java - 循环不会自动运行

Question

我是 Android 新手。我的程序模拟交通灯的操作，并根据经过的秒数显示适当的颜色。通过点击buttonRandom，从0到6秒显示绿色背景，从6到7秒显示黄色背景，从7到9秒显示红色背景。

public void onClick(View v) {
    switch (v.getId()) {
        case R.id.buttonRed:
            mTextView.setText(R.string.buttonRed);
            mRelativeLayout.setBackgroundColor(getResources().getColor(R.color.colorRed));
            break;
        case R.id.buttonYellow:
            mTextView.setText(R.string.buttonYellow);
            mRelativeLayout.setBackgroundColor(getResources().getColor(R.color.colorYellow));
            break;
        case R.id.buttonRandom:
            int count = 0;
            while (count <= 10) {
                Date date = new Date();
                int sec = date.getSeconds();
                if (sec % 10 >= 0 && sec % 10 < 6) {
                    mTextView.setText(R.string.buttonGreen);
                    mRelativeLayout.setBackgroundColor(getResources().getColor(R.color.colorGreen));
                    count++;
                }
                else if (sec % 10 >= 6 && sec % 10 < 7) {
                    mTextView.setText(R.string.buttonYellow);
                    mRelativeLayout.setBackgroundColor(getResources().getColor(R.color.colorYellow));
                    count++;
                }
                else if (sec % 10 >= 7 && sec % 10 < 9) {
                    mTextView.setText(R.string.buttonRed);
                    mRelativeLayout.setBackgroundColor(getResources().getColor(R.color.colorRed));
                    count++;
                }
            }
    }

但是，这段代码不会自行更改背景，需要每次按下按钮。如何确保按一次背景自动改变？

Answer 1

However, this code does not change the background on their own, it is necessary each time to press the button.

那是因为你的 while 循环运行得太快了，不到一秒就已经完成了 10 次循环。您想在此处使用处理程序或其他东西每秒进行检查

int sec = 0;
case R.id.buttonRandom:
    final Handler h = new Handler();
    h.postDelayed(new Runnable() {
        @Override
        public void run() {
            if (sec % 10 >= 0 && sec % 10 < 6) {
                mTextView.setText(R.string.buttonGreen);
                mRelativeLayout.setBackgroundColor(getResources().getColor(R.color.colorGreen));
            } else if (sec % 10 >= 6 && sec % 10 < 7) {
                mTextView.setText(R.string.buttonYellow);
                mRelativeLayout.setBackgroundColor(getResources().getColor(R.color.colorYellow));
            } else if (sec % 10 >= 7 && sec % 10 < 9) {
                mTextView.setText(R.string.buttonRed);
                mRelativeLayout.setBackgroundColor(getResources().getColor(R.color.colorRed));
            }

            sec++;
            if (sec < 11) {
                h.postDelayed(this);
            }
        }
    }, 1000);