在 Android Studio 中编译时出现“不是封闭类”错误

Question

我试图在单击按钮时打开一个新活动，但出现以下两个错误：

1. not an enclosing class:Main Activity
2. Execution failed for task ':app:compileDebugJavaWithJavac'

编译失败；有关详细信息，请参阅编译器错误输出。 这是 MainActivity.java 的代码

package com.example.admin.viewsandevents;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final EditText etUSN=(EditText) findViewById(R.id.etUSN);
        final EditText etPassword=(EditText) findViewById(R.id.etPassword);
        final Button bLogin=(Button) findViewById(R.id.bLogin);
        final TextView registerLink =(TextView) findViewById(R.id.tvRegisterhere);

        registerLink.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent registerIntent = new Intent(MainActivity.this,RegisterActivity.class);
                MainActivity.this.startActivity(registerIntent);
            }
        });

    }
}

这里是RegisterActivity.java的代码

package com.example.admin.viewsandevents;

import android.content.Intent;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.toolbox.Volley;

import org.json.JSONException;
import org.json.JSONObject;

public class RegisterActivity extends AppCompatActivity
{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_register);
        final EditText etAge=(EditText) findViewById(R.id.etAge);
        final EditText etName=(EditText) findViewById(R.id.etName);
        final EditText etUSN=(EditText) findViewById(R.id.etUSN);
        final EditText etPassword=(EditText) findViewById(R.id.etPassword);
        final Button bRegister=(Button) findViewById(R.id.bRegister);
     bRegister.setOnClickListener(new View.OnClickListener() {
     @Override
     public void onClick(View view) {
        final String name=etName.getText().toString();
        final String username=etUSN.getText().toString();
        final String password=etPassword.getText().toString();
        final int age=Integer.parseInt(etAge.getText().toString());

        Response.Listener<String> responseListener =new Response.Listener<String>(){
            @Override
            public void onResponse(String response) {
                try {
                    JSONObject jsonResponse =new JSONObject(response);
                    boolean success =jsonResponse.getBoolean("success");

                    if(success){
                        Intent myintent =new Intent(RegisterActivity.this, MainActivity.class);
                        RegisterActivity.this.startActivity(myintent);
                    }
                    else{
                        AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
                        builder.setMessage("Register Failed")
                                .setNegativeButton("Retry",null)
                                .create()
                                .show();
                    }

                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        };
        RegisterRequest registerRequest =new RegisterRequest(name,username,age,password, responseListener );
        RequestQueue queue = Volley.newRequestQueue(MainActivity.this);
        queue.add(registerRequest);
    }
});

    }
}

所以请帮我解决这个问题

Answer 1

问题出在RegisterActivity.java。您正在尝试从中创建一个警报对话框，但您使用 MainActivity.this 作为上下文：

AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
builder.setMessage("Register Failed")
       .setNegativeButton("Retry",null)
       .create()
       .show();

将其更改为使用RegisterActivity.this，例如：

AlertDialog.Builder builder = new AlertDialog.Builder(RegisterActivity.this);
builder.setMessage("Register Failed")
       .setNegativeButton("Retry",null)
       .create()
       .show();