Develop Reference

ButterKnife in multiple activity

This is the code that I try to use with ButterKnife but I got the following error when I run the project.
error: cannot find symbol class Activity
error: package Activity does not exist
error: package Activity does not exist
BaseActivity
public abstract class BaseActivity extends AppCompatActivity {
private Unbinder unbinder;
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(getLayoutResource());
ButterKnife.bind(this);
setupUI();
}
protected abstract int getLayoutResource();
protected abstract void setupUI();
}
MainActivity
public class MainActivity extends BaseActivity {
#Override
protected void setupUI() {
}
#Override
protected int getLayoutResource() {
return R.layout.activity_main;
}
}
RegisterActivity
public class RegisterActivity extends BaseActivity {
#BindView(R.id.editText_username)
EditText et;
#Override
protected void setupUI() {
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}
#Override
protected int getLayoutResource() {
return R.layout.activity_register;
}
#Override
public void onBackPressed() {
this.finish();
}
}
What's my mistake why I can't bind multiple Activities with the abstract class?
Github Project

First, you don't need Unbinder for Activitybecause Unbinder is only needed forFragment`.
Second, you better use another method to be override so that you don't need to set the onCreate. Something like this:
public abstract class BaseActivity extends AppCompatActivity {
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(getLayoutResource());
ButterKnife.bind(this);
setupUI();
}
protected abstract int getLayoutResource();
protected abstract void setupUI();
}
which then you can use:
public class MainActivity extends BaseActivity {
#Override
protected void setupUI() {
// setup the UI.
}
#Override
protected int getLayoutResource() {
return R.layout.activity_main;
}
}
Here is the working example for using ButterKnife with abstract class:
https://github.com/isnotmenow/ButterKnifeAbstractSample

How to create a method inside onCreate() in Android

How do I create a method inside onCreate() method? When I am creating its showing error:
Syntax error on token void # expected
And if method can not be created inside onCreate() method than please tell me how do I create a method outside the onCreate() and pass mContext and mActivity from the onCreate() method.

public class MainActivity extends Activity{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
yourmethod();
}
public void yourmethod(){
// your code here
}
}

public class MainActivity extends Activity {
//Declare a class variable to use in this class
public <data-type> mContext;
public <data-type> mActivity;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mContext = <Your value>;
mActivity = <Your value>;
myMethod (mContext , mActivity);
}
private void myMethod (<data-type> mContext, <data-type> mActivity) {
/*
Your Code Goes Here
*/
}
}
*Note that tags like should be replaced by actual types without inequality signs, such as "int" and "short".

How to set broadcast listener interface in fragment?

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.

cannot execute android activity

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

Interface lister

I have an interface MyListner
public interface MyListner{
public void onOperationComplete();
}
I have two Activity SignIn and SignUp which implements MyListner
public class SignIn extends Activity implements MyListner{
#Override
public void onOperationComplete(){
Log.e("SignIn","Operation Complete");
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Operation.doOperation();
}
}
public class SignUp extends Activity implements MyListner{
#Override
public void onOperationComplete(){
Log.e("SignUp","Operation Complete");
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Operation.doOperation();
}
}
Inside onCreate() of both Activity i am calling a static function doOperation() inside the class Operation for doing some operation by Operation.doOperation().
public class Operation{
publis static void doOperation(){
...........
...........
...........
//here i want a callback to interface funtion onOperationComplete()
}
}
My requirement is that i want to get a callback to the function onOperationComplete() inside all the class which implements MyListner

make your doOperation like this:
public class Operation{
publis static void doOperation(MyListener callBack){
...........
...........
...........
//here i want a callback to interface funtion onOperationComplete()
callBack.onOperationComplete();
}
}
In Your Activity:
public class SignIn extends Activity implements MyListner{
#Override
public void onOperationComplete(){
Log.e("SignIn","Operation Complete");
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Operation.doOperation(this);
}
}

You may want to look for Observer pattern
You can make your Operation class singleton
Add an attribute of "Collection listeners" inside Operation class
Add a public method called "addListener(MyListener)" which stores the passed parameter into the "listeners" attribute
Inside onCreate() of the Activity, call
Operation.getInstance().addListener(this);
When you want to perform the operation, call
for(MyListener listener : listeners){
listener.onOperationComplete();
}