gson NoSuchFieldException误差

Question

我正在尝试将自定义对象转换为JSON，然后将其保存到SharedPreferences中。当我尝试这样做时，应用程序会崩溃，从而产生一个NoSuchFieldException错误。

下面是代码：

User myUser= new User("a", "b", 2, getApplicationContext());
SharedPreferences.Editor prefsEditor = mPrefs.edit();
Gson gson = new Gson();
String json = gson.toJson(myUser);
prefsEditor.putString(myUser.getUserPhone(), json);
prefsEditor.commit();

我认为问题在于gson.toJson转换，因为当我评论它时，应用程序不再崩溃。

有什么建议吗？谢谢

Logcat:

   java.lang.AssertionError: java.lang.NoSuchFieldException: ASCENDING
        at com.google.gson.internal.bind.TypeAdapters$EnumTypeAdapter.<init>(TypeAdapters.java:791)
        at com.google.gson.internal.bind.TypeAdapters$30.create(TypeAdapters.java:817)
        at com.google.gson.Gson.getAdapter(Gson.java:423)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:115)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:164)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:100)
        at com.google.gson.Gson.getAdapter(Gson.java:423)
        at com.google.gson.internal.bind.CollectionTypeAdapterFactory.create(CollectionTypeAdapterFactory.java:53)
        at com.google.gson.Gson.getAdapter(Gson.java:423)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:115)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:164)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:100)
        at com.google.gson.Gson.getAdapter(Gson.java:423)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:115)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:164)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:100)
        at com.google.gson.Gson.getAdapter(Gson.java:423)
        at com.google.gson.internal.bind.MapTypeAdapterFactory.create(MapTypeAdapterFactory.java:126)
        at com.google.gson.Gson.getAdapter(Gson.java:423)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:115)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:164)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:100)
        at com.google.gson.Gson.getAdapter(Gson.java:423)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:115)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:164)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:100)
        at com.google.gson.Gson.getAdapter(Gson.java:423)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:115)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:164)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:100)
        at com.google.gson.Gson.getAdapter(Gson.java:423)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:115)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:164)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:100)
        at com.google.gson.Gson.getAdapter(Gson.java:423)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:115)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:164)
        at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:100)
        at com.google.gson.Gson.getAdapter(Gson.java:423)
        at com.google.gson.Gson.toJson(Gson.java:661)
        at com.google.gson.Gson.toJson(Gson.java:648)
        at com.google.gson.Gson.toJson(Gson.java:603)

Answer 1

首先，您应该从用户类构造函数中删除getApplicationContext()，因为对于json，您不能编写上下文对象。

User myUser= new User("a", "b", 2);
SharedPreferences.Editor prefsEditor = mPrefs.edit();
Gson gson = new Gson();
String json = gson.toJson(myUser);
prefsEditor.putString(myUser.getUserPhone(), json);
prefsEditor.commit();

如果要使用getApplicationContext()，请创建另一个辅助构造函数。并在用户类中分配上下文的瞬态关键字。

private transient Context context;

如果在Java类中生成一个瞬态字段，GSON将在序列化和反序列化中忽略它。

Answer 2

若要使用Gson将模型或对象转换为字符串，您必须遵循以下步骤：

第一步:确保将Gson依赖项添加到应用程序gradle文件中。(如果没有添加，请按下面所示添加。)

compile 'com.google.code.gson:gson:2.8.2'

第二步:你的模型类

public class ModelClass {

String name;
String number;

public ModelClass() {
}

public ModelClass(String name, String number, Context context) {
    this.name = name;
    this.number = number;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getNumber() {
    return number;
}

public void setNumber(String number) {
    this.number = number;
 }
}

第三步:最后使用Gson将模型或对象转换为字符串。

ModelClass modelClass=new ModelClass("abc","45465545",MainActivity.this); // here we pass three parameters to ModelClass. ( name, number and context )
Gson gson = new Gson();
String jsonString=gson.toJson(modelClass);