首先我们需要写一个私有方法,封装一下,以便于后面调用

我们需要在.h文件中写一个这样的方法

-(void)showAlertMsg:(NSString *)message Duration:(float)duration;

然后在.m文件中调用

-(void)showAlertMsg:(NSString *)message Duration:(float)duration
{
    UIWindow * window = [UIApplication sharedApplication].keyWindow;
    UIView *showview =  [[UIView alloc]init];
    showview.backgroundColor = [UIColor blackColor];
    showview.frame = CGRectMake(1, 1, 1, 1);
    
    showview.alpha = 1.0f;
    showview.layer.cornerRadius = 5.0f;
    showview.layer.masksToBounds = YES;
    [window addSubview:showview];
    
    UILabel *label = [[UILabel alloc]init];
    
    CGSize LabelSize = [message sizeWithFont:[UIFont systemFontOfSize:17] constrainedToSize:CGSizeMake(SCREEN_WIDTH-50, 9000)];
    label.frame = CGRectMake(10, 5, LabelSize.width, LabelSize.height);
    label.text = message;
    label.textColor = [UIColor whiteColor];
    label.textAlignment = 1;
    label.backgroundColor = [UIColor clearColor];
    label.font = [UIFont boldSystemFontOfSize:15];
    label.numberOfLines = 0; //
    
    [showview addSubview:label];
    showview.frame = CGRectMake((SCREEN_WIDTH - LabelSize.width)/2, SCREEN_HEIGHT/2 +50+LabelSize.height, LabelSize.width+10, LabelSize.height+10);
    [UIView animateWithDuration:duration animations:^{
        showview.alpha = 0;
    } completion:^(BOOL finished) {
        [showview removeFromSuperview];
    }];
}

最后在你需要的地方去调用此方法

[self showAlertMsg:@"你想输入的内容" Duration:3(希望出现多少秒)];