背景選擇器之代碼實現

        Drawable normal = null;
        Drawable pressed = null;
        Drawable focus = null;

        StateListDrawable stateListDrawable = new StateListDrawable();
        // 注意該處的順序，只要有一個狀態與之相配，背景就會被換掉
        // 所以不要把大範圍放在前面了，如果sd.addState(new[]{},normal)放在第一個的話，就沒有什麼效果了
        stateListDrawable.addState(new int[] { android.R.attr.state_enabled, android.R.attr.state_focused }, focus);
        stateListDrawable.addState(new int[] { android.R.attr.state_pressed, android.R.attr.state_enabled }, pressed);
        stateListDrawable.addState(new int[] { android.R.attr.state_focused }, focus);
        stateListDrawable.addState(new int[] { android.R.attr.state_pressed }, pressed);
        stateListDrawable.addState(new int[] { android.R.attr.state_enabled }, normal);
        stateListDrawable.addState(new int[] {}, normal);