App has stopped unexpectedly, and i don't know why

Question

I get no errors but when I run the app it crashes and I don't know why! Here is the code, I am sure the error is here because it was working until here. I've been trying to search for the problem for about 4 hours and still have no clue!

public class MainActivity extends Activity implements OnClickListener {

    EditText et1, et2, usuario1, password1, password2;
    Button ingresar, borrar, ajustes, cancelarBtn, okusBtn;
    Dialog dialog;
    Context context = this;
    String usuario = "";
    String password = "";

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

        et1=(EditText)findViewById(R.id.et1);
        et2=(EditText)findViewById(R.id.et2);
        ingresar=(Button)findViewById(R.id.ingresar);
        borrar=(Button)findViewById(R.id.borrar);
        ajustes=(Button)findViewById(R.id.ajustesBtn);
        cancelarBtn =(Button)dialog.findViewById(R.id.cancelarUs);
        okusBtn =(Button)dialog.findViewById(R.id.okUs);
        password1=(EditText)dialog.findViewById(R.id.password1);
        password2=(EditText)dialog.findViewById(R.id.password2);
        usuario1=(EditText)dialog.findViewById(R.id.usuario1);

        borrar.setOnClickListener(this);
        ingresar.setOnClickListener(this);
        ajustes.setOnClickListener(this);
        cancelarBtn.setOnClickListener(this);
        okusBtn.setOnClickListener(this);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public void onClick(View arg0) {
        switch(arg0.getId()){
        case R.id.ingresar:
            String usRecibido=et1.getText().toString();
            String pasRecibido=et2.getText().toString();

            if(usRecibido.equals(usuario) && pasRecibido.equals(password)){
                Intent pancar = new Intent("com.example.iniciosesion.Iniciado");
                Bundle bolsa = new Bundle();
                bolsa.putString("NombreKey", usRecibido);
                pancar.putExtras(bolsa);
                startActivity(pancar);
            }else{
                Toast ts=Toast.makeText(this, "Usuario o contraseña incorrecto", Toast.LENGTH_LONG);
                ts.show();
            }
            break;
        case R.id.borrar:
            et1.setText("");
            et2.setText("");
            break;
        case R.id.ajustesBtn:
             dialog = new Dialog(context);
             dialog.setContentView(R.layout.controlusuario);
             dialog.setTitle("Modificar usuario");
             if(usuario == "" && password == ""){
             password1.setHint("Crear password");
             }else{
             password1.setHint("Password actual");
             }
            break;
        case R.id.cancelarUs:
             dialog.dismiss();
            break;
        case R.id.okUs:
            if(usuario == "" && password == "" && password1.getText().toString() == password2.getText().toString()){
                 usuario = usuario1.getText().toString();
                 password = password1.getText().toString();
            }
            if(usuario1.equals(usuario) && password1.equals(password))
                 password = password2.getText().toString();
                 usuario = usuario1.getText().toString();
            break;
        }
    }
}

Answer 1

Try this code I have initialized the dialog in the onCreate() method

public class MainActivity extends Activity implements OnClickListener{

EditText et1, et2, usuario1, password1, password2;
Button ingresar, borrar, ajustes, cancelarBtn, okusBtn;
Dialog dialog;
Context context = this;
String usuario = "";
String password = "";


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

et1=(EditText)findViewById(R.id.et1);
et2=(EditText)findViewById(R.id.et2);
ingresar=(Button)findViewById(R.id.ingresar);
borrar=(Button)findViewById(R.id.borrar);
ajustes=(Button)findViewById(R.id.ajustesBtn);
dialog = new Dialog(getBaseContext);
         dialog.setContentView(R.layout.controlusuario);
         dialog.setTitle("Modificar usuario");
cancelarBtn =(Button)dialog.findViewById(R.id.cancelarUs);
okusBtn =(Button)dialog.findViewById(R.id.okUs);
password1=(EditText)dialog.findViewById(R.id.password1);
password2=(EditText)dialog.findViewById(R.id.password2);
usuario1=(EditText)dialog.findViewById(R.id.usuario1);

borrar.setOnClickListener(this);
ingresar.setOnClickListener(this);
ajustes.setOnClickListener(this);
cancelarBtn.setOnClickListener(this);
okusBtn.setOnClickListener(this);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public void onClick(View arg0) {
    switch(arg0.getId()){
    case R.id.ingresar:
        String usRecibido=et1.getText().toString();
        String pasRecibido=et2.getText().toString();

    if(usRecibido.equals(usuario) && pasRecibido.equals(password)){
        Intent pancar = new Intent("com.example.iniciosesion.Iniciado");
        Bundle bolsa = new Bundle();
        bolsa.putString("NombreKey", usRecibido);
        pancar.putExtras(bolsa);
        startActivity(pancar);
    }else{
        Toast ts=Toast.makeText(this, "Usuario o contraseña incorrecto", Toast.LENGTH_LONG);
        ts.show();
    }
    break;
case R.id.borrar:
    et1.setText("");
    et2.setText("");
    break;
case R.id.ajustesBtn:
     if(usuario == "" && password == ""){
     password1.setHint("Crear password");
     }else{
     password1.setHint("Password actual");
     }
    break;
case R.id.cancelarUs:
     dialog.dismiss();
    break;
case R.id.okUs:
    if(usuario == "" && password == "" && password1.getText().toString() == password2.getText().toString()){
         usuario = usuario1.getText().toString();
         password = password1.getText().toString();
    }
    if(usuario1.equals(usuario) && password1.equals(password))
         password = password2.getText().toString();
         usuario = usuario1.getText().toString();
    break;
}


}