadcastReceiver class. Also, I create interface OnReceiveListener, which used in Activity. Look at the code here:
Activity:
public class StartActivity extends AppCompatActivity
implements MyBroadcastReceiver.OnReceiveListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_start);
MyBroadcastReceiver receiver = new MyBroadcastReceiver();
receiver.setOnReceiveListener(this);
LocalBroadcastManager.getInstance(this).registerReceiver(receiver,
new IntentFilter(MyBroadcastReceiver.START));
...
}
#Override
public void onReceive(Intent intent) {
// Do smth here
}
}
MyBroadcastReceiver:
public class MyBroadcastReceiver extends BroadcastReceiver {
public static final String START = "com.example.myapp.START";
public static final String GET_LINKS = "com.example.myapp.GET_LINKS";
private OnReceiveListener onReceiveListener = null;
public interface OnReceiveListener {
void onReceive(Intent intent);
}
public void setOnReceiveListener(Context context) {
this.onReceiveListener = (OnReceiveListener) context;
}
#Override
public void onReceive(Context context, Intent intent) {
if(onReceiveListener != null) {
onReceiveListener.onReceive(intent);
}
}
}
Service isn't important on this question.
---- Question ----
So, what's problem: I want to use this receiver in fragment, but when it sets context - I get exception "enable to cast". What I should to do on this case?
Here is my code in fragment:
public class MainFragment extends Fragment
implements MyBroadcastReceiver.OnReceiveListener {
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
MyBroadcastReceiver myBroadcastReceiver = new MyBroadcastReceiver();
myBroadcastReceiver.setOnReceiveListener(getContext());
LocalBroadcastManager.getInstance(getContext()).registerReceiver(myBroadcastReceiver,
new IntentFilter(MyBroadcastReceiver.GET_LINKS));
}
#Override
public void onReceive(Intent intent) {
// Do smth here
}
}
Your MainFragment class implements your OnReceiveListener interface, not its Context as returned by getContext(). Instead of passing a Context object into setOnReceiveListener(), try directly passing an OnReceiveListener instance. Then your fragment and activity can both call setOnReceiveListener(this).
you don't need to dynamically register the receiver. i believe you must have registered it in manifest using <receiver> tag.
this is not required:
LocalBroadcastManager.getInstance(getContext()).registerReceiver(myBroadcastReceiver,
new IntentFilter(MyBroadcastReceiver.GET_LINKS));
and about callback registering listener, instead of using getContext() use MainFragment.this like this:
myBroadcastReceiver.setOnReceiveListener(MainFragment.this);
After searching for hours for the appropriate way to implement such a solution to this problem, I've found a way finally. It is based on RussHWolf's answer. The complete solution with code is below:
In this way, a setListener() method is exposed so that Fragment or Activity can set the listener by sending an instance of IStatusChangeListener.
public class StatusChangeReceiver extends BroadcastReceiver {
private IStatusChangeListener listener;
public void setListener(IStatusChangeListener listener) {
this.listener = listener;
}
#Override
public void onReceive(Context context, Intent intent) {
if (NetworkUtil.isNetworkConnected()) {
listener.onConnected();
} else {
listener.onDisconnected();
}
}
}
This is the interface:
public interface IStatusChangeListener {
void onConnected(String status);
void onDisonnected(String status);
}
Now, it is required to have an instance of IStatusChangeListener interface instead of implementing the IStatusChangeListener interface. And then, pass this instance of IStatusChangeListener to setListener() method.
public class MainFragment extends Fragment { //Not implementing the interface
private IStatusChangeListener listener = new IStatusChangeListener() {
#Override
void onConnected(String status) {
//some log here
}
#Override
void onDisonnected(String status) {
//some log here
}
}
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
StatusChangeReceiver r = new StatusChangeReceiver();
r.setListener(listener); // pass the IStatusChangeListener instance
LocalBroadcastManager.getInstance(getContext()).registerReceiver(r, new IntentFilter("connectionStatus"));
}
}
Note: Always use LocalBroadcastManager if you register BroadcastReceiver from Fragment.