多線程學習筆記(一) InvokeRequired 和 delegate

入門示例: 假若有一個label,咱們但願像走馬燈同樣,從1顯示到100

        private void button1_Click(object sender, EventArgs e)
        {
            for (int i = 0; i <= 100; i++)
            {
                label1.Text = i.ToString();
            }
 
        }

但這種寫法,只會卡一下,而後label顯示100,沒有變化的. 若是用doEvents,就能夠變化了

        private void button1_Click(object sender, EventArgs e)
        {
            for (int i = 0; i <= 100; i++)
            {
                label1.Text = i.ToString();
                Thread.Sleep(50); Application.DoEvents();
            }
 
        }

可是stackoverflow裏說Application.DoEvents是爲了適應vb項目遷移而設的,儘可能不推薦使用

改爲多線程,子線程是不能直接修改UI上的控件的,只能經過委託,讓UI線程來修改.

        delegate void D(object obj);
        private void button2_Click(object sender, EventArgs e)
        {

            for (int i = 0; i < 10; i++)
            {
                Thread t = new Thread(new ParameterizedThreadStart(SetTextBoxValue));
                t.IsBackground = true;
                t.Start(i.ToString());
                Debug.WriteLine("Thread #"+ i +" Start");
            }
        }

        void SetTextBoxValue(object obj)
        {
            if (label1.InvokeRequired)
            {
                Debug.WriteLine("Thread #" + obj + "InvokeRequired,set Delegate");
                D d = new D(SetTextBoxValue);
                label1.Invoke(d, obj); //異步的話,不保證哪一個線程先完成.最後的結果是8或9
            }
            else
            {
                Debug.WriteLine("Thread #" + obj + " UI Change ");

　　　　　　　　　　//An unhandled exception of type 'System.InvalidOperationException' occurred in System.Windows.Forms.dll
                //Additional information: 線程間操做無效: 從不是建立控件「label1」的線程訪問它。
                this.label1.Text = obj.ToString();
                Thread.Sleep(50);
                

            }
        }

debug的輸出以下: 啓動10個線程.10個線程把修改控件屬性的操做交給委託, 最後再UpdateUI

Thread #0 Start
Thread #0InvokeRequired,set Delegate
The thread 0x19ec has exited with code 259 (0x103).
Thread #1 Start
Thread #1InvokeRequired,set Delegate
The thread 0x570 has exited with code 259 (0x103).
Thread #2 Start
Thread #2InvokeRequired,set Delegate
The thread 0x1d04 has exited with code 259 (0x103).
Thread #3 Start
Thread #4 Start
Thread #4InvokeRequired,set Delegate
The thread 0x1a8c has exited with code 259 (0x103).
Thread #5InvokeRequired,set Delegate
Thread #3InvokeRequired,set Delegate
The thread 0x1a88 has exited with code 259 (0x103).
The thread 0xedc has exited with code 259 (0x103).
Thread #5 Start
Thread #6 Start
Thread #7 Start
Thread #7InvokeRequired,set Delegate
Thread #6InvokeRequired,set Delegate
The thread 0x1b58 has exited with code 259 (0x103).
The thread 0x694 has exited with code 259 (0x103).
Thread #8InvokeRequired,set Delegate
The thread 0x1680 has exited with code 259 (0x103).
Thread #8 Start
Thread #9 Start
Thread #0 UI Change 
Thread #9InvokeRequired,set Delegate
The thread 0x177c has exited with code 259 (0x103).
Thread #1 UI Change 
Thread #2 UI Change 
Thread #4 UI Change 
Thread #5 UI Change 
Thread #3 UI Change 
Thread #7 UI Change 
Thread #6 UI Change 
Thread #8 UI Change 
Thread #9 UI Change 
The thread 0x67c has exited with code 0 (0x0).