将null对象转换为String

Question

我编写了一个android程序,用于从Web服务向tablerow加载值.但是一个值为null,所以我需要将它转换为字符串.有人可以告诉我这样做的方法.

try{                    

    SoapObject request = service.getRequest();
    SoapSerializationEnvelope envelope = service.getEnvelope(request);
    SoapObject response = service.getResponse(envelope);
    Log.i("Service Master", response.toString());
    int count = response.getPropertyCount();
    for (int i = 0; i < count; i++) {
        SoapObject result = (SoapObject) response.getProperty(i);
        DeleteuserDetails deleteuserDetails=new DeleteuserDetails();
        deleteuserDetails.setUserId(result.getPropertyAsString(4));
        deleteuserDetails.setUserName(result.getPropertyAsString(2));
        deleteuserDetails.setUserRole(result.getPropertyAsString(3));
        deleteuserDetails.setCreatedDate(result.getPropertyAsString(1));
        deleteuserDetails.setCreatedBy(result.getPropertyAsString(0));
        userdetail.add(deleteuserDetails);
    }

现在deleteuserDetails.setCreatedBy(result.getPropertyAsString(0));从webservice获取null值,所以我需要将其转换为字符串"null".

logcat的:

12-20 18:48:52.608: W/System.err(2174): java.lang.NullPointerException
12-20 18:48:52.608: W/System.err(2174):     at org.ksoap2.serialization.SoapObject.getPropertyAsString(SoapObject.java:165)
12-20 18:48:52.608: W/System.err(2174):     at com.mvss.admin.Deleteuser$deteUserIdLoad.doInBackground(Deleteuser.java:81)
12-20 18:48:52.608: W/System.err(2174):     at com.mvss.admin.Deleteuser$deteUserIdLoad.doInBackground(Deleteuser.java:1)
12-20 18:48:52.608: W/System.err(2174):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
12-20 18:48:52.608: W/System.err(2174):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
12-20 18:48:52.608: W/System.err(2174):     at java.util.concurrent.FutureTask.run(FutureTask.java:137)
12-20 18:48:52.608: W/System.err(2174):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
12-20 18:48:52.608: W/System.err(2174):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
12-20 18:48:52.608: W/System.err(2174):     at java.lang.Thread.run(Thread.java:1096)

Answer 1

而不是捕获异常或放置条件,使用 String.valueOf(result.getPropertyAsString(0));

它将调用参数的toString()方法并将其转换为String,如果result.getPropertyAsString(0)为null,则将其更改为"null"

Answer 2

result.getPropertyAsString(0)当属性内部为null时,单独将导致NPE.你的stacktrace指向SoapObject.getPropertyAsString(SoapObject.java:165)应该是什么

public String getPropertyAsString(int index) {
    PropertyInfo propertyInfo = (PropertyInfo) properties.elementAt(index);
    return propertyInfo.getValue().toString();
}

源 -什么时候会崩溃propertyInfo或者 propertyInfo.getValue()是null.

为了防止这种情况发生,您需要获取属性,而不是通过getPropertyAsString并通过getProperty手动将其转换为String.

您可以将其封装到某个实用程序方法中

public static String getPropertyAsString(SoapObject object, int index) {
    Object prop = object.getProperty(index);
    if(prop instanceof PropertyInfo) {
        prop = ((PropertyInfo)prop).getValue();
    }
    return String.valueOf(prop); // will make it "null" if it is null
}

然后呢

deleteuserDetails.setUserId(getPropertyAsString(result, getPropertyAsString(4)));
deleteuserDetails.setUserName(getPropertyAsString(result, getPropertyAsString(2)));
deleteuserDetails.setUserRole(getPropertyAsString(result, getPropertyAsString(3)));

Answer 3

用这个,

try {
    deleteuserDetails.setCreatedBy(result.getPropertyAsString(0).toString());
}
catch(Exception e) {
    deleteuserDetails.setCreatedBy("null");
}

Answer 4

试试这个:

deleteuserDetails.setCreatedBy(result.getPropertyAsString(0) == null ? "null": result.getPropertyAsString(0));

Answer 5

尽管这不是一个好习惯，但是您可以将空值与“”连接起来，使其成为字符串。

例如：

    String str=null;
    System.out.println((str+"").length()); /// prints 4