从另一个片段

Question

好的，所以我有一个Android应用程序基本上是对node.js服务器的登录。文件结构包括：MainActivity.java，FirstFragment.java，MiddleMan.java和MySocket.java。

  

MainActivity.java

package "";

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.EditText;

import java.net.URISyntaxException;

public class MainActivity extends Activity implements MiddleMan {
    String SERVER_ADDRESS = "";
    MySocket my_socket;

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

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

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    public void onConnectButtonPressed(EditText editText_ID){
        System.out.println("Received connect request from first fragment.");
        my_socket = new MySocket();
        try {
            my_socket.EstablishConnection(SERVER_ADDRESS, editText_ID);
        } catch (URISyntaxException e) {
            e.printStackTrace();
        }
    }

    public void ConnectionEstablished() {
        System.out.println("Received established connection from MySocket.java.");
    }
}

  

FirstFragment.java

package "";

import android.app.Activity;
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class FirstFragment extends Fragment{
    MiddleMan mCallback;

    @Override
    public void onAttach(Activity activity){
        super.onAttach(activity);
        try {
            mCallback = (MiddleMan) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString() + " must implement ReqestConnect");
        }

    }
    private static TextView textView_state;
    private static EditText editText_ID;
    Button button_connect;
    Button button_disconnect;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        View view = inflater.inflate(R.layout.first_fragment_root,container,false);
        textView_state = (TextView) view.findViewById(R.id.textView_state);
        editText_ID = (EditText) view.findViewById(R.id.editText_ID);
        button_connect = (Button) view.findViewById(R.id.button_connect);
        button_connect.setOnClickListener(new View.OnClickListener(){
            public void onClick(View v){
                buttonConnectClicked();
            }
        });
        Button button_disconnect = (Button) view.findViewById(R.id.button_disconnect);

        return view;
    }

    private void buttonConnectClicked() {
        System.out.println("Connect Button Pressed ");
        mCallback.onConnectButtonPressed(editText_ID);
    }

}

  

MiddleMan.java

package "";

import android.widget.EditText;

public interface MiddleMan {
    void onConnectButtonPressed(EditText editText_ID);
    void ConnectionEstablished();
}

  

MySocket.java

package "";

import android.app.Activity;
import android.app.Fragment;
import android.widget.EditText;

import com.github.nkzawa.emitter.Emitter;
import com.github.nkzawa.socketio.client.IO;
import com.github.nkzawa.socketio.client.Socket;

import java.net.URISyntaxException;

public class MySocket extends Fragment{
    public Socket lobby;

    MiddleMan mCallBack;

    @Override
    public void onAttach(Activity activity){
        super.onAttach(activity);
        try {
            mCallBack = (MiddleMan) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString() + " must implement ReqestConnect");
        }
    }

    public String getUserID(EditText editText_ID) {
        String string = editText_ID.getText().toString();
        if (string.length() > 0) {
            return string;
        }
        else {
            return null;
        }
    }

    public void EstablishConnection(String SERVER_ADDRESS,EditText editText_ID) throws URISyntaxException {
        lobby = IO.socket(SERVER_ADDRESS);
        final String client = getUserID(editText_ID);
        System.out.println("client: " + client);
        lobby.on(Socket.EVENT_CONNECT, new Emitter.Listener() {
            @Override
            public void call(Object... args) {
                System.out.println("Connection established");
                mCallBack.ConnectionEstablished();
            }
        }).on("event", new Emitter.Listener() {

            @Override
            public void call(Object... args) {

            }
        }).on(Socket.EVENT_DISCONNECT, new Emitter.Listener() {

            @Override
            public void call(Object... args) {
                System.out.println("Connection terminated.");
            }
        });
        lobby.connect();
    }
}

有一个activity_main.xml，一个first_fragment_root.xml（占用了所有显示），而MySocket.java没有关联的布局。

到目前为止，应用程序启动会显示editText，textview和两个按钮：connect和disconnect。输入一些ID，然后单击连接按钮，在FirstFragment.java中执行以下代码：

private void buttonConnectClicked() {
        System.out.println("Connect Button Pressed ");
        mCallback.onConnectButtonPressed(editText_ID);
    }

将其转移到MiddleMan.java以使MainActivity.java执行此位：

public void onConnectButtonPressed(EditText editText_ID){
        System.out.println("Received connect request from first fragment.");
        my_socket = new MySocket();
        try {
            my_socket.EstablishConnection(SERVER_ADDRESS, editText_ID);
        } catch (URISyntaxException e) {
            e.printStackTrace();
        }
    }

将其发送到MySocket.java的EstablishConnection：

public void EstablishConnection(String SERVER_ADDRESS,EditText editText_ID) throws URISyntaxException {
        lobby = IO.socket(SERVER_ADDRESS);
        final String client = getUserID(editText_ID);
        System.out.println("client: " + client);
        lobby.on(Socket.EVENT_CONNECT, new Emitter.Listener() {
            @Override
            public void call(Object... args) {
                System.out.println("Connection established");
                mCallBack.ConnectionEstablished();
            }
        }).on("event", new Emitter.Listener() {

            @Override
            public void call(Object... args) {

            }
        }).on(Socket.EVENT_DISCONNECT, new Emitter.Listener() {

            @Override
            public void call(Object... args) {
                System.out.println("Connection terminated.");
            }
        });
        lobby.connect();
    }

一切正常，直到我添加了一点关于MySocket.java有自己的对象给Middle man所以它可以告诉MainActivity.java它已经完成了。而不是运行 mCallBack.ConnectionEstablished（）; 程序中断并告诉我Attempt to invoke interface method 'void MiddleMan.ConnectionEstablished()' on a null object reference

我不知道我做错了什么，我假设MySocket.java中的onAttach方法没有被调用，所以这里的mCallBack为null，但为什么呢？谢谢你的阅读。

结论

我已决定发布此版本的工作版本，以帮助可能遇到相同或类似问题的人。

  

MainActivity.java

package "";

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.EditText;


import java.net.URISyntaxException;

public class MainActivity extends Activity implements MiddleMan {
    String SERVER_ADDRESS = "";
    MySocket my_socket;

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

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

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    public void onConnectButtonPressed(EditText editText_ID){
        if (my_socket==null) {
            System.out.println("Received connect request from first fragment.");
            my_socket = new MySocket();
            my_socket.setListener(this);
            try {
                my_socket.EstablishConnection(SERVER_ADDRESS, editText_ID);
            } catch (URISyntaxException e) {
                e.printStackTrace();
            }
        }
    }

    public void ConnectionEstablished() {
        System.out.println("Received established connection from MySocket.java.");
        System.out.println("Attempting to establish room for client.");
        my_socket.requestRoom();
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                FirstFragment f = (FirstFragment) getFragmentManager().findFragmentById(R.id.first_fragment_root);
                f.updateTextViewState("Connected");
            }
        });
    }

    @Override
    public void onDisconnectButtonPressed() {
        if (my_socket!=null) {
            System.out.println("Received disconnect request from first fragment.");
            my_socket.requestDisconnect();
        }
    }

    @Override
    public void DisconnectEstablished() {
        System.out.println("Received disconnected from MySocket.java.");
        my_socket = null;
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                FirstFragment f = (FirstFragment) getFragmentManager().findFragmentById(R.id.first_fragment_root);
                f.updateTextViewState("Disconnected");
            }
        });

    }
}

  

FirstFragment.java

package "";

import android.app.Activity;
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class FirstFragment extends Fragment{
    MiddleMan mCallback;

    @Override
    public void onAttach(Activity activity){
        super.onAttach(activity);
        try {
            mCallback = (MiddleMan) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString() + " must implement ReqestConnect");
        }

    }
    private static TextView textView_state;
    private EditText editText_ID;
    Button button_connect;
    Button button_disconnect;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        View view = inflater.inflate(R.layout.first_fragment_root,container,false);
        textView_state = (TextView) view.findViewById(R.id.textView_state);
        editText_ID = (EditText) view.findViewById(R.id.editText_ID);
        button_connect = (Button) view.findViewById(R.id.button_connect);
        button_connect.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v){
                buttonConnectClicked();
            }
        });
        button_disconnect = (Button) view.findViewById(R.id.button_disconnect);
        button_disconnect.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                buttonDisconnectClicked();
            }
        });

        return view;
    }

    private void buttonDisconnectClicked() {
        System.out.println("Disconnect Button Pressed ");
        mCallback.onDisconnectButtonPressed();
    }

    private void buttonConnectClicked() {
        System.out.println("Connect Button Pressed ");
        if (this.editText_ID.getText().toString()!=null && !this.editText_ID.getText().toString().isEmpty()) {
            mCallback.onConnectButtonPressed(editText_ID);
        }
    }

    public void updateTextViewState(String s){
        textView_state.setText(s);
    }

}

  

MySocket.java

package "";

import android.app.Fragment;
import android.content.Context;
import android.widget.EditText;

import com.github.nkzawa.emitter.Emitter;
import com.github.nkzawa.socketio.client.IO;
import com.github.nkzawa.socketio.client.Socket;

import java.net.URISyntaxException;

public class MySocket extends Fragment{
    public Socket lobby;
    String client;

    MiddleMan mCallBack;

    public void setListener(Context callback) {
        try {
            mCallBack = (MiddleMan) callback;
        } catch (ClassCastException e) {
            throw new ClassCastException(callback.toString()  + " must implement ReqestConnect");
        }
    }

    public String getUserID(EditText editText_ID) {
        String string = editText_ID.getText().toString();
        if (string.length() > 0) {
            return string;
        }
        else {
            return null;
        }
    }

    public void EstablishConnection(String SERVER_ADDRESS,EditText editText_ID) throws URISyntaxException {
        lobby = IO.socket(SERVER_ADDRESS);
        final String client = getUserID(editText_ID);
        this.client = client;
        System.out.println("client: " + this.client);
        lobby.on(Socket.EVENT_CONNECT, new Emitter.Listener() {
            @Override
            public void call(Object... args) {
                System.out.println("Connection established");
                mCallBack.ConnectionEstablished();
            }
        }).on("event", new Emitter.Listener() {

            @Override
            public void call(Object... args) {
                String s = (String) args[0];
                System.out.println(s);
            }
        }).on(Socket.EVENT_DISCONNECT, new Emitter.Listener() {

            @Override
            public void call(Object... args) {
                System.out.println("Connection terminated.");
                if (lobby!=null) {
                    Disconnect();
                }
            }
        }).on("room_created", new Emitter.Listener() {

            @Override
            public void call(Object... args) {
                String s = (String) args[0];
                System.out.println(s);
            }
        });
        lobby.connect();
    }

    public void requestRoom() {
        lobby.emit("request_user_room", this.client);
    }

    public void requestDisconnect() {
        if (lobby!=null) {
            if (lobby.connected()) {
                lobby.disconnect();
            }
        }
    }

    private void Disconnect() {
        lobby.off(Socket.EVENT_CONNECT);
        lobby.off("event");
        lobby.off(Socket.EVENT_DISCONNECT);
        lobby.off("room_created");
        lobby = null;
        mCallBack.DisconnectEstablished();
    }
}

  

MiddleMan.java

package "";

import android.widget.EditText;

public interface MiddleMan {
    void onConnectButtonPressed(EditText editText_ID);
    void ConnectionEstablished();
    void onDisconnectButtonPressed();
    void DisconnectEstablished();
}

  

activity_main.xml中

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <fragment
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:name="<<PATH_TO_>>.FirstFragment"
        android:id="@+id/first_fragment_root"
        tools:layout="@layout/first_fragment_root"/>
</RelativeLayout>

  

first_fragment_root.xml

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

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="@string/textView_ID"
        android:id="@+id/textView_ID"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginTop="23dp" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="phone"
        android:ems="10"
        android:id="@+id/editText_ID"
        android:hint="@string/editText_ID"
        android:layout_marginLeft="23dp"
        android:layout_marginStart="23dp"
        android:layout_alignBottom="@+id/textView_ID"
        android:layout_toRightOf="@+id/textView_ID"
        android:layout_toEndOf="@+id/textView_ID" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="@string/textView_status"
        android:id="@+id/textView_status"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="@string/textView_state"
        android:id="@+id/textView_state"
        android:layout_alignParentBottom="true"
        android:layout_toRightOf="@+id/textView_status"
        android:layout_marginLeft="23dp"
        android:layout_marginStart="23dp" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/button_connect"
        android:id="@+id/button_connect"
        android:layout_below="@+id/textView_ID"
        android:layout_alignLeft="@+id/editText_ID"
        android:layout_alignStart="@+id/editText_ID"
        android:layout_marginTop="25dp" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/button_disconnect"
        android:id="@+id/button_disconnect"
        android:layout_alignBottom="@+id/button_connect"
        android:layout_alignRight="@+id/editText_ID"
        android:layout_alignEnd="@+id/editText_ID" />

</RelativeLayout>