应用程序尝试加密.txt文件时，Android：NullPointerException

Question

我正在尝试从我的虚拟设备（Genymotion）加密/解密文件。 我将向您展示代码和我所拥有的异常。 我想nullPointerException来自我在onActivityResult方法中声明View v = null的那一行，但是我不知道如何解决它。

例外情况

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)'

主要活动

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null，并且您正在尝试执行v.getId() 。 这就是为什么您得到NullPointerException 。

为了解决此问题，您可能想要向btnActivity1和btnActivity2添加一个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);
                    }
            });
    }

Answer 2

在MainActivity switch-case ，您正在使用v.getId()但是v初始化为null因此您将获得NullPointerException

猜测要执行的操作是根据是否单击布局中的两个按钮来决定是解密还是加密文件。 但是您没有以正确的方式进行操作。 对每个按钮使用OnClickListener并设置一个布尔标志，以检查在这些按钮的onClick事件时是解密还是加密。 然后显示您的FILE CHOOSER 。

您可以通过这种方式修改MainActivity

public class MainActivity extends Activity implements View.OnClickListener {

Button btnEncrypt;
Button btnDecrypt;
boolean encrypt=false;

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) {

                switch(v.getId()) {
                    case R.id.btnActivity1:
                        encrypt=true;
                        break;
                    case R.id.btnActivity2:
                        encrypt=false;
                        break;
                }
    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();

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

                switch(encrypt) {
                    case true:
                        crypto.encryptor(filePath);
                        break;
                    case false:
                        crypto.decryptor(filePath);
                        break;
                }
            }
        }
    }



}

}