一行代码解决：服务器返回null导致应用崩溃

来源：互联网发布：通关宝典软件编辑：程序博客网时间：2024/05/17 00:08

背景1：是否有这样一种感受，你的应用会崩溃，查看崩溃日志或者调试发现后台返回的数据字段里面有null，这个null居然还是导致应用崩溃的“元凶”。

背景2：服务器返回的字段名和不一致，如果model属性少，你可以一个个对应赋值，多了肯定都会想到用运行时机制来赋值:

[selfsetValue:temDic[key]forKeyPath:key],这时候需要对两个地方的字段做映射。

思路:1、先判断是否需要映射 2、把服务器返回的数据赋给model 3、model属性null检查（不同类型赋不同值，并不是把所有null都赋@""）4、这个写法应该适应所有自定义的类型，所有给NSObject 加一个Category。

#import"NSObject+runtime.h"

@implementation NSObject (runtime)

- (void)fetchValueFormNetDict:(NSDictionary *)dic andMapDic:(NSDictionary *)MapDic{

NSArray *properties = [selfgetAllProperties];

//需要映射

if (MapDic !=nil) {

NSArray *allKeys = dic.allKeys;

NSMutableDictionary *temDic = [NSMutableDictionarydictionaryWithCapacity:allKeys.count];

for (int i = 0; i < allKeys.count; i ++) {

NSString *key = allKeys[i];

[temDicsetObject:dic[key]forKey:MapDic[key]];

}

//遍历属性数组

for (NSString *key in properties) {

//判断字典中是否包含这个key

[selfsetValue:temDic[key]forKeyPath:key];

}

else//不需要映射

{

//遍历属性数组

for (NSString *key in properties) {

//判断字典中是否包含这个key

[selfsetValue:dic[key]forKeyPath:key];

}

//null或者 nil处理

[selfnullDeal];

}

//获取所有的属性名

- (NSArray *)getAllProperties

{

u_int count;

objc_property_t *properties =class_copyPropertyList([selfclass], &count);

NSMutableArray *propertiesArray = [NSMutableArrayarrayWithCapacity:count];

for (int i = 0; i<count; i++)

{

constchar* propertyName =property_getName(properties[i]);

[propertiesArrayaddObject: [NSStringstringWithUTF8String: propertyName]];

}

free(properties);

return propertiesArray;

}

-(void)nullDeal

{

//找到属性对应的类型

NSDictionary *typeDic = [selfclassPropsFor:[selfclass]];

NSArray *arr = typeDic.allKeys;//所有属性名字

for (int i = 0; i < arr.count; i++) {

//属性类型名字（字符串格式）

NSString *typeString = typeDic[arr[i]];

if ([[selfvalueForKey:arr[i]]isKindOfClass:[NSNullclass]] || [selfvalueForKey:arr[i]] ==nil) {

if ([typeStringisEqualToString:@"NSArray"]) {

[selfsetValue:@[]forKey:arr[i]];

}

if ([typeStringisEqualToString:@"NSString"]) {

[selfsetValue:@""forKey:arr[i]];

}

if ([typeStringisEqualToString:@"NSNumber"]) {

[selfsetValue:@0forKey:arr[i]];

}

if ([typeStringisEqualToString:@"NSDictionary"]) {

[selfsetValue:@{}forKey:arr[i]];

}

if ([typeStringisEqualToString:@"B"]) {

[selfsetValue:0forKey:arr[i]];

}

if ([typeStringisEqualToString:@"f"]) {

[selfsetValue:0forKey:arr[i]];

}

if ([typeStringisEqualToString:@"d"]) {

[selfsetValue:0forKey:arr[i]];

}

if ([typeStringisEqualToString:@"i"]) {

[selfsetValue:0forKey:arr[i]];

}

//获取属性名称数组

- (NSDictionary *)classPropsFor:(Class)klass

{

if (klass ==NULL) {

returnnil;

}

NSMutableDictionary *results = [[NSMutableDictionaryalloc]init];

unsignedint outCount, i;

objc_property_t *properties = class_copyPropertyList(klass, &outCount);

for (i =0; i < outCount; i++) {

objc_property_t property = properties[i];

constchar *propName =property_getName(property);

if(propName) {

constchar *propType =getPropertyType(property);

NSString *propertyName = [NSStringstringWithUTF8String:propName];

NSString *propertyType = [NSStringstringWithUTF8String:propType];

NSLog(@"propertyName %@ propertyType %@", propertyName, propertyType);

[resultssetObject:propertyTypeforKey:propertyName];

}

free(properties);

// returning a copy here to make sure the dictionary is immutable

return [NSDictionarydictionaryWithDictionary:results];

}

//获取属性类型的方法 c语言写法 T@"NSString",C,N,V_name Tf,N,V__float

staticconstchar *getPropertyType(objc_property_t property) {

constchar *attributes =property_getAttributes(property);

printf("attributes=%s\n", attributes);

char buffer[1 + strlen(attributes)];//多一个结束符号

strcpy(buffer, attributes);

char *state = buffer, *attribute;

while ((attribute =strsep(&state,",")) !=NULL) {

if (attribute[0] == 'T' && attribute[1] != '@') {

NSString *name = [[NSStringalloc]initWithBytes:attribute +1length:strlen(attribute) - 1encoding:NSASCIIStringEncoding];

return (constchar *)[namecStringUsingEncoding:NSASCIIStringEncoding];

}

elseif (attribute[0] == 'T' && attribute[1] == '@' &&strlen(attribute) ==2) {

// it's an ObjC id type:

return"id";

}

elseif (attribute[0] == 'T' && attribute[1] == '@') {

// it's another ObjC object type:

NSString *name = [[NSStringalloc]initWithBytes:attribute +3length:strlen(attribute) - 4encoding:NSASCIIStringEncoding];

return (constchar *)[namecStringUsingEncoding:NSASCIIStringEncoding];

}

return"";

}

@end

基本工作差不多完了，现在来自定义一个类型试试：

#import<Foundation/Foundation.h>

@interface UserModel :NSObject

@property(nonatomic,copy)NSString *name;

@property(nonatomic,copy)NSString *home;

@property(nonatomic,strong)NSNumber *old;

@property(nonatomic,strong)NSArray *arr;

@property(nonatomic,strong)NSDictionary *dic;

@property(nonatomic,assign)BOOL isBoll;

-(instancetype)initWithDic:(NSDictionary *)dic;

@end

#import"UserModel.h"

#import"NSObject+runtime.h"

@implementation UserModel

-(instancetype)initWithDic:(NSDictionary *)dic

{

if (self == [superinit]) {

// dic网络数据 mapDic 映射之后的字典

[selffetchValueFormNetDict:dicandMapDic:[selfmapDic]];

}

returnself;

}

////设置映射字典格式：@"网络数据字段名":@"model属性名"

//如果服务器返回的字段和 model的属性名字不一致则需要映射返回映射字典否则返回nil表示不需要映射

-(NSDictionary *)mapDic

{

return@{@"wzcName":@"name",@"wzcAddress":@"home",@"isbol":@"isBoll"};

}

@end

实列化一个UserModel对象

NSDictionary *data1 = @{@"wzcName":[NSNullnull],@"wzcAddress":@"杭州市西湖区",@"isbol":@1};

UserModel *model1 = [[UserModelalloc]initWithDic:data1];

结果如下：

这样在后面数据操作不会崩溃了。

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