这里有两个重要的参数，现拷贝如下： WindowManager.LayoutParams.FLAG_ALT_FOCUSABLE_IM和WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE 这两个参数相互作用能够应对dialog升起时，后台输入法的状态。
现有两个dialog，第一个dialog先弹出，上面有个EditText，第二个dialog后弹出，上面不可以输入内容，如何保持第二个dialog弹出时，第一个dialog上的输入法不消失呢？就是上面用到的两个参数。（如何判断一个dialog上有没有可编辑的输入框，AlertDialog会遍历View，并使用View的onCheckIsTextEditor()方法来检查有没有可编辑内容）
FLAG_ALT_FOCUSABLE_IM没有设置，FLAG_NOT_FOCUSABLE没有设置 不做讨论
FLAG_ALT_FOCUSABLE_IM设置，FLAG_NOT_FOCUSABLE没有设置 键盘会在底部，弹框能够覆盖在输入法上面，且能接受反馈键指令，按返回键第二个弹框消失。
FLAG_ALT_FOCUSABLE_IM没有设置，FLAG_NOT_FOCUSABLE设置 键盘会在底部，弹框能够覆盖在输入法上面，但是不能接受Button指令，按返回键，底部的键盘消失和第一个dialog消失，第二个dialog还在。
FLAG_ALT_FOCUSABLE_IM设置，FLAG_NOT_FOCUSABLE设置 键盘会在第二个dialog上面，弹框不能够覆盖在输入法上面，也不能接受Button指令，按返回键，底部的键盘消失，第一个dialog消失，第二个dialog还在。
/** Window flag: invert the state of {@link #FLAG_NOT_FOCUSABLE} with * respect to how this window interacts with the current method. That * is, if FLAG_NOT_FOCUSABLE is set and this flag is set, then the * window will behave as if it needs to interact with the input method * and thus be placed behind/away from it; if FLAG_NOT_FOCUSABLE is * not set and this flag is set, then the window will behave as if it * doesn't need to interact with the input method and can be placed * to use more space and cover the input method. */ public static final int FLAG_ALT_FOCUSABLE_IM = 0x00020000; /** Window flag: this window won't ever get key input focus, so the * user can not send key or other button events to it. Those will * instead go to whatever focusable window is behind it. This flag * will also enable {@link #FLAG_NOT_TOUCH_MODAL} whether or not that * is explicitly set. * * <p>Setting this flag also implies that the window will not need to * interact with * a soft input method, so it will be Z-ordered and positioned * independently of any active input method (typically this means it * gets Z-ordered on top of the input method, so it can use the full * screen for its content and cover the input method if needed. You * can use {@link #FLAG_ALT_FOCUSABLE_IM} to modify this behavior. */ public static final int FLAG_NOT_FOCUSABLE = 0x00000008;