I'm new on android development field. Last night I made a simple calculator from a youtube tutorial and fortunately I've successfully made it. Here is the code
main.xml:-
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="top|center">
<ImageView
android:layout_height="120dp"
android:layout_width="120dp"
android:src="@drawable/cal"/>
<EditText
android:layout_width="wrap_content"
android:inputType="number"
android:layout_height="wrap_content"
android:ems="10"
android:layout_marginTop="10dp"
android:gravity="center"
android:hint="@string/fstval"
android:id="@ id/etFirstValue"/>
<EditText
android:layout_width="wrap_content"
android:inputType="number"
android:layout_height="wrap_content"
android:ems="10"
android:layout_marginTop="10dp"
android:gravity="center"
android:hint="@string/sndval"
android:id="@ id/etSecondValue"/>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:layout_marginTop="10dp"
android:gravity="center"
android:hint="@string/ans"
android:textColorHint="#FF0F00"
android:id="@ id/tvAns"/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/add"
android:layout_marginTop="19dp"
android:layout_marginRight="10dp"
android:layout_marginLeft="10dp"
android:background="#4C5866"
android:padding="10dp"
android:textColor="#000000"
android:textSize="25sp"
android:id="@ id/btnAdd"
android:onClick="btnadd"/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/sub"
android:layout_marginRight="10dp"
android:layout_marginLeft="10dp"
android:background="#677789"
android:padding="10dp"
android:layout_marginTop="5dp"
android:textColor="#000000"
android:textSize="25sp"
android:id="@ id/btnSubtract"
android:onClick="btnsub"/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/mul"
android:layout_marginRight="10dp"
android:layout_marginLeft="10dp"
android:background="#405163"
android:padding="10dp"
android:layout_marginTop="5dp"
android:textColor="#000000"
android:textSize="25sp"
android:id="@ id/btnMultiply"
android:onClick="btnmul"/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/div"
android:layout_marginRight="10dp"
android:layout_marginLeft="10dp"
android:background="#19E6B1"
android:padding="10dp"
android:layout_marginTop="5dp"
android:textColor="#000000"
android:id="@ id/btnDivide"
android:textSize="25sp"
android:onClick="btndiv"/>
</LinearLayout>
mainactivity.java:-
package com.mycompany.myapp;
import android.app.*;
import android.os.*;
import android.widget.*;
import android.view.View.*;
import android.view.*;
public class MainActivity extends Activity
{
private EditText etn1;
private EditText etn2;
private TextView tvResult;
private Button btnadd , btnsub , btnmul , btndiv;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
etn1 = findViewById(R.id.etFirstValue);
etn2 = findViewById(R.id.etSecondValue);
tvResult = findViewById(R.id.tvAns);
Button btnadd = findViewById(R.id.btnAdd);
btnadd.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
int n1 = Integer.parseInt(etn1.getText().toString());
int n2 = Integer.parseInt(etn2.getText().toString());
int add = n1 n2;
tvResult.setText(String.valueOf(add));
}
});
Button btnsub = findViewById(R.id.btnSubtract);
btnsub.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
int n1 = Integer.parseInt(etn1.getText().toString());
int n2 = Integer.parseInt(etn2.getText().toString());
int add = n1 - n2;
tvResult.setText(String.valueOf(add));
}
});
Button btnmul = findViewById(R.id.btnMultiply);
btnmul.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
int n1 = Integer.parseInt(etn1.getText().toString());
int n2 = Integer.parseInt(etn2.getText().toString());
int add = n1 * n2;
tvResult.setText(String.valueOf(add));
}
});
Button btndiv = findViewById(R.id.btnDivide);
btndiv.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
int n1 = Integer.parseInt(etn1.getText().toString());
int n2 = Integer.parseInt(etn2.getText().toString());
int add = n1 / n2;
tvResult.setText(String.valueOf(add));
}
});
}
}
But the problem is when I don't put any value into the firstEditText or secondEditText or both of them and click on any button the app got crash and a pop up showing "myapp keeps stopping". I want something like " Please enter a value" shows on the blank EditText when I don't pun any value to any of EditText. Help me please
CodePudding user response：
The problem is your input (say, etn1.getText().toString()) may not be a number. So you get NumberFormatException.
To fix this, rewrite your code like this:
btnadd.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
int n1 = 0;
int n2 = 0;
try{
n1 = Integer.parseInt(etn1.getText().toString());
}catch(Exception x) {
x.printStackTrace();
n1 = 0;
}
try{
n2 = Integer.parseInt(etn2.getText().toString());
}catch(Exception x) {
x.printStackTrace();
n2 = 0;
}
int add = n1 n2;
tvResult.setText(String.valueOf(add));
}
});
CodePudding user response：
You're receiving a NumberFormatException because when you run
Integer.parseInt(etn1.getText().toString())
When a EditText field has no value it returns "". "" cannot be transcribed into a number. Therefore, it throws the NumberFormat Exception.
There are a number of ways to handle this but i would suggest using Uncle Bobs Clean Code methodology. You can encapsulate your within a try catch block for each button click like so:
try{
n1 = Integer.parseInt(etn1.getText().toString());
}catch(NumberFormatException x) {
x.printStackTrace();
n1 = 0;
}
But i would suggest that given this code will have multiple uses across all button types, you move your n variables to global variables (at the top of the code base i.e int n1) and produce a new method such as
Private void setNumbers(){
try{
n1 = Integer.parseInt(etn1.getText().toString());
n2 = Integer.parseInt(etn2.getText().toString());
}catch(NumberFormatException x) {
x.printStackTrace();
n1 = 0;
n2 = 0;
}
}
Then within each Button onClick Listener could look like:
btndiv.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
setNumbers();
int divide = n1 / n2;
tvResult.setText(String.valueOf(divide));
}
});
CodePudding user response：
Your app is crashing because when you don't enter any value and tap on buttons, it tries to parse an empty string to int which leads to a NumberFormatException and crashes your app.
However, you can first check if your edit texts are empty or not before parsing them, and show a toast or a snackbar if they are empty.
Use this
String number1 = etn1.getText().toString();
String number2 = etn2.getText().toString();
if(number1.isBlank() || number2.isBlank()){
Toast.makeText(this, "Please enter a value", Toast.LENGTH_LONG).show();
} else {
int n1 = Integer.parseInt(number1);
int n2 = Integer.parseInt(number2);
int add = n1 n2;
tvResult.setText(String.valueOf(add));
}