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Where am I wrong setOnClickListener is always in red [duplicate]

This question already has answers here:
OnClickListener in Android Studio
(5 answers)
Closed 6 years ago.
I am new to android studio and tried a tutorial where the presenter demonstrated his program but when I type out the code I am persistently getting an error like Cannot resolve Symbol setOnClickListener where the setOnClickListener is highlighted in red.
TextView Resultant = (TextView) findViewById(R.id.Resultant);
EditText Percentage_Input = (EditText) findViewById(R.id.Percentage_Input);
EditText Number_Input = (EditText) findViewById(R.id.Percentage_Input);
#Override
public View findViewById(#IdRes int id) {
return super.findViewById(R.id.Percentage_Input);
}
Button calc_btn = (Button) findViewById(R.id.calc_btn);
calc_btn.setOnClickListener(new View.OnClickListener(){
public void onClick((View) view); {
float percent = Float.parseFloat(Percentage_Input.getText().toString());
float dec = percent/100;
float Qty = Float.parseFloat(Number_Input.getText().toString());
float total = dec*Qty;
Resultant.setText(Float.toString(total));
}
})

I think your code is not in the right place. I see you are overriding findViewById (I wonder why) and rest of your code is also at the same level. You need to put all this code within a lifecycle method.
Maybe in onCreate()
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
TextView Resultant = (TextView) findViewById(R.id.Resultant);
EditText Percentage_Input = (EditText) findViewById(R.id.Percentage_Input);
EditText Number_Input = (EditText) findViewById(R.id.Percentage_Input);
Button calc_btn = (Button) findViewById(R.id.calc_btn);
calc_btn.setOnClickListener(new View.OnClickListener() {
public void onClick((View) view); {
float percent = Float.parseFloat(Percentage_Input.getText().toString());
float dec = percent / 100;
float Qty = Float.parseFloat(Number_Input.getText().toString());
float total = dec * Qty;
Resultant.setText(Float.toString(total));
}
});
}
Also you are missing a semicolon ; at the end of setting OnClickListener.

Move ; and put at the end, this:
TextView Resultant = (TextView) findViewById(R.id.Resultant);
EditText Percentage_Input = (EditText) findViewById(R.id.Percentage_Input);
EditText Number_Input = (EditText) findViewById(R.id.Percentage_Input);
#Override
public View findViewById(#IdRes int id) {
return super.findViewById(R.id.Percentage_Input);
}
Button calc_btn = (Button) findViewById(R.id.calc_btn);
calc_btn.setOnClickListener(new View.OnClickListener(){
public void onClick((View) view) {
float percent = Float.parseFloat(Percentage_Input.getText().toString());
float dec = percent/100;
float Qty = Float.parseFloat(Number_Input.getText().toString());
float total = dec*Qty;
Resultant.setText(Float.toString(total));
}
});

Remove you method findViewById, this is some weird stuff, returning always the same view.
Put the rest of your code inside onCreate and add the missing ; at the end.

Android run time error

I am a beginner Android developer and I have a runtime error in my code: when I want to run it in a emulator or a device it show "force close" massage. My log is here:
http://upir.ir/934/1_5e07a.jpg
My Java code:
public class Third extends Activity
{
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Button d = (Button) findViewById(R.id.btn4);
d.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
dialog();
}
});
}
public void dialog(){
final Dialog dialog = new Dialog(Third.this);
dialog.setContentView(R.layout.dialog);
dialog.setTitle("واحد عدد وارد شده را انتخاب کنید");
dialog.show();
RadioGroup rg = (RadioGroup) dialog.findViewById(R.id.rg);
final RadioButton rb1 = (RadioButton) dialog.findViewById(R.id.rb1);
final RadioButton rb2 = (RadioButton) dialog.findViewById(R.id.rb2);
rg.setOnCheckedChangeListener(new OnCheckedChangeListener() {
#Override
public void onCheckedChanged(RadioGroup arg0, int arg1) {
if(rb1.isChecked()) {
dialog.dismiss();
Button t = (Button)findViewById(R.id.btn5);
t.setOnClickListener(new OnClickListener() {
public void onClick(View arg0) {
EditText ft1 = (EditText)findViewById(R.id.f3);
TextView foot = (TextView)findViewById(R.id.foot);
TextView mile = (TextView)findViewById(R.id.mile);
TextView inch = (TextView)findViewById(R.id.inch);
TextView yard = (TextView)findViewById(R.id.yard);
TextView mm = (TextView)findViewById(R.id.millymeter);
TextView dm = (TextView)findViewById(R.id.decimeter);
TextView mim = (TextView)findViewById(R.id.micrometer);
TextView nm = (TextView)findViewById(R.id.nanometer);
TextView hand = (TextView)findViewById(R.id.hand);
TextView iron = (TextView)findViewById(R.id.iron);
TextView point = (TextView)findViewById(R.id.point);
if(ft1.getText().toString().length() == 0 ){return;}
int first = Integer.parseInt(ft1.getText().toString());
double equal = first *0.0328;
DecimalFormat formatf = new DecimalFormat("#.####");
String x = formatf.format(equal)+" فوت";
foot.setText(x);
first = Integer.parseInt(ft1.getText().toString());
equal = first * 0.000005;
DecimalFormat formatm = new DecimalFormat("#.####");
x = formatm .format(equal)+"مایل";
mile.setText(x);
equal = first * 0.393;
DecimalFormat formati = new DecimalFormat("#.####");
x = formati.format(equal)+"اینچ";
inch.setText(x);
equal = first * 0.0109;
DecimalFormat formaty = new DecimalFormat("#.#####");
x = formaty.format(equal)+"یارد";
yard.setText(x);
equal = first / 10;
DecimalFormat formatmi = new DecimalFormat("#.##");
x = formatmi.format(equal)+"دسی متر";
dm.setText(x);
int equalmm = first * 10;
x = equalmm+"میلی متر";
mm.setText(x);
int equalm = first * 10000;
x = equalm+"میکرو متر";
mim.setText(x);
int equaln = first * 10000000;
x = equaln + "نانو متر";
nm.setText(x);
equal = first * 0.098;
DecimalFormat formath = new DecimalFormat("#####.#####");
x = formath.format(equal)+"هَند";
hand.setText(x);
equal = first * 19;
x = equal+"آیرون";
iron.setText(x);
equal = first * 28;
x = equal+"پوینت";
point.setText(x);
}
});
}

You need to inflate your activity with a layout resource first before you can use the findViewById() method to retrieve views. If there's no layout, then there are no views which could possibly be found.

You are missing an important part. You need to add a view to your Activity in order to find the elements of that view like the Button you are trying to instantiate.
In your OnCreate method add this:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.the_xml_file); //Here add the xml file with the view you want to show
Button d = (Button) findViewById(R.id.btn4);
d.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
dialog();
}
});
}

After your super.onCreate(savedInstanceState); are you setting the content view?
e.g.
setContentView(R.layout.nameofxmlfilehere);

Hi! How do I store the fields and display the results on a different activity ? Please

I want the fields entered by the user to be displayed as a list view of the studentnoText and courseField in a new activity..
public class Student extends Activity {
private String totalStudents [];
private EditText studentnoText;
private EditText studentnameText;
private EditText courseField;
private Spinner departmentSpinner;
private EditText dobField;
private Button registerButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_student);
studentnoText = (EditText) findViewById(R.id.studentnoText);
studentnameText = (EditText) findViewById(R.id.studentnameText);
dobField = (EditText) findViewById(R.id.dobField);
courseField = (EditText) findViewById(R.id.courseField);
departmentSpinner = (Spinner) findViewById(R.id.departmentSpinner);
registerButton = (Button) findViewById(R.id.registerButton);
}
public void registerButtonPressed (View view){
Log.v("Register","Register Pressed!");
}
}

USE PUT EXTRA TO SEND DATA
mIntent.putExtra("TEXT", studentnoText.gettext().toString());
mIntent.putExtra("TEXT_1", studentName.gettext().toString());
USE GET EXTRA TO GET DATA
String strNO,strName;
strNO= extras.getString("TEXT");
strName = extras.getString("TEXT_1");

how do call another class in android?

I have a problem. I do not know how to call a different class. the code is for a button (when you click the button a message appears in random) so i thought it would be better if i placed it in a different class as i have also used arrays.Now i do not know how to call the class.
This is my code.I want to call "Firstin" inside SecondActivity.
public class SecondActivity extends Activity {
private Firstin mFirst = new Firstin ();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
//finds textview
final Text Ftext = (Text) findViewById(R.id.textView2);
#SuppressWarnings("unused")
final Text Stext = (Text) findViewById(R.id.textView3);
//finds button view
Button btnView = (Button) findViewById(R.id.button1);
#SuppressWarnings("unused")
Button btnView2 = (Button) findViewById(R.id.button2);
btnView.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
String Answer = mFirst.firstAnswer();
Ftext.setTextContent(Answer);
}
});
this is the class I'm trying to call:
package com.example.insultgenerator;
import java.util.Random;
public class Firstin {
public String firstAnswer(){
String [] mResults={
"its cool",
"we cool",
"im cool",
"he cool",
"she cool"
};
// the button was clicked so replace the answer label with answer
String Answer = "" ;
// the two double is a 'empty string
Random RandomGen = new Random();// telling the program to construct a random generator
int RandomNum= RandomGen.nextInt(mResults.length);
Answer = mResults[RandomNum];
return(Answer);
}
}

You should cast to TextView
final TextViewFtext = (TextView) findViewById(R.id.textView2);
#SuppressWarnings("unused")
final TextViewStext = (TextView) findViewById(R.id.textView3);
then use TextView.setText(...) method:
String Answer = mFirst.firstAnswer();
Ftext.setText(new Firstin().firstAnswer());
}
});
then last call the method from the other class with new Firstin().firstAnswer() which creates a instance of the class and executes the method.

I want to use a self made Class in android

I am currently new to Android Development and i am having a difficult time trying to use a self made class in my MainActivity Android class.
Let me give you an example;
I created a SquareArea class and want to use it in the MainActivity Class
public class SquareArea{
private double _length;
private double _width;
public SquareArea(double length , double width){
_length = length;
_width = width;
area();
}
private double area(){
return _length
}
}
When i instantiate the SquareClass in MainActivity class i want to be able to use the area() method and return when values that are Extracted from(EditText)
I want to use the value in order to place it in a text view;however this does not seem to happen.
I can do it with methods but i want to use my own classes instead.
Please help, I am getting frustrated with this.
///Below is my MainActivity Class///
public class MainActivity extends Activity {
EditText mEditText1;
EditText mEditText2;
EditText mEditText3;
TextView mTextView;
Button mButton;
Double value1, value2;
SquareArea sq1;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mEditText1 = (EditText) findViewById(R.id.editText1);
mEditText2 = (EditText) findViewById(R.id.editText2);
mEditText3 = (EditText) findViewById(R.id.editText3);
mTextView = (TextView) findViewById(R.id.textView1);
mEditText1.setBackgroundColor(Color.GREEN);
mEditText2.setBackgroundColor(Color.GREEN);
mEditText3.setBackgroundColor(Color.RED);
mButton = (Button) findViewById(R.id.button1);
mButton.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
//When the button is clicked, call the calucate method.
// calculate();
try {
value1 = Double.parseDouble(mEditText1.getText().toString());
value2 = Double.parseDouble(mEditText2.getText().toString());
sq1 = new SquareArea(value1, value2);
mTextView.setText(sq1.toString());
} catch (NumberFormatException e) {
mTextView.setText("Please use numbers");
}
});
}
}

You declare area() private, so cannot you call it
public double area(){
return _length
}
and you just have to call your area()
mTextView.setText(String.ValueOf(sq1.area()));

I see several problems
mTextView.setText(sq1.toString());
The toString method in SquareArea is not overridden. So the toString will return the default information about the object (location in memory, name, etc.)
public SquareArea(double length , double width){
_length = length;
_width = width;
area();
}
In the code above, you are inside the constructor. Why are you calling area() from here? A constructor can't return anything and the result from area() is being lost because area() returns a double.
And lastly:
private double area(){
return _length
}
This method is private. It cannot be called from outside the class/object.
To make your code work this is what I would change.
public class SquareArea{
private double _length;
private double _width;
public SquareArea(double length , double width){
_length = length;
_width = width;
}
public double area(){
return _length * _width;
}
}
///Below is my MainActivity Class///
public class MainActivity extends Activity {
EditText mEditText1;
EditText mEditText2;
EditText mEditText3;
TextView mTextView;
Button mButton;
Double value1, value2;
SquareArea sq1;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mEditText1 = (EditText) findViewById(R.id.editText1);
mEditText2 = (EditText) findViewById(R.id.editText2);
mEditText3 = (EditText) findViewById(R.id.editText3);
mTextView = (TextView) findViewById(R.id.textView1);
mEditText1.setBackgroundColor(Color.GREEN);
mEditText2.setBackgroundColor(Color.GREEN);
mEditText3.setBackgroundColor(Color.RED);
mButton = (Button) findViewById(R.id.button1);
mButton.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
//When the button is clicked, call the calucate method.
// calculate();
try {
value1 = Double.parseDouble(mEditText1.getText().toString());
value2 = Double.parseDouble(mEditText2.getText().toString());
sq1 = new SquareArea(value1, value2);
mTextView.setText(String.ValueOf(sq1.area()));
} catch (NumberFormatException e) {
mTextView.setText("Please use numbers");
}
});
}
}