————-LoadingAlerter.h———–

//
//  LoadingAlerter.h
//  SdkModle
//
//  Created by Sean on 15/2/10.
//  Copyright (c) 2015年 Feiyu. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>

@interface LoadingAlerter : NSObject

- (id) initWithParentView:(UIView*)parentView;

- (void
 
) startAlert;

- (void) stopAlert;

@end

——LoadingAlerter.m——

//
//  LoadingAlerter.m
//  SdkModle
//
//  Created by Sean on 15/2/10.
//  Copyright (c) 2015年 Feiyu. All rights reserved.
//

#import "LoadingAlerter.h"

@interface LoadingAlerter()

@property (nonatomic) UIActivityIndicatorView* indicatorWaiting;
@property
 
 (nonatomic) UIView* viewAlert;
@property (nonatomic) UIView* viewParent;
@property (nonatomic) UILabel* labWaiting;
@property (copy, nonatomic) NSString* strWaiting;
@property (nonatomic) BOOL isStart;

@end

@implementation LoadingAlerter

//初始化
//parentView 父view
- (id) initWithParentView:(UIView*)parentView {

    if
 
(self = [super init]) {
        self.viewParent = parentView;
        self.isStart = NO;
    }
    return self;
}

//彈出框彈出
- (void) startAlert {
    if (self.isStart == YES) {
        return;
    }

    //-----設定彈出框-----

    self.viewAlert = [[UIView alloc] init];
    //設定顏色
    [self.viewAlert setBackgroundColor:[UIColor blackColor]];
    //設定透明度
    [self.viewAlert setAlpha:0.6];
    //設定圓角
    self.viewAlert.layer.cornerRadius = 10;
    //填充圖片時,如果加圓角,圖片會超出圓角框,即還是直角,得加一句masksToBounds
    self.viewAlert.layer.masksToBounds = YES;
    //設定邊框的寬度，當然可以不要
    self.viewAlert.layer.borderWidth = 0;
    //設定邊框的顏色
    self.viewAlert.layer.borderColor = [[UIColor grayColor] CGColor];
    //防止了控制元件佈局與自動佈局衝突
    [self.viewAlert setTranslatesAutoresizingMaskIntoConstraints:NO];
    //將彈出框加入到父view
    [self.viewParent addSubview:self.viewAlert];
    //給彈出框新增約束，涉及到自動佈局的知識;
    //給控制元件新增約束之前一定先要將其新增到父控制元件上，不然會報異常
    [self.viewAlert addConstraint:[NSLayoutConstraint constraintWithItem:self.viewAlert
        attribute:NSLayoutAttributeHeight
        relatedBy:NSLayoutRelationEqual
        toItem:nil
        attribute:NSLayoutAttributeHeight
        multiplier:1
        constant:80]];
    [self.viewAlert addConstraint:[NSLayoutConstraint constraintWithItem:self.viewAlert
        attribute:NSLayoutAttributeWidth
        relatedBy:NSLayoutRelationEqual
        toItem:nil
        attribute:NSLayoutAttributeWidth
        multiplier:1
        constant:200]];
    [self.viewParent addConstraint:[NSLayoutConstraint constraintWithItem:self.viewAlert
        attribute:NSLayoutAttributeCenterY   
        relatedBy:NSLayoutRelationLessThanOrEqual
        toItem:self.viewParent
        attribute:NSLayoutAttributeCenterY
        multiplier:1
        constant:0]];
    [self.viewParent addConstraint:[NSLayoutConstraint constraintWithItem:self.viewAlert
        attribute:NSLayoutAttributeCenterX
        relatedBy:NSLayoutRelationLessThanOrEqual
        toItem:self.viewParent
        attribute:NSLayoutAttributeCenterX
        multiplier:1
        constant:0]];


    //-----設定指示器-----

    self.indicatorWaiting =  [[UIActivityIndicatorView alloc] init];
    [self.indicatorWaiting setActivityIndicatorViewStyle:UIActivityIndicatorViewStyleWhite];
    [self.indicatorWaiting setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.viewAlert addSubview:self.indicatorWaiting];
    [self.viewAlert addConstraint:[NSLayoutConstraint constraintWithItem:self.indicatorWaiting
        attribute:NSLayoutAttributeTop
        relatedBy:NSLayoutRelationLessThanOrEqual
        toItem:self.viewAlert
        attribute:NSLayoutAttributeTop
        multiplier:1
        constant:40]];
    [self.viewAlert addConstraint:[NSLayoutConstraint constraintWithItem:self.indicatorWaiting
        attribute:NSLayoutAttributeCenterX
        relatedBy:NSLayoutRelationLessThanOrEqual
        toItem:self.viewAlert
        attribute:NSLayoutAttributeCenterX
        multiplier:1
        constant:0]];

    //-----設定文字框-----

    self.strWaiting = @"正在努力載入中...";
    self.labWaiting = [[UILabel alloc] init];
    self.labWaiting.text = self.strWaiting;
    self.labWaiting.textAlignment = NSTextAlignmentCenter;
    self.labWaiting.font = [UIFont fontWithName:@"Helvetica" size:14];
    [self.labWaiting setTextColor:[UIColor whiteColor]];
    [self.labWaiting setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.viewAlert addSubview:self.labWaiting];
    [self.viewAlert addConstraint:[NSLayoutConstraint constraintWithItem:self.labWaiting
        attribute:NSLayoutAttributeTop
        relatedBy:NSLayoutRelationLessThanOrEqual
        toItem:self.viewAlert
        attribute:NSLayoutAttributeTop
        multiplier:1
        constant:20]];
    [self.viewAlert addConstraint:[NSLayoutConstraint constraintWithItem:self.labWaiting
        attribute:NSLayoutAttributeCenterX
        relatedBy:NSLayoutRelationLessThanOrEqual
        toItem:self.viewAlert
        attribute:NSLayoutAttributeCenterX
        multiplier:1
        constant:0]];
    //開始動畫
    [self.indicatorWaiting startAnimating];
    self.isStart = YES;
}

//彈出框收起
- (void) stopAlert {
    //停止動畫
    [self.indicatorWaiting stopAnimating];
    //將彈出框從父view刪除
    [self.viewAlert removeFromSuperview];
    self.isStart = NO;
}

@end

使用方式
1.初始化的時候

self.loadingAlert = [[LoadingAlerter alloc] initWithParentView:self.view];

2.開始載入的時候

[self.loadingAlert startAlert];

3.結束載入的時候

[self.loadingAlert stopAlert];

附：自動佈局的用法
1.要給控制元件加約束，要先找到它的父控制元件，將約束新增到齊父控制元件上

[self.viewAlert addConstraint:[NSLayoutConstraint                 constraintWithItem:self.indicatorWaiting
                                                               attribute:NSLayoutAttributeTop
                                                               relatedBy:NSLayoutRelationLessThanOrEqual
                                                                  toItem:self.viewAlert
                                                               attribute:NSLayoutAttributeTop
                                                              multiplier:1
                                                                constant:40]];

上面程式碼給指示器indicatorWaiting新增約束。

2.NSLayoutConstraint的constraintWithItem方法說明

+ (instancetype)constraintWithItem:(id)view1
                         attribute:(NSLayoutAttribute)attr1
                         relatedBy:(NSLayoutRelation)relation
                            toItem:(id)view2
                         attribute:(NSLayoutAttribute)attr2
                        multiplier:(CGFloat)multiplier
                          constant:(CGFloat)c

官方說明：
Create constraints explicitly. Constraints are of the form “view1.attr1 = view2.attr2 * multiplier + constant”
If your equation does not have a second view and attribute, use nil and NSLayoutAttributeNotAnAttribute.

意思是說view1的某某屬性的值 = view2的某某屬性*倍數 + 長度