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我试图加载一个带有透明背景的PNG文件到一个UIImageView中（如果它很重要，用Objective C，XCode 8.0开发IOS 10.0目标）。 当显示在UIImageView中时，图像的背景颜色显示为黑色（见下文）。iOS Objective C加载一个带有透明背景的PNG文件到一个UIImageView
如何将任意PNG文件加载到UIImageView，使其透明背景被保留？
奇怪的是，我的应用程序资产中有透明背景的PNG图像，并且它们显示在UIImageView中，没有任何额外的混乱。
请注意在下面的代码中，我尝试过的一件事是重建从imagePicker（请参阅imageWithImage）传递的UIImage，为新图像设置新的图形上下文。我曾经在某些帖子中看到过这种方法，它们涉及到模糊的类似问题，但它不起作用（更不用说，似乎愚蠢的IOS会要求它支持加载映像中定义的透明度）。
的PNG图像我与测试是一个标准的PNG32（从互联网上用于测试目的收获 - 注意，我已经尝试了许多其他图片）：
左下图显示之前的应用程序屏幕加载上面的图片，右键显示加载的图片： 
PNG图片文件是通过点击屏幕底部的'select image'打开的imagePicker来选择的。
我的视图控制器代码：
//
// ViewController.m
// ImageTest
//
#import "ViewController.h"
#import "MobileCoreServices/MobileCoreServices.h"
#define FONT_SIZE_BUTTON 32
@interface ViewController()
@end
@implementation ViewController
UIImageView *myImageView;
UIImage *myImage;
UIButton *btnSelect;
- (void)viewDidLoad {
NSLog(@"viewDidLoad");
[super viewDidLoad];
CGRect screenRect = [[UIScreen mainScreen] bounds];
CGFloat btnHeight = 40;
CGFloat btnMargin = 10;
CGFloat btnWidth = screenRect.size.width - 2*btnMargin;
CGFloat btnULY = screenRect.size.height - btnHeight - 2*btnMargin;
btnSelect = [[UIButton alloc] initWithFrame:CGRectMake(btnMargin, btnULY, btnWidth, btnHeight)];
[btnSelect.titleLabel setFont:[UIFont boldSystemFontOfSize:FONT_SIZE_BUTTON]];
[btnSelect setAutoresizingMask:UIViewAutoresizingFlexibleWidth];
[btnSelect setTitle :@"Select Image" forState:UIControlStateNormal];
[btnSelect.layer setBorderWidth:4.0f];
[btnSelect.layer setBorderColor:[UIColor blueColor].CGColor];
[btnSelect setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
[btnSelect setTitleColor:[UIColor grayColor] forState:UIControlStateSelected];
[btnSelect setTitleColor:[UIColor grayColor] forState:UIControlStateDisabled];
btnSelect.backgroundColor = [UIColor whiteColor];
btnSelect.tag = 4200;
[btnSelect addTarget:self action:@selector(onClick:) forControlEvents:UIControlEventTouchUpInside];
btnSelect.userInteractionEnabled = true;
CGFloat ulx = 10;
CGFloat uly = 20;
CGFloat width = screenRect.size.width - 2*ulx;
CGFloat height = width * 9.0/16.0;
CGRect imageFrame = CGRectMake(ulx, uly, width, height);
myImageView = [[UIImageView alloc] initWithFrame:imageFrame];
myImageView.alpha = 1.0f;
myImageView.backgroundColor = [UIColor lightGrayColor];
myImageView.contentMode = UIViewContentModeScaleAspectFit;
myImageView.opaque = false;
[[myImageView layer] setOpaque:false];
[[myImageView layer] setBorderWidth:4.0f];
[[myImageView layer] setBorderColor:[UIColor redColor].CGColor];
// Add elements to this view controller
[self.view addSubview:myImageView];
[self.view addSubview:btnSelect];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
// Ensure image is opened honoring transparency of PNGs
- (UIImage *)imageWithImage:(UIImage *)image {
CGSize newSize = image.size;
CGRect newRect = CGRectMake(0,0,newSize.width, newSize.height);
UIGraphicsBeginImageContextWithOptions(newSize, NO, 1.0);
CGContextRef ctx = UIGraphicsGetCurrentContext();
[[UIColor clearColor] set];
CGContextFillRect(ctx, newRect);
[image drawInRect:CGRectMake(0, 0, newSize.width, newSize.Height)];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
#pragma mark - Select Actions
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- (IBAction)onClick: (UIButton *)btn
{
NSLog(@"onClick");
// DDLogInfo(@"%@:%@", THIS_FILE, THIS_METHOD);
UIImagePickerController *picker = [[UIImagePickerController alloc] init];
picker.delegate = self;
picker.allowsEditing = YES;
picker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
NSMutableArray *mediaTypes = [[NSMutableArray alloc] init];
[mediaTypes addObject:(__bridge NSString *)kUTTypeImage];
picker.mediaTypes = mediaTypes;
[self presentViewController:picker animated:YES completion:NULL];
}
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
#pragma mark - UIImagePicker's Delegate
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {
NSLog(@"imagePickerController");
UIImage *chosenImage = [self imageWithImage:info[UIImagePickerControllerEditedImage]];
// UIImage *chosenImage = info[UIImagePickerControllerEditedImage];
// UIImage *chosenImage = [info[UIImagePickerControllerEditedImage] imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
if (myImageView != nil)
myImageView.image = chosenImage;
myImage = chosenImage;
[picker dismissViewControllerAnimated:YES completion:NULL];
}
- (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker {
[picker dismissViewControllerAnimated:YES completion:NULL];
}
@end
**
与Final修复编辑
**
更新后的应用屏幕的截屏显示问题：
和最终（固定）的代码，显示使用字典的键（UIImagePickerControllerOriginalImage）和字典键（UIImagePickerControllerEditedImage）之间的区别：
//
// ViewController.m
// ImageTest
//
// Created by Robb Main on 2016-11-21.
// Copyright © 2016 Robb Main. All rights reserved.
//
#import "ViewController.h"
#import "MobileCoreServices/MobileCoreServices.h"
#define FONT_SIZE_BUTTON 32
@interface ViewController()
@end
@implementation ViewController
UIImageView *myImageView1;
UIImageView *myImageView2;
UIImageView *myImageView3;
UIImage *myImage;
UIButton *btnSelect;
- (void)viewDidLoad {
NSLog(@"viewDidLoad");
[super viewDidLoad];
CGRect screenRect = [[UIScreen mainScreen] bounds];
CGFloat btnHeight = 40;
CGFloat btnMargin = 10;
CGFloat btnWidth = screenRect.size.width - 2*btnMargin;
CGFloat btnULY = screenRect.size.height - btnHeight - 2*btnMargin;
btnSelect = [[UIButton alloc] initWithFrame:CGRectMake(btnMargin, btnULY, btnWidth, btnHeight)];
[btnSelect.titleLabel setFont:[UIFont boldSystemFontOfSize:FONT_SIZE_BUTTON]];
[btnSelect setAutoresizingMask:UIViewAutoresizingFlexibleWidth];
[btnSelect setTitle :@"Select Image" forState:UIControlStateNormal];
[btnSelect.layer setBorderWidth:4.0f];
[btnSelect.layer setBorderColor:[UIColor blueColor].CGColor];
[btnSelect setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
[btnSelect setTitleColor:[UIColor grayColor] forState:UIControlStateSelected];
[btnSelect setTitleColor:[UIColor grayColor] forState:UIControlStateDisabled];
btnSelect.backgroundColor = [UIColor whiteColor];
btnSelect.tag = 4200;
[btnSelect addTarget:self action:@selector(onClick:) forControlEvents:UIControlEventTouchUpInside];
btnSelect.userInteractionEnabled = true;
CGFloat imgMargin = 60;
CGFloat ulx = imgMargin;
CGFloat uly = 20;
CGFloat imgWidth = screenRect.size.width - 2*imgMargin;
CGFloat imgHeight = imgWidth * 9.0/16.0;
CGRect imageFrame = CGRectMake(ulx, uly, imgWidth, imgHeight);
myImageView1 = [[UIImageView alloc] initWithFrame:imageFrame];
myImageView1.alpha = 1.0f;
myImageView1.backgroundColor = [UIColor lightGrayColor];
myImageView1.contentMode = UIViewContentModeScaleAspectFit;
myImageView1.opaque = NO;
[myImageView1.layer setOpaque:NO];
// myImageView.clearsContextBeforeDrawing = YES;
[myImageView1.layer setBorderWidth:4.0f];
[myImageView1.layer setBorderColor:[UIColor redColor].CGColor];
myImageView1.image = [UIImage imageNamed:@"imageTest.png"];
uly += imgHeight+8;
CGFloat lblHeight = 10;
CGRect lblFrame = CGRectMake(ulx, uly, imgWidth, lblHeight);
UILabel *myLabel1 = [[UILabel alloc] initWithFrame:lblFrame];
[myLabel1 setFont:[UIFont systemFontOfSize:12]];
myLabel1.text = @"PNG Image from assets";
uly += lblHeight+20;
imageFrame.origin.y = uly;
myImageView2 = [[UIImageView alloc] initWithFrame:imageFrame];
myImageView2.alpha = 1.0f;
myImageView2.backgroundColor = [UIColor lightGrayColor];
myImageView2.contentMode = UIViewContentModeScaleAspectFit;
myImageView2.opaque = NO;
[myImageView2.layer setOpaque:NO];
// myImageView2.clearsContextBeforeDrawing = YES;
[myImageView2.layer setBorderWidth:4.0f];
[myImageView2.layer setBorderColor:[UIColor redColor].CGColor];
uly += imgHeight+8;
lblFrame.origin.y = uly;
UILabel *myLabel2 = [[UILabel alloc] initWithFrame:lblFrame];
[myLabel2 setFont:[UIFont systemFontOfSize:12]];
myLabel2.text = @"UIImagePickerControllerOriginalImage";
uly += lblHeight+20;
imageFrame.origin.y = uly;
myImageView3 = [[UIImageView alloc] initWithFrame:imageFrame];
myImageView3.alpha = 1.0f;
myImageView3.backgroundColor = [UIColor lightGrayColor];
myImageView3.contentMode = UIViewContentModeScaleAspectFit;
myImageView3.opaque = NO;
[myImageView3.layer setOpaque:NO];
// myImageView3.clearsContextBeforeDrawing = YES;
[myImageView3.layer setBorderWidth:4.0f];
[myImageView3.layer setBorderColor:[UIColor redColor].CGColor];
uly += imgHeight+8;
lblFrame.origin.y = uly;
UILabel *myLabel3 = [[UILabel alloc] initWithFrame:lblFrame];
[myLabel3 setFont:[UIFont systemFontOfSize:12]];
myLabel3.text = @"UIImagePickerControllerEditedImage";
// Add elements to this view controller
[self.view addSubview:myImageView1];
[self.view addSubview:myLabel1];
[self.view addSubview:myImageView2];
[self.view addSubview:myLabel2];
[self.view addSubview:myImageView3];
[self.view addSubview:myLabel3];
[self.view addSubview:btnSelect];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
#pragma mark - Select Actions
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- (IBAction)onClick: (UIButton *)btn
{
NSLog(@"onClick");
// DDLogInfo(@"%@:%@", THIS_FILE, THIS_METHOD);
UIImagePickerController *picker = [[UIImagePickerController alloc] init];
picker.delegate = self;
picker.allowsEditing = NO;
picker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
NSMutableArray *mediaTypes = [[NSMutableArray alloc] init];
[mediaTypes addObject:(__bridge NSString *)kUTTypeImage];
picker.mediaTypes = mediaTypes;
[self presentViewController:picker animated:YES completion:NULL];
}
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
#pragma mark - UIImagePicker's Delegate
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {
NSLog(@"imagePickerController");
myImage = info[UIImagePickerControllerOriginalImage];
if (myImageView2 != nil)
myImageView2.image = myImage;
if (myImageView3 != nil)
myImageView3.image = info[UIImagePickerControllerEditedImage];
[picker dismissViewControllerAnimated:YES completion:NULL];
}
- (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker {
[picker dismissViewControllerAnimated:YES completion:NULL];
}
@end
这工作，虽然目前还不清楚我为什么：
imagePicker不会为无效的字典键返回nil（我指定了编辑是不允许的）。
'编辑'图像会去除透明度信息。
你的'imageWithImage：'方法有什么意义？为什么不直接在图像视图中使用选定的图像？为什么使用'UIImagePickerControllerEditedImage'而不是'UIImagePickerControllerOriginalImage'？ – rmaddy
谢谢，马迪。我imageWithImage：方法_is_真的毫无意义。我在尝试解决问题的选项时实施了它。然而，你的其他建议做到了。使用UIImagePickerControllerOriginalImage作为词典键显示图像应该是。我将添加最终代码和屏幕截图来完成此操作。请提交答案，以便我可以接受。 – gOnZo