显示 Toast 消息以添加文本而不是应用程序崩溃

Question

Hey guys I have a question when I add some text in the box it works but when I don't add anything inside, the project crashes. Is there a way to be able to add an if statement to the project to ask the user (via Toast) to add something instead of crashing the app? Thanks

this is the code I have so far

    @SuppressLint("DefaultLocale")
    public void convert(View view) {

        TextView textView = findViewById(R.id.enterNumber);

        double enteredNumber = Double.parseDouble(textView.getText().toString());
        double converted = (Double.parseDouble(textView.getText().toString()) * 100)/100*106.111;

        final String usFormat = String.format("%.2f", enteredNumber);
        final String japanFormat = String.format("%.2f",converted);




        Toast.makeText(MainActivity.this,  "$" +usFormat + " USD is = " +
              "¥" + japanFormat +  " Yen", Toast.LENGTH_SHORT).show();
        Log.i("Button pressed", "Pressed");
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}

this is the xml code I have to set up

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="68dp"
        android:text="Enter an amount to convert"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="convert"
        android:text="Button"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.254" />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="410dp"
        android:layout_height="287dp"
        android:scaleType="centerInside"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button2"
        app:srcCompat="@drawable/money" />

    <EditText
        android:id="@+id/enterNumber"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="7dp"
        android:ems="10"
        android:inputType="numberDecimal"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView" />

</androidx.constraintlayout.widget.ConstraintLayout>```

Answer 1

Yes, you can, all you need is validate the user input before converting it into an Double number.

Then, you may want to surround your code with try catch block to prevent when the input string is not a number.

Try this:

TextView textView = findViewById(R.id.enterNumber);
    
String value = textView.getText().toString();
if (value.equals("")) {
    Toast.makeText(MainActivity.this,  "Field must not empty", Toast.LENGTH_SHORT).show();
    return;
}
try {
    double enteredNumber = Double.parseDouble(textView.getText().toString());
    double converted = (Double.parseDouble(textView.getText().toString()) * 100) / 100 * 106.111;
    final String usFormat = String.format("%.2f", enteredNumber);
    final String japanFormat = String.format("%.2f", converted);


    Toast.makeText(MainActivity.this, "$" + usFormat + " USD is = " +
                "¥" + japanFormat + " Yen", Toast.LENGTH_SHORT).show();
    Log.i("Button pressed", "Pressed");
} catch (NumberFormatException ex) {
    Toast.makeText(MainActivity.this,  "Value is not a number!", Toast.LENGTH_SHORT).show();
    return;
}