Cannot read property 'stopRecord' of undefined

Question

I am going to record audio on android device. This is code.

curr_playing_file: MediaObject;
    recordaudio(){ 
    var nItem = localStorage.getItem('recordvoiceNum');
        var numstr = 0;
        if (nItem == null) {
            numstr = 1;
        }
        else {
            var numstr = parseInt(nItem, 10);
            numstr = numstr + 1;
        }
        //Create media file
        this.curfilename = 'audio' + numstr + '.3gp';
        this.curr_playing_file = this.createAudioFile(this.curfilename);
        localStorage.setItem('recordvoiceNum', numstr.toString());
        try {
            console.log('start Recording');
            if (this.curr_playing_file == undefined)
                console.log('dont start');
            this.curr_playing_file.startRecord();
        }
        catch (e) {
            console.log('record error');
            console.log(e.message);
        }
        setTimeout(function () {
            try {
                console.log('stop recording');
                //stop recording 
                if (this.curr_playing_file == undefined)
                    console.log('dont stop');
                this.curr_playing_file.stopRecord();
            }
            catch (error) {
                console.log('stoperror');
                console.log(error.message);
            }
        }, 10000);
}

I get "Cannot read property 'stopRecord' of undefined " error. Media object has function of "stopRecord()". But I couldn't know the reason of this error. Please give me advice. Thanks.