Hey there! Let's sort out that crash and get your calculation logic working smoothly. The issue here is that when you call toDouble() directly on an empty or invalid string, it throws a NumberFormatException which crashes your app. Instead, we'll use Kotlin's safe conversion function to handle empty inputs gracefully.

The Problem with Your Current Code #

Your current code assumes all EditText fields have valid numeric values, but if any field is empty (or has non-numeric text), toDouble() will crash the app:

calculate.setOnClickListener {
    val s = distance.text.toString().toDouble()
    val u = initalVelocity.text.toString().toDouble()
    val t = time.text.toString().toDouble()
    val a = (((2* s))-(2*(u*t)))/(t*t)
    answer.setText("answer $a m/(s)^2")
}

The Solution: Safe Conversion with toDoubleOrNull() #

Kotlin provides toDoubleOrNull() which returns null if the string can't be converted to a valid Double (like empty strings or non-numeric text). We'll use this to check if all inputs are valid before calculating, and show an error message if any are missing.

Here's the updated MainActivity.kt code:

calculate.setOnClickListener {
    // Safely convert input strings to nullable Double types
    val s = distance.text.toString().toDoubleOrNull()
    val u = initalVelocity.text.toString().toDoubleOrNull()
    val t = time.text.toString().toDoubleOrNull()

    // Check if all inputs are non-null and valid
    if (s != null && u != null && t != null) {
        // Perform calculation only when all values are present
        val a = ((2 * s) - (2 * u * t)) / (t * t)
        answer.text = "answer $a m/(s)^2"
    } else {
        // Show prompt if any input is missing or invalid
        answer.text = "Put a value"
    }
}

Key Changes Explained #

• toDoubleOrNull(): Replaces toDouble() to avoid crashes from empty/invalid inputs. It returns null instead of throwing an exception, which aligns with what you tried to do with "DecimalorNull" (you were probably referring to this Kotlin built-in function).
• Null Check: We verify that s, u, and t are all non-null before running the calculation. If any value is null, we set the error message in the answer TextView.
• Simplified Formula: Removed unnecessary parentheses from the calculation to make the code cleaner, without changing the underlying math logic.

Your Layout XML (for reference) #

<EditText 
    android:id="@+id/distance" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:ems="10" 
    android:hint="@string/distance" 
    android:inputType="number|numberDecimal|numberSigned" 
    app:layout_constraintBottom_toBottomOf="parent" 
    app:layout_constraintEnd_toEndOf="parent" 
    app:layout_constraintHorizontal_bias="0.094" 
    app:layout_constraintStart_toStartOf="parent" 
    app:layout_constraintTop_toTopOf="parent" 
    app:layout_constraintVertical_bias="0.034" />
<EditText 
    android:id="@+id/initalVelocity" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:ems="10" 
    android:hint="@string/initialVelocity" 
    android:inputType="number|numberDecimal|numberSigned" 
    app:layout_constraintBottom_toBottomOf="parent" 
    app:layout_constraintEnd_toEndOf="parent" 
    app:layout_constraintHorizontal_bias="0.094" 
    app:layout_constraintStart_toStartOf="parent" 
    app:layout_constraintTop_toTopOf="parent" 
    app:layout_constraintVertical_bias="0.133" />
<EditText 
    android:id="@+id/time" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:ems="10" 
    android:hint="@string/time" 
    android:inputType="number|numberDecimal|numberSigned" 
    app:layout_constraintBottom_toBottomOf="parent" 
    app:layout_constraintEnd_toEndOf="parent" 
    app:layout_constraintHorizontal_bias="0.094" 
    app:layout_constraintStart_toStartOf="parent" 
    app:layout_constraintTop_toTopOf="parent" 
    app:layout_constraintVertical_bias="0.232" />
<TextView 
    android:id="@+id/answer" 
    android:layout_width="219dp" 
    android:layout_height="37dp" 
    android:text="@string/answer" 
    app:layout_constraintBottom_toBottomOf="parent" 
    app:layout_constraintEnd_toEndOf="parent" 
    app:layout_constraintHorizontal_bias="0.096" 
    app:layout_constraintStart_toStartOf="parent" 
    app:layout_constraintTop_toTopOf="parent" 
    app:layout_constraintVertical_bias="0.35" />
<Button 
    android:id="@+id/calculate" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text="@string/calculate" 
    app:layout_constraintBottom_toBottomOf="parent" 
    app:layout_constraintEnd_toEndOf="parent" 
    app:layout_constraintStart_toStartOf="parent" 
    app:layout_constraintTop_toTopOf="parent" 
    app:layout_constraintVertical_bias="0.462" />

This should prevent the crash and show your desired prompt whenever any input is missing or invalid. Give it a try!

内容的提问来源于stack exchange，提问作者a2krocks