我的Android应用程序出了问题。 我正试图在我的Android设备和我的PC之间以串行方式进行通信。 这对我使用Android NDK。 一旦我开始使用serialport的方法，即时获取错误消息。 .getSerialPort（）或.getOutputStream（）
当然我已经尝试通过谷歌解决这个问题了。 但实际上我还没有找到解决问题的方法。 我检查了我的清单是否包含了所需的一切，我确信它确实如此。 希望有人能在我的代码中找到问题。
这是我第一次就stackoverflow问一个问题，所以我想提示如何在未来以更好的方式提问。 如果缺少任何信息，请告诉我，我会尽快发布。
这是我的主要活动：
package com.example.serialtest3;
import java.io.IOException;
import java.io.OutputStream;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import com.example.serialtest3.SerialPort;
public class MainActivity extends Activity {
TextView tv;
EditText et;
SerialPort s;
protected OutputStream out= new OutputStream() {
@Override
public void write(int oneByte) throws IOException {
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
out = s.getOutputStream();
try {
s.getSerialPort();
} catch (InvalidParameterException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (SecurityException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
Button b1 = (Button) findViewById(R.id.button1);
b1.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
String text = et.getText().toString();
if (v.getId()==R.id.button1){
try {
out.write(new String(text).getBytes());
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
});
et =(EditText) findViewById(R.id.editT);
}
的SerialPort：
package com.example.serialtest3;
import java.io.File;
import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.InvalidParameterException;
import android.util.Log;
import com.example.serialtest3.*;
public class SerialPort {
private static final String TAG = "SerialPort";
SerialPort serial;
/*
* Do not remove or rename the field mFd: it is used by native method close();
*/
private FileDescriptor mFd;
private FileInputStream mFileInputStream;
private FileOutputStream mFileOutputStream;
public SerialPort(File device, int baudrate, int flags) throws SecurityException, IOException {
/* Check access permission */
if (!device.canRead() || !device.canWrite()) {
try {
/* Missing read/write permission, trying to chmod the file */
Process su;
su = Runtime.getRuntime().exec("/system/bin/su");
String cmd = "chmod 666 " + device.getAbsolutePath() + "\n"
+ "exit\n";
su.getOutputStream().write(cmd.getBytes());
if ((su.waitFor() != 0) || !device.canRead()
|| !device.canWrite()) {
throw new SecurityException();
}
} catch (Exception e) {
e.printStackTrace();
throw new SecurityException();
}
}
mFd = open(device.getAbsolutePath(), baudrate, flags);
if (mFd == null) {
Log.e(TAG, "native open returns null");
throw new IOException();
}
mFileInputStream = new FileInputStream(mFd);
mFileOutputStream = new FileOutputStream(mFd);
}
public SerialPort getSerialPort() throws SecurityException, IOException, InvalidParameterException {
String path = "/dev/ttyO0";
int baudrate= 115200;
serial = new SerialPort(new File(path), baudrate, 0);
return serial;
}
// Getters and setters
public InputStream getInputStream() {
return mFileInputStream;
}
public OutputStream getOutputStream() {
return mFileOutputStream;
}
// JNI
private native static FileDescriptor open(String path, int baudrate, int flags);
public native void close();
static {
System.loadLibrary("serial_port"); // this lib contains open and close method which are written in the c-code
}
}
android manifest：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.serialtest3"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="10"
android:targetSdkVersion="17" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.serialtest3.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
错误消息：
01-01 04:03:29.451: D/AndroidRuntime(2370): Shutting down VM
01-01 04:03:29.451: W/dalvikvm(2370): threadid=1: thread exiting with uncaught exception (group=0x40a421f8)
01-01 04:03:29.451: E/AndroidRuntime(2370): FATAL EXCEPTION: main
01-01 04:03:29.451: E/AndroidRuntime(2370): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.serialtest3/com.example.serialtest3.MainActivity}: java.lang.NullPointerException
01-01 04:03:29.451: E/AndroidRuntime(2370): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
01-01 04:03:29.451: E/AndroidRuntime(2370): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
01-01 04:03:29.451: E/AndroidRuntime(2370): at android.app.ActivityThread.access$600(ActivityThread.java:123)
01-01 04:03:29.451: E/AndroidRuntime(2370): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
01-01 04:03:29.451: E/AndroidRuntime(2370): at android.os.Handler.dispatchMessage(Handler.java:99)
01-01 04:03:29.451: E/AndroidRuntime(2370): at android.os.Looper.loop(Looper.java:137)
01-01 04:03:29.451: E/AndroidRuntime(2370): at android.app.ActivityThread.main(ActivityThread.java:4424)
01-01 04:03:29.451: E/AndroidRuntime(2370): at java.lang.reflect.Method.invokeNative(Native Method)
01-01 04:03:29.451: E/AndroidRuntime(2370): at java.lang.reflect.Method.invoke(Method.java:511)
01-01 04:03:29.451: E/AndroidRuntime(2370): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
01-01 04:03:29.451: E/AndroidRuntime(2370): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
01-01 04:03:29.451: E/AndroidRuntime(2370): at dalvik.system.NativeStart.main(Native Method)
01-01 04:03:29.451: E/AndroidRuntime(2370): Caused by: java.lang.NullPointerException
01-01 04:03:29.451: E/AndroidRuntime(2370): at com.example.serialtest3.MainActivity.onCreate(MainActivity.java:65)
01-01 04:03:29.451: E/AndroidRuntime(2370): at android.app.Activity.performCreate(Activity.java:4465)
01-01 04:03:29.451: E/AndroidRuntime(2370): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
01-01 04:03:29.451: E/AndroidRuntime(2370): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
01-01 04:03:29.451: E/AndroidRuntime(2370): ... 11 more
01-01 04:04:56.035: D/AndroidRuntime(2421): Shutting down VM
01-01 04:04:56.035: W/dalvikvm(2421): threadid=1: thread exiting with uncaught exception (group=0x40a421f8)
01-01 04:04:56.035: E/AndroidRuntime(2421): FATAL EXCEPTION: main
01-01 04:04:56.035: E/AndroidRuntime(2421): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.serialtest3/com.example.serialtest3.MainActivity}: java.lang.NullPointerException
01-01 04:04:56.035: E/AndroidRuntime(2421): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
01-01 04:04:56.035: E/AndroidRuntime(2421): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
01-01 04:04:56.035: E/AndroidRuntime(2421): at android.app.ActivityThread.access$600(ActivityThread.java:123)
01-01 04:04:56.035: E/AndroidRuntime(2421): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
01-01 04:04:56.035: E/AndroidRuntime(2421): at android.os.Handler.dispatchMessage(Handler.java:99)
01-01 04:04:56.035: E/AndroidRuntime(2421): at android.os.Looper.loop(Looper.java:137)
01-01 04:04:56.035: E/AndroidRuntime(2421): at android.app.ActivityThread.main(ActivityThread.java:4424)
01-01 04:04:56.035: E/AndroidRuntime(2421): at java.lang.reflect.Method.invokeNative(Native Method)
01-01 04:04:56.035: E/AndroidRuntime(2421): at java.lang.reflect.Method.invoke(Method.java:511)
01-01 04:04:56.035: E/AndroidRuntime(2421): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
01-01 04:04:56.035: E/AndroidRuntime(2421): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
01-01 04:04:56.035: E/AndroidRuntime(2421): at dalvik.system.NativeStart.main(Native Method)
01-01 04:04:56.035: E/AndroidRuntime(2421): Caused by: java.lang.NullPointerException
01-01 04:04:56.035: E/AndroidRuntime(2421): at com.example.serialtest3.MainActivity.onCreate(MainActivity.java:54)
01-01 04:04:56.035: E/AndroidRuntime(2421): at android.app.Activity.performCreate(Activity.java:4465)
01-01 04:04:56.035: E/AndroidRuntime(2421): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
01-01 04:04:56.035: E/AndroidRuntime(2421): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
01-01 04:04:56.035: E/AndroidRuntime(2421): ... 11 more
01-01 04:05:03.232: I/Process(2421): Sending signal. PID: 2421 SIG: 9
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:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/textView1"
android:layout_centerHorizontal="true"
android:layout_marginTop="155dp"
android:text="Button" />
<EditText
android:id="@+id/editT"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/textView1"
android:layout_below="@+id/textView1"
android:layout_marginTop="80dp"
android:ems="10"
android:lines="1" />
答案 0 :(得分：3)
SerialPort s;
这未初始化。所以这将指向null。这就是它抛出Null Pointer Exception