help debugging a basic app in android studio

Question

Hey guys. Uber noob to programming but have started trying to make a really basic app using a tutorial (https://developer.android.com/training/basics/firstapp/starting-activity.html) but I've run into a few road blocks. I've tried making this app twice and failed miserably lol. One issue is that the line `import android.view.ViewGroup;' keeps disappearing from the code as soon as its entered. The second issue is that the app crashes as soon as it starts. I had the first activity working initially but the app would crash when the button was clicked. I've triad clean/rebuild but it hasn't helped at all. I've also tried other basic info I could like editing or removing certain parts of the code but they didn't help either. I tried posting in Stack Overflow but even that wouldn't help :/ So at this stage any and all help would be great;y appreciated! Thanks in advance!

Logcat error info

06-14 20:56:40.335 25791-25791/com.example.jacqueline.myfirstapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.jacqueline.myfirstapp, PID: 25791
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.jacqueline.myfirstapp/com.example.jacqueline.myfirstapp.MainActivity}: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2711)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2772)
at android.app.ActivityThread.-wrap12(ActivityThread.java)

Answer 1

Can you copy-paste your XML and Java code?

Answer 2

Main:
package com.example.jacqueline.myfirstapp;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {
public static final String EXTRA_MESSAGE = "com.example.jacqueline.myfirstapp.MESSAGE";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void sendMessage(View view) {
Intent intent = new Intent(this, DisplayMessageActivity.class);
EditText editText = (EditText) findViewById(R.id.editText);
String message = editText.getText().toString();
intent.putExtra(EXTRA_MESSAGE, message);
startActivity(intent);
}

public class EXTRA_MESSAGE {
}
}

Display message activity:
package com.example.jacqueline.myfirstapp;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
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 message 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 = (TextView) findViewById(R.id.textView);
textView.setText(message);
}
}

Answer 3

Manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.jacqueline.myfirstapp">

<application>
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity"
android:theme="@style/Theme.AppCompat.NoActionBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".DisplayMessageActivity"
android:parentActivityName=".MainActivity"
android:theme="@style/Theme.AppCompat.NoActionBar">
<!-- THe Meta-Data Tag is required if you support API level 15 or lower -->
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value=".MainActivity" />
</activity>
</application>

</manifest>

Answer 4

UPDATED LOGCAT -
06-16 02:08:47.505 15866-15866/com.example.jacqueline.myfirstapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.jacqueline.myfirstapp, PID: 15866
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.jacqueline.myfirstapp/com.example.jacqueline.myfirstapp.DisplayMessageActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2711)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2772)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1515)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:241)
at android.app.ActivityThread.main(ActivityThread.java:6217)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)

Answer 5

I've followed the instructions of the link (https://developer.android.com/training/basics/firstapp/creating-project.html) and it works for me.

At your Manifest you write:
<activity android:name=".DisplayMessageActivity"
android:parentActivityName=".MainActivity"
android:theme="@style/Theme.AppCompat.NoActionBar">

try it as it tells you instead:
<activity android:name=".DisplayMessageActivity"
android:parentActivityName=".MainActivity" >

Answer 6

I initially didn't have that line there. when I remove it I get other error -
06-16 15:51:17.532 19324-19324/com.example.jacqueline.myfirstapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.jacqueline.myfirstapp, PID: 19324
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.jacqueline.myfirstapp/com.example.jacqueline.myfirstapp.DisplayMessageActivity}: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2711)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2772)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1515)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:241)
at android.app.ActivityThread.main(ActivityThread.java:6217)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)