CODEWITHSUNDEEP
javaandroid
CarterTheSquatch
CarterTheSquatch

Reputation: 65

How to 'link' an activity to a java class in Android Studio

So, I'm trying to wrap my head around Android Studio, but I find something very confusing. When you make a new activity it also makes a Java class, yet coding anything into that java class doesn't seem to do anything. Yet coding something into the MainActivity does.

Example names

MainActivity SecondActivity main_activity second_activity

Adding an onClick event for a (Button for example) in second_activity, it checks the MainActivity class for the pubic void onClickName(){ } rather than the SecondActivity class. Is there something somewhere that I have to change?

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<EditText
    android:layout_width="match_parent"
    android:layout_height="40dp"
    android:text=""
    android:hint="Player name here"
    android:layout_alignParentTop="true"
    android:id="@+id/txtName"
    android:layout_toStartOf="@+id/btnAddPlayer" />
<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Back to Main menu"
    android:id="@+id/button"
    android:layout_alignParentBottom="true"
    android:layout_alignParentStart="true"
    android:onClick="backToMain"/>

<ListView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/spnCharacters"
    android:layout_below="@+id/txtName"
    android:layout_marginTop="56dp"
    android:layout_alignParentEnd="true"
    android:background="@drawable/bg_key"/>

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Add Player"
    android:id="@+id/btnAddPlayer"
    android:layout_alignBottom="@+id/txtName"
    android:layout_alignParentEnd="true"
    android:onClick="addPlayer"/>

Yet neither addPlayer nor backToMain in SecondActivity does nothing, yet if in MainActivity they do whatever I've coded in

SecondActivity onCreate

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

Upvotes: 3

Views: 13882

Answers (4)

Shenyuy Goodness-Divine Tata
Shenyuy Goodness-Divine Tata

Reputation: 1

In order to solve this issue simply go to your activity_second and use any of the palette tools before referencing your activity_second in your java file(SecondActivity).

Upvotes: 0

Geno Chen
Geno Chen

Reputation: 5214

An Activity "is a single, focused thing that the user can do.". The internal of make an Activity when developing is actually the bundle of several actions:

  1. Create a Java class that extends Activity directly or indirectly (for example, AppCompatActivity).
  2. Create a corresponding layout file (this is not necessary, you may generate the layouts inside that class with Java dynamically).
  3. Register this Activity inside AndroidManifest.xml, with a new tag like <activity android:name=".NecessaryActivityName" android:label="@string/optional" android:icon="@drawable/optional"/>, or you may specify more details of this Activity, for example the <intent-filter>.

So,

When you make a new activity it also makes a Java class.

Yes. A better description is, "When you make a new Activity, you are making a Java class that extends Activity".

yet coding anything into that java class doesn't seem to do anything.

"An activity is a single, focused thing that the user can do.". When you click on an application icon on Launcher ("desktop" of Android), you are starting a corresponding Activity (to be more precisely, sending an Intent to that Activity).

When you create another Activity, you are willing to have an Intent to start it, by adding a Launcher icon or by redirecting from another Activity (for example, MainActivity). The way of adding it to Launcher is posted by @J0B, by adding an <intent-filter> as the child of <activity> inside AndroidManifest.xml. The way of redirecting from another Activity is to build an Intent then call startActivity(), for example in Java:

Intent intent = new Intent(this, SecondActivity.class);
startActivity(intent);

Upvotes: 2

J0B
J0B

Reputation: 1648

Each Android Application contains Activities. Each activity is declared in AndroidManifest.xml e.g. main_activity.xml and MainActivity.java is an 'Activity'. java classes, interfaces... can be used as normal in the java controller part of an activity.

<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>

Should be part of the activity that launches first.

Upvotes: 0

bahaeddin sagar
bahaeddin sagar

Reputation: 93

\ make sure that the Java file is connected to the XML file

the first line of the Java file should show something like this

public class balance extends AppCompatActivity {

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

this means that my class(Java file) balance is connected to activity (layout) activity_balance.

if this is not the case, make sure that you are adding new activities from (file >new>activity> (blank activity for example)

Hope this helps

Upvotes: 1

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