我在运行代码时遇到错误。我正在创建登录页面并注册页面。我无法确定错误是什么。
public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
Intent intent = new Intent(this, LoginActivity.class);
startActivity(intent);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.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();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
用户输入密码和用户名
的登录活动public class LoginActivity extends AppCompatActivity {
private static final String TAG = "LoginActivity";
private static final int REQUEST_SIGNUP = 0;
EditText _emailText;
EditText _passwordText;
Button _loginButton;
TextView _signupLink;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//ButterKnife.bind(this);
_loginButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
login();
}
});
_signupLink.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// Start the Signup activity
Intent intent = new Intent(getApplicationContext(), SignupActivity.class);
startActivityForResult(intent, REQUEST_SIGNUP);
}
});
}
public void login() {
Log.d(TAG, "Login");
if (!validate()) {
onLoginFailed();
return;
}
_loginButton.setEnabled(false);
final ProgressDialog progressDialog = new ProgressDialog(LoginActivity.this,
R.style.AppTheme_Dark_Dialog);
progressDialog.setIndeterminate(true);
progressDialog.setMessage("Authenticating...");
progressDialog.show();
String email = _emailText.getText().toString();
String password = _passwordText.getText().toString();
// TODO: Implement your own authentication logic here.
new android.os.Handler().postDelayed(
new Runnable() {
public void run() {
// On complete call either onLoginSuccess or onLoginFailed
onLoginSuccess();
// onLoginFailed();
progressDialog.dismiss();
}
}, 3000);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == REQUEST_SIGNUP) {
if (resultCode == RESULT_OK) {
// TODO: Implement successful signup logic here
// By default we just finish the Activity and log them in automatically
this.finish();
}
}
}
@Override
public void onBackPressed() {
// Disable going back to the MainActivity
moveTaskToBack(true);
}
public void onLoginSuccess() {
_loginButton.setEnabled(true);
finish();
}
public void onLoginFailed() {
Toast.makeText(getBaseContext(), "Login failed", Toast.LENGTH_LONG).show();
_loginButton.setEnabled(true);
}
public boolean validate() {
boolean valid = true;
String email = _emailText.getText().toString();
String password = _passwordText.getText().toString();
if (email.isEmpty() || !android.util.Patterns.EMAIL_ADDRESS.matcher(email).matches()) {
_emailText.setError("enter a valid email address");
valid = false;
} else {
_emailText.setError(null);
}
if (password.isEmpty() || password.length() < 4 || password.length() > 10) {
_passwordText.setError("between 4 and 10 alphanumeric characters");
valid = false;
} else {
_passwordText.setError(null);
}
return valid;
}
}
注册活动
public class SignupActivity extends AppCompatActivity {
private static final String TAG = "SignupActivity";
EditText _nameText;
EditText _emailText;
EditText _passwordText;
Button _signupButton;
TextView _loginLink;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.acitivity_signup);
//ButterKnife.bind(this);
_signupButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
signup();
}
});
_loginLink.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// Finish the registration screen and return to the Login activity
finish();
}
});
}
public void signup() {
Log.d(TAG, "Signup");
if (!validate()) {
onSignupFailed();
return;
}
_signupButton.setEnabled(false);
final ProgressDialog progressDialog = new ProgressDialog(SignupActivity.this,
R.style.AppTheme_Dark_Dialog);
progressDialog.setIndeterminate(true);
progressDialog.setMessage("Creating Account...");
progressDialog.show();
String name = _nameText.getText().toString();
String email = _emailText.getText().toString();
String password = _passwordText.getText().toString();
// TODO: Implement your own signup logic here.
new android.os.Handler().postDelayed(
new Runnable() {
public void run() {
// On complete call either onSignupSuccess or onSignupFailed
// depending on success
onSignupSuccess();
// onSignupFailed();
progressDialog.dismiss();
}
}, 3000);
}
public void onSignupSuccess() {
_signupButton.setEnabled(true);
setResult(RESULT_OK, null);
finish();
}
public void onSignupFailed() {
Toast.makeText(getBaseContext(), "Login failed", Toast.LENGTH_LONG).show();
_signupButton.setEnabled(true);
}
public boolean validate() {
boolean valid = true;
String name = _nameText.getText().toString();
String email = _emailText.getText().toString();
String password = _passwordText.getText().toString();
if (name.isEmpty() || name.length() < 3) {
_nameText.setError("at least 3 characters");
valid = false;
} else {
_nameText.setError(null);
}
if (email.isEmpty() || !android.util.Patterns.EMAIL_ADDRESS.matcher(email).matches()) {
_emailText.setError("enter a valid email address");
valid = false;
} else {
_emailText.setError(null);
}
if (password.isEmpty() || password.length() < 4 || password.length() > 10) {
_passwordText.setError("between 4 and 10 alphanumeric characters");
valid = false;
} else {
_passwordText.setError(null);
}
return valid;
}
}
，日志是
FATAL EXCEPTION: main
Process: com.example.bhardwaj.logintrialtrans, PID: 21617
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.bhardwaj.logintrialtrans/com.example.bhardwaj.logintrialtrans.LoginActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.bhardwaj.logintrialtrans.LoginActivity.onCreate(LoginActivity.java:35)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
答案 0 :(得分：2)
您尚未在LoginActivity
在onCreate
LoginActivity中执行此操作
_signupLink = (Button) findViewById(R.id.signuplink); // use your id
_loginButton = (Button) findViewById(R.id.loginbutton); // use your id
致电setContentView()
注意：我猜您在MainActivity和LoginActivity中使用了错误的xml。
MainAcitivity setContentView(R.layout.activity_login); LoginActivity setContentView(R.layout.activity_main); {{1}} {{1}}只是说基于那些xmls的名字
答案 1 :(得分：0)
在尝试为其设置onClickListener之前，您需要使用findViewById（R.id.YOUR_BUTTON_ID）来获取对该按钮的引用。目前，您只需在代码中创建一个按钮对象，但不将其链接到布局中的按钮。