问方法调用'editText.getText().toString()‘可以由Android生成'java.lang.NullPointerException’

EN

package com.hello.app;
import android.app.Activity;
import android.app.AlertDialog;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.util.Log;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.os.Build;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends ActionBarActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment())
                    .commit();
        }
    }


    @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;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    public void alertMe(View view){
        AlertDialog alertDialog = new AlertDialog.Builder(MainActivity.this).create();
        alertDialog.setTitle("Hi");
        EditText editText= (EditText)findViewById(R.id.editText);
        String lp_text = editText.getText().toString();
        if (lp_text == null || lp_text.length() == 0 || lp_text.equals("") || lp_text.isEmpty()){

            alertDialog.setMessage("Edittext is null");
            alertDialog.show();
        }
        else

        {
        alertDialog.setMessage(lp_text);
        alertDialog.show();
            }
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container, false);
            return rootView;
        }
    }

}

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:inputType="textMultiLine"
    android:ems="10"
    android:id="@+id/editText"
    android:layout_centerVertical="true"
    android:layout_centerHorizontal="true"
    android:hint="@string/lp_placeholder"
    android:width="250dp"
    android:height="40dp"
    android:background="@drawable/white_background_with_radius"
    />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/landingPageButton"
    android:id="@+id/button"
    android:layout_below="@+id/editText"
    android:background="#FFFFFF"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="51dp"
    android:onClick="alertMe"

    />

03-12 05:15:53.913 508-519/com.android.inputmethod.latin W/Binder﹕ Caught a RuntimeException from the binder stub implementation. java.lang.NullPointerException at android.inputmethodservice.IInputMethodWrapper.setSessionEnabled(IInputMethodWra‌​pper.java:280)
 at com.android.internal.view.IInputMethod$Stub.onTransact(IInputMethod.java:129) at android.os.Binder.execTransact(Binder.java:404) 
at dalvik.system.NativeStart.run(Native Method)