java - 将字符串 ArrayList 从一个 Activity 传递到另一个 Activity 时，为什么会出现空指针异常？

Question

我正在尝试从 UpdateLocation Activity 中获取 ScanLocate Activity 中的数组列表。

我正在使用 startActivityForResult 方法调用填充 ArrayList wifiList 的 scan 方法，然后我想将 ArrayList 发送到更新位置类。

我首先在更新位置中调用startActivityForResult:

private void getScan(){
    //Create an intent to start ScanLocate
    final Intent i = new Intent(this, ScanLocate.class);
    //Start scanLocate with request code
    startActivityForResult(i, REQUEST_READINGS);
}

接下来，在 ScanLocate 中，我创建了 sendData 方法(注意:检查确认 ArrayList 数据此时完好无损):

private void sendData(){
    //create a new intent as container for the result
    final Intent readings = new Intent(this, UpdateLocation.class);

    //check that data is in wifiList
    for(String s:wifiList){
        Log.v(TAG,"List Items: " + s);
    }

    //create bundle for string array
    Bundle b = new Bundle();
    b.putStringArrayList(key, wifiList);

    //add readings to send to updateLoc
    readings.putExtras(b);

    //set code to indicate success and attach Intent
    setResult(RESULT_OK, readings);

    //call finish to return
    finish();
}

最后一部分通过 onActivityResult 返回到 UpdateLocation:

    @Override
        public void onActivityResult(int requestCode, int resultCode, Intent readings){
    super.onActivityResult(requestCode, resultCode, readings);

    //check if request code matches the one set above
    if(requestCode == REQUEST_READINGS){

        //check if sendData() in ScanLocate was successful
        if(resultCode == RESULT_OK){
            //get the readings from the Intent
            Log.v(TAG, "HERE");
            result = getIntent().getExtras().getStringArrayList(ScanLocate.key);
            Log.v(TAG, "HERE2");

            for(String s : result) {
                Log.v(TAG, "Location 5: " + s);
            }
        }else{
            //ScanLocate was unsuccessful
        }
    }
}

显示第一个“Here”，但它随后落在下一行，getStringArrayList()抛出空指针异常。

我已经查看了文档和之前的问题，但我看不出出了什么问题。

如有任何建议，我们将不胜感激，谢谢。

之前的问题:

startactivityforResult not working

How to pass an ArrayList to the StartActivityForResult activity

Answer 1

您不需要调用getIntent()，使用方法提供的参数:

result = readings.getStringArrayListExtra(ScanLocate.key);