Question

我有一个名为RandoMessenger的课程。该类有一个名为message的字符串数据成员。我有一个EditText组件。该组件有一个监听器，用于指示用户何时按下Enter键。执行此操作后，变量消息将设置为用户键入的文本。稍后在程序中（侦听器外部），我有一个if语句，用于检查消息是否为空。如果验证，则将消息传递给服务器。这个if语句永远不会验证，除非我在声明时将messenger设置为某个东西。相关评论全部包含在下面的代码中。

我正在测试Andy模拟器4.4.2和三星Galaxy S3 4.4.2

package com.Rando;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.text.Editable;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.MenuItem; 
import android.view.View;
import android.view.View.OnKeyListener;
import android.widget.EditText;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

public class RandoMessenger extends ActionBarActivity {

public PrintWriter out;
public BufferedReader in;

//THE IF STATEMENT VALIDATES IF I SET MESSAGE TO SOMETHING HERE. IT DOES NOT VALIDATE 
// IF MESSAGE IS SET IN THE LISTENER BELOW
public String message="";

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


    new Thread(){
        public void run(){
            final EditText edit1 = (EditText) findViewById(R.id.editText2); 
            final EditText edit = (EditText) findViewById(R.id.editText1);

            edit.setOnKeyListener(new OnKeyListener() {
                public boolean onKey(View v, int keyCode, KeyEvent event) {
                    // If the event is a key-down event on the "enter" button
                    if ((event.getAction() == KeyEvent.ACTION_DOWN) &&
                        (keyCode == KeyEvent.KEYCODE_ENTER)) {

                   //MESSAGE IS INITIALIZED HERE INSIDE THE LISTENER BUT THE IF STATEMENT 
                   //BELOW NEVER VALIDATES INDICATING MESSAGE IS "" OUTSIDE THE LISTENER
                        message=edit.getText().toString();
                        edit1.append("\n");
                        edit1.append("Listener Works");
                        edit.setText("");

                      return true;
                    }
                    return false;
                }
            });


                //Edited out the actual IP
                String serverAddress = "00.000.00.000";
                Socket socket;


                try {

                    socket = new Socket(serverAddress, 9001);

                    in = new BufferedReader(new InputStreamReader(
                        socket.getInputStream()));
                    out = new PrintWriter(socket.getOutputStream(), true);


                while (true) {
                    String line = in.readLine();

                    //THIS IF STATEMENT DOES NOT VALIDATE WHEN MESSAGE IS SET
                    //INSIDE THE LISTENER ABOVE
                    if(message != "")
                    {

                        out.println("Test");
                        edit1.setText(message);
                        message="";
                    }

                    if (line.startsWith("SUBMITNAME")) {
                        out.println("User");
                    } else if (line.startsWith("NAMEACCEPTED")) {
                      edit1.append("Connection Successful");
                    } else if (line.startsWith("MESSAGE")) {
                        //Append message to output field here
                        edit1.append("\n");
                        edit1.append(line);
                    }   
                }
            }
                   catch(IOException e)
                    {
                       e.printStackTrace();
                    }
        }
        }.start();

    //Temporary dialog for server IP input
    /*******************************************************************/
    AlertDialog.Builder alert = new AlertDialog.Builder(this);

    alert.setTitle("Server");
    alert.setMessage("Enter the server IP address:");

    // Set an EditText view to get user input 
    final EditText input = new EditText(this);
    alert.setView(input);
    alert.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
    public void onClick(DialogInterface dialog, int whichButton) {
    Editable value = input.getText();
    //edit1.append(value);
    }
    });

    alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
    public void onClick(DialogInterface dialog, int whichButton) {
    // Canceled.
    }   
    });

    alert.show();

}


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

}



}

Answer 1

我认为主要的错误是使用message != ""来比较消息。在Java中，应使用!string1.equals(string2)或本例!message.equals("")进行字符串比较。

Java / Android类数据成员在监听器之后不保留值

1 个答案: