[英]Calling Serial Port Class from a JFrame Class
我正在通過串行端口在Arduino上使用Java的JFrame進行實驗,但遇到了一個問題,我不確定如何繼續執行我的代碼。
我試圖使用構造函數從另一個類的JFrame代碼中調用一個類的串行端口部分。 基本上,我正在嘗試將Java程序與Arduino Uno連接。
我的問題是,當我嘗試從GUI類運行代碼時,請訪問SerialOut.write(“ test” .getBytes());。 ,錯誤提示“線程“ main”中的異常java.lang.NullPointerException”。
有人可以看一下構造函數,然后告訴我是否犯了任何錯誤嗎? 謝謝!
設置串行端口的類該代碼本身可以工作[我使用Uno和LED對其進行測試以查看其是否點亮。 (確實)]
package javaapplication1;
import javaapplication1.RCDA_JFrame;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStream;
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import gnu.io.SerialPortEvent;
import gnu.io.SerialPortEventListener;
import java.util.Enumeration;
import java.io.IOException;
public class SerialTest implements SerialPortEventListener {
//constructor
public SerialTest(){
this.initialize();
this.close();
this.serialEvent(null);
}
SerialPort serialPort;
/** The port we're normally going to use. */
private static final String PORT_NAMES[] = {
"COM8",}; // Windows
private BufferedReader input;
private static OutputStream SerialOut;/** The output stream to the port */
private static final int TIME_OUT = 2000;/** Milliseconds to block while waiting for port open */
private static final int DATA_RATE = 9600;/** Default bits per second for COM port. */
public void initialize() {
CommPortIdentifier portId = null;
Enumeration portEnum = CommPortIdentifier.getPortIdentifiers();
//First, Find an instance of serial port as set in PORT_NAMES.
while (portEnum.hasMoreElements()) {
CommPortIdentifier currPortId = (CommPortIdentifier) portEnum.nextElement();
for (String portName : PORT_NAMES) {
if (currPortId.getName().equals(portName)) {
portId = currPortId;
break;
}
}
}
if (portId == null) {
System.out.println("Could not find COM port.");
return;
}
try {
// open serial port, and use class name for the appName.
serialPort = (SerialPort) portId.open(this.getClass().getName(),
TIME_OUT);
// set port parameters
serialPort.setSerialPortParams(DATA_RATE,
SerialPort.DATABITS_8,
SerialPort.STOPBITS_1,
SerialPort.PARITY_NONE);
// open the streams
input = new BufferedReader(new InputStreamReader(serialPort.getInputStream()));
SerialOut = serialPort.getOutputStream();
// add event listeners
serialPort.addEventListener(this);
serialPort.notifyOnDataAvailable(true);
} catch (Exception e) {
System.err.println(e.toString());
}
}
/**
* This should be called when you stop using the port.
* This will prevent port locking on platforms like Linux.
*/
public synchronized void close() {
if (serialPort != null) {
serialPort.removeEventListener();
serialPort.close();
}
}
//Handle an event on the serial port. Read the data and print it.
public synchronized void serialEvent(SerialPortEvent oEvent) {
if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE) {
try {
String inputLine=input.readLine();
System.out.println(inputLine);
} catch (Exception e) {
System.err.println(e.toString());
}
}
}
public static void main(String[] args) throws Exception {
SerialTest main = new SerialTest();
main.initialize();
Thread t=new Thread() {
public void run() {
//the following line will keep this app alive for 1000 seconds,
//waiting for events to occur and responding to them (printing incoming messages to console).
try {Thread.sleep(1000000);} catch (InterruptedException ie) {}
}
};
t.start();
System.out.println("Started");
//testing
try {
System.out.println("This is a test");
System.out.println("test".getBytes());
SerialOut.write("test".getBytes()); //SEND STRING THROUGH SERIAL PORT
} catch (IOException e1) {
e1.printStackTrace();
} //end of testing
}
}
JFrame類-我試圖在上面調用的類:
package javaapplication1;
import javaapplication1.SerialTest;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStream;
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import gnu.io.SerialPortEvent;
import gnu.io.SerialPortEventListener;
import java.util.Enumeration;
import java.io.IOException;
public class NewJFrame extends javax.swing.JFrame implements SerialPortEventListener {
@Override
public void serialEvent(SerialPortEvent ev) {
SerialTest ST1 = new SerialTest();
}
private static OutputStream SerialOut;
SerialPort serialPort;
/** The port we're normally going to use. */
// private static final String PORT_NAMES[] = {
// "COM8"}; // Windows
// private BufferedReader input;
// private static final int TIME_OUT = 2000;/** Milliseconds to block while waiting for port open */
// private static final int DATA_RATE = 9600;/** Default bits per second for COM port. */
//
public NewJFrame() {
initComponents();
}
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
}
public static void main(String args[]) {
//constructor from SerialTest
SerialTest ST1 = new SerialTest();
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new NewJFrame().setVisible(true);
}
});
try {
System.out.println("This is a test");
System.out.println("test".getBytes());
SerialOut.write("test".getBytes()); //SEND STRING THROUGH SERIAL PORT
} catch (IOException e1) {
e1.printStackTrace();
}
}
// Variables declaration - do not modify
private javax.swing.JButton jButton1;
// End of variables declaration
}
您需要進行錯誤檢查,以查看端口在通過可用端口列表之后是否為空。 確保它確實在獲取可用端口,並且確實為它分配了一個值。
if (portId == null) {
System.out.println("Could not find COM port.");
return;
}
要進行確認,請嘗試打印出portName,以查看端口實際獲得的端口,如portId.getName()
並檢查以確保其不為null。 如果是這樣,那就是您的問題。
private static OutputStream SerialOut;/** The output stream to the port */
這是在SerialTest.
注意,它不應該是靜態的。 如果已找到端口,則在調用initialize()
時將對其進行initialize()
,並且initialize()
不會引發異常或返回任何狀態,因此無法知道它是否成功。 解決這個。
private static OutputStream SerialOut;
在NewJFrame
。 它與上一個數據項不同。 它永遠不會被初始化,因此它為null,因此您將獲得NullPointerException
。 刪除它,然后在SerialTest.
使用它SerialTest.
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