Android - Set text to TextView

In your layout XML:

<TextView
        android:id="@+id/myAwesomeTextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:text="Escriba el mensaje y luego clickee el canal a ser enviado"
        android:textSize="20sp" />

Then, in your activity class:

// globally 
TextView myAwesomeTextView = (TextView)findViewById(R.id.myAwesomeTextView);

//in your OnCreate() method
myAwesomeTextView.setText("My Awesome Text");

PUT THIS CODE IN YOUR XML FILE

<TextView
    android:id="@+id/textview1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"/>

PUT THIS CODE IN YOUR JAVA FILE

// Declaring components like TextView globally is a good habit

TextView mTextView = (TextView) findViewById(R.id.textview1);

// Put this in OnCreate

mTextView.setText("Welcome to Dynamic TextView");