google 注册中的 java.lang.NullPointerException 抛出 null

Question

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

    public SignInButton login;
    private TextView name;
    private GoogleApiClient googleApiClient;
    private GoogleSignInOptions signInOptions;
    private static final int REQUEST_CODE = 100;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        signInOptions = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN).requestEmail().build();

        googleApiClient = new GoogleApiClient.Builder(this).enableAutoManage(this, this).addApi(Auth.GOOGLE_SIGN_IN_API, signInOptions).addApi(AppIndex.API).build();
        login = (SignInButton) findViewById(R.id.login);
        name = (TextView) findViewById(R.id.name);
        login.setSize(SignInButton.SIZE_WIDE);
        login.setScopes(signInOptions.getScopeArray());
        login.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Intent signInIntent = Auth.GoogleSignInApi.getSignInIntent(googleApiClient);
                startActivityForResult(signInIntent, REQUEST_CODE);
            }
        });
    }

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

        if (requestCode == REQUEST_CODE) {
            GoogleSignInResult result = Auth.GoogleSignInApi.getSignInResultFromIntent(data);
            GoogleSignInAccount account = result.getSignInAccount();

            name.setText(account.getDisplayName());
        }

    }

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

    }

    /**
     * ATTENTION: This was auto-generated to implement the App Indexing API.
     * See https://g.co/AppIndexing/AndroidStudio for more information.
     */
    public Action getIndexApiAction() {
        Thing object = new Thing.Builder()
                .setName("Main Page") // TODO: Define a title for the content shown.
                // TODO: Make sure this auto-generated URL is correct.
                .setUrl(Uri.parse("http://[ENTER-YOUR-URL-HERE]"))
                .build();
        return new Action.Builder(Action.TYPE_VIEW)
                .setObject(object)
                .setActionStatus(Action.STATUS_TYPE_COMPLETED)
                .build();
    }

    @Override
    public void onStart() {
        super.onStart();

        // ATTENTION: This was auto-generated to implement the App Indexing API.
        // See https://g.co/AppIndexing/AndroidStudio for more information.
        googleApiClient.connect();
        AppIndex.AppIndexApi.start(googleApiClient, getIndexApiAction());
    }

    @Override
    public void onStop() {
        super.onStop();

        // ATTENTION: This was auto-generated to implement the App Indexing API.
        // See https://g.co/AppIndexing/AndroidStudio for more information.
        AppIndex.AppIndexApi.end(googleApiClient, getIndexApiAction());
        googleApiClient.disconnect();
    }

}

 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.gms.common.SignInButton.setSize(int)' on a null object reference
                  at snapdirectcom.snap.MainActivity.onCreate(MainActivity.java:42) 

厌倦了检查许多更改，但它们都不起作用

Answer 1

我注意到您打开了两个布局 - 仔细检查您评论中的 SignInButton 是否位于 Activity_login 中，因为这是正在搜索的布局，其他所有内容似乎都按顺序排列