Dex文件结构及对应的数据结构
string_ids_off字段：
typedef struct DexStringId {
u4 stringDataOff;
} DexStringId;
type_ids_off字段：
struct DexTypeId {
u4 descriptorIdx; /* index into stringIds list for type descriptor */
};
proto_ids_off字段：
struct DexProtoId{
u4 shortyIdx; /* index into stringIds forshorty descriptor */
u4 returnTypeIdx; /* index into typeIds list for return type */
u4 parametersOff; /* file offset to type_list for parameter types */
};
field_ids_off字段：
struct DexFieldId{
u2 classIdx; /* index into typeIds list for defining class */
u2 typeIdx; /* index into typeIds for field type */
u4 nameIdx; /* index into stringIds for field name */
};
method_ids_off字段：
struct DexMethodId{
u2 classIdx; /* index into typeIds list for defining class */
u2 protoIdx; /* index into protoIds for method prototype */
u4 nameIdx; /* index into stringIds for method name */
};
class_defs_off字段：
struct DexClassDef{
u4 classIdx; /* index into typeIds for this class */
u4 accessFlags;
u4 superclassIdx; /* index into typeIds for superclass */
u4 interfacesOff; /* file offset to DexTypeList */
u4 sourceFileIdx; /* index into stringIds for source file name */
u4 annotationsOff; /* file offset to annotations_directory_item */
u4 classDataOff; /* file offset to class_data_item */
u4 staticValuesOff; /* file offset to DexEncodedArray */
};