Develop Reference

Intent doesnt hand over variable from one class to another

I am new to Android programming and tried to create a small App. I have a MainClass with one EditText and one TextField. EditText is for users to type in a number and the TextField shows the value of the input when clicking on the first button. The second button is for switching to the other class (MainClass2). Now i want to show the input number from EditText (that I defined as "number") in the next class MainClass2 in an empty TextField. I implemented an OnClickListener for the two different buttons mentioned in the MainClass (first screen). Since I only defined the input variable "number" when clicking the first button (cause "number" is then shown in the TextField as mentioned because it is only created via EditText when clicking the first button), "number" is not defined in the code of clicking the second button. Therefore I cant hand it over to the MainClass2 via Intent. Do you have any solutions for this? Thank you in advance. These are the codes for my Classes:
package com.example.teilnehmeranzahl;
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 java.util.Random;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button = findViewById(R.id.button);
Button button2 = findViewById(R.id.button2);
Button one = (Button) findViewById(R.id.button);
one.setOnClickListener(this); // calling onClick() method
Button two = (Button) findViewById(R.id.button2);
two.setOnClickListener(this);
}
public void onClick(View v) {
// default method for handling onClick Events..
switch (v.getId()) {
case R.id.button:
EditText editText2 = findViewById(R.id.editText2);
String name2=editText2.getText().toString();
int number=Integer.parseInt(name2);
TextView textView = findViewById(R.id.textView);
textView.setText(String.valueOf(number));
Random randomizer = new Random();
int name = randomizer.nextInt(number+1);
TextView textView2 = findViewById(R.id.textView2);
if (name == 1 ) {
textView2.setText("Player 1");
}
if (name == 2 ) {
textView2.setText("Player 2");
}
break;
case R.id.button2:
Intent intent = new Intent(MainActivity.this,MainActivity2.class);
intent.putExtra("number",number); //here is the error cause number is not
defined, although it is..
startActivity(intent);
break;
default:
break;
}
}
}
And this is the code for MainClass2:
package com.example.teilnehmeranzahl;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.TextView;
public class MainActivity2 extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
TextView textView3 = findViewById(R.id.textView3);
Intent intent = getIntent();
String number = intent.getStringExtra("number");
textView3.setText(number);
}
}

In case R.id.button2: you have not set the value of number. So it will give number undefined error. To solve this issue either you have to initialize number globally or get the value of number in case R.id.button2: also. Like
case R.id.button2:
EditText editText2 = findViewById(R.id.editText2);
String name2=editText2.getText().toString();
int number=Integer.parseInt(name2);
Intent intent =
new Intent(MainActivity.this,MainActivity2.class);
intent.putExtra("number",number);
startActivity(intent);
break;

how to prevent a user from clicking on a button after another button has been clicked?

I am new to android programming and am building a quiz app in which a question has 4 options and if the user clicks on one of the options the other options should be unclickable. I am currently able to only make a single button unclickable. Here is the java code.
package com.example.android.quiz;
import android.graphics.Color;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
//This method is called when option 1 of question 1 is selected
public void verifyQuestion1Option1(View view) {
Button QuestionOption1 = (Button) findViewById(R.id.question1_option1);
QuestionOption1.setBackgroundColor(getResources().getColor(R.color.solid_red));
question1Answer();
}
public void verifyQuestion1Option2(View view) {
Button Question1Option2 = (Button) findViewById(R.id.question1_option2);
Question1Option2.setBackgroundColor(getResources().getColor(R.color.solid_red));//solid red is not a predefined colour. It is declared in colors.xml
question1Answer();
}
public void verifyQuestion1Option3(View view) {
Button Question1Option3 = (Button) findViewById(R.id.question1_option3);
Question1Option3.setBackgroundColor(getResources().getColor(R.color.solid_green));
question1Answer();
}
public void verifyQuestion1Option4(View view) {
Button Question1Option4 = (Button) findViewById(R.id.question1_option4);
Question1Option4.setBackgroundColor(getResources().getColor(R.color.solid_red));//We call the getResources() method because R.colour.solid_red passed the id of the color not the actual colour value.
question1Answer();
}
public void question1Answer() {
TextView q1Answer = (TextView) findViewById(R.id.question1_answer);
String answer = "Rajinish Kumar is the current Chairman of SBI who took over after Arundhati Bhattacharya retired on 6 October.Shikha Sharma is the Managing Director and CEO of Axis Bank and Chanda Kochhar is the managing director and CEO of ICICI Bank";
q1Answer.setText(answer);
}
}

Either you can use a buttongroup which will have only 1 active button at any point of time or else, you need to disable other button programatically.
To disable the button you can use the following code:
Button button = (Button) findViewById(R.id.button);
button.setEnabled(false);

You can use .setEnabled(false); to disable a button. That button will grey out and does not respond to click events any more.
To disable all buttons, get the handle to each button and set them to disabled.
Button Question1Option1 = (Button) findViewById(R.id.question1_option1);
Button Question1Option2 = (Button) findViewById(R.id.question1_option2);
Button Question1Option3 = (Button) findViewById(R.id.question1_option3);
Button Question1Option4 = (Button) findViewById(R.id.question1_option4);
Question1Option1.setEnabled(false);
Question1Option2.setEnabled(false);
Question1Option3.setEnabled(false);
Question1Option4.setEnabled(false);
That way, all buttons of this question become disabled.
You can also come up with a solution where you save that the button is already pressed and ignore further click events. You could introduce some sort of variable bool question1answered = false; that is set to true as soon as the onClick event is fired.
public void verifyQuestion1Option4(View view) {
if (question1Answered == true) {return;}
question1Answered =true;
//Do the rest of your checks here
}
Two tips for for programming Java:
Java (in contrast to i.e C#) used lower letter variables as convention.
Button question1Option1 = (Button) findViewById(R.id.question1_option1); would be a better way.
If you have more questions, it would make sense to put them in some sort of array and reuse the same four buttons multiple times. That would save you much programming overhead and code rewrites if you have to change something. And it keeps the code cleaner.

Radio group not working in android

I ahve made a simple radioButton demo in android.In that i have put a radiogroup with two radio buttons named "male" and "female"...and a button .I want is when one of them pressed the name related to that particular radiobutton should be in toast.I have tried as below thats not working:
Activity.java
package com.example.radiobuttondemo;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.Toast;
public class MainActivity extends Activity {
RadioButton rd1,rd2;
Button b;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
rd1=(RadioButton)findViewById(R.id.radio0);
rd2=(RadioButton)findViewById(R.id.radio1);
b.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
if(rd1.isChecked()){
Toast.makeText(getApplicationContext(), "male", 0).show();
}
else{
Toast.makeText(getApplicationContext(), "Female", 0).show();
}
}
});
}
}

You forgot to initialize your Button b.
So when you're doing b.setOnClickListener, your program throws a NullPointerException and make your app closed.

You must bind your button with the Button object (that you named b) in your MainActivity class.
There is an action listener on b, but b is not binded...

Personally, I've always used RadioGroup for my radio buttons. If you didn't use that, how would it know to uncheck one radio button when you checked the other radio button?
See http://www.mkyong.com/android/android-radio-buttons-example/
Now if you're dealing with a normal checkbox, your approach would be fine I suppose. A normal checkbox wouldn't need to know about its siblings.

Do the check against RadioButton group itself:
switch (radioGroup.getCheckedRadioButtonId()) {
case rd1:
Toast.makeText(getApplicationContext(), "male", 0).show();
break;
case rd2:
Toast.makeText(getApplicationContext(), "Female", 0).show();
break;
)

How to switch text view from one thing to the next when a button is clicked - Android

Below is my main activity file. I am stuck with the bottom area (commented out). I want to make it so that when I hit button b1, the text changes from what it is for default. So say it says "hello" by default, I want to switch the text to something like "how are you" when you press button b1. I have tried many things, but I always get errors. Can someone help me?
package com.wdmc85.donottouch;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
public class DoNotTouchActivity extends Activity
implements OnClickListener {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button b1 = (Button) this.findViewById(R.id.b1);
b1.setOnClickListener(this);
}
#Override
public void onClick(View v)
{
switch(v.getId())
{
case R.id.b1:
//WHAT DO I PUT IN HERE?? I WANT IT SO WHEN YOU HIT BUTTON B1, THE
//TEXT CHANGES FROM WHAT IT IS FOR DEFAULT. SO SAY IT SAYS "HELLO"
//AS DEFAULT, HOW DO I MAKE IT SO WHEN YOU PRESS BUTTON B1 THE TEXT
//CHANGES FROM "HELLO" TO "HOW ARE YOU?" I HAVE TRIED ALL SORTS OF
//THINGS BUT NOTHING HAS WORKED
break;
}
}
}

if want to change text of the button itself
switch(v.getId())
{
case R.id.b1:
Button b1 = (Button) v;
b1.setText("HOW ARE YOU?");
break;
}
if want to change text of the any other Textview
switch(v.getId())
{
case R.id.b1:
TextView tv = (TextView ) this.findViewById(R.id.<tvid>);
tv .setText("HOW ARE YOU?");
break;
}

You should use below method to change text of text view.
textView.setText("your text");
reference link is >> textview>>setText()
can use same for button and other views.

How the detect the "edittext" box whether it is nothing in Android?

I want to program a function that the toast exist when there is nothing
in the "edittext" box (id / password), but it dosen't work.
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.content.Intent;
import android.widget.EditText;
import android.widget.Toast;
import android.view.View.OnClickListener;
import android.text.Editable;
public class Test extends Activity
{
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button button1 = (Button) findViewById(R.id.button1);
EditText id = (EditText) findViewById(R.id.id);
EditText pwd = (EditText) findViewById(R.id.pwd);
Editable Str_id;
Editable Str_pwd;
Str_id = id.getText();
Str_pwd = pwd.getText();
button1.setOnClickListener(new Button.OnClickListener()
{
public void onClick(View v){
if(Str_id==null || Str_pwd == null){
Toast.makeText(Test.this, "Please Enter User ID / Password", Toast.LENGTH_LONG).show();
}
});
}
}

move the following lines inside onClick and try:
Str_id = id.getText();
Str_pwd = pwd.getText();
EDIT: Move
Editable Str_id;
Editable Str_pwd;
Str_id = id.getText();
Str_pwd = pwd.getText();
inside onClick().

I do not recommend toasting a message that a field is required. You're better off just giving the EditText focus, this focus tells the user that this field is required. Its less information on the screen and its subtle, which is important. You don't want to disturb the user too much.
The idea is...
When the submit button is clicked, check the EditTexts if any of them are empty, notify the user through requesting focus, also make sure your UI tells them before hand that the fields required. The hint of the EditText works well for this.