原因：java.lang.NullPointerException：尝试调用虚拟方法'void android.widget.Button

Question

帮助任何人！我坚持了很长时间:( 我有一个初始屏幕，一个开始游览页面，一个Carousell页面，然后是一个登录页面，但是在我从Carousell页面上单击继续后，没有用户界面，它是空白的，并且该应用程序一直在停止。我需要帮助！

这是我的错误：

public interface ICreateNotificationEndpoint:
PushNotification.Endpoints.ICreateNotificationEndpoint<CreateNotificationResponse, CreateNotification>

这是我的主要活动：

Process: com.labawsrh.aws.introscreen, PID: 1997
**java.lang.RuntimeException:** Unable to start activity ComponentInfo{com.labawsrh.aws.introscreen/com.sl2.rk.rct.LoginRegister.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3116)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3259)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1950)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:214)
    at android.app.ActivityThread.main(ActivityThread.java:7073)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)
 **Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference**
    at com.sl2.rk.rct.LoginRegister.MainActivity.onCreate(MainActivity.java:38)
    at android.app.Activity.performCreate(Activity.java:7327)
    at android.app.Activity.performCreate(Activity.java:7318)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3096)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3259) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1950) 
    at android.os.Handler.dispatchMessage(Handler.java:106) 
    at android.os.Looper.loop(Looper.java:214) 
    at android.app.ActivityThread.main(ActivityThread.java:7073) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)

这是我的xml：

public class MainActivity extends AppCompatActivity {
private static final String TAG = "LoginActivity";
private static final int REQUEST_SIGNUP = 0;

@InjectView(R.id.input_email) EditText _emailText;
@InjectView(R.id.input_password) EditText _passwordText;
@InjectView(R.id.btn_login) Button _loginButton;
@InjectView(R.id.link_signup) TextView _signupLink;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ButterKnife.inject(this);

    _loginButton.setOnClickListener(new View.OnClickListener() {

        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(MainActivity.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;

   }
}

<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
android:paddingTop="56dp"
android:paddingLeft="24dp"
android:paddingRight="24dp">

<ImageView
    android:layout_width="wrap_content"
    android:layout_height="72dp"
    android:layout_marginBottom="24dp"
    android:src="@drawable/rklogo"
    android:layout_gravity="center_horizontal">

</ImageView>

<!-- Email Label -->

<android.support.design.widget.TextInputLayout

    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginTop="8dp"
    android:layout_marginBottom="8dp">

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/input_email"
        android:inputType="textEmailAddress"
        android:hint="Email"/>