我试图隐藏表视图,直到加载所有数据.我发现了这个问题：

UITableView – hide all groups/cells while data is loading

他们说将部分设置为0直到加载所有数据,然后重新加载单元格和表格视图,但他们没有详细说明如何操作.

非常感谢

你可以隐藏你的桌面视图

[self.tableView setHidden:YES];

直到您获得所有数据并使其可见

[self.tableView setHidden:NO];

我遇到了下一个错误,无法理解如何解决它.

Can’t resolve all parameters for AuthenticationService: ([object Object],?,[object Object])

我已经检查了几乎每个主题,并尝试了多种方法来解决它,但仍然无法在第二天击败它.

我试图像这样在appService中注入第一个authService但是得到了同样的错误

@Inject(forwardRef(() => AuthenticationService)) public authService: AuthenticationService

我检查了所有DI和服务内部的导入顺序,在我看来一切都是正确的

如果有人可以帮我处理它,我很感激.

Angular 4.0.0

AuthService

import { Injectable } from '@angular/core';
import {Http,Headers,Response} from '@angular/http';
import 'rxjs/add/operator/toPromise';
import {Observable} from 'rxjs/Rx';

import {AppServices} from "../../app.services";
import {Router} from "@angular/router";

@Injectable()
export class AuthenticationService {
  public token: any;

  constructor(
    private http: Http,private appService: AppServices,private router: Router
  ) {
    this.token = localStorage.getItem('token');
  }

  login(username: string,password: string): Observable<boolean> {
    let headers = new Headers();
    let body = null;
    headers.append("Authorization",("Basic " + btoa(username + ':' + password)));

    return this.http.post(this.appService.api + '/login',body,{headers: headers})
      .map((response: Response) => {
        let token = response.json() && response.json().token;
        if (token) {
          this.token = token;
          localStorage.setItem('Conform_token',token);
          return true;
        } else {
          return false;
        }
      });
  }

  logout(): void {
    this.token = null;
    localStorage.removeItem('Conform_token');
    this.router.navigate(['/login']);
  }
}

应用服务

import {Injectable} from '@angular/core';
import {Headers,Http,RequestOptions} from '@angular/http';
import {Router} from "@angular/router";
import {AuthenticationService} from "./auth/auth.service";

import 'rxjs/add/operator/toPromise';
import {Observable} from 'rxjs/Rx';

@Injectable()

export class AppServices {

  api = '//endpoint/';

  public options: any;
  constructor(
    private http: Http,private router: Router,public authService: AuthenticationService // doesn't work
  //  @Inject(forwardRef(() => AuthenticationService)) public authService: AuthenticationService // doesn't work either
      ) {
        let head = new Headers({
      'Authorization': 'Bearer ' + this.authService.token,"Content-Type": "application/json; charset=utf8"
    });
    this.options = new RequestOptions({headers: head});
  }

  // ====================
  //    data services
  // ====================

  getData(): Promise<any> {
    return this.http
      .get(this.api + "/data",this.options)
      .toPromise()
      .then(response => response.json() as Array<Object>)
      .catch((err)=>{this.handleError(err);})
  }

应用模块

import { browserModule } from '@angular/platform-browser';
import { browserAnimationsModule } from '@angular/platform-browser/animations';

import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
import {BaseRequestOptions,HttpModule} from '@angular/http';

import { MaterialModule} from '@angular/material';
import {FlexLayoutModule} from "@angular/flex-layout";
import 'hammerjs';

import { routing,appRoutingProviders }  from './app.routing';
import { AppServices } from './app.services';
import {AuthGuard} from "./auth/auth.guard";
import {AuthenticationService} from "./auth/auth.service";

import {AppComponent} from './app.component';
import {AuthComponent} from './auth/auth.component';
import {NotFoundComponent} from './404/not-found.component';
import { HomeComponent } from './home/home.component';

@NgModule({
  declarations: [
    AppComponent,AuthComponent,NotFoundComponent,HomeComponent
  ],imports: [
    browserModule,browserAnimationsModule,FormsModule,HttpModule,routing,MaterialModule,FlexLayoutModule
  ],providers: [AppServices,AuthGuard,AuthenticationService],bootstrap: [AppComponent]
})
export class AppModule { }

AppServices和AuthenticationService之间存在循环依赖关系 – 这与Angular使用的构造函数注入无法实现.

你可以使用

export class AuthenticationService {
  public token: any;
  appService: AppServices;
  constructor(
    private http: Http,// private appService: AppServices,injector:Injector;
    private router: Router
  ) {
    setTimeout(() => this.appService = injector.get(AppServices));
    this.token = localStorage.getItem('token');
  }

另见DI with cyclic dependency with custom HTTP and ConfigService

要避免使用setTimeout,您还可以从AppService的构造函数中设置AuthenticationService.appService(或者相反)

根据apple objective-c文档,NSObject使用C指针来跟踪它们.我对iOS很新,并且将NSObjects上的指针操作与C指针进行比较会让人感到困惑.
例如：

Nsstring *string1 = @"This is a string";
Nsstring *string2;
string2 = string 1;

在C中,(如果我错了请纠正我)this = b / w 2指针使它们指向相同的“指针”.这意味着更改string1也应该更改string2.但它似乎没有像这样工作,并且Nsstrings无论如何都是严格不变的,所以这增加了一些混乱.

string1 = @"new string";

如果这些指针像C指针一样操作,那么这不应该改变string2,因为它指向与string1相同的位置.此外,在C中,必须先将指针指定给指针对象才能取消引用.此规则似乎不适用于NSObjects.什么是’@’在做什么？最后,为什么我没有看到NSObjects的解引用发生如下：

*string1 = @"modifying the string"; //shouldn't this be how to access the contents of the pointer string1 if it operates like a c pointer?

有人可以对Objective-C指针下的内容以及它们与C指针的比较和对比有所了解吗？任何帮助将不胜感激.

您将在C中获得与Objective-C中相同的行为：如果您这样做

char *a = "hello";
char *b = a;
b = "world";

然后a不会改变.当对象可变时,对多个指针指向的公共对象所做的更改将变为可见. Nsstring和C字符串文字都不可变,所以让我们构建一个不同的例子：

NSMutableString *string1 = [NSMutableString string:@"This is a string"];
NSMutableString *string2;
string2 = string1;
NSLog(string1);
NSLog(string2);
[string1 appendString:@" (a very long one!)"];
NSLog(string1);
NSLog(string2);

现在string2“看到”对string1所做的更改,因为该对象是可变的.

C中的类似示例如下所示：

char[] a = "hello";
char b = a;
printf("%s %s\n",a,b);
strcpy(b,"world");
printf("%s %s\n",b);

如何使用此代码将对象添加到NSArray？尝试执行此操作时出现此错误消息.

NSArray *shoppingList = @[@"Eggs",@"Milk"];
Nsstring *flour = @"Flour";
[shoppingList addobject:flour];
shoppingList += @["Baking Powder"]

错误信息

/Users/xxxxx/Documents/iOS/xxxxx/main.m:54:23: No visible @interface for 'NSArray' declares the selector 'addobject:'

请指教.谢谢.

addobject适用于NSMutableArray,而不适用于NSArray,它是不可变的.

如果您可以控制您创建的数组,请使shoppingList NSMutableArray：

NSMutableArray *shoppingList = [@[@"Eggs",@"Milk"] mutablecopy];
[shoppingList addobject:flour]; // Works with NSMutableArray

否则,使用效率较低

shoppingList = [shoppingList arrayByAddingObject:flour]; // Makes a copy

是否有任何方法可以在其视图的“底部”添加子视图,例如当您使用图层时z = 0？我需要这个,因为当我产生物体时,它们需要在另一张照片下,而不是在上面.

UIView的子视图的排序方式是数组的最后一个是最前面的一个,然后第一个(索引0)是后面的那个.所以,要将它插入“底部”,这样做就足够了：

[view insertSubview:aView atIndex:0]