Java 如何在android中使用gson序列化具有自定义对象属性的类?
我想使用Gson库序列化和存储一个名为“Battery”的自定义类的对象。在Battery类中,我定义了另一个自定义对象的数组,即“Cannon”。以下是我的两门课: Cannon.java:Java 如何在android中使用gson序列化具有自定义对象属性的类?,java,android,object,sharedpreferences,gson,Java,Android,Object,Sharedpreferences,Gson,我想使用Gson库序列化和存储一个名为“Battery”的自定义类的对象。在Battery类中,我定义了另一个自定义对象的数组,即“Cannon”。以下是我的两门课: Cannon.java: import android.widget.ImageView; public class Cannon { private String id; // used for object storage private int number; // Cannon number in bat
import android.widget.ImageView;
public class Cannon {
private String id; // used for object storage
private int number; // Cannon number in battery
private ImageView icon;
private long utmEast, utmNorth; // Used to define cannon global location
private boolean isBase; // Defines if the cannon is base
private double flyingTime;
private int angle, side;
public Cannon() {
}
public Cannon(String id, int number, ImageView icon, String connectionNumber){
this.id = id;
this.number = number;
this.icon = icon;
this.connectionNumber = connectionNumber;
}
public String getId() {
return this.id;
}
public int getNumber() {
return this.number;
}
public ImageView getIcon() {
return this.icon;
}
public long getUtmNorth() {
return utmNorth;
}
public void setUtmNorth(long utmNorth) {
this.utmNorth = utmNorth;
}
public long getUtmEast() {
return utmEast;
}
public void setUtmEast(long utmEast) {
this.utmEast = utmEast;
}
public void setAsBase(boolean isBase) {
this.isBase = isBase;
}
public boolean isBaseCannon() {
return isBase;
}
}
Battery.java:
public class Battery {
private String id; // used for object storage
private final Cannon cannons[] = new Cannon[6];
public Battery(String id){
this.id = id;
}
public String getId() {
return this.id;
}
public Cannon[] getCannons() {
return cannons;
}
public void setCannon(Cannon cannon, int position) {
this.getCannons()[position] = cannon;
}
public Cannon getCannon(String cannonId) {
for (Cannon cn: this.getCannons()) {
if (cn.getId() == cannonId) {
return cn;
}
}
return null;
}
public Cannon getCannon(int position) {
return getCannons()[position];
}
}
这是我的首选项类,它使用共享首选项存储特定于应用程序的字段,包括使用Gson库的电池对象
import android.content.Context;
import android.content.SharedPreferences;
import com.google.gson.Gson;
import net.adeveloper.firecontrol.data.Battery;
/** stores the user object in SharedPreferences */
public class Preferences {
/** This application's preferences label */
private static final String PREFS_NAME = "net.adeveloper.firecontrol.preferences";
/** This application's preferences */
private static SharedPreferences settings;
/** This application's settings editor*/
private static SharedPreferences.Editor editor;
/** Constructor takes an android.content.Context argument*/
private final Gson gson = new Gson();
/**************************************************/
private final Battery battery = new Battery(Reference.BATTERY_ID);
/**************************************************/
public Preferences(Context ctx){
if(settings == null){
settings = ctx.getSharedPreferences(PREFS_NAME,
Context.MODE_PRIVATE );
}
/*
* Get a SharedPreferences editor instance.
* SharedPreferences ensures that updates are atomic
* and non-concurrent
*/
editor = settings.edit();
// Initialize battery
String battery_json = gson.toJson(battery);
// store in SharedPreferences
String id = battery.getId(); // get storage key
editor.putString(id, battery_json);
editor.commit();
}
public Battery getBattery() {
String battery_json = settings.getString(Reference.BATTERY_ID, "");
Battery battery = gson.fromJson(battery_json, Battery.class);
return battery;
}
//...
}
我使用MainActivity中的首选项对象存储应用程序字段:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//...
/********************************************************/
prefs = new Preferences(this.getApplicationContext());
/********************************************************/
但是,当它启动应用程序时崩溃并输出Gson StackOverflower错误:
02-10 16:39:03.110 13187-13187/net.adeveloper.firecontrol E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.StackOverflowError
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:375)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:380)
at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:355)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:117)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:72)
at com.google.gson.Gson.getAdapter(Gson.java:356)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.<init>(ReflectiveTypeAdapterFactory.java:82)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:81)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:118)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:72)
at com.google.gson.Gson.getAdapter(Gson.java:356)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.<init>(ReflectiveTypeAdapterFactory.java:82)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.cr
现在stackoverflow异常已经消失,但是现在出现了另一个问题,那就是toJson()和fromJson()方法返回的Json字符串为null,当我使用Preference object通过battery类设置cannon对象时,实际上无法再次访问它,它返回null:
Cannon cannon = new Cannon(id, number, icon, phone);
prefs.getBattery().setCannon(cannon, position);
if (prefs.getBattery().getCannons() == null) {
Log.d("Cannon", "NULL");
} else {
for (Cannon cn: prefs.getBattery().getCannons()) {
Log.d("Cannon", cn + "");
}
}
产出:
Cannon: null
Cannon: null
Cannon: null
Cannon: null
Cannon: null
Cannon: null
我没有得到你想要的东西??但是你可以
1.将objec转换为json
2.保存在SharedReference中,然后
3.同样可以从首选项获取json
4.并将其转换为java对象 范例
class Test
{
int id = 1;
int name = "testing";
}
class Main{
Test t = new Test;
String s = ConvertToJson(t);
/* save the string in SharedPreferecne and you can get any
time string and convert again for eg.*/
Test t2 = ConvertToTest(TestJsonSring);
public Test ConvertToTest(String json) {
return new Gson().fromJson(json, Test.class);
}
public String ConvertToJson(Object object) {
Gson gson = new Gson();
return gson.toJson(object);
}
}
尝试在这两个类中实现Serializable接口,并在Battery类中创建一个默认构造函数。我这样做了,现在它输出一个致命的异常。如您所见,我已在Preferences类构造函数中将我的Battery类对象转换为Json,并通过方法“getBattery”将其取回.问题是Cannon类的
ImageView
。您不能直接将ImageView转换为json字符串。正确的问题是ImageView,我尝试过使用ImageView,但没有ImageView,它工作正常。为什么我们必须在类中只使用基本数据类型,正如您所看到的,我定义了一个自定义对象(Cannon数组)在我的电池课上,我听说它不会有任何问题。为什么与图像视图不同?图像视图包含的显示元素和位图格式完全不同,如果要存储IamgeView,请转到文件系统并将路径指定给字符串变量。GSON是专门为基本数据类型设计的。
class Test
{
int id = 1;
int name = "testing";
}
class Main{
Test t = new Test;
String s = ConvertToJson(t);
/* save the string in SharedPreferecne and you can get any
time string and convert again for eg.*/
Test t2 = ConvertToTest(TestJsonSring);
public Test ConvertToTest(String json) {
return new Gson().fromJson(json, Test.class);
}
public String ConvertToJson(Object object) {
Gson gson = new Gson();
return gson.toJson(object);
}
}