iOS相册存图片不重复

原理：
相册存完之后，可以得到文件唯一名称。

  PHAssetChangeRequest *req = [PHAssetChangeRequest creationRequestForAssetFromImage:image];
        localIdentifier = req.placeholderForCreatedAsset.localIdentifier;//存储，并拿到返回的随机文件名称

根据这个名称，可以读取相册中的图片

phAsset = [PHAsset fetchAssetsWithLocalIdentifiers:@[localIdentifier] options:nil].firstObject;//尝试去相册拿图片
        if (phAsset != nil) {
//读取图片成功
}

所以封装一下存入相册的函数：

//保存图片到相册  mark 即唯一文件名
+(void)saveImagePhoto:(UIImage *)image mark:(NSString *)mark{
  // 1.权限验证
  PHAuthorizationStatus status = [PHPhotoLibrary authorizationStatus];
  if (status == PHAuthorizationStatusDenied) {
      TNSLog(@"请到【设置-隐私-照片】打开访问开关");
      dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.25 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
          [WJAlertUtils alertMsg:@"请到【设置-隐私-照片】打开访问开关" vc:nil];
      });
      return;
  } else if (status == PHAuthorizationStatusRestricted) {
       TNSLog(@"没有相册权限");
      dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.25 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
          [WJAlertUtils alertMsg:@"没有相册权限" vc:nil];
      });
      return;
  }
  //2.检查是否存过
  TNSLog(@"检查是否存过");
  NSString *localIdentifier = [[NSUserDefaults standardUserDefaults] objectForKey:mark];
  if (localIdentifier == nil) {//没存过，肯定要存一下
      [WJCommonUtils doSavePhotoAction:image withMark:mark];
  }else{
      PHAsset * asset = [PHAsset fetchAssetsWithLocalIdentifiers:@[localIdentifier] options:nil].firstObject;
      if (asset == nil) {//拿不到图片资源，可能被删除了，重新存一下
          [WJCommonUtils doSavePhotoAction:image withMark:mark];
      }else {
          dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.25 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
              [WJAlertUtils alertMsg:@"该图片已存在" vc:nil];
          });
          TNSLog(@"已经存在该资源");
      }
  }
}

存图片的函数

+(void)doSavePhotoAction:(UIImage *)image withMark:(NSString *)mark{
    NSError *err = nil;
    __block PHAsset *phAsset = nil;
    __block NSString *localIdentifier = nil;
    [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
        //写入图片到相册
        PHAssetChangeRequest *req = [PHAssetChangeRequest creationRequestForAssetFromImage:image];
        localIdentifier = req.placeholderForCreatedAsset.localIdentifier;//存储，并拿到返回的随机文件名称
    } error:&err];
    if (err) {
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.25 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            TNSLog(@"保存照片出错:%@",err.localizedDescription);
            [WJAlertUtils alertMsg:@"保存失败" vc:nil];
        });
    }else {
          phAsset = [PHAsset fetchAssetsWithLocalIdentifiers:@[localIdentifier] options:nil].firstObject;//尝试去相册拿图片
        if (phAsset != nil) {//成功拿到图片，说明存成功了，NSUserDefaults记录一下文件名
            [[NSUserDefaults standardUserDefaults] setObject:phAsset.localIdentifier forKey:mark];
            [[NSUserDefaults standardUserDefaults] synchronize];
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.25 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                [WJAlertUtils alertMsg:@"保存成功" vc:nil];
            });
        }
    }
}