向Android Studio添加活动

android:onClick="onClick"从你的Button.删除login_layout.xml

编辑

在你的下面进行以下更改 LoginActivity

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Toast;

public class LoginActivity extends AppCompatActivity implements View.OnClickListener {

    Button loginButton;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login_layout);
        loginButton=findViewById(R.id.btnLogin);
        loginButton.setOnClickListener(this);
    }
    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.btnLogin:
                Toast.makeText(this, "Login button clicked!", Toast.LENGTH_SHORT).show();
                break;
            default:
                break;
        }
    }
}