Question

我的备份当前数据库的方法似乎有问题。方法如下：

当使用nexus 4，运行4.2.2时，该方法可以正常工作，但是当使用模拟器模拟版本API 15时，会发生错误。发生错误的行是os.write（）谢谢。

public void backupDatabase() throws IOException {

    File file = context.getDatabasePath(DATABASE_NAME);
    FileInputStream fis = null;
    try {
        fis = new FileInputStream(file);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
    File appDir = new File( Environment.getExternalStorageDirectory() + "/AppName/");
    appDir.mkdir();
    File outputDB = new File(appDir, "BackupFile.file");
    //String outputDB = Environment.getExternalStorageDirectory() +"/AppName/BackupFile.file";
    OutputStream os = null;
    try {
        os = new FileOutputStream(outputDB);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }

    // Transfer bytes from the inputfile to the outputfile
    byte[] buffer = new byte[1024];
    int length;
    while ((length = fis.read(buffer))>0) {
           os.write(buffer, 0, length); //<---Error.... (Only on emulator)
    }
    // Close the streams
    os.flush();
    os.close();
    fis.close();

    Toast.makeText(context, "Data successfully backed up!", Toast.LENGTH_SHORT).show();
}


01-18 18:57:38.077: E/ACRA(1961): PACKAGE_NAME fatal error : Could not execute method of the activity
01-18 18:57:38.077: E/ACRA(1961): java.lang.IllegalStateException: Could not execute method of the activity
01-18 18:57:38.077: E/ACRA(1961):   at android.view.View$1.onClick(View.java:3044)
01-18 18:57:38.077: E/ACRA(1961):   at android.view.View.performClick(View.java:3511)
01-18 18:57:38.077: E/ACRA(1961):   at android.view.View$PerformClick.run(View.java:14105)
01-18 18:57:38.077: E/ACRA(1961):   at android.os.Handler.handleCallback(Handler.java:605)
01-18 18:57:38.077: E/ACRA(1961):   at android.os.Handler.dispatchMessage(Handler.java:92)
01-18 18:57:38.077: E/ACRA(1961):   at android.os.Looper.loop(Looper.java:137)
01-18 18:57:38.077: E/ACRA(1961):   at android.app.ActivityThread.main(ActivityThread.java:4424)
01-18 18:57:38.077: E/ACRA(1961):   at java.lang.reflect.Method.invokeNative(Native Method)
01-18 18:57:38.077: E/ACRA(1961):   at java.lang.reflect.Method.invoke(Method.java:511)
01-18 18:57:38.077: E/ACRA(1961):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
01-18 18:57:38.077: E/ACRA(1961):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
01-18 18:57:38.077: E/ACRA(1961):   at dalvik.system.NativeStart.main(Native Method)
01-18 18:57:38.077: E/ACRA(1961): Caused by: java.lang.reflect.InvocationTargetException
01-18 18:57:38.077: E/ACRA(1961):   at java.lang.reflect.Method.invokeNative(Native Method)
01-18 18:57:38.077: E/ACRA(1961):   at java.lang.reflect.Method.invoke(Method.java:511)
01-18 18:57:38.077: E/ACRA(1961):   at android.view.View$1.onClick(View.java:3039)
01-18 18:57:38.077: E/ACRA(1961):   ... 11 more
01-18 18:57:38.077: E/ACRA(1961): Caused by: java.lang.NullPointerException
01-18 18:57:38.077: E/ACRA(1961):   at     PACKAGE_NAME.backupDatabase(DbHelper.java:85)

Answer 1

在我看来，os目前是空的。如果是，则创建FileOutputStream投掷FileNotFoundException。如果你有任何日志，你应该发布任何日志。

另请务必设置permission READ_EXTERNAL_STORAGE和WRITE_EXTERNAL_STORAGE。

我的建议是检查os当前是否不是null，然后再写，因为文件打开可能会失败。

此外，我不会依赖于实际设备上的模拟器，因为它只是模拟系统。如果您有任何可以测试的真实设备，请使用它们。

NullPointerException / IllegalStateException OutputStream.write（）

1 个答案: