獲得的NullPointerException從SharedPreferences

Question

這裏設置TextView的值時，是我SignInActivityCode

public class SignInActivity extends AppCompatActivity implements GoogleApiClient.OnConnectionFailedListener, View.OnClickListener { 

GoogleApiClient mGoogleApiClient; 
private static final int RC_SIGN_IN=0; 
private String TAG = "SignInActivity"; 

@Override 
protected void onCreate(@Nullable Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.signin_activity); 

    try{ 
     getSupportActionBar().hide(); 
    }catch (Exception e){ 
     e.printStackTrace(); 
    } 

    GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN) 
      .requestEmail() 
      .build(); 

    mGoogleApiClient = new GoogleApiClient.Builder(this) 
      .enableAutoManage(this, this) 
      .addApi(Auth.GOOGLE_SIGN_IN_API, gso) 
      .build(); 

    SignInButton signInButton = (SignInButton) findViewById(R.id.sign_in_button); 
    signInButton.setSize(SignInButton.SIZE_STANDARD); 
    signInButton.setOnClickListener(this); 

} 

@Override 
protected void onStart() { 
    super.onStart(); 
    mGoogleApiClient.connect(); 
} 

@Override 
public void onConnectionFailed(@NonNull ConnectionResult connectionResult) { 

} 

@Override 
public void onClick(View v) { 
    switch (v.getId()){ 
     case R.id.sign_in_button: 
      signIn(); 
      break; 
    } 
} 

private void signIn(){ 
    Intent signInIntent = Auth.GoogleSignInApi.getSignInIntent(mGoogleApiClient); 
    startActivityForResult(signInIntent, RC_SIGN_IN); 
} 


@Override 
protected void onActivityResult(int requestCode, int resultCode, Intent data) { 
    super.onActivityResult(requestCode, resultCode, data); 

    // Result returned from launching the Intent from GoogleSignInApi.getSignInIntent(...); 
    if (requestCode == RC_SIGN_IN){ 
     GoogleSignInResult result = Auth.GoogleSignInApi.getSignInResultFromIntent(data); 
     handleSignInIntent(result); 
    } 
} 

private void handleSignInIntent(GoogleSignInResult result){ 
    Log.d(TAG, "handleSignInResult:" + result.isSuccess()); 
    if(result.isSuccess()){ 
     GoogleSignInAccount acct = result.getSignInAccount(); 

     Toast.makeText(this, "Sign in successful!", Toast.LENGTH_LONG).show(); 
     setDefaults(acct.getDisplayName(), acct.getEmail(), acct.getIdToken()); 
     Intent intent = new Intent(SignInActivity.this, MainActivity.class); 
     startActivity(intent); 
    } 
    else{ 
     Toast.makeText(this, "Sign In Failed!\nPlease try again.", Toast.LENGTH_LONG).show(); 
    } 
} 

public void setDefaults(String name, String email, String token){ 
    SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this); 
    SharedPreferences.Editor editor = sharedPref.edit(); 
    editor.putString("userName", name); 
    editor.putString("userEmail", email); 
    editor.putString("userIdToken", token); 
    editor.apply(); 
} 

}

這裏是我正在申請傳遞給在MainActivity我nav_header_main.xml文件中的信息

@Override 
protected void onCreate(Bundle savedInstanceState) { 
initializeUserInfo(); 
} 
private void initializeUserInfo() { 

    userName = (TextView) findViewById(R.id.nav_user_name_tv); 
    userEmail = (TextView) findViewById(R.id.nav_user_email_tv); 

    final SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(getBaseContext()); 

    name = sharedPref.getString("userName", ""); 
    email = sharedPref.getString("userEmail", ""); 

    try{ 
     userName.setText(name); 
     userEmail.setText(email); 
    }catch(Exception e){ 
     e.printStackTrace(); 
    } 
} 

和我在日誌中得到的錯誤

塊引用 顯示java.lang.NullPointerException：嘗試在空對象引用

Answer 1

調用虛擬方法「無效android.widget.TextView.setText（java.lang.CharSequence中）」這是你如何初始化和申報導航查看項目

private NavigationView navigationView; 
private DrawerLayout drawer; 
private View navHeader; 

drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
navigationView = (NavigationView) findViewById(R.id.nav_view); 

// Navigation view header 
navHeader = navigationView.getHeaderView(0); 
txtName = (TextView) navHeader.findViewById(R.id.nameNav);