// Create an SDK instance in singleton mode and set an event listener
// Create trtc instance(singleton) and set up event listeners
_trtcCloud = [TRTCCloud sharedInstance];
_trtcCloud.delegate = self;


// Create an SDK instance in singleton mode and set an event listener
// Create trtc instance (singleton) and set up event listeners
trtc_cloud_ = getTRTCShareInstance();
trtc_cloud_->addCallback(this);


You can make your business class inherit **TRTCCloudDelegate**, reload the `onError` function, and use the **delegate** attribute of `TRTCCloud` to pass in the `this` pointer to the SDK, so as to listen for callback events from the SDK in the current class.
```ObjectiveC
// Listen for SDK events, and print logs for error messages such as "Current application is not authorized to use the camera"
// Listen to the "onError" event, and print logs for errors such as "Camera is not authorized"
_trtcCloud = [TRTCCloud sharedInstance];
_trtcCloud.delegate = self;

- (void)onError:(TXLiteAVError)errCode
         errMsg:(nullable NSString *)errMsg
        extInfo:(nullable NSDictionary *)extInfo{
    if (ERR_CAMERA_NOT_AUTHORIZED == errCode) {
        NSString *errorInfo = @"Current application is not authorized to use the camera:";
        errorInfo = [errorInfo stringByAppendingString errMsg];
        [self toastTip:errorInfo];
    }
}
```


You can make your business class inherit **ITRTCCloudCallback**, reload the `onError` function, and use the **addCallback** API to pass in the `this` pointer to the SDK, so as to listen for callback events from the SDK in the current class.
```C++
// Listen for SDK events, and print logs for error messages such as "Current application is not authorized to use the camera"
// Listen to the "onError" event, and print logs for errors such as "Camera is not authorized"
trtc_cloud_ = getTRTCShareInstance();
trtc_cloud_->addCallback(this);

// Reload the `onError` function
void onError(TXLiteAVError errCode, const char* errMsg, void* extraInfo) {
    if (errCode == ERR_CAMERA_NOT_AUTHORIZED) {
        printf("Current application is not authorized to use the camera");
    }
}
```


self.trtcCloud = [TRTCCloud sharedInstance];
self.trtcCloud.delegate = self;

// Assemble TRTC room entry parameters. Replace the field values in `TRTCParams` with your own parameter values
// Replace each field in TRTCParams with your own parameters
TRTCParams *params = [[TRTCParams alloc] init];
params.sdkAppId = 1400000123;  // Replace with your own SDKAppID
params.roomId = 123321; // Replace with your own room number
params.userId = @"denny";   // Replace with your own userid  
params.userSig = @"xxx"; // Replace with your own userSig
params.role = TRTCRoleAnchor;

// If your scenario is live streaming, set the application scenario to `TRTC_APP_SCENE_LIVE`
// If your application scenario is a group video call, use "TRTC_APP_SCENE_LIVE"
[self.trtcCloud enterRoom:params appScene:TRTCAppSceneLIVE];


trtc_cloud_ = getTRTCShareInstance();
trtc_cloud_->addCallback(this);

// Assemble TRTC room entry parameters. Replace the field values in `TRTCParams` with your own parameter values
// Replace each field in TRTCParams with your own parameters
liteav::TRTCParams params;
params.sdkAppId = 1400000123;  // Replace with your own SDKAppID
params.userId = "denny";       // Replace with your own user ID  
params.roomId = 123321;        // Replace with your own room number
params.userSig = "xxx";        // Replace with your own userSig
params.role = liteav::TRTCRoleAnchor;

// If your scenario is live streaming, set the application scenario to `TRTC_APP_SCENE_LIVE`
// If your application scenario is a group video call, use "TRTC_APP_SCENE_LIVE"
trtc_cloud_->enterRoom(params, liteav::TRTCAppSceneLIVE);        


// Listen for the `onEnterRoom` event of the SDK to get the room entry result
// Listen for the `onEnterRoom` event of the SDK and learn whether the room is successfully entered
- (void)onEnterRoom:(NSInteger)result {
    if (result > 0) {
        [self toastTip:@"Enter room succeed!"];
    } else {
        [self toastTip:@"Enter room failed!"];
    }
}


// Listen for the `onEnterRoom` event of the SDK to get the room entry result
// override to the onEnterRoom event of the SDK and learn whether the room is successfully entered
void onEnterRoom(int result) {
    if (result > 0) {
        printf("Enter room succeed");
    } else {
        printf("Enter room failed");
    }
}