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I'm currently following the Android Studio "Build Your First App" tutorial (
https://developer.android.com/training/basics/firstapp/starting-activity
) and I can't seem to get the DisplayMessageActivity working. The variable "R.id.textView" doesn't seem to exist and I can't see any differences between the tutorial and my own code. I know this is just me being stupid somewhere but I can't pinpoint it.
Here's my code for DisplayMessageActivity.java:
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.TextView;
public class DisplayMessageActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_display_message);
// Get the Intent that started this activity and extract the string
Intent intent = getIntent();
String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
// Capture the layout's TextView and set the string as its text
TextView textView = findViewById(R.id.textView); <-- Cannot resolve symbol 'textView'
textView.setText(message);
And MainActivity.java, which is trying to run it:
package com.example.myapplication;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
public class MainActivity extends AppCompatActivity {
public static final String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
/** Called when the user taps the Send button */
public void sendMessage(View view) {
Intent intent = new Intent(this, DisplayMessageActivity.class);
EditText editText = (EditText) findViewById(R.id.editTextTextPersonName);
String message = editText.getText().toString();
intent.putExtra(EXTRA_MESSAGE, message);
startActivity(intent);
When I try to run the app on the virtual device it doesn't crash, but the button which calls the DisplayMessage activity does nothing.
EDIT: As requested, the xml code for both activities:
activity_display_message.xml
<?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=".DisplayMessageActivity">
</androidx.constraintlayout.widget.ConstraintLayout>
activity_main.xml
<?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">
<EditText
android:id="@+id/editTextTextPersonName"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="16dp"
android:ems="10"
android:hint="@string/edit_message"
android:inputType="textPersonName"
app:layout_constraintEnd_toStartOf="@+id/button2"
app:layout_constraintHorizontal_bias="0.5"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginEnd="16dp"
android:onClick="sendMessage"
android:text="@string/button_send"
app:layout_constraintBaseline_toBaselineOf="@+id/editTextTextPersonName"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.5"
app:layout_constraintStart_toEndOf="@+id/editTextTextPersonName" />
</androidx.constraintlayout.widget.ConstraintLayout>
I read the tutorial and I think they missed this part of code:
android:onClick="sendMessage"
so, the code should be like this:
<Button
android:id="@+id/button"
android:onClick="sendMessage"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="16dp"
android:layout_marginStart="16dp"
android:text="@string/button_send"
app:layout_constraintBaseline_toBaselineOf="@+id/editText"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.5"
app:layout_constraintStart_toEndOf="@+id/editText" />
and I think that's it, let me know if it helps
–
After looking more closely at @Vishal Naikawadi's comment, I realised what the problem was. R.id.textView is not some sort of variable, placeholder, or constant as I had assumed, it is literally getting the object with id "textView" (or so I think). I had accidentally changed the id of the object I was trying to reference in the visual editor, so there was no object with that id. I changed the id of the object back to the same as is referenced in the code and everything seems to be fine now.
Apologies to anyone whose time I've wasted with this, I'm really new to this concept in Java.
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