[Android Studio] tuliobarata:
Really thanks for the reply [MENTION=3873834]MMDeveloper[/MENTION], but had some problems here, I'm trying to find a Solution for almost 1hr, and nothing.. I saw some ppeople with the same problem, but couldnt use the answers I've read to solve this code.

With the first solution you gave to me, I just delete the button part, just to try make all automatic. In this first sample I have just a simple math that should convert a CV power do kW

The studio shows that to me:

addTextChangedListener - Cannot resolve symbol;

TextWatcher

- Invalid method declaration, return type required;

@Override

- Annotations are not allowed here;

Editable arg0 - Cannot resolve symbols, for both;

I tried to put this code in different places in my main java, but nothing. Below is my XML and then my Java, could you take a look in it please ? I guess I'm used to copy and paste some codes from some classes, and that is harming me, i really need to start all over from the java sintaxe.

The fields I've changed to be those in your code are: torque_p_cv (edit) and torque_p_cv (view)

XML:

<RelativeLayout xmlns:android="CANT SHOW LINK UNDER 10 POSTS"
xmlns:tools="CANT SHOW LINK UNDER 10 POSTS"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".Calculos001_Main">

<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Cálc. do torque em função de P e n"
android:id="@+id/torque_titulo"
android:layout_gravity="center_horizontal"
android:textAlignment="center"
android:layout_marginTop="10dp"
android:textSize="20dp"
android:textStyle="bold|italic" />

<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="50dp">

<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content">

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="P"
android:id="@+id/torque_tits_p" />

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="Potência do motor"
android:id="@+id/textView"
android:layout_marginStart="10dp" />

<EditText
android:layout_width = "0dp"
android:layout_height="wrap_content"
android:id="@+id/torque_p_cv"
android:layout_weight="1"
android:inputType="number"
android:hint="Potência"
android:gravity="end"
android:layout_marginStart="10dp" />

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="CV"
android:id="@+id/unidade_CV"
android:textAlignment="textEnd"
android:gravity="end"
android:layout_marginStart="10dp" />

</LinearLayout>

<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content">

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="xxxxx"
android:id="@+id/torque_p_kw"
android:textAlignment="textEnd"
android:gravity="end"
android:layout_marginStart="10dp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="kW"
android:id="@+id/unidade_kW"
android:textAlignment="textEnd"
android:gravity="end"
android:layout_marginStart="10dp" />
</LinearLayout>
</LinearLayout>
</LinearLayout>
</RelativeLayout>

and the Java:

package com.example.tbarata.calculos_001;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.EditText;
import android.widget.TextView;

public class Calculos001_Main extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_calculos001__main);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_calculos001__main, menu);
return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();

//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}

return super.onOptionsItemSelected(item);
}

final EditText et1 = (EditText) findViewById(R.id.torque_p_cv);
final TextView tv2 = (TextView) findViewById(R.id.torque_p_kw);

et1.addTextChangedListener(new TextWatcher() {
@Override
public void afterTextChanged(Editable arg0) {
//This is called AFTER the text has changed

//Now update the tv2
String textOutput = "0";
//tv2.setText(textOutput);

}

@Override
public void beforeTextChanged(CharSequence s, int start, int count,
int after) {
//This is called BEFORE the text has changed
}

@Override
public void onTextChanged(CharSequence s, int start, int before,
int count) {
//This is called WHENEVER the text has changed
}

});
}

Really thanks,

Barata