ios - iPhone 应用程序 : avoiding white screen after splash screen. 让闪屏停留，在 UIWebview 加载后隐藏它？闪屏没有正确隐藏

Question

对于 iPhone 应用程序，我们的目标很简单:显示初始页面，然后在 UIWebview 准备好显示其页面时将其隐藏。

我们需要默认启动画面一直停留到 UIWebview 准备好显示为止。否则，会短暂出现白屏。

不幸的是，启动画面在我们让它逗留后无法隐藏。默认启动画面仍然可见，隐藏了 UIWebview。

我们知道这可能违反了 Apple 准则。

这更像是一个原型(prototype)，我们想了解我们做错了什么。有什么线索吗？

我们正在使用 Xcode 4.2。

AppDelegate.m:

//
//  AppDelegate.m
//
//  Created by Macintosh User on 6/4/12.
//  Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//

#import "AppDelegate.h"

#import "ViewController.h"

@implementation AppDelegate

@synthesize window = _window;
@synthesize viewController = _viewController;
@synthesize imgv;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    self.viewController = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];

    imgv = [[UIImageView alloc] init];
    [imgv setImage:[UIImage imageNamed:@"Default.png"]];
    [imgv setFrame:CGRectMake(0, 0, 320, 480)];
    [self.window addSubview:imgv];

    return YES;
}

@end

ViewController.m:

//
//  ViewController.m
// 
//
//  Created by Macintosh User on 6/4/12.
//  Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//

#import "AppDelegate.h"
#import "ViewController.h"

@implementation ViewController

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    CGRect webFrame = CGRectMake(0.0, 0.0, 320.0, 460.0);
    UIWebView *webView = [[UIWebView alloc] initWithFrame:webFrame];
    [webView setBackgroundColor:[UIColor clearColor]];
    NSString *urlAddress = @"http://www.cnn.com";
    NSURL *url = [NSURL URLWithString:urlAddress];
    NSURLRequest *requestObj = [NSURLRequest requestWithURL:url];
    [webView loadRequest:requestObj];

    for (id subview in webView.subviews)
        if ([[subview class] isSubclassOfClass: [UIScrollView class]])
            ((UIScrollView *)subview).bounces = NO;

    AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
    UIImageView *imageView = appDelegate.imgv;
    [imageView removeFromSuperview];
    [imageView setHidden:YES];
    imageView = nil;

    [self.view addSubview:webView];
    [self.view bringSubviewToFront:webView];
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    NSLog(@"Done loading UIWebView");
}

@end

当前 ViewController.m 生成错误:

//
//  ViewController.m
//  Stroll
//
//  Created by Macintosh User on 6/4/12.
//  Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//

#import "AppDelegate.h"
#import "ViewController.h"

@implementation ViewController

@synthesize splash;

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    CGRect webFrame = CGRectMake(0.0, 0.0, 320.0, 460.0);
    UIWebView *webView = [[UIWebView alloc] initWithFrame:webFrame];

    webView.delegate = self;

    [webView setBackgroundColor:[UIColor clearColor]];
    NSString *urlAddress = @"http://www.cnn.com";
    NSURL *url = [NSURL URLWithString:urlAddress];
    NSURLRequest *requestObj = [NSURLRequest requestWithURL:url];
    [webView loadRequest:requestObj];

    for (id subview in webView.subviews)
        if ([[subview class] isSubclassOfClass: [UIScrollView class]])
            ((UIScrollView *)subview).bounces = NO;

    /*
    AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
    UIImageView *imageView = appDelegate.imgv;
    [imageView removeFromSuperview];
    [imageView setHidden:YES];
    imageView = nil; */

    [self.view addSubview:webView];
    [self.view bringSubviewToFront:webView];
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    NSLog(@"Done loading UIWebView");
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];

    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{

        self.view.userInteractionEnabled = NO;

        splash = [[UIImageView alloc] initWithFrame:[UIScreen mainScreen].bounds];

        splash.image = [UIImage imageNamed:@"Default.png"];
        [self.view addSubview:splash];
    });
}

-(void) webViewDidFinishLoad:(UIWebView *)webView {

    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        [splash removeFromSuperView];
    });
}

@end

Answer 1

这是实现它的一种方法，首先摆脱 AppDelegate 中的所有代码。在您的 Root View Controller 中添加一个名为“splash”的 UIImageView 类的实例变量。

现在在 rootViewController.m 中:

-(void) viewWillAppear:(BOOL) animated {

    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{

        self.view.userInteractionEnabled = NO;

        splash = [[UIImageView alloc] initWithFrame:[UIScreen mainScreen].bounds];

        splash.image = [UIImage imageNamed:@"Default.png"];
        [self.view addSubview:splash];
    });
    }

现在在你的 webView 加载完成回调方法/ block 中

static dispatch_once_t onceToken;
        dispatch_once(&onceToken, ^{

          [splash removeFromSuperView];
        });

因此 dispatch_once 确保该方法将在应用程序的生命周期内运行一次且仅运行一次。

编辑:

得到你的回调:

在 viewController.h -> viewC : UIViewController < UIWebViewDelegate >

在 viewController.m 中

-(void) viewDidLoad{

    CGRect webFrame = CGRectMake(0.0, 0.0, 320.0, 460.0);
    UIWebView *webView = [[UIWebView alloc] initWithFrame:webFrame];

    webView.delegate = self;

    [webView setBackgroundColor:[UIColor clearColor]];
    NSString *urlAddress = @"http://www.cnn.com";
    NSURL *url = [NSURL URLWithString:urlAddress];
    NSURLRequest *requestObj = [NSURLRequest requestWithURL:url];
    [webView loadRequest:requestObj];
}

然后

-(void) webViewDidFinishLoad:(UIWebView *)webView {

    static dispatch_once_t onceToken;
        dispatch_once(&onceToken, ^{

          [splash removeFromSuperView];
        });
}