Develop Reference

Listeners from all types don't work and they are greyed out

I'm trying to create a listener from the simplest kind but for some reason I can't.
Code:
package com.example.check;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button = findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Toast.makeText(MainActivity.this, "this is a test",
Toast.LENGTH_LONG).show();
}
});
}
}
And the .xml file:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="#+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/buttton"
tools:ignore="MissingConstraints" />
</androidx.constraintlayout.widget.ConstraintLayout>
It's a very simple listener but for some reason it doesn't work. The IDE doesn't detect any error, the problem is in this part of the code: new View.OnClickListener()
The IDE marks it in gray as it never been used in the code. I searched for days in every possible forum but no one has this problem.
Here's a Picture: new View.OnClickListener() is grey
If I put my mouse on: new View.OnClickListener() it suggests I replace it with lambda. If I do replace it, there's no more gray section but when I run the app the code inside the onClick(View view) function is not been executed.
When I run the app with new View.OnClickListener() or with lambda instead, I don't get any error messages.
I think the problem is somehow related to the Gradle but that's just an idea. Please someone help, I am really desperate because the code is correct and it's not working!

Android Studio - Button Click Crash (Simple)

I'm brand new to Android Studio and for whatever reason am experiencing really weird errors if I could please get some help.
I have very basic code that is supposed to, on button click change the text of my button from "button" to "clicked!". However everytime I press the button, the app crashes and I get "Appname has stopped" on the emulator.
What is incredibly weird is that in my activity_main.xml Design view, the onClick dropdown shows two functions of the same name (https://puu.sh/t2h5I/42ad4379d6.png)
H owever the code only works when the bottom one is selected. AND each time I run the app, it deselects the bottom one and reselects the top, only to stop working.
Here is my MainActivity:
package com.example.john.ameladay;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
public Button melButtonCode;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void buttonPress(View v){
melButtonCode = (Button) v;
((Button) v).setText("Has been clicked!");
}
}
Here is my activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context="com.example.john.ameladay.MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/mainText"
android:id="#+id/textView" />
<ImageView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:src="#drawable/mela"
android:id="#+id/melPhoto" />
<Button
android:text="Button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_toRightOf="#+id/textView"
android:layout_toEndOf="#+id/textView"
android:layout_marginLeft="32dp"
android:layout_marginStart="32dp"
android:layout_marginBottom="43dp"
android:id="#+id/button"
android:onClick="buttonPress (MainActivity)" />
Any help would be greatly appreciated!!

Simple. You should write:
android:onClick="buttonPress"
Why happened
If you wrote buttonPress (MainActivity), Android tries to find buttonPress (MainActivity) method (not MainActivity.buttonPress()), but MainActivity doesn't have buttonPress (MainActivity) method. So the error happened.

Simply replace this Tag in button
Remove this
android:onClick="buttonPress (MainActivity)"
And Paste This
android:onClick="buttonPress"

A better way to do it is, get a reference to the button in your Java code using findViewById() method and set an OnClickListener to the button.
For your current problem, use
android:onClick="buttonPress"
instead of
android:onClick="buttonPress (MainActivity)"

According to me this is the better way to set click on button
public class MainActivity extends AppCompatActivity {
public Button melButtonCode;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
melButtonCode = (Button).findViewById(R.id.button);//find button by Id
melButtonCode.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
melButtonCode.setText("Has been clicked!");
}
});
}
}
For your problem
replace it
android:onClick="buttonPress (MainActivity)"
With
android:onClick="buttonPress"

Make the method public - protected works when you are in instantrun mode, but not when not. No idea why!

Android project display error on R.id.button

I surdenly noticed that My project starts throwing error anytime I try to access a resources that is a button. It underlines R.id.button. I dont understand why. I even deleted the last xml that I created but problem persist.
This is an example of my xml file
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#drawable/layoutborder"
android:orientation="vertical" >
<TextView
android:id="#+id/chat"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:text="#string/stepone"
android:textAppearance="?android:attr/textAppearanceMedium"
android:textColor="#color/wine" />
<ImageView
android:id="#+id/imageView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:src="#drawable/ai" />
<Button
android:id="#+id/drugdetails"
style="#style/smallButtonStyleBlackpearl"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:layout_marginRight="20dp"
android:layout_marginTop="10dp"
android:text="#string/nextbut" />
</LinearLayout>
My Java code
package com.example.rhemahealthcare;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import com.actionbarsherlock.app.SherlockActivity;
import com.example.rhemahealthcare.R;
public class SteponeActivity extends SherlockActivity{
#Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.steponeactivity);
final Button button = (Button)findViewById(R.id.button1);
button.setOnClickListener(new OnClickListener(){
#Override
public void onClick(View v){
// TODO Auto-generated method stub
Intent intent = new Intent(SteponeActivity.this,SteptwoActivity.class);
startActivity(intent);
}
});
}
}

i think you change any button1 id buy clicking right click and choose edit id. this option changes all the ids with that name in all the layouts.

As #Aleks G gussed it right in the comment, you don't have any button with id as button1 in your xml file. You've mentioned it :
final Button button = (Button)findViewById(R.id.button1);
Use the appropriate ID or put one in your layout file.

I have figured out the problem. My button ids were automatically change to button1 so they did not reference their previous ids that I gave to them. Thanks alot

onClick method not called on Android

I am doing the simplest of onClick models and cannot get the onClick method to fire. I know it is something simple, and I am new to Android. Any help is appreciated.
package com.bordeloniphone.timeentry;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;
public class TimeEntryActivity extends Activity implements OnClickListener{
/** Called when the activity is first created. */
Button okButton;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
okButton = (Button) findViewById(R.id.btnOK);
okButton.setText(":)");
okButton.setOnClickListener(this);
//setContentView(okButton);
}
public void onClick(View v) {
Log.d("TEST", "TEST");
Toast.makeText(this, "TEST", Toast.LENGTH_SHORT).show();
}
}
Here is the main.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<Button
android:id="#+id/btnOK"
android:layout_width="80dp"
android:layout_height="wrap_content"
android:text="OK" />
</LinearLayout>

After much angst and gnashing of teeth, I figured it out. I had to delete the emulator device and add an new one and now it works like a champ. I appreciate everyone trying to help.

Instead of setting the onClicklistener to this, try this approach:
okButton.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
Log.d("TEST", "TEST");
Toast.makeText(this, "TEST", Toast.LENGTH_SHORT).show();
}
});

You should try Cleaning your project or try to restart your Eclipse or any other Editor you are using as it is a valid code and should work fine.
UPDATE:
Also, you should check your Logcat, are you getting the output of Log.d("TEST", "TEST"); because your Toast seems to be implemented in a wrong manner.
Toast.makeText(this, "TEST", Toast.LENGTH_SHORT).show(); // wrong
Toast.makeText(Activity_name.this, "TEST", Toast.LENGTH_SHORT).show(); // correct
Using this in Toast inside the Listener means you are Referencing the Listener, which indeed should not be the case. You have to reference to the Activity itself so better use Activity_name.this.

Button iv_StyleInspiration_Back = (Button) findViewById(R.id.iv_StyleInspiration_Back);
iv_StyleInspiration_Back.setOnClickListener(this);
Try this Whenever you implement onclick in your activity you need to set as above to make it work for all controls and onclick should look something as below
#Override
public void onClick(View pView) {
if (null != pView) {
switch (pView.getId()) {
case R.id.iv_StyleInspiration_Back:
//do what you want
break;
default:
break;
}
}
}

Check for Three Steps:
find the button by id correctly
link the button to a listener. (adding the actionListener)
you specify a condition for this button in case of implementing an actionListener class.

try making the button clickable
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<Button
android:id="#+id/btnOK"
android:layout_width="80dp"
android:layout_height="wrap_content"
android:text="OK"
android:clickable="true" />

Error "android (name of project) has stopped unexpectedly

package com.iperetz1.android.testbutton1;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class TestButton extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button test2 = (Button)findViewById(R.id.test2);
test2.setOnClickListener(new OnClickListener()
{
#Override
public void onClick(View v)
{
setContentView(R.layout.test2);;
}
});
Button other = (Button)findViewById(R.id.backmain);
other.setOnClickListener(new OnClickListener()
{
#Override
public void onClick(View v)
{
setContentView(R.layout.main);;
}
});
}
}
main.xls
<?xml version="1.0" encoding="utf-8"?>
<AbsoluteLayout
android:id="#+id/widget0"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android"
>
<Button
android:id="#+id/test2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="test2"
android:layout_x="24px"
android:layout_y="165px"
>
</Button>
</AbsoluteLayout>
test2.xml
<?xml version="1.0" encoding="utf-8"?>
<AbsoluteLayout
android:id="#+id/widget0"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android"
>
<Button
android:id="#+id/backmain"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="backmain"
android:layout_x="24px"
android:layout_y="165px"
>
</Button>
</AbsoluteLayout>

findViewById is a lot simpler than people tend to think it is. It traverses the view hierarchy looking for a view with the given ID. If it's not found, findViewById returns null.
You started by setting the content view to your main layout but later on you tried to findViewById(R.id.backmain). Since there is no view with that ID in your main layout, it returns null. At that point attempting other.setOnClickListener will fail. You will only be able to do this when your button actually exists in the view hierarchy.
There's nothing inherently wrong with dynamically changing your view hierarchy, but you'll have to handle some things differently if you go that route. (Such as when you wire up events to views that don't exist during onCreate like you're trying to do above.)

As #Cristian Castiblanco said, changing the view dynamically is causing the problem, for these kind of scenarios, you have to create separate activities and invoke them using intents and pass data between them using bundles.