mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-11-10 03:19:40 +00:00
142 lines
4 KiB
Markdown
142 lines
4 KiB
Markdown
# iOS tutorial 1: Link against GStreamer
|
||
|
||
# Goal
|
||
|
||
The first iOS tutorial is simple. The objective is to get the GStreamer
|
||
version and display it on screen. It exemplifies how to link against the
|
||
GStreamer library from Xcode using objective-C.
|
||
|
||
# Hello GStreamer\!
|
||
|
||
The code for this project can be found in the tutorials folder of your
|
||
GStreamer SDK iOS installation. It was created using the GStreamer
|
||
Single View Application template. The view contains only a
|
||
`UILabel` that will be used to display the GStreamer's version to the
|
||
user.
|
||
|
||
# The User Interface
|
||
|
||
The UI uses storyboards and contains a single `View` with a centered
|
||
`UILabel`. The `ViewController` for the `View` links its
|
||
`label` variable to this `UILabel` as an `IBOutlet`.
|
||
|
||
**ViewController.h**
|
||
|
||
```
|
||
#import <UIKit/UIKit.h>
|
||
|
||
@interface ViewController : UIViewController {
|
||
IBOutlet UILabel *label;
|
||
}
|
||
|
||
@property (retain,nonatomic) UILabel *label;
|
||
|
||
@end
|
||
```
|
||
|
||
# The GStreamer backend
|
||
|
||
All GStreamer-handling code is kept in a single Objective-C class called
|
||
`GStreamerBackend`. In successive tutorials it will get expanded, but,
|
||
for now, it only contains a method to retrieve the GStreamer version.
|
||
|
||
The `GStreamerBackend` is made in Objective-C so it can take care of the
|
||
few C-to-Objective-C conversions that might be necessary (like `char
|
||
*` to `NSString *`, for example). This eases the usage of this class by
|
||
the UI code, which is typically made in pure Objective-C.
|
||
`GStreamerBackend` serves exactly the same purpose as the JNI code in
|
||
the [Android tutorials](Android%2Btutorials.html).
|
||
|
||
**GStreamerBackend.m**
|
||
|
||
```
|
||
#import "GStreamerBackend.h"
|
||
|
||
#include <gst/gst.h>
|
||
|
||
@implementation GStreamerBackend
|
||
|
||
-(NSString*) getGStreamerVersion
|
||
{
|
||
char *version_utf8 = gst_version_string();
|
||
NSString *version_string = [NSString stringWithUTF8String:version_utf8];
|
||
g_free(version_utf8);
|
||
return version_string;
|
||
}
|
||
|
||
@end
|
||
```
|
||
|
||
The `getGStreamerVersion()` method simply calls
|
||
`gst_version_string()` to obtain a string describing this version of
|
||
GStreamer. This [Modified
|
||
UTF8](http://en.wikipedia.org/wiki/UTF-8#Modified_UTF-8) string is then
|
||
converted to a `NSString *` by ` NSString:stringWithUTF8String `and
|
||
returned. Objective-C will take care of freeing the memory used by the
|
||
new `NSString *`, but we need to free the `char *` returned
|
||
by `gst_version_string()`.
|
||
|
||
# The View Controller
|
||
|
||
The view controller instantiates the GStremerBackend and asks it for the
|
||
GStreamer version to display at the label. That's it\!
|
||
|
||
**ViewController.m**
|
||
|
||
```
|
||
#import "ViewController.h"
|
||
#import "GStreamerBackend.h"
|
||
|
||
@interface ViewController () {
|
||
GStreamerBackend *gst_backend;
|
||
}
|
||
|
||
@end
|
||
|
||
@implementation ViewController
|
||
|
||
@synthesize label;
|
||
|
||
- (void)viewDidLoad
|
||
{
|
||
[super viewDidLoad];
|
||
// Do any additional setup after loading the view, typically from a nib.
|
||
gst_backend = [[GStreamerBackend alloc] init];
|
||
|
||
label.text = [NSString stringWithFormat:@"Welcome to %@!", [gst_backend getGStreamerVersion]];
|
||
}
|
||
|
||
- (void)didReceiveMemoryWarning
|
||
{
|
||
[super didReceiveMemoryWarning];
|
||
// Dispose of any resources that can be recreated.
|
||
}
|
||
|
||
@end
|
||
```
|
||
|
||
# Conclusion
|
||
|
||
This ends the first iOS tutorial. It has shown that, due to the
|
||
compatibility of C and Objective-C, adding GStreamer support to an iOS
|
||
app is as easy as it is on a Desktop application. An extra Objective-C
|
||
wrapper has been added (the `GStreamerBackend` class) for clarity, but
|
||
calls to the GStreamer framework are valid from any part of the
|
||
application code.
|
||
|
||
The following tutorials detail the few places in which care has to be
|
||
taken when developing specifically for the iOS platform.
|
||
|
||
It has been a pleasure having you here, and see you soon\!
|
||
|
||
## Attachments:
|
||
|
||
|
||
[ios-tutorial1-screenshot.png](attachments/3014792/3113602.png)
|
||
(image/png)
|
||
|
||
[ios-tutorial1-screenshot.png](attachments/3014792/3113603.png)
|
||
(image/png)
|
||
|
||
[ios-tutorial1-screenshot.png](attachments/3014792/3113601.png)
|
||
(image/png)
|