Sending pluginResult from delegate method in iOS cordova - ios

Question

I have a issue that seems to have not been answered yet. I am new to cordova so I am not sure if this is a call in the framework. I have a a plugin which uses the Zbar libaray to scan barcodes. The resulting of the scan is managed by a delegate and is returning in the method imagePickerController:didFinishPickingMediaWithInfo: . My plugin calls the scan method but returns after my scan method ends. I need it to return the date to my website which requested it. I need to know how I can get get my scan method to wait for my zbar delegate to complete before sending a responds to my webview. Thank you in advance if you can solve this for me. and no the call [super writeJavascript:jsCallback] doesn't work, I am using cordova not phonegap.
#import "Camera.h"
#import <Cordova/CDV.h>
#import "AppDelegate.h"
#implementation Camera
#synthesize resultStr, command, hasPendingOperation;
//Override
- (void)pluginInitialize
{
NSLog(#"%#", #"init Camera");
}
- (void)scan:(CDVInvokedUrlCommand*)mycommand{
NSLog(#"%#", #"Camera.scan");
self.command = mycommand;
ZBarReaderViewController *reader = [ZBarReaderViewController new];
reader.readerDelegate = self;
reader.supportedOrientationsMask = ZBarOrientationMaskAll;
ZBarImageScanner *scanner = reader.scanner;
// TODO: (optional) additional reader configuration here
// EXAMPLE: disable rarely used I2/5 to improve performance
[scanner setSymbology: ZBAR_I25
config: ZBAR_CFG_ENABLE
to: 0];
// present and release the controller
[self.viewController presentViewController:reader animated:YES completion:nil];
NSLog(#"%#", #"finsihed plugin");
}
- (void) imagePickerController: (UIImagePickerController*) reader
didFinishPickingMediaWithInfo: (NSDictionary*) info
{
// ADD: get the decode results
id<NSFastEnumeration> results =
[info objectForKey: ZBarReaderControllerResults];
ZBarSymbol *symbol = nil;
for(symbol in results)
// EXAMPLE: just grab the first barcode
break;
self.resultStr = symbol.data;
// ADD: dismiss the controller (NB dismiss from the *reader*!)
[reader dismissViewControllerAnimated:YES completion:nil];
CDVPluginResult* pluginResult = nil;
if (self.resultStr != nil && [self.resultStr length] > 0) {
pluginResult = [CDVPluginResult resultWithStatus:CDVCommandStatus_OK messageAsString:self.resultStr];
} else {
pluginResult = [CDVPluginResult resultWithStatus:CDVCommandStatus_ERROR messageAsString:#"Failed to scan barcode!"];
}
NSLog(#"%#", self.resultStr); //<----- this is the date I need to return to my //webview this issue is scan: has already completed and returned
[self.commandDelegate sendPluginResult:pluginResult callbackId:command.callbackId];
}
#end

Answer 1

When you call the plugin from javascript, you provide a callback for success and failure. This callback is the only way for your plugin to communicate values back to your web layer.
Specifically, your javascript will look something like this.
cordova.exec(
function (result) {
// do stuff with plugin result! Hurray!
},
function (error) {
self.alert("Things went downhill, sorry... :\r\r" + error);
},
"PluginName", "MethodName", [parameters]
);
As the plugin result is already communicated through a callback, the fact that it is provided from a delegate should be irrelevant.
Update
Your question inquired about waiting on the Objective-C side. Do not wait. That's not how Cordova is designed, you'll even see warnings pop up in the console if you do not return immediately from the call.
Cordova plugin calls are designed to call asynchronous callbacks, and you have to design your web interface around those.
A common approach is to display a spinner or placeholder text while performing the call
Display spinner or placeholder text ("retrieving data")
Call plugin
In callback:
Remove spinner / placeholder.
Display result.

Answer 2

I discovered the issue, it has to do with the scope of the UIImagePickerController. This object is the only thing that is still within scope when the delegate method runs. I was mistakenly saving the callback ID as a class property, I thought I could retrieve it when the imagePickerController:didFinishPickingMediaWithInfo: method was called.
The fix was simply to extend the ZBAR reader class and add a property so I can store the call back ID. All Cordova plugins need the correct callback ID to return to the JS-side property.