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java - Android Studio 无法识别课程？

问题描述

我正在尝试通过 WiFi 在 2 个设备之间进行一些简单的通信，并且一直在关注Sarthi Technology 的教程。

不幸的是，我无法让 Android Studio 识别一个类......

在此处输入图像描述

从图片中您可以看到它WifiDirectBroadcastReceiver以红色突出显示，即使您也可以看到它存在于下一个选项卡中。

类声明public class WifiDirectBroadcastReceiver extends BroadcastReceiver

在 MainActivity mReceiver 中声明为BroadcastReceiver mReceiver;

当我单击红色灯泡时，它会询问我是否要创建课程，然后抱怨该课程已经存在！

我是 Java 新手，所以我在这里缺少什么？（顺便说一句，教程中的那个人没有这个问题）

编辑#1：提供一个工作示例的完整代码清单

MainActivity.java

package qdivision.org.wifiexample2;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.IntentFilter;
import android.net.wifi.WifiManager;
import android.net.wifi.p2p.WifiP2pManager;
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.ListView;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    Button btnOnOff, btnDiscover, btnSend;
    ListView listView;
    TextView read_msg_box, connectionStatus;
    EditText writeMsg;

    WifiManager wifiManager;
    WifiP2pManager mManger;
    WifiP2pManager.Channel mChanel;

    BroadcastReceiver mReceiver;
    IntentFilter mIntentFilter;

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

    private void exqListener() {
        btnOnOff.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(wifiManager.isWifiEnabled()){
                    wifiManager.setWifiEnabled(false);
                    btnOnOff.setText("ON");
                }else{
                    wifiManager.setWifiEnabled(true);
                    btnOnOff.setText("OFF");
                }
            }
        });
    }

    private void initialWork() {

        btnOnOff = (Button) findViewById(R.id.onOff);
        btnDiscover = (Button) findViewById(R.id.discover);
        btnSend = (Button) findViewById(R.id.sendButton);
        listView = (ListView) findViewById(R.id.peerListView);
        read_msg_box = (TextView) findViewById(R.id.readMsg);
        connectionStatus = (TextView) findViewById(R.id.connectionStatus);
        writeMsg = (EditText) findViewById(R.id.writeMsg);

        wifiManager = (WifiManager) getApplicationContext().getSystemService(Context.WIFI_SERVICE);

        mManger = (WifiP2pManager) getSystemService(Context.WIFI_P2P_SERVICE);
        mChanel = mManger.initialize(this, getMainLooper(), null);

        mReceiver = new WifiDirectBroadcastReceiver(mManger, mChanel, this);
        mIntentFilter = new IntentFilter();
        mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION);
        mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION);
        mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION);
        mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION);
    }

    @Override
    protected void onResume() {
        super.onResume();
        registerReceiver(mReceiver, mIntentFilter);
    }

    @Override
    protected void onPause() {
        super.onPause();
        unregisterReceiver(mReceiver);
    }
}

WifiDirectBroadcastReceiver.java

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.net.wifi.p2p.WifiP2pManager;
import android.widget.Toast;

import qdivision.org.wifiexample2.MainActivity;

public class WifiDirectBroadcastReceiver extends BroadcastReceiver {

    private WifiP2pManager mManager;
    private WifiP2pManager.Channel mChanel;
    private MainActivity mActivity;

    public WifiDirectBroadcastReceiver(WifiP2pManager mManager, WifiP2pManager.Channel mChanel, MainActivity mActivity)
    {
        this.mManager = mManager;
        this.mChanel = mChanel;
        this.mActivity = mActivity;
    }

    @Override
    public void onReceive(Context context, Intent intent)
    {
        String action = intent.getAction();

        if(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION.equals(action)){
            int state = intent.getIntExtra(WifiP2pManager.EXTRA_WIFI_STATE, -1);
            if(state == WifiP2pManager.WIFI_P2P_STATE_ENABLED){
                Toast.makeText(context, "Wifi is ON", Toast.LENGTH_SHORT).show();
            }else {
                Toast.makeText(context, "Wifi is OFF", Toast.LENGTH_SHORT).show();
            }
        }else if(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)){
            //do something
        }else if(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)){
            //do something
        }else if(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION.equals(action)){
            //do something
        }
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/onOff"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_marginStart="28dp"
        android:layout_marginTop="55dp"
        android:text="Wifi On" />

    <Button
        android:id="@+id/discover"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/onOff"
        android:layout_alignBottom="@+id/onOff"
        android:layout_centerHorizontal="true"
        android:text="discover" />

    <ListView
        android:id="@+id/peerListView"
        android:layout_width="match_parent"
        android:layout_height="200dp"
        android:layout_alignParentStart="true"
        android:layout_below="@+id/onOff"
        android:layout_marginTop="25dp"
        android:background="@android:color/holo_orange_light" />

    <TextView
        android:id="@+id/readMsg"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentEnd="true"
        android:layout_alignParentStart="true"
        android:layout_below="@+id/peerListView"
        android:layout_marginTop="31dp"
        android:text="Message"
        android:textAlignment="center"
        android:textSize="20sp"
        android:textStyle="italic" />

    <EditText
        android:id="@+id/writeMsg"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentStart="true"
        android:ems="10"
        android:inputType="textPersonName"
        android:layout_toStartOf="@+id/sendButton" />

    <Button
        android:id="@+id/sendButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentEnd="true"
        android:text="Send" />

    <TextView
        android:id="@+id/connectionStatus"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_marginTop="15dp"
        android:text="Connection Status"
        android:textAlignment="center"
        android:textColor="@android:color/holo_blue_dark"
        android:textSize="18sp"
        android:textStyle="italic" />
</RelativeLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="qdivision.org.wifiexample2">
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
    <uses-permission android:name="android.permission.CHANGE_WIFI_STATE"/>
    <uses-permission android:name="android.permission.CHANGE_NETWORK_STATE"/>
    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

进度更新：我已经尝试了迄今为止的所有建议，但仍然WifiDirectBroadcastReceiver无法识别该课程MainActivity

解决方案：该类被保存在错误的文件夹中，一旦移动它就一切正常

标签： javaandroidclassandroid-studio

解决方案

检查您创建的课程是否为“公共”。

如果是，点击“Rebuild Project”或重启Android Studio，有时会解决很多问题。

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