Add player-read-write-nbt.java

Signed-off-by: Forgejo <forgejo@mctaylors.ddns.net>

player-read-write-nbt.java

@@ -0,0 +1,96 @@
+package org.example.examplemod.mixin;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.UUID;
+import net.minecraft.entity.player.PlayerEntity;
+import net.minecraft.nbt.NbtCompound;
+import net.minecraft.nbt.NbtElement;
+import net.minecraft.nbt.NbtList;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Unique;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+@Mixin(PlayerEntity.class)
+public abstract class PlayerEntityMixin {
+    @Unique
+    public List<MyObject> myList = new ArrayList<>();
+
+    // I recommend you read writeMyDataToNbt first before trying to understand readCustomDataFromNbt
+    @Inject(method = "readCustomDataFromNbt", at = @At("TAIL"))
+    public void readMyDataFromNbt(NbtCompound playerNbt, CallbackInfo ci) {
+        // read our serialized list
+        NbtList myListNbt = playerNbt.getList("MyList", NbtElement.COMPOUND_TYPE);
+
+        // iterate over its items
+        for (int i = 0; i < myListNbt.size(); i++) {
+            // construct the object we need to deserialize
+            MyObject myObject = new MyObject();
+            // read the serialized object
+            NbtCompound myObjectNbt = myListNbt.getCompound(i);
+
+            // read properties that are supported and write them to our object
+            myObject.mySupportedObject = myObjectNbt.getInt("MySupportedObject");
+            // if mySupportedList was int[], we could've just used getIntArray, but since it's a List<Integer>, we have to do something else
+            Arrays.stream(myObjectNbt.getIntArray("MySupportedList")).forEach(myInteger -> myObject.mySupportedList.add(myInteger));
+
+            // read properties that aren't supported
+            MyAnotherObject myAnotherObject = new MyAnotherObject();
+            NbtCompound myNotSupportedObjectNbt = myObjectNbt.getCompound("MyNotSupportedObject");
+            myAnotherObject.myUuid = myNotSupportedObjectNbt.getUuid("MyUUID");
+
+            // write them to our object
+            myObject.myNotSupportedObject = myAnotherObject;
+
+            // finally, add our constructed object to our list
+            myList.add(myObject);
+        }
+    }
+
+    @Inject(method = "writeCustomDataToNbt", at = @At("TAIL"))
+    public void writeMyDataToNbt(NbtCompound playerNbt, CallbackInfo ci) {
+        // create a new NBT record for our list
+        NbtCompound myListNbt = new NbtCompound();
+
+        // you can use a regular for-loop if you want, there's no difference. FabricMC wiki uses Iterable#forEach so that's why it's used here
+        myList.forEach(myObject -> {
+            // create a new NBT record for our object
+            NbtCompound myObjectNbt = new NbtCompound();
+            // write properties that are supported
+            myObjectNbt.putInt("MySupportedObject", myObject.mySupportedObject);
+            myObjectNbt.putIntArray("MySupportedList", myObject.mySupportedList);
+
+            // write myNotSupportedObject, which doesn't have a method for reading/writing in NbtCompound
+            NbtCompound myNotSupportedObjectNbt = new NbtCompound();
+            myNotSupportedObjectNbt.putUuid("MyUUID", myObject.myNotSupportedObject.myUuid);
+
+            // you can nest NBT records infinitely
+            myObjectNbt.put("MyNotSupportedObject", myNotSupportedObjectNbt);
+
+            // put our newly created record into the list record
+            myListNbt.put("MyObject", myObjectNbt);
+        });
+
+        // finally, put our list record into the player's NBT
+        playerNbt.put("MyList", myListNbt);
+    }
+}
+
+// these classes are in the same file for simplicity sake. you should make them public and put them in their own files
+class MyObject {
+    // the NbtCompound class has methods to write and read this object - putInt and getInt
+    public int mySupportedObject = 0;
+    // there are even some supported lists! this one uses putIntArray
+    public List<Integer> mySupportedList = new ArrayList<>();
+    // if there's no method in NbtCompound to handle your class,
+    // you'll have to write their properties separately and, when reading, construct the objects using the written properties
+    // just how are we currently doing with this object
+    public MyAnotherObject myNotSupportedObject;
+}
+
+class MyAnotherObject {
+    public UUID myUuid;
+}