点击按钮后，应用程序停止工作

Question

当我点击注册按钮时，我的应用程序停止工作。我希望应用程序移至注册活动。 我已经正确地遵循了YouTube的一些教程，但是当我点击注册按钮时，它说不幸的应用程序停止工作。

public class LoginActivity extends AppCompatActivity implements LoaderCallbacks<Cursor> { 

    /** 
    * Id to identity READ_CONTACTS permission request. 
    */ 
    private static final int REQUEST_READ_CONTACTS = 0; 

    /** 
    * A dummy authentication store containing known user names and passwords. 
    * TODO: remove after connecting to a real authentication system. 
    */ 
    private static final String[] DUMMY_CREDENTIALS = new String[]{ 
      "foo@example.com:hello", "bar@example.com:world" 
    }; 
    /** 
    * Keep track of the login task to ensure we can cancel it if requested. 
    */ 
    private UserLoginTask mAuthTask = null; 

    // UI references. 
    private AutoCompleteTextView mEmailView; 
    private EditText mPasswordView; 
    private View mProgressView; 
    private View mLoginFormView; 

    private static Button SignUpButton; 

    public void OnClickButtonSignUp(){ 
     SignUpButton=(Button)findViewById(R.id.button1); 
     SignUpButton.setOnClickListener(
       new OnClickListener() { 
        @Override 
        public void onClick(View view) { 
         Intent intent=new Intent("com.example.shari.fyp01.SignUp"); 
         startActivity(intent); 
        } 
       } 
     ); 
    } 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_login); 
     // Set up the login form. 
     mEmailView = (AutoCompleteTextView) findViewById(R.id.email); 
     populateAutoComplete(); 

     mPasswordView = (EditText) findViewById(R.id.password); 
     mPasswordView.setOnEditorActionListener(new TextView.OnEditorActionListener() { 
      @Override 
      public boolean onEditorAction(TextView textView, int id, KeyEvent keyEvent) { 
       if (id == R.id.login || id == EditorInfo.IME_NULL) { 
        attemptLogin(); 
        return true; 
       } 
       return false; 
      } 
     }); 

     Button mEmailSignInButton = (Button) findViewById(R.id.email_sign_in_button); 
     mEmailSignInButton.setOnClickListener(new OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       attemptLogin(); 
      } 
     }); 

     mLoginFormView = findViewById(R.id.login_form); 
     mProgressView = findViewById(R.id.login_progress); 
     OnClickButtonSignUp(); 

    } 



    private void populateAutoComplete() { 
     if (!mayRequestContacts()) { 
      return; 
     } 

     getLoaderManager().initLoader(0, null, this); 
    } 

    private boolean mayRequestContacts() { 
     if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) { 
      return true; 
     } 
     if (checkSelfPermission(READ_CONTACTS) == PackageManager.PERMISSION_GRANTED) { 
      return true; 
     } 
     if (shouldShowRequestPermissionRationale(READ_CONTACTS)) { 
      Snackbar.make(mEmailView, R.string.permission_rationale, Snackbar.LENGTH_INDEFINITE) 
        .setAction(android.R.string.ok, new View.OnClickListener() { 
         @Override 
         @TargetApi(Build.VERSION_CODES.M) 
         public void onClick(View v) { 
          requestPermissions(new String[]{READ_CONTACTS}, REQUEST_READ_CONTACTS); 
         } 
        }); 
     } else { 
      requestPermissions(new String[]{READ_CONTACTS}, REQUEST_READ_CONTACTS); 
     } 
     return false; 
    } 

    /** 
    * Callback received when a permissions request has been completed. 
    */ 
    @Override 
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, 
              @NonNull int[] grantResults) { 
     if (requestCode == REQUEST_READ_CONTACTS) { 
      if (grantResults.length == 1 && grantResults[0] == PackageManager.PERMISSION_GRANTED) { 
       populateAutoComplete(); 
      } 
     } 
    } 


    /** 
    * Attempts to sign in or register the account specified by the login form. 
    * If there are form errors (invalid email, missing fields, etc.), the 
    * errors are presented and no actual login attempt is made. 
    */ 
    private void attemptLogin() { 
     if (mAuthTask != null) { 
      return; 
     } 

     // Reset errors. 
     mEmailView.setError(null); 
     mPasswordView.setError(null); 

     // Store values at the time of the login attempt. 
     String email = mEmailView.getText().toString(); 
     String password = mPasswordView.getText().toString(); 

     boolean cancel = false; 
     View focusView = null; 

     // Check for a valid password, if the user entered one. 
     if (!TextUtils.isEmpty(password) && !isPasswordValid(password)) { 
      mPasswordView.setError(getString(R.string.error_invalid_password)); 
      focusView = mPasswordView; 
      cancel = true; 
     } 

     // Check for a valid email address. 
     if (TextUtils.isEmpty(email)) { 
      mEmailView.setError(getString(R.string.error_field_required)); 
      focusView = mEmailView; 
      cancel = true; 
     } else if (!isEmailValid(email)) { 
      mEmailView.setError(getString(R.string.error_invalid_email)); 
      focusView = mEmailView; 
      cancel = true; 
     } 

     if (cancel) { 
      // There was an error; don't attempt login and focus the first 
      // form field with an error. 
      focusView.requestFocus(); 
     } else { 
      // Show a progress spinner, and kick off a background task to 
      // perform the user login attempt. 
      showProgress(true); 
      mAuthTask = new UserLoginTask(email, password); 
      mAuthTask.execute((Void) null); 
     } 
    } 

    private boolean isEmailValid(String email) { 
     //TODO: Replace this with your own logic 
     return email.contains("@"); 
    } 

    private boolean isPasswordValid(String password) { 
     //TODO: Replace this with your own logic 
     return password.length() > 4; 
    } 

    /** 
    * Shows the progress UI and hides the login form. 
    */ 
    @TargetApi(Build.VERSION_CODES.HONEYCOMB_MR2) 
    private void showProgress(final boolean show) { 
     // On Honeycomb MR2 we have the ViewPropertyAnimator APIs, which allow 
     // for very easy animations. If available, use these APIs to fade-in 
     // the progress spinner. 
     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB_MR2) { 
      int shortAnimTime = getResources().getInteger(android.R.integer.config_shortAnimTime); 

      mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE); 
      mLoginFormView.animate().setDuration(shortAnimTime).alpha(
        show ? 0 : 1).setListener(new AnimatorListenerAdapter() { 
       @Override 
       public void onAnimationEnd(Animator animation) { 
        mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE); 
       } 
      }); 

      mProgressView.setVisibility(show ? View.VISIBLE : View.GONE); 
      mProgressView.animate().setDuration(shortAnimTime).alpha(
        show ? 1 : 0).setListener(new AnimatorListenerAdapter() { 
       @Override 
       public void onAnimationEnd(Animator animation) { 
        mProgressView.setVisibility(show ? View.VISIBLE : View.GONE); 
       } 
      }); 
     } else { 
      // The ViewPropertyAnimator APIs are not available, so simply show 
      // and hide the relevant UI components. 
      mProgressView.setVisibility(show ? View.VISIBLE : View.GONE); 
      mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE); 
     } 
    } 

    @Override 
    public Loader<Cursor> onCreateLoader(int i, Bundle bundle) { 
     return new CursorLoader(this, 
       // Retrieve data rows for the device user's 'profile' contact. 
       Uri.withAppendedPath(ContactsContract.Profile.CONTENT_URI, 
         ContactsContract.Contacts.Data.CONTENT_DIRECTORY), ProfileQuery.PROJECTION, 

       // Select only email addresses. 
       ContactsContract.Contacts.Data.MIMETYPE + 
         " = ?", new String[]{ContactsContract.CommonDataKinds.Email 
       .CONTENT_ITEM_TYPE}, 

       // Show primary email addresses first. Note that there won't be 
       // a primary email address if the user hasn't specified one. 
       ContactsContract.Contacts.Data.IS_PRIMARY + " DESC"); 
    } 

    @Override 
    public void onLoadFinished(Loader<Cursor> cursorLoader, Cursor cursor) { 
     List<String> emails = new ArrayList<>(); 
     cursor.moveToFirst(); 
     while (!cursor.isAfterLast()) { 
      emails.add(cursor.getString(ProfileQuery.ADDRESS)); 
      cursor.moveToNext(); 
     } 

     addEmailsToAutoComplete(emails); 
    } 

    @Override 
    public void onLoaderReset(Loader<Cursor> cursorLoader) { 

    } 

    private void addEmailsToAutoComplete(List<String> emailAddressCollection) { 
     //Create adapter to tell the AutoCompleteTextView what to show in its dropdown list. 
     ArrayAdapter<String> adapter = 
       new ArrayAdapter<>(LoginActivity.this, 
         android.R.layout.simple_dropdown_item_1line, emailAddressCollection); 

     mEmailView.setAdapter(adapter); 
    } 


    private interface ProfileQuery { 
     String[] PROJECTION = { 
       ContactsContract.CommonDataKinds.Email.ADDRESS, 
       ContactsContract.CommonDataKinds.Email.IS_PRIMARY, 
     }; 

     int ADDRESS = 0; 
     int IS_PRIMARY = 1; 
    } 

    /** 
    * Represents an asynchronous login/registration task used to authenticate 
    * the user. 
    */ 
    public class UserLoginTask extends AsyncTask<Void, Void, Boolean> { 

     private final String mEmail; 
     private final String mPassword; 

     UserLoginTask(String email, String password) { 
      mEmail = email; 
      mPassword = password; 
     } 

     @Override 
     protected Boolean doInBackground(Void... params) { 
      // TODO: attempt authentication against a network service. 

      try { 
       // Simulate network access. 
       Thread.sleep(2000); 
      } catch (InterruptedException e) { 
       return false; 
      } 

      for (String credential : DUMMY_CREDENTIALS) { 
       String[] pieces = credential.split(":"); 
       if (pieces[0].equals(mEmail)) { 
        // Account exists, return true if the password matches. 
        return pieces[1].equals(mPassword); 
       } 
      } 

      // TODO: register the new account here. 
      return true; 
     } 

     @Override 
     protected void onPostExecute(final Boolean success) { 
      mAuthTask = null; 
      showProgress(false); 

      if (success) { 
       finish(); 
      } else { 
       mPasswordView.setError(getString(R.string.error_incorrect_password)); 
       mPasswordView.requestFocus(); 
      } 
     } 

     @Override 
     protected void onCancelled() { 
      mAuthTask = null; 
      showProgress(false); 
     } 
    } 
} 

Answer 1

由于您使用Intent的方式而出现错误。Intent结构如下。

Intent intent = new Intent(Context,The class name that u have to go); 
startActivity(intent); 

所以答案如下，在清单

Intent intent = new Intent(LoginActivity.this,SignUp.class); 
startActivity(intent); 

Answer 2

添加默认类别开展此项活动。以这种方式定义清单中的活动

<activity 
    android:name=".YourActivityName" > 
    <intent-filter> 
    <action android:name="com.example.shari.fyp01.SignUp" /> 
    <category android:name="android.intent.category.DEFAULT" /> 
    </intent-filter> 
</activity>