java - Android:当应用程序尝试加密 .txt 文件时出现 NullPointerException

Question

我正在尝试从我的虚拟设备 (Genymotion) 加密/解密文件。我将向您展示我的代码和异常(exception)情况。我猜想 nullPointerException 来 self 在 onActivityResult 方法中声明 View v = null 的行，但我不知道如何修复它。

异常

07-22 13:34:10.241  10419-10419/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: application.nikola.com.encryptdecrypt, PID: 10419
    java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1, result=-1, data=Intent { dat=file:///storage/emulated/0/nikola.txt }} to activity {application.nikola.com.encryptdecrypt/application.nikola.com.encryptdecrypt.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getId()' on a null object reference
            at android.app.ActivityThread.deliverResults(ActivityThread.java:3539)
            at android.app.ActivityThread.handleSendResult(ActivityThread.java:3582)
            at android.app.ActivityThread.access$1300(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1327)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            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:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getId()' on a null object reference
            at application.nikola.com.encryptdecrypt.MainActivity.onActivityResult(MainActivity.java:70)
            at android.app.Activity.dispatchActivityResult(Activity.java:6135)
            at android.app.ActivityThread.deliverResults(ActivityThread.java:3535)
            at android.app.ActivityThread.handleSendResult(ActivityThread.java:3582)
            at android.app.ActivityThread.access$1300(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1327)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            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:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
07-22 13:34:10.263     765-1598/? W/ActivityManager﹕ Force finishing activity application.nikola.com.encryptdecrypt/.MainActivity
07-22 13:34:10.350     765-1598/? E/ActivityManager﹕ Invalid thumbnail dimensions: 576x576
07-22 13:34:10.400     765-2035/? I/OpenGLRenderer﹕ Initialized EGL, version 1.4
07-22 13:34:10.466     765-2035/? W/EGL_emulation﹕ eglSurfaceAttrib not implemented
07-22 13:34:10.466     765-2035/? W/OpenGLRenderer﹕ Failed to set EGL_SWAP_BEHAVIOR on surface 0x9ea263c0, error=EGL_SUCCESS
07-22 13:34:10.903      765-786/? W/ActivityManager﹕ Activity pause timeout for ActivityRecord{2ef175ff u0 application.nikola.com.encryptdecrypt/.MainActivity t26 f}
07-22 13:34:11.032    1006-1265/? W/EGL_emulation﹕ eglSurfaceAttrib not implemented
07-22 13:34:11.033    1006-1265/? W/OpenGLRenderer﹕ Failed to set EGL_SWAP_BEHAVIOR on surface 0xa095a020, error=EGL_SUCCESS
07-22 13:34:11.786    2640-2640/? I/art﹕ Explicit concurrent mark sweep GC freed 3007(201KB) AllocSpace objects, 0(0B) LOS objects, 24% free, 16MB/21MB, paused 301us total 21.960ms
07-22 13:34:11.808    2640-2640/? I/art﹕ Explicit concurrent mark sweep GC freed 3080(224KB) AllocSpace objects, 4(252KB) LOS objects, 24% free, 15MB/21MB, paused 173us total 7.668ms
07-22 13:34:11.822    2640-2640/? I/art﹕ Explicit concurrent mark sweep GC freed 3(96B) AllocSpace objects, 0(0B) LOS objects, 24% free, 15MB/21MB, paused 237us total 13.937ms
07-22 13:34:12.735  10419-10419/? I/Process﹕ Sending signal. PID: 10419 SIG: 9
07-22 13:34:12.738      765-823/? W/AudioTrack﹕ AUDIO_OUTPUT_FLAG_FAST denied by client
07-22 13:34:12.764      765-805/? W/InputDispatcher﹕ channel '25d12a93 application.nikola.com.encryptdecrypt/application.nikola.com.encryptdecrypt.MainActivity (server)' ~ Consumer closed input channel or an error occurred.  events=0x9
07-22 13:34:12.764      765-805/? E/InputDispatcher﹕ channel '25d12a93 application.nikola.com.encryptdecrypt/application.nikola.com.encryptdecrypt.MainActivity (server)' ~ Channel is unrecoverably broken and will be disposed!
07-22 13:34:12.777      765-782/? I/ActivityManager﹕ Process application.nikola.com.encryptdecrypt (pid 10419) has died
07-22 13:34:12.778      765-981/? I/WindowState﹕ WIN DEATH: Window{25d12a93 u0 application.nikola.com.encryptdecrypt/application.nikola.com.encryptdecrypt.MainActivity}
07-22 13:34:12.778      765-981/? W/InputDispatcher﹕ Attempted to unregister already unregistered input channel '25d12a93 application.nikola.com.encryptdecrypt/application.nikola.com.encryptdecrypt.MainActivity (server)'

主要 Activity

public class MainActivity extends Activity implements View.OnClickListener {

    Button btnEncrypt;
    Button btnDecrypt;

    final int ACTIVITY_CHOOSE_FILE = 1;

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

        btnEncrypt = (Button) this.findViewById(R.id.btnActivity1);
        btnEncrypt.setOnClickListener(this);

        btnDecrypt = (Button) this.findViewById(R.id.btnActivity2);
        btnDecrypt.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {

        Intent chooseFile;
        Intent intent;
        chooseFile = new Intent(Intent.ACTION_GET_CONTENT);
        chooseFile.setType("file*//*");
        intent = Intent.createChooser(chooseFile, "Choose a file");
        startActivityForResult(intent, ACTIVITY_CHOOSE_FILE);


    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        EncryptDecrypt crypto = new EncryptDecrypt();
        View v = null;
        String filePath = null;
        switch(requestCode) {
            case ACTIVITY_CHOOSE_FILE: {
                if (resultCode == RESULT_OK){
                    Uri uri = data.getData();
                    filePath = uri.getPath();

                    switch(v.getId()) {
                        case R.id.btnActivity1:
                            crypto.encryptor(filePath);
                            break;
                        case R.id.btnActivity2:
                            crypto.decryptor(filePath);
                            break;
                    }
                }
            }
        }



    }
}

这是我使用的加密/解密算法。

public class EncryptDecrypt {

    public void encryptor(String inputFilePath) {

        FileOutputStream fos = null;
        File file = new File(inputFilePath);
        String keyString = "140405PX_0.$88";
        String algorithm = "DESede";
        try {
            FileInputStream fileInputStream = new FileInputStream(file);
            byte[] fileByteArray = new byte[fileInputStream.available()];
            fileInputStream.read(fileByteArray);
            for (byte b : fileByteArray) {
                System.out.println(b);
            }
            SecretKey secretKey = getKey(keyString);
            Cipher cipher = Cipher.getInstance(algorithm);
            cipher.init(Cipher.ENCRYPT_MODE, secretKey);
            ObjectOutputStream objectOutputStream = new ObjectOutputStream(new CipherOutputStream(new FileOutputStream("encrypt.file"), cipher));
            objectOutputStream.writeObject(fileByteArray);
            objectOutputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void decryptor(String inputFilePath) {

        String outputFilePath = "decrypt.txt";

        String keyString = "140405PX_0.$88";
        String algorithm = "DESede";
        try {
            File inputFileNAme = new File(inputFilePath);
            FileInputStream fileInputStream = new FileInputStream(inputFileNAme);
            FileOutputStream fileOutputStream = new FileOutputStream(outputFilePath);
            SecretKey secretKey = getKey(keyString);
            Cipher cipher = Cipher.getInstance(algorithm);
            cipher.init(Cipher.DECRYPT_MODE, secretKey);
            ObjectInputStream objectInputStream = new ObjectInputStream(new CipherInputStream(fileInputStream, cipher));
            System.out.println(objectInputStream.available());
            fileOutputStream.write((byte[]) objectInputStream.readObject());
            fileOutputStream.flush();
            fileOutputStream.close();
            fileInputStream.close();
            objectInputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    public static SecretKey getKey(String message) throws Exception {
        String messageToUpperCase = message.toUpperCase();
        byte[] digestOfPassword = messageToUpperCase.getBytes();
        byte[] keyBytes = Arrays.copyOf(digestOfPassword, 24);
        SecretKey key = new SecretKeySpec(keyBytes, "DESede");
        return key;
    }


}

Answer 1

    View v = null; // v is null
    String filePath = null;
    switch(requestCode) {
        case ACTIVITY_CHOOSE_FILE: {
            if (resultCode == RESULT_OK){
                Uri uri = data.getData();
                filePath = uri.getPath();

                switch(v.getId()) { // v is still null
                    case R.id.btnActivity1:
                        crypto.encryptor(filePath);
                        break;
                    case R.id.btnActivity2:
                        crypto.decryptor(filePath);
                        break;
                }
            }
        }
     }

您的v为空，并且您正在尝试执行v.getId()。这就是为什么您会收到 NullPointerException。

为了解决此问题，您可能需要向 btnActivity1 和 btnActivity2 添加 OnClickListener。

   btnActivity1.setOnCLickListerner(new OnClickListener() {
                    @Override
                    public void onClick(View arg0) {                                                      
                        crypto.encryptor(filePath);
                    }
            });
    }

    btnActivity2.setOnCLickListerner(new OnClickListener() {
                    @Override
                    public void onClick(View arg0) {
                        crypto.decryptor(filePath);
                    }
            });
    }