LogCat错误，为什么会发生？

Question

here is the java file that produces the error "08-02 19:17:22.265: E/AndroidRuntime(17817): java.lang.ClassCastException: android.widget.RelativeLayout cannot be cast to android.widget.TextView"

 package tip.calculator;


import android.os.Bundle;
import android.app.Activity;
import android.text.TextUtils;
import android.view.View.OnClickListener;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
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((myEditField2 != null) && (!TextUtils.isEmpty(myEditField2.getText().toString()))){


                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 + " $");

             } else{
                //Toast.makeToast(.....).show(); //Inform user about the error
             }

        }
    });

    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();

        }


    });
}
}

here is the logcat error that i don't understand why it occurs...

08-02 19:17:22.265: E/AndroidRuntime(17817): java.lang.ClassCastException: android.widget.RelativeLayout cannot be cast to android.widget.TextView
08-02 19:17:22.265: E/AndroidRuntime(17817):    at tip.calculator.TipCalculator$1.onClick(TipCalculator.java:48)
08-02 19:17:22.265: E/AndroidRuntime(17817):    at android.view.View.performClick(View.java:3620)
08-02 19:17:22.265: E/AndroidRuntime(17817):    at android.view.View$PerformClick.run(View.java:14292)
08-02 19:17:22.265: E/AndroidRuntime(17817):    at android.os.Handler.handleCallback(Handler.java:605)
08-02 19:17:22.265: E/AndroidRuntime(17817):    at android.os.Handler.dispatchMessage(Handler.java:92)
08-02 19:17:22.265: E/AndroidRuntime(17817):    at android.os.Looper.loop(Looper.java:137)
08-02 19:17:22.265: E/AndroidRuntime(17817):    at android.app.ActivityThread.main(ActivityThread.java:4507)
08-02 19:17:22.265: E/AndroidRuntime(17817):    at java.lang.reflect.Method.invokeNative(Native Method)
08-02 19:17:22.265: E/AndroidRuntime(17817):    at java.lang.reflect.Method.invoke(Method.java:511)
08-02 19:17:22.265: E/AndroidRuntime(17817):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
08-02 19:17:22.265: E/AndroidRuntime(17817):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
08-02 19:17:22.265: E/AndroidRuntime(17817):    at dalvik.system.NativeStart.main(Native Method)

here is the xml with all the textViews and such sorry took a while...

<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"
        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" />

</RelativeLayout>

Answer 1

There are a lot of errors here. You have to match the xml view types in your code.

errors = (RelativeLayout)findViewById(R.id.errorText);
EditText textView3 = (EditText)findViewById(R.id.billText);
EditText textView2 = (EditText)findViewById(R.id.percentText);

I'm not sure what you are trying to do here but TextView's must be cast to TextView's. EditText's must be cast to EditText's. etc...

UPDATED

Show me your xml file that you are inflating. One of the View IDs is for a RelativeLayout and you are trying to cast it to a TextView.

One of these R.id's are for a RelativeLayout:

textView = (TextView) findViewById(R.id.textView1);
errors = (TextView)findViewById(R.id.errorText);
TextView textView = (TextView)findViewById(R.id.errorText);
TextView textView2 = (TextView)findViewById(R.id.percentText);
TextView textView3 = (TextView)findViewById(R.id.billText);
TextView textView1 = (TextView)findViewById(R.id.textView1);

Answer 2

You can not compare strings with == or != in java instead use .equals()

if(myEditField2.getText().toString().equals("")) && (!TextUtils.isEmpty(myEditField2.getText().toString())))

Hope that helps.