Develop Reference

Where to call bind and unbind method in custom view when using ButterKnife?

I'm new to Android. I wrote a custom view, but I just don't know where to call the bind and unbind method. I have searched for this documentation. And it seemingly suggests to use bind in the onFinishInflate() callback. But I bind the view in its constructor function and there is no crash any way. Is it correct? And how about the unbind? I find this question, it suggests to use unbind in the onDetachedFromWindow() callback. Is it required or necessary?
public class BloodIndicatorView extends FrameLayout {
#Bind(R.id.ll_record_bloodpress)
LinearLayout llRecordBloodpress;
#Bind(R.id.ll_record_bloodsugar)
LinearLayout llRecordBloodsugar;
private Context mContext;
public BloodIndicatorView(Context context) {
this(context, null);
}
public BloodIndicatorView(Context context, AttributeSet attrs) {
this(context, attrs, -1);
}
public BloodIndicatorView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
mContext = context;
init();
}
private void init() {
LayoutInflater.from(mContext).inflate(R.layout.health_blood_indicator, this);
ButterKnife.bind(this);
}
public void update() {
}
#OnClick(R.id.ll_record_bloodpress)
public void recordBloodpress() {
Intent intent = BloodPressActivity.getIntent2Act(mContext);
mContext.startActivity(intent);
}
#OnClick(R.id.ll_record_bloodsugar)
public void recordBloodsugar() {
Intent intent = BloodSugarActivity.getIntent2Act(mContext);
mContext.startActivity(intent);
}
}

You can annotate the view inside the class which you are doing correctly and since there is no error that means ButterKnife.bind(this); is happening correctly. And its not necessary to unbind this should work completely fine.

Android Button internal onClick actions

I'm making a custom button which is designed to handle onClick events internally. Here's a simplified version of my implementation:
public class CustomButton extends Button implements View.OnClickListener {
public CustomButton(Context context) {
super(context);
setOnClickListener(this);
}
#Override
public void onClick(View v) {
setText("Clicked!");
}
}
No surprises in the above code! The problem is that the activity/fragment/whatever containing the button could call setOnClickListener(View) which would prevent the onClick(View) method inside the button from receiving the onClick event, thus changing the function of my button in an undesirable way. I though about overriding setOnClickListener(View) to throw an exception if the argument is not this, but I don't want to prevent the button from having external listeners, I just want to add an internal feature.
Which method of Button if any can I override to do extra stuff when the button is clicked without taking away the ability of other classes to listen to onClick events? Basically, which method in Button dispatches OnClick events?

I thought of a solution. I made CustomButton as follows:
public class CustomButton extends Button implements View.OnClickListener {
private OnClickListener externalOnClickListener;
public CustomButton(Context context) {
super(context);
super.setOnClickListener(this);
}
public CustomButton(Context context, AttributeSet attrs) {
super(context, attrs);
super.setOnClickListener(this);
}
public CustomButton(Context context, AttributeSet attrs, int defStyleAttrs) {
super(context, attrs, defStyleAttrs);
super.setOnClickListener(this);
}
#Override
public void onClick(View v) {
// Do all of my stuff
setText("Clicked!");
setBackground(Color.GREEN);
// Pass onClick event to external listener
if (externalOnClickListener != null) {
externalOnClickListener.onClick(v);
}
}
#Override
public void setOnClickListener(OnClickListener l) {
externalOnClickListener = l;
}
}
Basically setOnClickListener() is overriden so that it just stores the passed listener as an instance variable. At construction, the button sets itself as its own on click listener, so that it can receive the on click events, do something, then pass the event on to the stored listener.

Creating custom control with overriding onclick

I am working on an android app and I have a custom GUI component which extends a TextView.
I want to have my custom control do a task when clicked from my custom control class and my overridden onclick method.
For example my class that extends the TextView implements the OnClick listener and writes a log to the log cat.
Then in my activity, I set an onclick listener to my custom control, and this shows a toast notification.
What I want to happen, is when my custom control is clicked, my activities overridden onclick shows the toast and the custom control class on click method also is run to show the log. But I can only seem to get one working or the other, for example, if I don't run myCustom.setOnClickListener(myListener) then the classes onclick is used and does the log, if I set the onClick listener then I only get the toast not the log.
Below is my custom control class
public class NavTextView extends TextView implements View.OnClickListener
{
public NavTextView(Context context) {
super(context);
setOnClickListener(this);
}
public NavTextView(Context context, AttributeSet attrs) {
super(context, attrs);
setOnClickListener(this);
}
public NavTextView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
setOnClickListener(this);
}
public NavTextView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
setOnClickListener(this);
}
#Override
public void onClick(View v) {
Log.d("NavTextView", "This has been clicked");
}
}
Below is my activities onCreate method
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
navTextView = (NavTextView)findViewById(R.id.navTextView);
navTextView.setOnClickListener(mClickListener);
}
Hope this makes sense

A View can only have one OnClickListener. In your NavTextView you are setting it there. If you later call setOnClickListener again, you are replacing the previous listener.
What you can do is override setOnClickListener in your custom View, then wrap the OnClickListener and call both.
public class MyTextView extends TextView implements View.OnClickListener
{
OnClickListener _wrappedOnClickListener;
public MyTextView(Context context) {
super(context);
super.setOnClickListener(this);
}
#Override
public void onClick(View view) {
Log.d("NavTextView", "This has been clicked");
if (_wrappedOnClickListener != null)
_wrappedOnClickListener.onClick(view);
}
#Override
public void setOnClickListener(OnClickListener l) {
_wrappedOnClickListener = l;
}
}

Android and making `this` a listener for one of its buttons

I have a custom view MyView inflated from my_view.xml (with a corresponding Java class MyView.java).
I override MyView(Context context, AttributeSet attrs) to connect subviews up to members of the class.
Now one of these subviews is a Button, and I'd like for my view to listen for a click on its button before passing this event on to a delegate. However if I declare
this.myButton.setOnClickListener(this);
in the constructor MyView(Context context, AttributeSet attrs) (where this is an instance of MyView) I get a NullPointerException.
Where is an appropriate place in MyClass.java to call this.myButton.setOnClickListener(this);?
%%
Edit. Some code:
public MyView(Context ctx, AttributeSet attrs)
{
super(context, attrs);
this.myButton = (Button) this.findViewById(R.id.my_button);
this.myButton.setOnClickListener(this); // Raises null pointer;'id' is correct.
}

Instead of trying to do the setOnClickListener(this) call in the constructor, do it after the button has been fully initialized. Try moving setOnClickListener(this) so that it's called (indirectly) from the parent activity's onResume method like this:
public class MainMenuActivity extends Activity {
#Override
public void onResume() {
super.onResume();
new MyView(this, attrs).onResume();
}
...
}
public class MyView {
public void onResume() {
myButton.setOnClickListener(this);
}
...
}
I use Roboguice all the time for this sort of thing, and highly recommend it. My button handler code looks like this:
class ButtonHandler implements OnClickListener {
#InjectView(R.id.MainMenuButton)
private Button button;
public void onResumeEvent( #Observes OnResumeEvent onResume ) {
button.setOnClickListener(this);
}
#Override
public void onClick(View v) {
doSomethingUseful();
}
}

The problem is I've missed off an inflate in the constructor:
LayoutInflater i = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
i.inflate(R.layout.my_view, this);
This is confusing for me as I'd thought the constructor MyView(Context ctx, AttributeSet attrs) would be called in inflating the view, not the other way around.

How to create our own Listener interface in android?

Could someone help me to create user defined listener interface with some code snippets?

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");
}
}

please do read observer pattern
listener interface
public interface OnEventListener {
void onEvent(EventResult er);
// or void onEvent(); as per your need
}
then in your class say Event class
public class Event {
private OnEventListener mOnEventListener;
public void setOnEventListener(OnEventListener listener) {
mOnEventListener = listener;
}
public void doEvent() {
/*
* code code code
*/
// and in the end
if (mOnEventListener != null)
mOnEventListener.onEvent(eventResult); // event result object :)
}
}
in your driver class MyTestDriver
public class MyTestDriver {
public static void main(String[] args) {
Event e = new Event();
e.setOnEventListener(new OnEventListener() {
public void onEvent(EventResult er) {
// do your work.
}
});
e.doEvent();
}
}

I have created a Generic AsyncTask Listener which get result from AsycTask seperate class and give it to CallingActivity using Interface Callback.
new GenericAsyncTask(context,new AsyncTaskCompleteListener()
{
public void onTaskComplete(String response)
{
// do your work.
}
}).execute();
Interface
interface AsyncTaskCompleteListener<T> {
public void onTaskComplete(T result);
}
GenericAsyncTask
class GenericAsyncTask extends AsyncTask<String, Void, String>
{
private AsyncTaskCompleteListener<String> callback;
public A(Context context, AsyncTaskCompleteListener<String> cb) {
this.context = context;
this.callback = cb;
}
protected void onPostExecute(String result) {
finalResult = result;
callback.onTaskComplete(result);
}
}
Have a look at this , this question for more details.

There are 4 steps:
1.create interface class (listener)
2.use interface in view 1 (define variable)
3.implements interface to view 2 (view 1 used in view 2)
4.pass interface in view 1 to view 2
Example:
Step 1: you need create interface and definde function
public interface onAddTextViewCustomListener {
void onAddText(String text);
}
Step 2: use this interface in view
public class CTextView extends TextView {
onAddTextViewCustomListener onAddTextViewCustomListener; //listener custom
public CTextView(Context context, onAddTextViewCustomListener onAddTextViewCustomListener) {
super(context);
this.onAddTextViewCustomListener = onAddTextViewCustomListener;
init(context, null);
}
public CTextView(Context context, #Nullable AttributeSet attrs) {
super(context, attrs);
init(context, attrs);
}
public CTextView(Context context, #Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init(context, attrs);
}
#RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
public CTextView(Context context, #Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
init(context, attrs);
}
public void init(Context context, #Nullable AttributeSet attrs) {
if (isInEditMode())
return;
//call listener
onAddTextViewCustomListener.onAddText("this TextView added");
}
}
Step 3,4: implements to activity
public class MainActivity extends AppCompatActivity implements onAddTextViewCustomListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//get main view from layout
RelativeLayout mainView = (RelativeLayout)findViewById(R.id.mainView);
//create new CTextView and set listener
CTextView cTextView = new CTextView(getApplicationContext(), this);
//add cTextView to mainView
mainView.addView(cTextView);
}
#Override
public void onAddText(String text) {
Log.i("Message ", text);
}
}

Create listener interface.
public interface YourCustomListener
{
public void onCustomClick(View view);
// pass view as argument or whatever you want.
}
And create method setOnCustomClick in another activity(or fragment) , where you want to apply your custom listener......
public void setCustomClickListener(YourCustomListener yourCustomListener)
{
this.yourCustomListener= yourCustomListener;
}
Call this method from your First activity, and pass the listener interface...

In the year of 2018, there's no need for listeners interfaces. You've got Android LiveData to take care of passing the desired result back to the UI components.
If I'll take Rupesh's answer and adjust it to use LiveData, it will like so:
public class Event {
public LiveData<EventResult> doEvent() {
/*
* code code code
*/
// and in the end
LiveData<EventResult> result = new MutableLiveData<>();
result.setValue(eventResult);
return result;
}
}
and now in your driver class MyTestDriver:
public class MyTestDriver {
public static void main(String[] args) {
Event e = new Event();
e.doEvent().observe(this, new Observer<EventResult>() {
#Override
public void onChanged(final EventResult er) {
// do your work.
}
});
}
}
For more information along with code samples you can read my post about it, as well as the offical docs:
When and why to use LiveData
Official docs

In Android,you can create an interface such as Listener,and your Activity implements it,but i don't think it is a good idea.
if we have many components to listen the changes of their state,we can create a BaseListener implements interface Listener,and use type code to handle them.
we can bind the method when we create XML file,for example:
<Button
android:id="#+id/button4"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Button4"
android:onClick="Btn4OnClick" />
and the source code:
public void Btn4OnClick(View view) {
String strTmp = "点击Button04";
tv.setText(strTmp);
}
but i don't think it is a good idea...

I have done it something like below for sending my model class from the Second Activity to First Activity. I used LiveData to achieve this, with the help of answers from Rupesh and TheCodeFather.
Second Activity
public static MutableLiveData<AudioListModel> getLiveSong() {
MutableLiveData<AudioListModel> result = new MutableLiveData<>();
result.setValue(liveSong);
return result;
}
"liveSong" is AudioListModel declared globally
Call this method in the First Activity
PlayerActivity.getLiveSong().observe(this, new Observer<AudioListModel>() {
#Override
public void onChanged(AudioListModel audioListModel) {
if (PlayerActivity.mediaPlayer != null && PlayerActivity.mediaPlayer.isPlaying()) {
Log.d("LiveSong--->Changes-->", audioListModel.getSongName());
}
}
});
May this help for new explorers like me.

Simple method to do this approach. Firstly implements the OnClickListeners in your Activity class.
Code:
class MainActivity extends Activity implements OnClickListeners{
protected void OnCreate(Bundle bundle)
{
super.onCreate(bundle);
setContentView(R.layout.activity_main.xml);
Button b1=(Button)findViewById(R.id.sipsi);
Button b2=(Button)findViewById(R.id.pipsi);
b1.SetOnClickListener(this);
b2.SetOnClickListener(this);
}
public void OnClick(View V)
{
int i=v.getId();
switch(i)
{
case R.id.sipsi:
{
//you can do anything from this button
break;
}
case R.id.pipsi:
{
//you can do anything from this button
break;
}
}
}