Develop Reference

The button of a Android project simply does not work [duplicate]

I am developing a small project of test, and I wrote the following code.
I already created in the xml file, a button with id called "registerBtn".
I erased the imports of this source code to shorten space of this source code.
In the java file, I created a variable called mRegisterBtn, in the type of Button.
Inside the method called onCreate(Bundle savedInstanceState) the mRegisterBtn receives the method called findViewById(R.id.registerBtn);
However, in the mRegisterBtn.setOnClickListener, the part of new View.OnClickListener appears in gray color, and it is not working when trying to test this code.
This image shows what I really mean. Please, perceive that the the part of new View.OnClickListener appears in gray color. It means a error. But trying to compile, this code runs, but the button simply does not work.
Can anyone know how to fix this error, please?
public class Register2 extends AppCompatActivity {
Button mRegisterBtn;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_register2);
mRegisterBtn = findViewById(R.id.registerBtn);
mRegisterBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Toast.makeText(getApplicationContext(), "Testing", Toast.LENGTH_LONG).show();
}
});
}
}```
<?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"
android:background="#007FFF"
tools:context=".Register">
<Button
android:id="#+id/registerBtn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:backgroundTint="#color/white"
android:text="Register"
android:textColor="#color/black"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.499" />
</androidx.constraintlayout.widget.ConstraintLayout>

Try using the Activity itself as the Context.
If you want a log, then make one
If you want the gray to go away, use a lambda
Log.d("REGISTER", "Setting listener");
mRegisterBtn.setOnClickListener(view -> {
Log.d("REGISTER", "Clicked!");
Toast.makeText(Register2.this, "Testing", Toast.LENGTH_LONG).show();
});

Relative Layout All Childs Clickable

This Question Is Pretty Silly to ask but out, but i Would like to know how it Works?
I had a Relative Layout with 2 ImageViews as Child having separate clickListner instances. One above Another, of same Size and Attributes.
Overlaps Each other. Both having Different images.
Question is When i click on one image both ImageView Click listners are Called.
Or if i disable the Click on ImageView Top, The ImageView Below Still Works, I was Clicking on Image View Above though. How it is I'ts Getting callback from both.
I Just Want to know How it works? not The code, i do not have any issue writing code for clickListners Whether only one Working or Both.
<RelativeLayout
----
---
>
<ImageView
---
---<!--Child 1-->
<ImageView
---
---<!--Child 2-->
<RelativeLayout/>

Taken from here:
if you are working with just one clicklistener, you can do:
View.OnClickListener myOnlyhandler = new View.OnClickListener() {
public void onClick(View v) {
switch(v.getId()) {
case R.id.b1:
// it was the first button
break;
case R.id.b2:
// it was the second button
break;
}
}
}

Use ImageButton
Layout
<?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" >
<ImageButton
android:id="#+id/imageButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:contentDescription="#string/content"
android:src="#drawable/ic_launcher" />
</LinearLayout>
Activity class
public class MainActivity extends Activity {
ImageButton imgButton;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
addButtonListener();
}
public void addButtonListener() {
imgButton = (ImageButton) findViewById(R.id.imageButton);
imgButton.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View view) {
Toast.makeText(MainActivity.this,"ImageButton is working!", Toast.LENGTH_SHORT).show();
}
});
}
}

Give this to your parent layout
android:context="Yourclasshere"
then give this to your image view
android:onclick="onclick"
and then implement the on click listener or make the method like Vitly A make above

Android Studio: How to change the Background to jpg. images using OnclickListener

So far I know how to change the Background's color via html codes. Now I am Trying to change the background of the Layout of my main activity to different images using a button click. If possible using only one single button.
Thank you!

The following code is from this link Setting background image in java from Omi0301.
//assuming your Layout is named linearlayout1:
LinearLayout ll = (LinearLayout) findViewById(R.id.linearlayout1);
ll.setBackgroundResource(R.drawable.sample);
All you do is create a layout variable and set its background resource with the image that you would like it to be.

try to use "setImageResource" instead the "setBackgroundResourse"

Try below code
main.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/myLayout"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginLeft="64dp"
android:layout_marginTop="71dp"
android:text="changeColor" />
</LinearLayout>
MainActivity.java
public class MainActivity extends Activity {
/** Called when the activity is first created. */
Button button;
LinearLayout mainLayout;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mainLayout=(LinearLayout)findViewById(R.id.myLayout);
button=(Button)findViewById(R.id.button1);
button.setOnClickListener(new OnClickListener() {
public void onClick(View arg0) {
// TODO Auto-generated method stub
mainLayout.setBackgroundResource(R.drawable.newImage);
}
});
}
}

Cannot Change Layout Content In Java Code

Very simple question but very weird as well :
I have a class PanelGlobalActivity that extends Activity and it is set to the layout panel_view_activity. I have a button and a text view, both have IDs.
When I do findViewById(R.id.*) it can see my button and my text view but there is no way I can change their values or anything. Like button.setText("Hello") would compile but wouldn't change it.
Any ideas ?
Here is my xml file (panel_view_activity):
<?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:orientation="vertical" >
<Button
android:id="#+id/button1"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<TextView
android:id="#+id/text1"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
</LinearLayout>
And here is my java class :
public class PanelGlobalActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.panel_view_activity);
TextView label = (TextView)findViewById(R.id.text1);
label.setText("Test");
}
}
Thanks.
Nic.

You can try something like this:
public class PanelGlobalActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Button someButton = (Button) findViewById(R.id.yourButtonId);
someButton.setText("text changed");
}
}
some tips in coding if your using eclipse:
1.Use Ctrl + Shift + O (Imports necessary libraries or whatsoever automatically)
2.Use Ctrl + W (this lists all the possible methods for an object) just like when you're typing the "someButton.s" then press Ctrl + W, all available methods will be showed

You don't have any problem on your sample code ... I've run it it's perfectly fine . ..

Android app and java activities, issues with onCreate() method and XML

I am trying use the onClick() function in an activity for an android app. So far I have:
public class Activity2 extends Activity implements OnClickListener {
private ImageButton closeButton;
#Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity2);
Button myButton = (Button) findViewById(R.id.wowButton);
myButton.setOnClickListener(this);
this.closeButton = (ImageButton)this.findViewById(R.id.close);
this.closeButton.setOnClickListener(new OnClickListener(){
public void onClick(View v){
finish();
}
});
}
public void onClick(View v) {
// TODO Auto-generated method stub
TextView lowerText = (TextView) findViewById(R.id.textView2);
EditText boxText = (EditText) findViewById(R.id.editText1);
lowerText.setText(boxText.getText());
}
}
This is just a stripped down version of my project. When I enter my app as usual in the emualtor, everything works fine. When I click the button to open up this particular activity, everything crashes. I assume the issue lies within the onClick() method. This code was sent to me by my project partner without the XML files so I think thats where the problem lies.
here is my basic XML file that I thought should work:
<?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:orientation="vertical">
<Button android:id="#+id/wowButton" android:layout_width="fill_parent"
android:layout_height="200dp" android:text="WoW" android:typeface="sans"
android:background="#drawable/btn_default_normal_red" />
<EditText
android:id="#+id/editText1"
/>
<TextView
android:id="#+id/textView2"
/>
</LinearLayout>
While very basic, I though it should work. Thanks for your help.

you instantiate an ImageButton through this.closeButton = (ImageButton)this.findViewById(R.id.close);
But you don't declare it in the xml file. That's why it's null and throws a NullPointer Exception.