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Android app crashes when no value is in edit text

I am making a unit converter, but if I do not enter any value into edit text and press the calculate button the app crashes with error Invalid float: "". Also, I want to forbid zeroes from being entered before numbers (eg. 0300). How do I accomplish this?
//handle calculate
calcButton=(Button)findViewById(R.id.calcButton);
calcButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Spinner spinner = (Spinner) findViewById(R.id.unit_spinner);
String spinnerText = spinner.getSelectedItem().toString();
EditText unit_edit = (EditText) findViewById(R.id.unit_edit);
amount = Float.valueOf(unit_edit.getText().toString());
if (unit_edit.getText().toString().equals(null)) {
Toast.makeText(getApplicationContext(), "Insert Value To Convert",
Toast.LENGTH_LONG).show();
} else {
switch (spinnerText) {
case "Kilograms":
kilograms = amount;
grams = amount * 1000;
ListView();
break;
case "Grams":
grams = amount;
kilograms = amount / 1000;
ListView();
break;
}
}
}
});
}

You are probably getting an NumberFormatException thrown since the EditText fields text is "" and "" is not a valid float value, the exception is thrown at the following line:
amount = Float.valueOf(unit_edit.getText().toString());
What you'll need to do is add some validation and checking before trying to get the float value of a String.
Check the methods documentation for more details http://docs.oracle.com/javase/7/docs/api/java/lang/Double.html#valueOf(java.lang.String)

This might be useful for your EditText to limit input to numbers only.
<EditText
android:id="#+id/unit_edit"
android:inputType="number"
/>
You can also limit the digits, type of number such as decimal
<EditText
android:id="#+id/unit_edit"
android:digits="0123456789."
android:inputType="numberDecimal"
/>

You can't parse an empty value to float. You should first test if it's empty, and then do what you want, something like this:
String text = unit_edit.getText().toString();
if(!text.isEmpty()){ // Test if the text is empty
if(text.matches("[0-9]+")){ // Test if it only contains numbers, using REGEX
amount = Float.valueOf(text); // Only then parse to float.
// Switch and rest of the stuff
} else {
Toast.makeText(getApplicationContext(), "Use only numbers from 0 to 9.",
Toast.LENGTH_LONG).show();
}
} else {
Toast.makeText(getApplicationContext(), "The field is empty",
Toast.LENGTH_LONG).show();
}
The comments explain what's going on. About the leading 0 in some numbers, using "valueOf" will remove it already, and 0300 will be parsed as 300, so there's nothing to worry about.If you still want something related to it, let me know and i'll edit my answer.

Android slpit string doubleparse and pass it to a method that converts degrres to decimal

I have a android method that converts degrees minutes and seconds to decimal. I am getting the text from edittext split it and convert it to double array before I pass it to the method. Then I wanted to get the double returned in a decimal form to be displayed in the original edittext as string. Here is the code,
public double DegreeToDecimal(double d, double m, double s)
{
double decimal;
decimal = d + m/60 + s/3600;
return decimal;
}
try
{
String string = dtod.getText().toString();
String[] s = string.split(":");
String decimal;
double d = DegreeToDecimal(Double.parseDouble(s[0]), Double.parseDouble(s[1]), Double.parseDouble(s[2]));
decimal = String.valueOf(d);
dtod.setText(decimal);
}catch (Exception e){
e.printStackTrace();
}
When I do this on a button click, nothing happens. The Logcat doesn't show anything and the code is simply ignored. What am I doing wrong?
Thanks for the help.

Your code formatting is all over the place and hard to read, please try to use correct indentation next time!
From the code you posted it's hard to tell what happens. If Logcat doesn't show any stacktraces like you said, and if your code is "ignored" as you say then my guess is that it doesn't get called.
Did you attach an OnClickListener to that button?
Otherwise try to log something between your lines or use a debugger to find out what really happens!

Getting Int from EditText causes error?

So first of all sorry if this has already been asked and answered before, I couldn't find anything relating to my issue.
So I'm working on a project for college and I need to get int values from EditText widgets. I was told to use parseInt to do this however when running my program, that line of code causes the application to crash. I don't know what I'm doing wrong, I'm still very new to android development, thanks for the help :)
public void Calculate (View view)
{
int MilesTravelled;
int FuelUsed;
int MPG;
/* the two lines below are what cause the application to crash */
MilesTravelled = Integer.parseInt(txtMilesTravelled.getText().toString());
FuelUsed = Integer.parseInt(txtFuelUsed.getText().toString());
FuelUsed = (int) (FuelUsed / 4.55);
MPG = MilesTravelled / FuelUsed;
lblMPG.setText(FuelUsed);
}

Do you have this in the onCreate() function?
EditText txtMilesTravelled = (EditText) findViewById(R.id.YourEditText);
But I think you mixed Integer and int. They are not the same:
See this link!

First of all, don't capitalize the first letter of an variables or method names. Following the Java coding conventions, only do that for classes.
What is probably causing your app to crash is you trying to set the text of a label to an integer. The setText method for a TextView needs to take in a string.
So change:
lblMPG.setText(FuelUsed);
to:
lblMPG.setText(String.valueOf(FuelUsed));
Otherwise it might be that it's trying to parse a non-numerical string to an integer.
For exmaple, if the EditText is blank, it will cause your app to crash. To prevent that, try this:
int MilesTravelled = 0, FuelUsed = 0;
try {
MilesTravelled = Integer.parseInt(txtMilesTravelled.getText().toString());
FuelUsed = Integer.parseInt(txtFuelUsed.getText().toString());
} catch (NumberFormatException nfe) {
Toast.makeText(getApplicationContext(), "Error NFE!", 0).show();
nfe.printStackTrace();
}
This way, it will catch a NumberFormatException error (parsing a string to an integer that can't be represented as an integer, such as "hello"). If it catches the error, it will toast that an error has occurred and your integer variables will remain 0.
Or you could just test if the strings contain only digits using the following regex:
int MilesTravelled = 0, FuelUsed = 0;
if (txtMilesTravelled.getText().toString().matches("[0-9]+")) {
MilesTravelled = Integer.parseInt(txtMilesTravelled.getText().toString());
} else {
// contains characters that are not digits
}
if (txtFuelUsed.getText().toString().matches("[0-9]+")) {
FuelUsed = Integer.parseInt(txtFuelUsed.getText().toString());
} else {
// contains characters that are not digits
}
If that's not the problem, then make sure you define your variables properly.
txtMilesTravelled and txtFuelUsed should be EditText:
EditText txtMilesTravelled = (EditText)findViewById(R.id.txtMilesTravelled);
EditText txtFuelUsed = (EditText)findViewById(R.id.txtFuelUsed);
And make sure that your R.id.editText actually exists on your layout and that the IDs are the correct ones.
Last thing, make sure FuelUsed is not 0 before calculating MPG because then you are dividing by 0:
int MPG = 0;
if (FuelUsed != 0) {
MPG = MilesTravelled / FuelUsed;
}

I am assuming that you're entering perfect integers in the EditTexts. It might be a good idea to use the trim function txtMilesTravelled.getText().toString().trim() before using parseInt.
However, I think the major problem is here : lblMPG.setText(FuelUsed);
FuelUsed is an integral value, when you pass an integer to setText(), it looks for a string resource with that integral value. So you should be passing a String to the setText() method.
Use : lblMPG.setText(Integer.toString(FuelUsed));

Get EditTextValue and parse it into a decimal with only one digit for integer part

I'm having an issue when I get a whole number from an EditText and try to change that to a decimal so I can use it for calculations. Could someone explain how to do this?
For Example. if someone was to enter 120 into the EditText and I got the integer from it, how would I then change that integer of 120 into 1.20 and continue calculations with it?
Thanks!!

EditText myEditText = (EditText)findViewById(R.id.YOUR_EDIT_TEXT_ID);
String numberAsString = myEditText.getText().toString();
double myDecimal;
try {
myDecimal = Double.parseDouble(numberAsString);
if (myDecimal >= 10)
{
int digits = 1 + (int)Math.floor(Math.log10(myDecimal));
myDecimal = myDecimal / ((Math.pow((double)10, ((double)digits) - 1)));
System.out.println(myDecimal);
}
} catch (NumberFormatException e) {
//handle exeption
e.printStackTrace();
}

You need to get the contents from your EditText as a string, and from there you can parse it into an integer. This is done like so:
int wholeNum = Integer.parseInt(yourEditText.getText().toString());

int three = Integer.parse("3");
I know you can use this to parse a string into an integer, there is probably a parse method in double aswell!
Check this also :
Convert a String to Double - Java
+1 to anthony for answering 1 minute before me haha

How to Avoid Scientific Notation in Double?

Here is my simple code
#Override
public void onClick(View v) {
try {
double price = Double.parseDouble(ePrice.getText().toString());
double percent = Double.parseDouble(ePercent.getText().toString());
double priceValue = price * percent/100.0f;
double percentValue = price - priceValue;
moneyToGet.setText(String.valueOf(priceValue));
moneyToPay.setText(String.valueOf(percentValue));
moneyToGet.setText("" + priceValue);
moneyToPay.setText("" + percentValue);
// catch
} catch (NumberFormatException ex) {
// write a message to users
moneyToGet.setText("");
}
}
});
This is a simple code for Percentage Calculator.
What I want is to avoid the Scientific Notation in my Calculator cause I don't want to explain to user what is Scientific Notation.
For example if I want to calculate 100,000,000 and cut 50% of it, it Should give me 50,000,000 which is giving me 5.0E7 And in my case this doesn't make any sense to the user. And of course I know both results are correct.
Thanks in Advance.

Check answer here. You can write
moneyToGet.setText(String.format("%.0f", priceValue));

You can try this DecimalFormat
DecimalFormat decimalFormatter = new DecimalFormat("############");
number.setText(decimalFormatter.format(Double.parseDouble(result)));

I would suggest using BigDecimals instead of doubles. That way you will have a more precise control over your calculation precision. Also you can get a non-scientific String using BigDecimal.toPlainString().

DecimalFormat decimalFormatter = new DecimalFormat("##.############");
decimalFormatter.setMinimumFractionDigits(2);
decimalFormatter.setMaximumFractionDigits(15);
This option will help you ##.## suffix 0 before decimal, otherwise output will be .000
btc.setText(decimalFormatter.format(btcval));
use this for displaying content

Use NumberFormater like
NumberFormat myformatter = new DecimalFormat("########");
String result = myformatter.format(yourValue);