XCode 防止 UIWebView 在启动图像后闪烁白屏

XCode Prevent UIWebView flashing white screen after Launch Image

提问by adamdehaven

I am fairly new to XCode - I'm designing an app with a single view that just displays a UIWebView that loads my jQuery mobile web site.

我对 XCode 相当陌生 - 我正在设计一个带有单个视图的应用程序，该视图只显示一个加载我的 jQuery 移动网站的 UIWebView。

I have the Default.png and [email protected] files for the Launch images in place. When I run the app on my test device or in the emulator, it shows my Launch Image, and then flashes a white screen while the UIWebView loads the first page.

我有用于启动图像的 Default.png 和 [email protected] 文件。当我在我的测试设备或模拟器中运行应用程序时，它会显示我的启动图像，然后在 UIWebView 加载第一页时闪烁白屏。

I know that I can change the background color and opacity so it will flash a different color than white, but I would like to prevent the flash altogether. I would like the app to launch, show the Launch image, and not show the UIWebView until the first page has completely loaded. Help?

我知道我可以更改背景颜色和不透明度，因此它会闪烁与白色不同的颜色，但我想完全防止闪烁。我希望应用程序启动，显示启动图像，并且在第一页完全加载之前不显示 UIWebView。帮助？

回答by adamdehaven

@ Andreas Volz (and anyone else wondering how I solved the problem of the white "flash")

@ Andreas Volz（以及其他想知道我如何解决白色“闪光”问题的人）

First, add the name-of-loading-image.pngand [email protected]files to your Xcode project. The regular image should be 320 x 460, and the @2ximage should be 640 x 920.

首先，将name-of-loading-image.png和[email protected]文件添加到您的 Xcode 项目中。常规图像应为 320 x 460，@2x图像应为 640 x 920。

Then, in my ViewController.hfile I added these properties:

然后，在我的ViewController.h文件中，我添加了这些属性：

@property (nonatomic, retain) UIWebView *webView;
@property(nonatomic, strong) UIImageView *loadingImageView;
@end

And then in my ViewController.mfile I added this:

然后在我的ViewController.m文件中我添加了这个：

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController;

@synthesize webView;
@synthesize loadingImageView;

- (void)viewDidLoad
{
    [super viewDidLoad];


    //**************** Set website URL for UIWebView
    [webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.example.com"] cachePolicy:NSURLCacheStorageAllowed timeoutInterval:20.0]];


    //**************** Add Static loading image to prevent white "flash" ****************/  
    UIImage *loadingImage = [UIImage imageNamed:@"name-of-loading-image.png"];
    loadingImageView = [[UIImageView alloc] initWithImage:loadingImage];
        loadingImageView.animationImages = [NSArray arrayWithObjects:
                                            [UIImage imageNamed:@"name-of-loading-image.png"],
                                            nil];
    [self.view addSubview:loadingImageView];   

}

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

    // Remove loading image from view
    [loadingImageView removeFromSuperview];

}

回答by jimmyb

To know when your webView has finished loading, you must implement the UIWebViewDelegate protocol.

要知道您的 webView 何时完成加载，您必须实现 UIWebViewDelegate 协议。

In your viewController's .h file:

在您的 viewController 的 .h 文件中：

@interface viewController : UIViewController <UIWebViewDelegate>
{
    UIWebView *webView;
}
@end

Then in your viewController's .m file, add this method:

然后在你的 viewController 的 .m 文件中，添加这个方法：

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

    NSLog(@"content loading finished");
    // Display your webView
    [self.view addSubview:webView];

}

You can use the -viewDidLoad method in your viewController's .m to continue displaying your launch image. You can also begin the loading of content for your webView:

您可以在 viewController 的 .m 中使用 -viewDidLoad 方法来继续显示您的启动图像。您还可以开始为您的 webView 加载内容：

- (void)viewDidLoad {
    [super viewDidLoad];

    // continue to display launch image
    UIImage *launchImage = [[UIImage alloc] initWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"launchImage.png" ofType:nil ]];
    UIImageView *launchImageView = [[[UIImageView alloc] initWithImage:launchImage] autorelease];
    [self.view addSubview:launchImageView];

    // now setup the base view for the webView controller
    UIView *contentView = [[UIView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame]];
    contentView.backgroundColor = [UIColor blueColor];

    // for rotation
    contentView.autoresizingMask = (UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight);
    self.view = contentView;

    //create a frame to size and place the web view
    CGRect webFrame = [[UIScreen mainScreen] applicationFrame];
    UIWebView *aWebView = [[UIWebView alloc] initWithFrame:webFrame];
    self.webView = aWebView;

    //aWebView.scalesPageToFit = YES;
    aWebView.autoresizesSubviews = YES;
    aWebView.autoresizingMask=(UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth);

    //set the web view delegates for the web view to be itself
    [aWebView setDelegate:self];

    //determine the path the to the index.html file in the Resources directory
    NSURL *url = [[NSBundle mainBundle] URLForResource:@"index" withExtension:@"html"];
    NSURLRequest *requestObj = [NSURLRequest requestWithURL:url];
    [aWebView loadRequest:requestObj];
}