我有一个LED连接到rts和5v引脚通过CH340g。我在Android上的UsbTerminal应用程序上进行了测试，它工作正常但我的应用程序没有检测到任何USB串行设备，当我尝试检查RTS复选框时它崩溃了。
我是编程和Android的新手，也是我第一次使用这些组件的经验，所以任何帮助都会受到赞赏。
这是我的代码：
package com.example.dell.cashregister;
import android.content.Context;
import android.hardware.usb.UsbDeviceConnection;
import android.hardware.usb.UsbManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import com.hoho.android.usbserial.driver.UsbSerialDriver;
import com.hoho.android.usbserial.driver.UsbSerialPort;
import com.hoho.android.usbserial.driver.UsbSerialProber;
import com.hoho.android.usbserial.driver.UsbSerialPort;
import com.hoho.android.usbserial.util.HexDump;
import com.hoho.android.usbserial.util.SerialInputOutputManager;
import java.io.IOException;
import java.util.List;
import java.io.*;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.hardware.usb.UsbDeviceConnection;
import android.hardware.usb.UsbManager;
import android.os.Bundle;
import android.util.Log;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.ScrollView;
import android.widget.TextView;
import com.hoho.android.usbserial.driver.UsbSerialPort;
import com.hoho.android.usbserial.util.HexDump;
import com.hoho.android.usbserial.util.SerialInputOutputManager;
import java.io.IOException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class MainActivity extends Activity {
private final String TAG = MainActivity.class.getSimpleName();
private static UsbSerialPort sPort = null;
private TextView mTitleTextView;
private TextView mDumpTextView;
private ScrollView mScrollView;
private CheckBox chkDTR;
private CheckBox chkRTS;
private final ExecutorService mExecutor = Executors.newSingleThreadExecutor();
private SerialInputOutputManager mSerialIoManager;
private final SerialInputOutputManager.Listener mListener =
new SerialInputOutputManager.Listener() {
@Override
public void onRunError(Exception e) {
Log.d(TAG, "Runner stopped.");
}
@Override
public void onNewData(final byte[] data) {
MainActivity.this.runOnUiThread(new Runnable() {
@Override
public void run() {
MainActivity.this.updateReceivedData(data);
}
});
}
};
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mTitleTextView = (TextView) findViewById(R.id.demoTitle);
mDumpTextView = (TextView) findViewById(R.id.consoleText);
mScrollView = (ScrollView) findViewById(R.id.demoScroller);
chkDTR = (CheckBox) findViewById(R.id.checkBoxDTR);
chkRTS = (CheckBox) findViewById(R.id.checkBoxRTS);
chkDTR.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
try {
sPort.setDTR(isChecked);
}catch (IOException x){}
}
});
chkRTS.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
try {
sPort.setRTS(isChecked);
}catch (IOException x){}
}
});
}
@Override
protected void onPause() {
super.onPause();
stopIoManager();
if (sPort != null) {
try {
sPort.close();
} catch (IOException e) {
// Ignore.
}
sPort = null;
}
finish();
}
void showStatus(TextView theTextView, String theLabel, boolean theValue){
String msg = theLabel + ": " + (theValue ? "enabled" : "disabled") + "\n";
theTextView.append(msg);
}
@Override
protected void onResume() {
super.onResume();
Log.d(TAG, "Resumed, port=" + sPort);
if (sPort == null) {
mTitleTextView.setText("No serial device.");
} else {
final UsbManager usbManager = (UsbManager) getSystemService(Context.USB_SERVICE);
UsbDeviceConnection connection = usbManager.openDevice(sPort.getDriver().getDevice());
if (connection == null) {
mTitleTextView.setText("Opening device failed");
return;
}
try {
sPort.open(connection);
sPort.setParameters(115200, 8, UsbSerialPort.STOPBITS_1, UsbSerialPort.PARITY_NONE);
showStatus(mDumpTextView, "CD - Carrier Detect", sPort.getCD());
showStatus(mDumpTextView, "CTS - Clear To Send", sPort.getCTS());
showStatus(mDumpTextView, "DSR - Data Set Ready", sPort.getDSR());
showStatus(mDumpTextView, "DTR - Data Terminal Ready", sPort.getDTR());
showStatus(mDumpTextView, "DSR - Data Set Ready", sPort.getDSR());
showStatus(mDumpTextView, "RI - Ring Indicator", sPort.getRI());
showStatus(mDumpTextView, "RTS - Request To Send", sPort.getRTS());
} catch (IOException e) {
Log.e(TAG, "Error setting up device: " + e.getMessage(), e);
mTitleTextView.setText("Error opening device: " + e.getMessage());
try {
sPort.close();
} catch (IOException e2) {
// Ignore.
}
sPort = null;
return;
}
mTitleTextView.setText("Serial device: " + sPort.getClass().getSimpleName());
}
onDeviceStateChange();
}
private void stopIoManager() {
if (mSerialIoManager != null) {
Log.i(TAG, "Stopping io manager ..");
mSerialIoManager.stop();
mSerialIoManager = null;
}
}
private void startIoManager() {
if (sPort != null) {
Log.i(TAG, "Starting io manager ..");
mSerialIoManager = new SerialInputOutputManager(sPort, mListener);
mExecutor.submit(mSerialIoManager);
}
}
private void onDeviceStateChange() {
stopIoManager();
startIoManager();
}
private void updateReceivedData(byte[] data) {
final String message = "Read " + data.length + " bytes: \n"
+ HexDump.dumpHexString(data) + "\n\n";
mDumpTextView.append(message);
mScrollView.smoothScrollTo(0, mDumpTextView.getBottom());
}
/**
* Starts the activity, using the supplied driver instance.
*
* @param context
* @param driver
*/
static void show(Context context, UsbSerialPort port) {
sPort = port;
final Intent intent = new Intent(context, MainActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP | Intent.FLAG_ACTIVITY_NO_HISTORY);
context.startActivity(intent);
}
}
如果需要更改任何内容以便检测我的设备或是否有任何其他问题，请告诉我。
这是logcat：
12-05 16:32:34.677 17322-17322/com.example.dell.cashregister
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.dell.cashregister, PID: 17322
java.lang.NullPointerException: Attempt to invoke interface method 'void com.hoho.android.usbserial.driver.UsbSerialPort.setRTS(boolean)' on a null object reference
at com.example.dell.cashregister.MainActivity$3.onCheckedChanged(MainActivity.java:101)
at android.widget.CompoundButton.setChecked(CompoundButton.java:161)
at android.widget.CompoundButton.toggle(CompoundButton.java:115)
at android.widget.CompoundButton.performClick(CompoundButton.java:127)
at android.view.View$PerformClick.run(View.java:20755)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5835)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
答案 0 :(得分：0)
您确定使用static void show(Context context, UsbSerialPort port)方法初始化了活动，并为UsbSerialPort port传递了一个NonNull值吗？从日志中，似乎mPort变量尚未初始化。从查看代码时，只有在调用此方法时才能初始化它。
我的猜测是你试图在不调用此方法的情况下初始化Activity。出于此示例的目的，应仅使用show方法初始化活动（至少是第一次）。
我还看了一下你试图重新创建的例子，并且在那里声明使用静态变量进行端口引用是一种实现这个的hacky方式。对于一个快速的例子它应该没问题，但它可能会在某些情况下崩溃，如果你打算进一步使用它，最好找到一种不同的初始化方法。