有谁可以告诉我为什么我在这个类中得到一个空指针异常？
public class Login extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.login);
// Get buttons from xml file
final Button existingUser = (Button)findViewById(R.id.but01);
final Button play = (Button)findViewById(R.id.but02);
final ImageView image1 = (ImageView)findViewById(R.id.iv01);
final ImageView image2 = (ImageView)findViewById(R.id.iv02);
final EditText email = (EditText)findViewById(R.id.et01);
final EditText screenName = (EditText)findViewById(R.id.et02);
// Add listener for play button and send stuff to database
play.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// TO DO Send user's entered data to database/server
}
});
/*
I have a feeling this may be causing the problem.
I validate the text from the email and screen name text boxes as the user enters text
and display a tick or cross to the side of the box, and then validate the whole form
on pressing a button:
*/
// Add listener for existing user button and move to registered user screen. Pass entered email
existingUser.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
String enteredEmail = email.getText().toString();
String enteredScreenName = screenName.getText().toString();
if (validateEmail(enteredEmail) == true && (validateScreenName(enteredScreenName) == true)) {
Intent myIntent = new Intent(getApplicationContext(), RegisteredUser.class);
myIntent.putExtra("enteredEmail", enteredEmail);
startActivity(myIntent);
}
else if (validateEmail(enteredEmail) == false && (validateScreenName(enteredScreenName) == true)) {
Toast myToast = Toast.makeText(getApplicationContext(), "That email address is not valid. Please enter a valid email address", Toast.LENGTH_SHORT);
myToast.show();
}
else if (validateEmail(enteredEmail) == true && (validateScreenName(enteredScreenName) == false)) {
Toast myToast = Toast.makeText(getApplicationContext(), "You need to enter a valid screen name to play. Please use only a - Z, 0 - 9, - and _.", Toast.LENGTH_SHORT);
myToast.show();
}
else {
Toast myToast = Toast.makeText(getApplicationContext(), "Invalid email address or screen name.", Toast.LENGTH_SHORT);
myToast.show();
}
}
});
// Add key listener to email edittext and validate as user enters data
email.addTextChangedListener(new TextWatcher() {
@Override
public void afterTextChanged(Editable s) {
String enteredEmail = email.getText().toString();
if (validateEmail(enteredEmail) == true) {
image1.setImageResource(R.drawable.greentick);
}
else {
image1.setImageResource(R.drawable.redcross);
}
}
@Override
public void beforeTextChanged(CharSequence s, int start, int count,
int after) {
// TODO Auto-generated method stub
}
@Override
public void onTextChanged(CharSequence s, int start, int before,
int count) {
// TODO Auto-generated method stub
}
});
// Add key listener to screen name field to validate as user types
screenName.addTextChangedListener(new TextWatcher() {
@Override
public void afterTextChanged(Editable arg0) {
String enteredScreenName = screenName.getText().toString();
if (validateScreenName(enteredScreenName) == true) {
image2.setImageResource(R.drawable.greentick);
}
else {
image2.setImageResource(R.drawable.redcross);
}
}
@Override
public void beforeTextChanged(CharSequence s, int start, int count,
int after) {
// TODO Auto-generated method stub
}
@Override
public void onTextChanged(CharSequence s, int start, int before,
int count) {
// TODO Auto-generated method stub
}
});
}
验证方法：
public boolean validateEmail(String email) {
// Check email against email patter matcher and for not empty field
boolean validated = false;
if (android.util.Patterns.EMAIL_ADDRESS.matcher(email).matches() && (! email.equals(""))) {
validated = true;
}
else {
validated = false;
}
return validated;
}
public boolean validateScreenName(String screenName) {
// Check screen name has > 0 chars and that it contains only a-z, A-Z, _ and -
boolean validated = false;
if (screenName.matches("[a-zA-Z0-9_-]{1,20}") && (! screenName.equals("")) && (! screenName.contains("\\s"))) {
validated = true;
}
else {
validated = false;
}
return validated;
}
}