android - instanceof JSONObject 不检测 JSONObject

Question

我发现 variable instanceof JSONObject 有奇怪的行为。我有以下代码:

Object value;
try {
    value = customer.get(key);
    Log.v("type", String.valueOf(value.getClass())); // Returns JSONObject
    if (value instanceof JSONObject) {
        // Handle JSONObject
    } else {
        String text = (String)value;  // HERE COMES THE ERROR
        // Handle String
    }

当日志返回 JSONObject 时，它以异常结束:

01-15 12:24:46.206 4111-4111/cz.jacon.goldympos V/CUSTOMER type: class org.json.JSONObject$1
01-15 12:24:46.207 4111-4111/cz.jacon.goldympos D/AndroidRuntime: Shutting down VM
01-15 12:24:46.279 4111-4111/cz.jacon.goldympos E/AndroidRuntime: FATAL EXCEPTION: main
                   Process: cz.jacon.goldympos, PID: 4111
                   java.lang.RuntimeException: Unable to start activity ComponentInfo{cz.jacon.goldympos/cz.jacon.goldympos.activities.CustomerDetailActivity}: java.lang.ClassCastException: org.json.JSONObject$1 cannot be cast to java.lang.String
                            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
                            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
                            at android.app.ActivityThread.access$800(ActivityThread.java:151)
                            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
                            at android.os.Handler.dispatchMessage(Handler.java:102)
                            at android.os.Looper.loop(Looper.java:135)
                            at android.app.ActivityThread.main(ActivityThread.java:5254)
                            at java.lang.reflect.Method.invoke(Native Method)
                            at java.lang.reflect.Method.invoke(Method.java:372)
                            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
                            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
                            Caused by: java.lang.ClassCastException: org.json.JSONObject$1 cannot be cast to java.lang.String
                            at cz.jacon.goldympos.activities.CustomerDetailActivity.getText(CustomerDetailActivity.java:260)
                            at cz.jacon.goldympos.activities.CustomerDetailActivity.createLayout(CustomerDetailActivity.java:222)
                            at cz.jacon.goldympos.activities.CustomerDetailActivity.onCreate(CustomerDetailActivity.java:92)
                            at android.app.Activity.performCreate(Activity.java:5990)
                            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
                        ...........

我错过了什么吗？看起来很简单...

编辑:json

我使用的 json 示例。第一个是 JSONObject，第二个是 Integer(可以转换为 String)

{
"viewers_edit_time":
    {
     "date":"2016-01-14 22:53:56.000000",
     "timezone_type":3,
     "timezone":"Asia/Kolkata"
    },
"viewers_edit_users_id":1
}

That's full json ，和我用的完全一样。再说一遍:

Log.v("type", String.valueOf(value.getClass())); // Returns JSONObject not JSONObject$1

---

已解决

问题解决了。从我有问题发布的完整 JSON 中:

"viewers_postcode": null

我没有注意到 null 不在引号中......在我认为我是“null”之前，它是 String。我被错误消息弄错了，它说 JSONObject$1 cannot be cast to String。但是 JSONObject$1 是 NULL(感谢@Natix)

也许它可以帮助其他有相同错误消息的人。

Answer 1

您需要特别注意日志消息。重点是 org.json.JSONObject$1 与 org.json.JSONObject 类不相同。

$1 后缀表示它是 JSONObject 类的匿名内部类。如果你看the source ，你会发现这段代码:

public static final Object NULL = new Object() {
    @Override public boolean equals(Object o) {
        return o == this || o == null; // API specifies this broken equals implementation
    }
    @Override public String toString() {
        return "null";
    }
};

这意味着您应该首先检查您的值是否等于此 NULL 常量:

Object value = customer.get(key);
if (value == JSONObject.NULL {
    // Handle NULL
} else if (value instanceof JSONObject) {
    // Handle JSONObject
} else {
    // Handle String
}