Question

This is a tip calculator app in Java. If both fields are not filled in, it should show an error message in a TextView, but it just freezes the app… any tips?

package tip.calculator;


import android.os.Bundle;
import android.app.Activity;
import android.view.View.OnClickListener;
import android.widget.EditText;
import android.widget.TextView;
import android.view.View;
import android.widget.Button;




public class TipCalculator extends Activity 
{

private Button enter;
EditText myEditField ;
EditText myEditField2;
float percentage = 0;
float percentageInp = 0;
float billAmount = 0;
double output = 0; 
String output1 = "";
Button clearButton ;
TextView textView;

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    myEditField = (EditText) findViewById(R.id.percentText);
    enter = (Button)findViewById(R.id.button1);
    myEditField2 = (EditText) findViewById(R.id.billText);
    clearButton = (Button) findViewById(R.id.clearButton);


    enter.setOnClickListener(new OnClickListener() {


        public void onClick(View v) {

             TextView errors;
             textView = (TextView) findViewById(R.id.textView1);
             errors = (TextView) findViewById(R.id.errorText);    




             if(myEditField.getText().equals("")){
                 errors.setText("Percent must be filled in");


             }

             if(myEditField.getText().equals("")){
                 errors.setText("Bill Amount must be filled in");

             }




            percentageInp = Float.parseFloat(myEditField.getText().toString());
            billAmount = Float.parseFloat(myEditField2.getText().toString());

            percentage = ((float)percentageInp /100);

            output = (double)(billAmount * percentage);

            double result = output * 100;
            result = Math.round(result);
            result = result / 100;

            output1 = Double.toString(result);

            textView.setText(output1 + " $");

        }
    });

    clearButton.setOnClickListener(new OnClickListener() {

        public void onClick(View arg0) {

            percentage = 0;
            output = 0;
            output1 = "";

            TextView textView = (TextView)findViewById(R.id.errorText);
            textView.setText("");

            TextView textView2 = (TextView)findViewById(R.id.percentText);
            textView2.setText("");

            TextView textView3 = (TextView)findViewById(R.id.billText);
            textView3.setText("");


            TextView textView1 = (TextView)findViewById(R.id.textView1);
            textView1.setText("");


            percentageInp = 0;
            billAmount = 0;

            myEditField.clearComposingText();
            myEditField2.clearComposingText();



            return;
        }


    });
}*

}

here is the layout xml(provided by request)…

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/errorText"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:onClick="onEnterClick" >

    <EditText
        android:id="@+id/billText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:ems="10"
        android:hint="Bill Amount"
        android:inputType="numberDecimal|textAutoComplete"
        android:singleLine="true" />

    <EditText
        android:id="@+id/percentText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/billText"
        android:layout_below="@+id/billText"
        android:ems="10"
        android:hint="Percent"
        android:inputType="number"
        android:singleLine="true" >

        <requestFocus />
    </EditText>

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/percentText"
        android:layout_centerHorizontal="true"
        android:text="Calculate" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@+id/percentText"
        android:layout_toRightOf="@+id/billText"
        android:text="$"
        android:textAppearance="?android:attr/textAppearanceLarge" />

    <TextView
        android:id="@+id/textView3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/percentText"
        android:layout_alignLeft="@+id/textView2"
        android:text="%"
        android:textAppearance="?android:attr/textAppearanceLarge" />

    <Button
        android:id="@+id/clearButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/button1"
        android:layout_centerHorizontal="true"
        android:text="Clear" />

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignRight="@+id/textView3"
        android:layout_below="@+id/clearButton"
        android:text="Solution Will Appear Here"
        android:textAppearance="?android:attr/textAppearanceLarge" />

    <TextView
        android:id="@+id/textView4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/button1"
        android:layout_below="@+id/errorText"
        android:text=""
        android:textAppearance="?android:attr/textAppearanceLarge" />

</RelativeLayout>

here is the LogCat output (errors only)

08-01 20:49:08.424: E/(13643): URE: SkPaint in getMeasureCacheProc index: 2
08-01 20:49:08.689: E/(13643): URE: SkPaint in getMeasureCacheProc index: 2
08-01 20:49:10.844: E/(13643): URE: SkPaint in getMeasureCacheProc index: 2
08-01 20:49:12.074: E/(13643): URE: SkPaint in getMeasureCacheProc index: 2
08-01 20:49:12.254: E/(13643): URE: SkPaint in getMeasureCacheProc index: 2
08-01 20:49:16.649: E/AndroidRuntime(13643): FATAL EXCEPTION: main
08-01 20:49:16.649: E/AndroidRuntime(13643): java.lang.ClassCastException: android.widget.RelativeLayout cannot be cast to android.widget.TextView
08-01 20:49:16.649: E/AndroidRuntime(13643):    at tip.calculator.TipCalculator$2.onClick(TipCalculator.java:91)
08-01 20:49:16.649: E/AndroidRuntime(13643):    at android.view.View.performClick(View.java:3620)
08-01 20:49:16.649: E/AndroidRuntime(13643):    at android.view.View$PerformClick.run(View.java:14292)
08-01 20:49:16.649: E/AndroidRuntime(13643):    at android.os.Handler.handleCallback(Handler.java:605)
08-01 20:49:16.649: E/AndroidRuntime(13643):    at android.os.Handler.dispatchMessage(Handler.java:92)
08-01 20:49:16.649: E/AndroidRuntime(13643):    at android.os.Looper.loop(Looper.java:137)
08-01 20:49:16.649: E/AndroidRuntime(13643):    at android.app.ActivityThread.main(ActivityThread.java:4507)
08-01 20:49:16.649: E/AndroidRuntime(13643):    at java.lang.reflect.Method.invokeNative(Native Method)
08-01 20:49:16.649: E/AndroidRuntime(13643):    at java.lang.reflect.Method.invoke(Method.java:511)
08-01 20:49:16.649: E/AndroidRuntime(13643):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
08-01 20:49:16.649: E/AndroidRuntime(13643):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
08-01 20:49:16.649: E/AndroidRuntime(13643):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

From your LogCat, I get it there is no TextView with the id errorText, but you don’t see any errors at compiling time, as you have a RelativeLayout with this id; but you get the ClassCastException error at runtime.

 errors = (TextView) findViewById(R.id.errorText);

Also, always use ""..equals(myEditField.getText()) instead myEditField.getText().equals("") (that is, the hardcoded value first).

Otherwise, if your EditText is empty, myEditField.getText() will return null, so you’ll have an error trying to use the equals() method on null.

Alternatively, you can use myEditField.getText().length() = 0 to check if the EditText is empty.