I have a one android class which extends Activity.
public class MainAct extends Activity{
Context context;
SourceJava srcClass;
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
context = this;
System.out.println("inside oncreate");
setContentView(R.layout.main);
srcClass = new SourceJava();
}
}
I have another Java class as like below and which this is calling from MainAct class.
public class SourceJava {
public SourceJava(){
System.out.println("inside constructor***");
MyClass myClass = new MyClass();
if(myClass != null){
System.out.println("**not null");
myClass.powerOff();
}
}
}
In the SourceJava I am calling another class. i.e
public class MyClass extends Activity{
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
System.out.println("**inside myclass");
powerOff();
}
public void powerOff(){
System.out.println("**inside powerOff");
Intent call = new Intent(Intent.ACTION_DIAL,Uri.parse("tel:5555"));
startActivity(call);
}
}
}
I am getting NullPointerException on line startActivity(call),
myClass.powerOff(); and
srcClass = new SourceJava();
what is the problem with this code?
You are treating MyClass (which is an Activity class) as regular Java class. The MyClass activity is neither registered nor loaded so call to startActivity is pointless here. To do so you need to pass reference of Context to the SourceClass and MyClass via constructors.
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.
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".
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.
Some basic stuff:
I have two override methods in java:
#Override
protected void onCreate(Bundle savedInstanceState) {
...
Car car = new Car();
}
im creating an object inside
and want to call this object in second #Override
#Override
public void onBackPressed() {
car.drive();
}
How can i pass this object between this two methods ?
Declare the variable outside the onCreate and initialize it inside the onCreate.
Car car = null;
#Override
protected void onCreate(Bundle savedInstanceState) {
car = new Car();
}
#Override
public void onBackPressed() {
if (car != null) {
car.drive();
}
}
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();
}