im making a tableview loaded with some NSArrays, the cell contains two labels and a background image view loaded with a URL image. The problem is that the scrolling of the tableview is slow, its like freeze or something.... i think that is because of the Imageview but what can i do???
heres some of my code so you can see:
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
// Return the number of rows in the section.
return _Title.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
MyCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
int row = [indexPath row];
cell.TitleLabel.text = _Title[row];
cell.DescriptionLabel.text = _content[row];
cell.CellImageView.image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:_ImageUrl[row]]]];
cell.CellImageView.contentMode = UIViewContentModeTop;
cell.CellImageView.contentMode = UIContentSizeCategoryMedium;
cell.backgroundColor = [UIColor clearColor];
return cell;
}
For extra info this tableview presents a Detailviewcontroller with this same info.
Load the image asynchronously(load it as the images come in). Look into great classes such as SDWebImage https://github.com/rs/SDWebImage
You are blocking the main thread with the following line of code:
cell.CellImageView.image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:_ImageUrl[row]]]];
My suggestion would be to use AFNetworking and replace the code with the following:
[cell.cellImageView setImageWithURL:[NSURL URLWithString:#"http://example.com/image.png"]];
Also, your pointers should start with a lower case letter. For instance, CellImageView should be cellImageView.
You are calling [NSData dataWithContentsOfURL:[NSURL URLWithString:_ImageUrl[row]]] from cellForRowAtIndexPath , which is not good idea. Because it'll go to the server every time a UITableViewCell is loaded.
You must use Asynchronous image loading & cache. These libraries might help you : (My personal favourite is SDWebImage)
1) https://github.com/rs/SDWebImage
2) https://github.com/nicklockwood/AsyncImageView
And more, you can refer to the sample code by Apple about LazyTableImages - https://developer.apple.com/library/ios/samplecode/LazyTableImages/Introduction/Intro.html
UPDATE:
For SDWebImage follow this guide. It's very good.
http://iosmadesimple.blogspot.in/2013/04/lazy-image-loading.html
To expand on #vborra's answer - the reason why your tableview is slow is that (in your code) the entire image MUST have finished downloading before it displays.
This is because dataWithContentsOfURL: is a synchronous method. You need to use asynchronous APIs to download images in the background and when they've finished downloading, display them on the screen.
Here is a code snippet from the github page adapted for your example. Make sure you add the folder SDWebImage and it's contents from https://github.com/rs/SDWebImage to your project.
#import <SDWebImage/UIImageView+WebCache.h>
...
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
MyCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
int row = [indexPath row];
cell.TitleLabel.text = _Title[row];
cell.DescriptionLabel.text = _content[row];
[cell.CellImageView setImageWithURL:[NSURL URLWithString:_ImageUrl[row]]
placeholderImage:[UIImage imageNamed:#"placeholder.png"]];
cell.CellImageView.contentMode = UIViewContentModeTop;
cell.CellImageView.contentMode = UIContentSizeCategoryMedium;
cell.backgroundColor = [UIColor clearColor];
return cell;
}
Note, if you're downloading images of all different sizes, you may end up with resizing issues which will also decrease your performance. The SDWebImage page has a link to an article to help you with this problem if you come across it. http://www.wrichards.com/blog/2011/11/sdwebimage-fixed-width-cell-images/
You may also experience a performance bump when using transparency and tableviews, but it depends on the rest of your code.
AFNetworking is an excellent tool to use, but might be overkill if you're not using networking anywhere else in your app.
load your image like this
//get a dispatch queue
dispatch_queue_t concurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
//this will start the image loading in bg
dispatch_async(concurrentQueue, ^{
NSData *imageData = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:mapUrlStr]];
//this will set the image when loading is finished
dispatch_async(dispatch_get_main_queue(), ^{
cell.CellImageView.image = [UIImage imageWithData:imageData]
});
});
Related
im making a tableview loaded with some NSArrays, the cell contains two labels and a background image view loaded with a URL image. The problem is that the scrolling of the tableview is slow, its like freeze or something.... i think that is because of the Imageview but what can i do???
heres some of my code so you can see:
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
// Return the number of rows in the section.
return _Title.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
MyCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
int row = [indexPath row];
cell.TitleLabel.text = _Title[row];
cell.DescriptionLabel.text = _content[row];
cell.CellImageView.image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:_ImageUrl[row]]]];
cell.CellImageView.contentMode = UIViewContentModeTop;
cell.CellImageView.contentMode = UIContentSizeCategoryMedium;
cell.backgroundColor = [UIColor clearColor];
return cell;
}
For extra info this tableview presents a Detailviewcontroller with this same info.
Load the image asynchronously(load it as the images come in). Look into great classes such as SDWebImage https://github.com/rs/SDWebImage
You are blocking the main thread with the following line of code:
cell.CellImageView.image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:_ImageUrl[row]]]];
My suggestion would be to use AFNetworking and replace the code with the following:
[cell.cellImageView setImageWithURL:[NSURL URLWithString:#"http://example.com/image.png"]];
Also, your pointers should start with a lower case letter. For instance, CellImageView should be cellImageView.
You are calling [NSData dataWithContentsOfURL:[NSURL URLWithString:_ImageUrl[row]]] from cellForRowAtIndexPath , which is not good idea. Because it'll go to the server every time a UITableViewCell is loaded.
You must use Asynchronous image loading & cache. These libraries might help you : (My personal favourite is SDWebImage)
1) https://github.com/rs/SDWebImage
2) https://github.com/nicklockwood/AsyncImageView
And more, you can refer to the sample code by Apple about LazyTableImages - https://developer.apple.com/library/ios/samplecode/LazyTableImages/Introduction/Intro.html
UPDATE:
For SDWebImage follow this guide. It's very good.
http://iosmadesimple.blogspot.in/2013/04/lazy-image-loading.html
To expand on #vborra's answer - the reason why your tableview is slow is that (in your code) the entire image MUST have finished downloading before it displays.
This is because dataWithContentsOfURL: is a synchronous method. You need to use asynchronous APIs to download images in the background and when they've finished downloading, display them on the screen.
Here is a code snippet from the github page adapted for your example. Make sure you add the folder SDWebImage and it's contents from https://github.com/rs/SDWebImage to your project.
#import <SDWebImage/UIImageView+WebCache.h>
...
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
MyCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
int row = [indexPath row];
cell.TitleLabel.text = _Title[row];
cell.DescriptionLabel.text = _content[row];
[cell.CellImageView setImageWithURL:[NSURL URLWithString:_ImageUrl[row]]
placeholderImage:[UIImage imageNamed:#"placeholder.png"]];
cell.CellImageView.contentMode = UIViewContentModeTop;
cell.CellImageView.contentMode = UIContentSizeCategoryMedium;
cell.backgroundColor = [UIColor clearColor];
return cell;
}
Note, if you're downloading images of all different sizes, you may end up with resizing issues which will also decrease your performance. The SDWebImage page has a link to an article to help you with this problem if you come across it. http://www.wrichards.com/blog/2011/11/sdwebimage-fixed-width-cell-images/
You may also experience a performance bump when using transparency and tableviews, but it depends on the rest of your code.
AFNetworking is an excellent tool to use, but might be overkill if you're not using networking anywhere else in your app.
load your image like this
//get a dispatch queue
dispatch_queue_t concurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
//this will start the image loading in bg
dispatch_async(concurrentQueue, ^{
NSData *imageData = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:mapUrlStr]];
//this will set the image when loading is finished
dispatch_async(dispatch_get_main_queue(), ^{
cell.CellImageView.image = [UIImage imageWithData:imageData]
});
});
I added images to my tableView cells and it made it laggy. I am still new to objective c and I do not understand what is causing this or how to fix it. Any help is greatly appreciated!
group[PF_GROUP_LOGO] is simply a string in my database that is unique to each object. The code works, it is just really laggy when trying to scroll.
//-------------------------------------------------------------------------------------------------------------------------------------------------
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
//-------------------------------------------------------------------------------------------------------------------------------------------------
{
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"cell"];
if (cell == nil) cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:#"cell"];
PFObject *group = groups[indexPath.row];
UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:group[PF_GROUP_LOGO]]]];
cell.imageView.image = image;
cell.detailTextLabel.text = [NSString stringWithFormat:#"%d users", (int) [group[PF_GROUP_MEMBERS] count]];
cell.detailTextLabel.textColor = [UIColor lightGrayColor];
return cell;
}
There are so many tools out there that can help you with this.
At a base level, the issue is that you are running a long process on the main thread, which blocks the UI. Loading an image from a non-local URL is time consuming, and you should do this on a background thread, so the UI is not blocked.
Again, there are so many ways to do this, and I strongly suggest you do some research on async resource loading, but this is one thing you can do within the confines of your own example:
//-------------------------------------------------------------------------------------------------------------------------------------------------
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
//-------------------------------------------------------------------------------------------------------------------------------------------------
{
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"cell"];
if (cell == nil) cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:#"cell"];
PFObject *group = groups[indexPath.row];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{ // go to a background thread to load the image and not interfere with the UI
UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:group[PF_GROUP_LOGO]]]];
dispatch_async(dispatch_get_main_queue(), ^{ // synchronize back to the main thread to update the UI with your loaded image
cell.imageView.image = image;
});
});
cell.detailTextLabel.text = [NSString stringWithFormat:#"%d users", (int) [group[PF_GROUP_MEMBERS] count]];
cell.detailTextLabel.textColor = [UIColor lightGrayColor];
return cell;
}
I would also recommend using AFNetworking as the author has built a very good category on top of UIImageView that allows you to load an image from a web URL in the background automatically. Again, there are many schools of thought on this process, and this is just one idea. I would recommend reading this for a full on tutorial on the topic.
I hope this is helpful!
In my app I load cell's photo right in cellforrowatindexpath, but it takes main thread for a long period, and when I scroll, my app stops for a while.
What should I do? If I add async thread it would call it every time I scroll and there could be 2 or more equal photo loading requests, and this is not good... Is there any idea without spaghetti coding?
Try SDWebImage framework
https://github.com/rs/SDWebImage
Sample Code
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *MyIdentifier = #"MyIdentifier";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:MyIdentifier];
if (cell == nil)
{
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault
reuseIdentifier:MyIdentifier];
}
// Here we use the new provided sd_setImageWithURL: method to load the web image
[cell.imageView sd_setImageWithURL:[NSURL URLWithString:#"Get each url from array and set it here using indexpath.row"]
placeholderImage:[UIImage imageNamed:#"placeholder.png"]];
cell.textLabel.text = #"My Text";
return cell;
}
It supports variety of features like caching etc.
In my app i have to fetch images from a json webservice and display them in a table view. While scrolling downwards all the images come correct order but while i revert backwards all the images get over each other. I am using [ tableview reloaddata] then too its happening.
This happened to me in my app, where I have a leaderboards table. It is definitely because the tables are being reused.
The easiest way to fix this is simply setting the cell's image to nil first, then downloading and displaying the new image.
There are definitely other ways to do this, but I can definitely vouch for this one, as I use it in my own app, and it works great!!
Here's how I solve the problem.
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString * cellIdentifier = #"Cell";
UITableViewCell * cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
if (!cell)
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];
// Make sure you set the image for the cell to nil first
[cell.imageView setImage:nil];
// Then load your new image using the url and display it
dispatch_queue_t backgroundQueue = dispatch_queue_create("com.example.imagedownloadqueue", NULL);
dispatch_async(backgroundQueue, ^(void){
NSUrl * url = [NSUrl UrlWithString:#"www.example.com"]; // Url of image to download
UIImage * image = [UIImage imageWithData:[NSData dataWithContentsOfUrl:url]];
if (image)
{
dispatch_async(dispatch_get_main_queue(), ^(void) {
[cell.imageView setImage:image]; // Display image after it is downloaded
});
}
});
return cell;
}
I am having a problem viewing my tableview when i get the data of my cells from a server. If i do not use photos there is no breaks in the scrolling, but i want to use the images also. Can anyone knows how can i resolve this? I am getting the data from a plist in my server.
Here is the code of the image that makes the scrolling breaks (i am using custom style cell)
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
NSURL *URL = [[NSURL alloc] initWithString:[[self.content objectAtIndex:indexPath.row] valueForKey:#"imageName"]];
NSData *URLData = [[NSData alloc] initWithContentsOfURL:URL];
UIImage *img = [[UIImage alloc] initWithData:URLData];
UIImageView *imgView = (UIImageView *)[cell viewWithTag:100];
imgView.image = img;
....
If you mean that the scrolling stops and starts, this might be because if the images are loaded from a server (which might take a noticeable amount of time to do), executing on the main thread causes freezing.
If this is the case, the fix is to fetch the images in another thread. Fortunately iOS has a fairly easy to use multithreading system called Grand Central Dispatch.
Here's some example code:
dispatch_queue_t q = dispatch_queue_create("FetchImage", NULL);
dispatch_async(q, ^{
/* Fetch the image from the server... */
dispatch_async(dispatch_get_main_queue(), ^{
/* This is the main thread again, where we set the tableView's image to
be what we just fetched. */
});
});