java - FileInputStream 在另一个类中？

Question

我正在加载另一个类通过 FileOutputstream 方法保存的文件。无论如何，我想在另一个类中加载该文件，但它要么给我语法错误，要么使我的应用程序崩溃。

我能找到的唯一教程是在同一个类中保存和加载文件的位置，但我想将其加载到另一个类中，并且找不到如何解决加载到另一个类中的问题。

谢谢

我的代码:

public class LogIn extends Activity implements OnClickListener {
EditText eTuser;
EditText eTpassword;
CheckBox StaySignedIn;
Button bSubmit;
String user;
String pass;
FileOutputStream fos;
FileInputStream fis = null;
String FILENAME = "userandpass";

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.login);
    eTuser = (EditText) findViewById(R.id.eTuser);
    eTpassword = (EditText) findViewById(R.id.eTpassword);
    StaySignedIn = (CheckBox) findViewById(R.id.Cbstay);
    bSubmit = (Button) findViewById(R.id.bLogIn);
    bSubmit.setOnClickListener(this);
    File file = getBaseContext().getFileStreamPath(FILENAME);
    if (file.exists()) {
        Intent i = new Intent(LogIn.this, ChatService.class);
        startActivity(i);
    }
    // if if file exist close bracket
    try {
        fos = openFileOutput(FILENAME, Context.MODE_PRIVATE);
        fos.close();
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } // end of catch bracket
    catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } // end of catch

} // create ends here

public void onClick(View v) {
    // TODO Auto-generated method stub
    switch (v.getId()) {

    case R.id.bLogIn:
        String user = eTuser.getText().toString();
        String pass = eTpassword.getText().toString();
        Bundle userandpass = new Bundle();
        userandpass.putString("user", user);
        userandpass.putString("pass", pass);
        Intent login = new Intent(LogIn.this, logincheck.class);
        login.putExtra("pass", user);
        login.putExtra("user", pass);
        startActivity(login);

        if (StaySignedIn.isChecked())
            ;
        String userstaysignedin = eTuser.getText().toString();
        String passstaysignedin = eTpassword.getText().toString();
        try {
            fos = openFileOutput(FILENAME, Context.MODE_PRIVATE);
            fos.write(userstaysignedin.getBytes());
            fos.write(passstaysignedin.getBytes());
            fos.close();
        } catch (IOException e) {
            // end of try bracket, before the Catch IOExceptions e.
            e.printStackTrace();

        } // end of catch bracket

    } // switch and case ends here
}// Click ends here

}// main class ends here

B类(加载数据的类。)

public class ChatService extends Activity {
String collected = null;
FileInputStream fis = null;
String FILENAME;
TextView userandpass;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.chatservice);
    userandpass = (TextView) findViewById(R.id.textView1);

    try {
        fis = openFileInput(FILENAME);
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    byte[] dataArray = null;
    try {
        dataArray = new byte[fis.available()];
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    try {
        while (fis.read(dataArray) != -1)
            ;
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    {
        // while statement
    }
    userandpass.setText(collected);

}// create ends here

}//类(class)到此结束

日志猫:

03-03 21:03:34.725: E/AndroidRuntime(279): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gta5news.bananaphone/com.gta5news.bananaphone.ChatService}: java.lang.NullPointerException
03-03 21:03:34.725: E/AndroidRuntime(279):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
03-03 21:03:34.725: E/AndroidRuntime(279):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
03-03 21:03:34.725: E/AndroidRuntime(279):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
03-03 21:03:34.725: E/AndroidRuntime(279):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
03-03 21:03:34.725: E/AndroidRuntime(279):  at android.os.Handler.dispatchMessage(Handler.java:99)
03-03 21:03:34.725: E/AndroidRuntime(279):  at android.os.Looper.loop(Looper.java:123)
03-03 21:03:34.725: E/AndroidRuntime(279):  at android.app.ActivityThread.main(ActivityThread.java:4627)
03-03 21:03:34.725: E/AndroidRuntime(279):  at java.lang.reflect.Method.invokeNative(Native Method)
03-03 21:03:34.725: E/AndroidRuntime(279):  at java.lang.reflect.Method.invoke(Method.java:521)
03-03 21:03:34.725: E/AndroidRuntime(279):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
03-03 21:03:34.725: E/AndroidRuntime(279):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
03-03 21:03:34.725: E/AndroidRuntime(279):  at dalvik.system.NativeStart.main(Native Method)
03-03 21:03:34.725: E/AndroidRuntime(279): Caused by: java.lang.NullPointerException
03-03 21:03:34.725: E/AndroidRuntime(279):  at android.app.ContextImpl.makeFilename(ContextImpl.java:1599)
03-03 21:03:34.725: E/AndroidRuntime(279):  at android.app.ContextImpl.openFileInput(ContextImpl.java:399)
03-03 21:03:34.725: E/AndroidRuntime(279):  at android.content.ContextWrapper.openFileInput(ContextWrapper.java:152)
03-03 21:03:34.725: E/AndroidRuntime(279):  at com.gta5news.bananaphone.ChatService.onCreate(ChatService.java:25)
03-03 21:03:34.725: E/AndroidRuntime(279):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
03-03 21:03:34.725: E/AndroidRuntime(279):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
03-03 21:03:34.725: E/AndroidRuntime(279):  ... 11 more

Answer 1

ChatService 类中的 FILENAME 字符串为 null。因此，当您尝试使用 fis = openFileInput(FILENAME) 加载文件时，您会收到 NullPointerException。

此外，您的读取循环会丢弃数据:

    while (fis.read(dataArray) != -1)
        ;

它需要收集数据并设置您的收集字符串的值。