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delegate void IntParameterDelegate(int value);
        public void SetProgBarValue(int value)
        {
            if (progressBar.InvokeRequired)
            {
                if (value > 100) // überflüssig, aber ich habs einfach nochmal eingebaut um zu zeigen, was ich meine
                    value = 100;
                progressBar.Invoke(new IntParameterDelegate(SetProgBarValue), new object[] { value });
                return;
            }
            progressBar.Value++;
            progressBar.Value--;
            progressBar.Value = value;
        }

        private void SimpleProgressBarChanger()
        {
            int value = 0;
            while (doProgBarChange)
            {
                if (value == 100)
                    value = 0;
                SetProgBarValue(++value);
                Thread.Sleep(350);                
            }
        }					

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progressBar.Value++;