ошибка при компиляции этого кода:

Question

Мое приложение падает после его выполнения и показывает 'Ошибка: NullPointerException'. Не знаю, что делать. Я пытаюсь сделать простой конвертер валют в eclipse с помощью Android SDK. Если кто-нибудь может сказать мне, как сделать одно это wolud быть большим (новичок в андроид и затмение)

package com.example.converter; 
import android.app.Activity; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.TextView; 

public class MainActivity extends Activity implements OnClickListener{ 
EditText et = (EditText) findViewById(R.id.editText1); 
EditText et1 = (EditText) findViewById(R.id.editText2); 
TextView textView = (TextView) findViewById(R.id.textView1); 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    Button btn = (Button) findViewById(R.id.button1); 
    btn.setOnClickListener(this); 


} 

    public void onClick(View v) { 
     // TODO Auto-generated method stub 

     //EditText edit = (EditText) findViewById(R.id.editText1); 
     String value = et.getText().toString(); // get the value from editText 
     String result =convertToAED(value); 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.main, menu); 
    return true; 
} 

public String convertToAED(String value) 
{ double input = 0; 
    try{ 
    input = Double.parseDouble(value); 
     }catch(NumberFormatException e) 
     { 
      e.printStackTrace(); 
     } 
    double rate = Double.parseDouble(et1.getText().toString()); 
    double output = input*rate; 
    return output+""; 
} 

public String convertToUSD(String value) 
{try{ 
    input = Double.parseDouble(value); 
     }catch(NumberFormatException e) 
     { 
      e.printStackTrace(); 
     } 
    double rate = Double.parseDouble(et1.getText().toString()); 
    double output = input*rate; 
    return output+""; 
} 

}

XML-файла:!.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:paddingBottom="@dimen/activity_vertical_margin" 
android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
tools:context=".MainActivity" > 

<EditText 
    android:id="@+id/editText1" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:layout_alignLeft="@+id/spinner1" 
    android:layout_alignParentTop="true" 
    android:layout_marginTop="27dp" 
    android:ems="10" 
    android:hint="@string/edit" > 

    <requestFocus /> 
</EditText> 

<Spinner 
    android:id="@+id/spinner1" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:layout_below="@+id/editText1" 
    android:layout_centerHorizontal="true" 
    android:layout_marginTop="15dp" 
    android:prompt="@array/Currency" 
    tools:listitem="@android:layout/simple_spinner_dropdown_item" /> 

<TextView 
    android:id="@+id/textView1" 
    android:layout_width="match_parent" 
    android:layout_height="50dp" 
    android:layout_alignLeft="@+id/button1" 
    android:layout_below="@+id/spinner1" 
    android:layout_marginTop="121dp" 
    android:hint="@string/output" 
    android:textAppearance="?android:attr/textAppearanceLarge" /> 

<EditText 
    android:id="@+id/editText2" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:layout_alignLeft="@+id/button1" 
    android:layout_below="@+id/spinner1" 
    android:hint="Enter rate" 
    android:ems="10" /> 

<Button 
    android:id="@+id/button1" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignLeft="@+id/spinner1" 
    android:onClick="onClick" 
    android:layout_centerVertical="true" 
    android:text="@string/Convert" /> 

</RelativeLayout> 

Logcat:

11-24 01:11:18.720: D/dalvikvm(2030): Not late-enabling CheckJNI (already on) 
11-24 01:11:23.960: I/Choreographer(2030): Skipped 484 frames! The application may be doing too much work on its main thread. 
11-24 01:11:24.250: D/gralloc_goldfish(2030): Emulator without GPU emulation detected. 
11-24 01:11:33.440: D/AndroidRuntime(2030): Shutting down VM 
11-24 01:11:33.440: W/dalvikvm(2030): threadid=1: thread exiting with uncaught exception (group=0xb0f4b648) 
11-24 01:11:33.470: E/AndroidRuntime(2030): FATAL EXCEPTION: main 
11-24 01:11:33.470: E/AndroidRuntime(2030): java.lang.NumberFormatException: Invalid double: "android.widget.EditText{b11f6860 VFED..CL .F....I. 24,250-456,309 #7f080002 app:id/editText1}" 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at java.lang.StringToReal.invalidReal(StringToReal.java:63) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at java.lang.StringToReal.initialParse(StringToReal.java:114) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at java.lang.StringToReal.parseDouble(StringToReal.java:263) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at java.lang.Double.parseDouble(Double.java:295) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at com.example.converterbase.MainActivity.conevrt(MainActivity.java:43) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at com.example.converterbase.MainActivity$1.onClick(MainActivity.java:27) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at android.view.View.performClick(View.java:4240) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at android.view.View$PerformClick.run(View.java:17721) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at android.os.Handler.handleCallback(Handler.java:730) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at android.os.Handler.dispatchMessage(Handler.java:92) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at android.os.Looper.loop(Looper.java:137) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at android.app.ActivityThread.main(ActivityThread.java:5103) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at java.lang.reflect.Method.invokeNative(Native Method) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at java.lang.reflect.Method.invoke(Method.java:525) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
11-24 01:11:33.470: E/AndroidRuntime(2030):  at dalvik.system.NativeStart.main(Native Method) 
11-24 01:11:36.240: I/Process(2030): Sending signal. PID: 2030 SIG: 9 

Answer 1

Изменение на

@Override 
    public void onClick(View v) { 
     // TODO Auto-generated method stub 

     EditText edit = (EditText) findViewById(R.id.editText1); 
     String value = edit.getText().toString(); // get the value from editText 
     String result =conevrt(value); // pass the value as param 

    } 

Вы создаете экземпляр MainActivity MainActivity ma = new MainActivity(), который является неправильным. Активность имеет жизненный цикл.

Также

http://docs.oracle.com/javase/7/docs/api/java/lang/Double.html#parseDouble(java.lang.String)

try 
    { 
    Double input = Double.parseDouble(value); // numberformatexception if value is not a double value 
    }catch(NumberFormatException e) 
    { 
     e.printStacktrace(); 
    }