删除文件：空指针异常

Question

我正在使用这个逻辑来删除SD卡中的文件。它正在删除所有文件，但在文件删除操作期间，我在日志中收到 NullPointer 异常。有帮助吗？

我的代码是：

void DeleteRecursive(File fileOrDirectory) {
    if (fileOrDirectory.isDirectory()) {
        try {
            for (File child : fileOrDirectory.listFiles()) {
                DeleteRecursive(child);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    fileOrDirectory.delete();
}

这是我在删除操作期间收到的消息：

01-01 01:28:43.440: W/System.err(4183): java.lang.NullPointerException
01-01 01:28:43.450: W/System.err(4183):     at com.stericsson.sdcard.Delete_sdcard1Activity.DeleteRecursive(Delete_sdcard1Activity.java:34)
01-01 01:28:43.450: W/System.err(4183):     at com.stericsson.sdcard.Delete_sdcard1Activity.DeleteRecursive(Delete_sdcard1Activity.java:35)
01-01 01:28:43.450: W/System.err(4183):     at com.stericsson.sdcard.Delete_sdcard1Activity.DeleteRecursive(Delete_sdcard1Activity.java:35)
01-01 01:28:43.450: W/System.err(4183):     at com.stericsson.sdcard.Delete_sdcard1Activity.DeleteRecursive(Delete_sdcard1Activity.java:35)
01-01 01:28:43.450: W/System.err(4183):     at com.stericsson.sdcard.Delete_sdcard1Activity.DeleteRecursive(Delete_sdcard1Activity.java:35)
01-01 01:28:43.450: W/System.err(4183):     at com.stericsson.sdcard.Delete_sdcard1Activity.DeleteRecursive(Delete_sdcard1Activity.java:35)
01-01 01:28:43.450: W/System.err(4183):     at com.stericsson.sdcard.Delete_sdcard1Activity.DeleteRecursive(Delete_sdcard1Activity.java:35)
01-01 01:28:43.450: W/System.err(4183):     at com.stericsson.sdcard.Delete_sdcard1Activity.DeleteRecursive(Delete_sdcard1Activity.java:35)
01-01 01:28:43.450: W/System.err(4183):     at com.stericsson.sdcard.Delete_sdcard1Activity.onCreate(Delete_sdcard1Activity.java:23)
01-01 01:28:43.450: W/System.err(4183):     at android.app.Activity.performCreate(Activity.java:4465)
01-01 01:28:43.450: W/System.err(4183):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
01-01 01:28:43.450: W/System.err(4183):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)
01-01 01:28:43.450: W/System.err(4183):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
01-01 01:28:43.450: W/System.err(4183):     at android.app.ActivityThread.access$600(ActivityThread.java:122)
01-01 01:28:43.450: W/System.err(4183):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
01-01 01:28:43.450: W/System.err(4183):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-01 01:28:43.450: W/System.err(4183):     at android.os.Looper.loop(Looper.java:137)
01-01 01:28:43.450: W/System.err(4183):     at android.app.ActivityThread.main(ActivityThread.java:4340)
01-01 01:28:43.450: W/System.err(4183):     at java.lang.reflect.Method.invokeNative(Native Method)
01-01 01:28:43.450: W/System.err(4183):     at java.lang.reflect.Method.invoke(Method.java:511)
01-01 01:28:43.450: W/System.err(4183):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
01-01 01:28:43.450: W/System.err(4183):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
01-01 01:28:43.450: W/System.err(4183):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

如果 File 对象表示的路径名不是目录或者发生某些 I/O 错误，listFIles() 函数可能返回 null。
作为标准做法，您应该为 listFiles() 的返回值添加 null 检查。

Answer 2

递归删除文件/文件夹：

public boolean deleteDir(File dir) {
    if (dir != null && dir.isDirectory()) {
        String[] children = dir.list();
        for (int i = 0; i < children.length; i++) {
            boolean success = deleteDir(new File(dir, children[i]));
            if (!success) {
                return false;
            }
        }
    }

           return dir.delete();
}

Answer 3

这个： if(fileOrDirectory.isDirectory()) 应该是 if(fileOrDirectory != null && fileOrDirectory.isDirectory()) 和 filesOrDirectory.delete( ); 应该是

   if(filesOrDirectory != null) {
       filesOrDirectory.delete();
   }

Answer 4

Apache 的 commons-io FileUtils

FileUtils.deleteDirectory(new File("directory"));