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