We Keep Coding

Android Studio - The (Very) Basics - startActivty doesn't work

im trying to move the info of a user from one activity to the other, but everytime i run the app it crashes at the "startActivity(i)" Line (i checked everything else, it only crashes at that line).
that's the MainActivity Code
package com.example.hw1511;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import com.example.hw1511.Model.User;
import org.w3c.dom.Text;
import java.io.Serializable;
import java.util.LinkedList;
import java.util.List;
public class MainActivity extends AppCompatActivity implements Serializable {
private EditText Name;
private EditText Age;
private EditText Birth;
private Button AddUser;
private Button Send;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Name = findViewById(R.id.Name);
Age = findViewById(R.id.Age);
Birth = findViewById(R.id.Birth);
AddUser = findViewById(R.id.AddUser);
Send = findViewById(R.id.Send);
Intent i = new Intent(MainActivity.this, SecondActivity.class);
List<User> list1 = new LinkedList<>();
AddUser.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (Name.getText().toString().trim().length() > 0 && Age.getText().toString().trim().length() > 0 && Birth.getText().toString().trim().length() > 0) {
User u = new User(Name.getText().toString(), Integer.parseInt(Age.getText().toString()), Birth.getText().toString());
list1.add(u);
Name.setText("");
Age.setText("");
Birth.setText("");
}
else {
Toast.makeText(MainActivity.this, "Fill All", Toast.LENGTH_SHORT).show();
}
}
});
Send.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
i.putExtra("Users", (Serializable) list1);
startActivity(i);
}
});
}
}
and that's the SecondActivty Code (it's preety much empty)
package com.example.hw1511;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
import com.example.hw1511.Model.User;
import java.io.Serializable;
import java.util.LinkedList;
import java.util.List;
import java.util.jar.Attributes;
public class SecondActivity extends AppCompatActivity{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
}
}
please if anyone help me understand what is making my app crash everytime i press the send button! it would really help me a lot.

Your User objects need to implement Serializable as well.
Also, since LinkedLists are Serializable you can use putSerializable(String key, Serializable value) instead of putExtra

Android Studio, Screeen To Screen Problem

basically im trying to make it so LoginScreen goes to Category screen .
package Screens;
import androidx.appcompat.app.AppCompatActivity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.provider.Settings;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import com.hr111.User.R;
import Utils.DisplayUtils;
import Utils.PlanUtils;
import Utils.SharedPreferencesUtils;
public class CategoryScreen extends AppCompatActivity {
Button btnExit;
Button btnChemistry;
Button btnBiology;
Button btnPhysics;
TextView textPlayerName;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_category_screen);
btnExit = findViewById(R.id.btnExit);
textPlayerName = findViewById(R.id.textViewName);
btnBiology = findViewById(R.id.btnBiology);
btnPhysics = findViewById(R.id.btnPhysics);
btnChemistry = findViewById(R.id.btnChemistry);
String username = SharedPreferencesUtils.getStringPreference(CategoryScreen.this, "username");
textPlayerName.append(username);
btnBiology.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
goToQuestions(btnBiology.getText().toString());
}
});
btnPhysics.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
goToQuestions(btnPhysics.getText().toString());
}
});
btnChemistry.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
goToQuestions(btnChemistry.getText().toString());
}
});
btnExit.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
DisplayUtils.DisplayScript(CategoryScreen.this, "Exit", "Cikmak Istiyor Musunuz?",
"Hayır", "Evet", null, null);
}
});
}
void goToQuestions(String CategoryName){
SharedPreferencesUtils.settingStringPreference(CategoryScreen.this, "category", CategoryName);
SharedPreferencesUtils.settingIntegerPreference(CategoryScreen.this, "questionCount", 1);
SharedPreferencesUtils.settingIntegerPreference(CategoryScreen.this, "score", 0);
PlanUtils.GoToActivity(CategoryScreen.this, GameScreen.class);
}
}
package Screens;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import com.hr111.User.MainActivity;
import com.hr111.User.R;
import Utils.DisplayUtils;
import Utils.ExcerciseClass;
import Utils.PlanUtils;
import Utils.SharedPreferencesUtils;
public class LoginScreen extends AppCompatActivity implements View.OnClickListener {
Button btnNext;
TextView username;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login_screen);
btnNext = findViewById(R.id.buttonLogin);
username = findViewById(R.id.plaintextName);
btnNext.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String name = username.getText().toString().trim();
if(nameCheck(name))
{
SharedPreferencesUtils.settingStringPreference(LoginScreen.this, "playername", name);
PlanUtils.GoToActivity(LoginScreen.this, CategoryScreen.class);
}
else
{
DisplayUtils.DisplayScript(LoginScreen.this, "ERROR!", "Gecerli bir oyuncu adi seciniz!", null, null, null, null);
}
}
});
}
boolean nameCheck(String name){
if(name == null) return false;
if(name.length() == 0) return false;
return true;
}
#Override
public void onClick(View v) {
}
}
Both screens are in different Classes.
But it simply crashes before LoginScreen can reach to Category Screen. Any clue why this is not working? I have been trying to figure out and i used different variations of codes but all led me to to nothing. I have also tried on a different project but that also led me to nowhere. Thanks in advance

how to fix my intent when i put the parameters

i get some problem when i use the intent, he said "cannot resolve constructor Intent('....')" , i dont know what is wrong in my code but you can see what i m importing here
package com.example.noen.myintentapp;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button btn = findViewById(R.id.btn_move);
btn.setOnClickListener(this);
}
#Override
public void onClick(View v) {
switch (v.getId())
{
case R.id.btn_move:
Intent intn = new Intent(MainActivity.this,target1.class);
break;
}
}
}

Class or interface expected at the end of the first set of closing brackets

Keep getting a class or interface expected error at the end of the first set of closing brackets, I have a feeling it has to do with the onCreate method, but I'm not sure how to go about fixing it.
package shake.shake;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import android.content.Intent;
import android.view.View.OnClickListener;
import android.widget.Button;
public class MainPage extends AppCompatActivity {
private static Button ShakeButton1;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_page);
OnClickButtonListener();
}
}
public void OnClickButtonListener()
{
ShakeButton1 = (Button)findViewById(R.id.ShakeButton);
ShakeButton1.setOnClickListener(
new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intentSecondActivity = new
Intent(MainPage.this, ShakePage.class);
startActivity(intentSecondActivity);
}
}
);
}}

you have extra braces here
public class MainPage extends AppCompatActivity {
private static Button ShakeButton1;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_page);
OnClickButtonListener();
}
} <-------- extra brace.

It's better having a look at codes before posting.
Your method public void OnClickButtonListener() is outside the class MainPage. Move that method inside your class.

Using simple text view and button widgets in android

Im trying to make a basic program where you press a button and it adds to an integer. Im having trouble updating the text view.
package com.example.curtis.simpleapplication;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity {
int num;
TextView numview;
private void updateNumber(){
TextView numview = (TextView)findViewById(R.id.Number);
numview.setText(num);
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setupButton();
}
private void setupButton() {
Button button = (Button) findViewById(R.id.Button);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
num = num + 1;
numview.setText(num);
}
});
}
Help would be great im trying to get into android and books havent been very helpful

There are a few mistakes here. First, you are never calling updateNumber() so numviewis never set. Moreover, you have two TextView numView once global in your MainActivity and again in updateNumber(). There is a better way to do this. But first go to activity_main.xml file and within the button tag add the the line android:onClick="onClick" something like this :
<Button
android:id="#+id/button1"
...
android:onClick="onClick"/>
Next in your MainActivity.java, add the following lines of code :
package com.example.curtis.simpleapplication;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity {
int num = 0;
TextView numview;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
numview = (TextView)findViewById(R.id.Number);
}
public void onClick(View view){
num += 1;
numview.setText(String.valueOf(num));
}
}
onClick() will be automatically called when your button is clicked because of the android:onClick property.

you have two different objects with same name and it would cause error.
one of them is defined in your class (TextView numview;) and the other one is defined in your function update number.
in your onClick method you want to change numView defined in your class and it's not initialized. you have to add change your code :
package com.example.curtis.simpleapplication;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity {
int num;
TextView numview;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
numview = (TextView)findViewById(R.id.Number);
setupButton();
}
private void setupButton() {
Button button = (Button) findViewById(R.id.Button);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
num = num + 1;
numview.setText(num);
}
});
}

Put this code in your onClick function
num = num + 1;
updateNumber();

You are never calling updateNumber()
package com.example.curtis.simpleapplication;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity {
int num=0;
TextView numview;
private void updateNumber(int number){
numview = (TextView)findViewById(R.id.Number);
numview.setText(number);
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setupButton();
}
private void setupButton() {
Button button = (Button) findViewById(R.id.Button);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
num = num + 1;
updateNumber(num);
}
});
}