So I have a custom listview. It's like Instagram layout with 1 image and bunch of buttons in each list items. So here's the problem:
I want to implement the share button. To do this, I tried to create a callback from adapter to activity. But it didn't seem to work. Here is what I have so far(I cropped out the unrelated parts):
MainActivity
public class MainActivity extends ActionBarActivity implements ListAdapter.OnShareClickedListener{
ListView main_list;
List<String> url_list;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
main_list = (ListView) findViewById(R.id.listView);
ListAdapter nListAdapter = new ListAdapter(context, url_list);
main_list.setAdapter(nListAdapter);
}
#Override
public void ShareClicked(String url) {
Log.e("Test",url);
}
}
ListAdapter
public class ListAdapter extends BaseAdapter implements View.OnClickListener {
OnShareClickedListener mCallback;
Context context;
public static List<String> url_list;
public ListAdapter(Context c, List<String> list) {
this.context = c;
url_list = list;
}
public interface OnShareClickedListener {
public void ShareClicked(String url);
}
#Override
public void onClick(View v) {
mCallback.ShareClicked("Share this text.");
}
}
}
Error Log:
Attempt to invoke interface method 'void com.packagename.ListAdapter$OnShareClickedListener.ShareClicked(java.lang.String)' on a null object reference
You need to tell the adapter which implementation of the OnShareClickedListener() to use. Right now in your adapter the field mCallback is never assigned to, either you need to have a setOnSharedClickedListener() method in your adapter which you then call from your mainActivity and set it with the main activity's implementation or you need to take in the constructor.
My suggestion would be to use a setter instead of constructor. So what you need to do is this.
Your ListAdapter
public class ListAdapter extends BaseAdapter implements View.OnClickListener {
OnShareClickedListener mCallback;
Context context;
public static List<String> url_list;
public ListAdapter(Context c, List<String> list) {
this.context = c;
url_list = list;
}
public void setOnShareClickedListener(OnShareClickedListener mCallback) {
this.mCallback = mCallback;
}
public interface OnShareClickedListener {
public void ShareClicked(String url);
}
#Override
public void onClick(View v) {
mCallback.ShareClicked("Share this text.");
}
}
Your MainActivty
public class MainActivity extends ActionBarActivity implements ListAdapter.OnShareClickedListener{
ListView main_list;
List<String> url_list;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
main_list = (ListView) findViewById(R.id.listView);
ListAdapter nListAdapter = new ListAdapter(this, url_list);
nListAdapter.setOnShareClickedListener(this);
main_list.setAdapter(nListAdapter);
}
#Override
public void ShareClicked(String url) {
Log.e("Test", url);
}
}
Related
I have an Activity which creates a class that does some work. What is the typical Android method of having this class report back to the Activity in order to update the UI?
My activity, which creates the class:
public class MainActivity extends Activity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
MyClass obj = new MyClass(this);
obj.DoWork();
}
}
The class that does the work, and wants to report back some
public class MyClass(Context context) {
private Context context;
public void DoWork() {
//Do some work with a countdown timer
//Report back some values
}
}
You can create your own interface like this:
public class MainActivity extends Activity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
MyClass obj = new MyClass(this);
obj.setOnWorkDoneListener(new MyClass.OnWorkDoneListener(){
#Override
public void onDone(Values values) {
//Work done, use values
updateUI(values);
}
});
obj.DoWork();
}
}
public class MyClass(Context context) {
private Context context;
public interface OnWorkDoneListener{
void onDone(Values values);
}
private OnWorkDoneListener listener;
public void setOnWorkDoneListener(OnWorkDoneListener listener){
this.listener = listener;
}
public void DoWork() {
//Do some work with a countdown timer
when(workEnded) listener.onDone(backValues);
}
}
I am trying to understand better how to create a custom listener with a simple example but I don't know how to start the interface so that it is not null:
public class MainActivity extends AppCompatActivity implements ListenerButton{
TextView helloToOther;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
helloToOther = findViewById(R.id.helloWorldToOtherActivity);
helloToOther.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this, ButtonActivity.class));
}
});
}
#Override
public void onClickButton(View view) {
Toast.makeText(this, "Estoy en la primera activity", Toast.LENGTH_SHORT).show();
}
}
This is the second activity:
public class ButtonActivity extends AppCompatActivity {
Button btnInterface;
ListenerButton listenerButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_button);
btnInterface = findViewById(R.id.button_activity__btn__button_interface);
setUpButtonInterface();
}
private void setUpButtonInterface() {
btnInterface.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
listenerButton.onClickButton(v);
}
});
}
}
And there's the interface:
public interface ListenerButton {
void onClickButton(View view);
}
Basically I get a null pointer exception on the second activity because the interface is null, but I don't fall right now as I can start it. Thank you very much.
the reason you are getting a null pointer exception is because you haven't assigned anything to variable listenerButton and therefor it is in fact null!!
you don't need a new interface for that you just need to do this:
public class ButtonActivity extends AppCompatActivity {
Button btnInterface;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_button);
btnInterface = findViewById(R.id.button_activity__btn__button_interface);
setUpButtonInterface();
}
private void setUpButtonInterface() {
btnInterface.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//do whatever you want to do when button is clicked!
}
});
}
}
if you want to define whatever you want to do when button is clicked you need a class and not an interface:
public class ButtonListener implements View.OnClickListener{
#Override
public void onClick(View v) {
//do whatever you want to do when button is clicked!
}
}
and then in your activity do this:
public class ButtonActivity extends AppCompatActivity {
Button btnInterface;
ListenerButton listenerButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_button);
listenerButton = new ButtonListener();
btnInterface = findViewById(R.id.button_activity__btn__button_interface);
setUpButtonInterface();
}
private void setUpButtonInterface() {
btnInterface.setOnClickListener(listenerButton);
}
}
Create a new file:
MyListener.java:
public interface MyListener {
// you can define any parameter as per your requirement
public void callback(View view, String result);
}
In your activity, implement the interface:
MyActivity.java:
public class MyActivity extends Activity implements MyListener {
#override
public void onCreate(){
MyButton m = new MyButton(this);
}
// method is invoked when MyButton is clicked
#override
public void callback(View view, String result) {
// do your stuff here
}
}
In your custom class, invoke the interface when needed:
MyButton.java:
public class MyButton {
MyListener ml;
// constructor
MyButton(MyListener ml) {
//Setting the listener
this.ml = ml;
}
public void MyLogicToIntimateOthers() {
//Invoke the interface
ml.callback(this, "success");
}
}
How can I start getdata() method to another class. I want to show the output to a `ListView which is in another Java class.
tab1Background.java
public class tab1Background extends Activity{
ListView lv;
lv = (ListView) findViewById(R.id.lv);
//some code here
public void getdata() {
//some code here
}
}
tab1report.java i want to start the getdata() activity to show data in listview
public class tab1report extends Fragment {
//some code here
}
public class tab1report extends Fragment {
public void startSomething()
{
((tab1Background) getActivity()).getdata();
}
}
You could use callback method.
public class tab1report extends Fragment {
Callback callback;
public interface Callback {
void call();
}
onAttach(Context context) {
callback = (Callback) context;
}
onStart() {
// Some code here
callback.call();
}
}
public class tab1Background extends Activity implements tab1report.Callback {
ListView lv;
lv = (ListView) findViewById(R.id.lv);
//some code here
public void getdata() {
//some code here
}
public void call() {
getdate();
}
}
This will ensure that the functionality is passed back to the activity.
I am developing an Android app and thus, I have a MainActivity class. Inside of that MainActivity class, I have a method, let's call it doSomething():
public class MainActivity extends AppCompatActivity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void doSomething(){
// bla bla bla
}
}
I also have a different class (with different layout) that is called OtherActivity. I want to use the doSomething method inside it:
public class OtherActivity extends AppCompatActivity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.other_activity_layout);
// Let's use doSomething()
}
}
I tried this:
public class OtherActivity extends AppCompatActivity {
MainActivity main;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.other_activity_layout);
// Let's use doSomething()
MainActivity main = new MainActivity();
main.doSomething();
}
}
But it does not work. I also tried to make OtherActivity to extend the MainActivity, doing the following:
public class OtherActivity extends MainActivity{
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.other_activity_layout);
// Let's use doSomething()
super.doSomething();
}
}
But it does not allow me to initialize the layout...
How can I do?
Thanks in advance.
To communicate between to Activity Broadcast is the best way, and for the same application, we can use local broadcast using LocalBroadcastManager.
First, we should register one broadcast in MainActivity,
public class MainActivity1 extends AppCompatActivity {
public static final String INTENT_FILTER = "do_some_action";
public static final String INTENT_BUNDLE_VALUE = "value1";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main1);
LocalBroadcastManager.getInstance(this).registerReceiver(
mChangeListener, new IntentFilter(INTENT_FILTER));
}
#Override
protected void onDestroy() {
super.onDestroy();
LocalBroadcastManager.getInstance(this).unregisterReceiver(mChangeListener);
}
private BroadcastReceiver mChangeListener = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intentData) {
// you can do anything here
if (intentData != null && intentData.hasExtra(INTENT_BUNDLE_VALUE)) {
String value = intentData.getStringExtra(INTENT_BUNDLE_VALUE);
doSomeAction(value);
}
}
};
private void doSomeAction(String value) {
}
}
Then to do some action in MainActivity from OtherActivity, we can send Local broadcast from OtherActivity it will reach the receiver of Which we register in MainActivity,
public class OtherActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_other);
// You can call MainActivity to do some actions
Intent intent = new Intent(MainActivity1.INTENT_FILTER);
intent.putExtra(MainActivity1.INTENT_BUNDLE_VALUE, "Any string or any value");
LocalBroadcastManager.getInstance(this).sendBroadcast(intent);
}
}
Done!!!.
Something like this should do the trick, I'm going to make a static navigator to handle your navigation logic. If you are opposed to static methods you could also make them on your Application object to make it easier to manage dependencies, I'm just making it static for simplicity.
//Making this fully static for simplicity, this is fine for a small app
//you can make it a singleton on the application class for more flexibility
public class Navigator {
//static member vars that determine navigation
// pass in Context if needed for navigation purposes
public static void doSomething(Context context){
// bla bla bla
}
}
public class MainActivity extends AppCompatActivity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_activity_layout);
}
private void doSomething() {
Navigator.doSomething(this);
}
}
public class OtherActivity extends AppCompatActivity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.other_activity_layout);
}
private void doSomething() {
Navigator.doSomething(this);
}
}
I want to use the button for different calls in the different classes. However, when I declare and try to call the Button click method in the Activity class, it throws a null exception. In my Class I want to do this:
public class CustomFeedListViewAdapter extends BaseAdapter {
holder.feedUpVoteButton = (Button) view.findViewById(R.id.feedUpVoteButton);
holder.feedUpVoteButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//do stuff
}
});
private class ViewHolder {
Button feedUpVoteButton;
}
And in my main activity I want to do this:
public class Feed extends AppCompatActivity {
Button upVoteButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_feed);
upVoteButton = (Button) findViewById(R.id.feedUpVoteButton);
feedUpVoteButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//do stuff
}
});
}
}
You are getting NullPointerException because you are trying to access feedUpVoteButton which is present in the item layout used in CustomFeedListViewAdapter and not in the layout used by Feed activity.
Do you want to have access to the ClickListener whenever you create an adapter of type CustomFeedListViewAdapter? If yes then do this...
Your Activity class
public class Feed extends AppCompatActivity {
CustomFeedListViewAdapter adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_feed);
adapter = new CustomFeedListViewAdapter( new OnClickListener() {
#Override
public void onClick(View v) {
// Handle click here
}
});
}
}
And your custom adapter class
public class CustomFeedListViewAdapter extends BaseAdapter {
View.OnClickListener clickListener;
// Constructor
public CustomFeedListViewAdapter(View.OnClickListener listener) {
clickListener = listener;
}
#Override
void getView(){
holder.feedUpVoteButton = (Button) view.findViewById(R.id.feedUpVoteButton);
holder.feedUpVoteButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//do stuff
}
});
}
}
This way you can set a different listener for each instance of the adapter you create.