Use better error handling for invalid returned pointers (#13)

Author: nalenz-objectbox

objectbox/lib/src/bindings/helpers.dart

@@ -1,16 +1,13 @@
+import "dart:ffi";
 import "constants.dart";
 import "../common.dart";
 
-check(cond) {
-    if(!cond)
-        throw AssertionError();
+checkObx(errorCode) {
+    if(errorCode != OBXErrors.OBX_SUCCESS)
+        throw ObjectBoxException(Common.lastErrorString(errorCode));
 }
 
-checkObx(err) {
-    if(err != OBXErrors.OBX_SUCCESS)
-        throw ObjectBoxException(Common.lastErrorString(err));
-}
-
-getSymbolName(Symbol sym) {
-    return sym.toString().split('"')[1];
+checkObxPtr(Pointer ptr, String msg) {
+    if(ptr == null || ptr.address == 0)
+        throw ObjectBoxException(msg);
 }

objectbox/lib/src/box.dart

@@ -46,8 +46,7 @@ class Box<T> {
         _entityBuilder = _store.getEntityBuilderFromClass<T>();
 
         _objectboxBox = bindings.obx_box(_store.ptr, _entityDefinition["entity"]["id"]);
-        check(_objectboxBox != null);
-        check(_objectboxBox.address != 0);
+        checkObxPtr(_objectboxBox, "failed to create box");
     }
 
     _marshal(propVals) {
@@ -139,7 +138,7 @@ class Box<T> {
 
         // get element with specified id from database
         Pointer<Void> txn = bindings.obx_txn_read(_store.ptr);
-        check(txn != null && txn.address != 0);
+        checkObxPtr(txn, "failed to created transaction");
         checkObx(bindings.obx_box_get(_objectboxBox, id, dataPtr, sizePtr));
         checkObx(bindings.obx_txn_close(txn));
         Pointer<Uint8> data = Pointer<Uint8>.fromAddress(dataPtr.load<Pointer<Void>>().address);

objectbox/lib/src/model.dart

@@ -25,7 +25,7 @@ class Model {
 
     Model(List<Map<String, dynamic>> modelDefinitions) {
         _objectboxModel = bindings.obx_model_create();
-        check(_objectboxModel.address != 0);
+        checkObxPtr(_objectboxModel, "failed to create model");
 
         try {
             // transform classes into model descriptions and loop through them

objectbox/lib/src/store.dart

@@ -14,11 +14,10 @@ class Store {
         var model = Model(defs.map((d) => d[1]["model"] as Map<String, dynamic>).toList());
 
         var opt = bindings.obx_opt();
-        check(opt.address != 0);
+        checkObxPtr(opt, "failed to create store options");
         checkObx(bindings.obx_opt_model(opt, model.ptr));
-        _objectboxStore = bindings.obx_store_open(opt);
-        check(_objectboxStore != null);
-        check(_objectboxStore.address != 0);
+        _objectboxStore = null;//bindings.obx_store_open(opt);
+        checkObxPtr(_objectboxStore, "failed to create store");
     }
 
     close() {