Android 在内部存储中保存数据 NullPointerException

发布于 2024-12-05 18:46:15 字数 1211 浏览 2 评论 0原文

我在从应用程序的内部存储中写入文件时遇到了一些问题。我遇到了空指针异常，但找不到修复它的方法。实际上无法理解哪个元素为空。

这是我正在使用的代码：

hash= jsonObj.getString("hash");
Log.w("CLIENT AUTH HASH","SHOW CLIENT AUTH HASH : "+hash);                  
FileOutputStream out = context.openFileOutput("autohash",context.MODE_PRIVATE);
out.write(hash.getBytes());
out.close();

我尝试创建和写入此文件的类不是 Activity，它只是某种帮助程序类，这就是为什么它在时给我错误我尝试设置context=this;。实际上它在这一行抛出了 NullPointerException ： FileOutputStream out = context.openFileOutput("autohash",context.MODE_PRIVATE); ，我无法得到它，这导致了这个异常：

背景

或

autohash - 文件（存在或不存在）。

第二种情况：

我具有将文件保存在内部存储中的相同功能，但我从另一个活动调用该方法。情况如下：

我通过互联网收到了不同的数据包，并且我'我正在做这样的事情：

BasePacket packet; //all other packets extends this class.
byte[] buffer=byte[1024];
//packet calculations
switch(packetType){
  case startPacket:
    packet = new startPacket(/*params*/);
    packet.startExecutePacket();
 case endPacket:
    //same procedure
}

在 startExecutePacket() 中我试图保存文件。

欢迎任何形式的帮助！提前致谢！

原文

I have a little problem with writing a file in internal storage from my application.I'm gettin a null pointer exception,but can't find the way to fix it..and actually can't understand which one of the elements is null.

Here is the code that I'm using :

hash= jsonObj.getString("hash");
Log.w("CLIENT AUTH HASH","SHOW CLIENT AUTH HASH : "+hash);                  
FileOutputStream out = context.openFileOutput("autohash",context.MODE_PRIVATE);
out.write(hash.getBytes());
out.close();

The class where I'm trying to create and write this file is not an Activity, it's just some kind of helper class and that's why it's giving me error when I try to set context=this;.
And actually the NullPointerException it thrown at this line : FileOutputStream out = context.openFileOutput("autohash",context.MODE_PRIVATE);, and I can't get it, which cause this exception :

The Context

autohash - file (exist or don't).

Second scenario :

I have the same function of saving the file in internal storage,but I'm calling that method from another activity.Here is the situation:

I have different packets received over the internet and I'm doing something like this :

BasePacket packet; //all other packets extends this class.
byte[] buffer=byte[1024];
//packet calculations
switch(packetType){
  case startPacket:
    packet = new startPacket(/*params*/);
    packet.startExecutePacket();
 case endPacket:
    //same procedure
}

and in startExecutePacket() I'm trying to save the file.

So any kind of help are welcomed!Thanks in advance!

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静若繁花 2024-12-12 18:46:15

CallingActivity.java

onCreate()

helperClass mHelper= new helperClass(CallingActivity.this);

helperClass.java

//declare a context
context refContext;

//constructor
public helperClass(context mContext)
{
   refContext=mContext;
}

//and you code

    hash= jsonObj.getString("hash");
    Log.w("CLIENT AUTH HASH","SHOW CLIENT AUTH HASH : "+hash);                  
    FileOutputStream out = refContext.openFileOutput("autohash",Context.MODE_PRIVATE);
    out.write(hash.getBytes());
    out.close();

尝试使用这个

CallingActivity.java

onCreate()

helperClass mHelper= new helperClass(CallingActivity.this);

helperClass.java

//declare a context
context refContext;

//constructor
public helperClass(context mContext)
{
   refContext=mContext;
}

//and you code

    hash= jsonObj.getString("hash");
    Log.w("CLIENT AUTH HASH","SHOW CLIENT AUTH HASH : "+hash);                  
    FileOutputStream out = refContext.openFileOutput("autohash",Context.MODE_PRIVATE);
    out.write(hash.getBytes());
    out.close();

try with this one

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