WindowManager.LayoutParams的探究

上次在子線程更新UI時用了一下WindowManager.LayoutParams，當時覺得不太順手。以前都是用空參構造器，這次用了type和flag屬性，出現了意想不到的效果。也看看源碼吧，多鍛煉鍛煉。

public static class WindowManager.LayoutParams
extends ViewGroup.LayoutParams implements Parcelable

WindowManager.LayoutParams是WindowManager里的靜態類，源碼兩千多行，不過大部分都是一些常量。

/**
* The general type of window. There are three main classes of　　　　　　window主要的type分為三種：
* window types:
*

*
• Application windows (ranging from 應用窗口（從FIRST_APPLICATION_WINDOW到LAST_APPLICATION_WINDOW）是普通的頂層應用窗口，
  * {@link #FIRST_APPLICATION_WINDOW} to
  * {@link #LAST_APPLICATION_WINDOW}) are normal top-level application
  * windows. For these types of windows, the {@link #token} must be　　　　對這類window而言，它們的token必須設置給它們所屬的activity的token
  * set to the token of the activity they are a part of (this will
  * normally be done for you if {@link #token} is null).
  *
• Sub-windows (ranging from 子窗口從FIRST_SUB_WINDOW到LAST_SUB_WINDOW與另一個頂層的window
  * {@link #FIRST_SUB_WINDOW} to 關聯。這些window的token必須與它們依附的window的token一致。
  * {@link #LAST_SUB_WINDOW}) are associated with another top-level
  * window. For these types of windows, the {@link #token} must be
  * the token of the window it is attached to.
  *
• System windows (ranging from 系統窗口從FIRST_SYSTEM_WINDOW到lAST_SYSTEM_WINDOW是系統出於
  * {@link #FIRST_SYSTEM_WINDOW} to 特別的目的使用的一類特殊的窗口。它們不應被應用隨意使用，而且使用時
  * {@link #LAST_SYSTEM_WINDOW}) are special types of windows for　　　　　　　　需要特殊的許可權。

  * use by the system for specific purposes. They should not normally
  * be used by applications, and a special permission is required
  * to use them.
  *

實在太多了，留到後面總結吧。

周一剛好整理一下。WindowManager是個介面。源碼中是這樣介紹的：用Context.geSystemService(Context.WINDOW_SERVICE)得到WindowManager的實例，內部類LayoutParams可以通過getWindow.getAttributes或者new出來。然後是設置參數的一些變數，例如type，flag，format，x，y等。特意對照源碼做了一個參照表格，此外，還要說一下源碼中的@hide。帶有@hide標識的方法或者介面是Android系統不想讓開發者使用的功能，是那些當前版本尚未穩定的架構。在下一個API，這些帶有@hide的方法屬性等可能得到驗證刪除@hide並予以開發者調用也有可能這些功能不合適被移除掉。因此，這些可以看做是Android下個版本的新功能的趨勢，但也可能胎死腹中，而且一般開發人員都不會用到這些。因此，LayoutParams中帶有@hide、@Deprecated的變數方法不在本文中予以收錄。

接下來是flag：

下面是format的說明：

/**
* The desired bitmap format. May be one of the constants in
* {@link android.graphics.PixelFormat}. Default is OPAQUE.
*/bitmap格式。PixelFormat的一個常量。默認是OPAQUE
public int format;

說明flag的設置決定了window能否接收鍵盤輸入：

/**
* Given a particular set of window manager flags, determine whether
* such a window may be a target for an input method when it has
* focus. In particular, this checks the
* {@link #FLAG_NOT_FOCUSABLE} and {@link #FLAG_ALT_FOCUSABLE_IM}
* flags and returns true if the combination of the two corresponds
* to a window that needs to be behind the input method so that the
* user can type into it.
*
* @param flags The current window manager flags.
*
* @return Returns true if such a window should be behind/interact
* with an input method, false if not.
*/
public static boolean mayUseInputMethod(int flags) {
switch (flags&(FLAG_NOT_FOCUSABLE|FLAG_ALT_FOCUSABLE_IM)) {
case 0:
case FLAG_NOT_FOCUSABLE|FLAG_ALT_FOCUSABLE_IM:
return true;
}
return false;
}

softInputMode：輸入法模式，也可以在theme的WindowSoftInputMode設置。

/**
* Desired operating mode for any soft input area. May be any combination
* of:
*
*

*
• One of the visibility states
  * {@link #SOFT_INPUT_STATE_UNSPECIFIED}, {@link #SOFT_INPUT_STATE_UNCHANGED},
  * {@link #SOFT_INPUT_STATE_HIDDEN}, {@link #SOFT_INPUT_STATE_ALWAYS_VISIBLE}, or
  * {@link #SOFT_INPUT_STATE_VISIBLE}.
  *
• One of the adjustment options
  * {@link #SOFT_INPUT_ADJUST_UNSPECIFIED},
  * {@link #SOFT_INPUT_ADJUST_RESIZE}, or
  * {@link #SOFT_INPUT_ADJUST_PAN}.
  *

*
*
*

This flag can be controlled in your theme through the
* {@link android.R.attr#windowSoftInputMode} attribute.

*/
public int softInputMode;

Gravity：

/**
* Placement of window within the screen as per {@link Gravity}. Both
* {@link Gravity#apply(int, int, int, android.graphics.Rect, int, int,
* android.graphics.Rect) Gravity.apply} and
* {@link Gravity#applyDisplay(int, android.graphics.Rect, android.graphics.Rect)
* Gravity.applyDisplay} are used during window layout, with this value
* given as the desired gravity. For example you can specify
* {@link Gravity#DISPLAY_CLIP_HORIZONTAL Gravity.DISPLAY_CLIP_HORIZONTAL} and
* {@link Gravity#DISPLAY_CLIP_VERTICAL Gravity.DISPLAY_CLIP_VERTICAL} here
* to control the behavior of
* {@link Gravity#applyDisplay(int, android.graphics.Rect, android.graphics.Rect)
* Gravity.applyDisplay}.
*
* @see Gravity
*/
public int gravity;

horizontalMargin：

/**
* The horizontal margin, as a percentage of the container"s width,
* between the container and the widget. See
* {@link Gravity#apply(int, int, int, android.graphics.Rect, int, int,
* android.graphics.Rect) Gravity.apply} for how this is used. This
* field is added with {@link #x} to supply the xAdj parameter.
*/
public float horizontalMargin;

verticalMargin:

/**
* The vertical margin, as a percentage of the container"s height,
* between the container and the widget. See
* {@link Gravity#apply(int, int, int, android.graphics.Rect, int, int,
* android.graphics.Rect) Gravity.apply} for how this is used. This
* field is added with {@link #y} to supply the yAdj parameter.
*/
public float verticalMargin;

動畫：必須使用系統資源，不能使用應用內自定義的動畫。

/**
* A style resource defining the animations to use for this window.
* This must be a system resource; it can not be an application resource
* because the window manager does not have access to applications.
*/
public int windowAnimations;

還有一些window屬性不再一一列舉：

/**
* An alpha value to apply to this entire window.
* An alpha of 1.0 means fully opaque and 0.0 means fully transparent
*/
public float alpha = 1.0f;

/**
* When {@link #FLAG_DIM_BEHIND} is set, this is the amount of dimming
* to apply. Range is from 1.0 for completely opaque to 0.0 for no
* dim.
*/
public float dimAmount = 1.0f;

當然，還發現了一個屬性，systemUiVisibility：

/**
* Control the visibility of the status bar.
*
* @see View#STATUS_BAR_VISIBLE
* @see View#STATUS_BAR_HIDDEN
*/
public int systemUiVisibility;

源碼中介紹這個變數可以控制狀態欄的visibility，接著跳到View.STATUS_BAR_HIDDEN看看。

/**
* @deprecated Use {@link #SYSTEM_UI_FLAG_LOW_PROFILE} instead.
*/
public static final int STATUS_BAR_HIDDEN = SYSTEM_UI_FLAG_LOW_PROFILE;

發現已經被棄用了，SYSTEM_UI_FLAG_LOW_PROFILE替代了它。

/**
* Flag for {@link #setSystemUiVisibility(int)}: View has requested the
* system UI to enter an unobtrusive "low profile" mode.
*
*

This is for use in games, book readers, video players, or any other
* "immersive" application where the usual system chrome is deemed too distracting.
*
*

In low profile mode, the status bar and/or navigation icons may dim.
*
* @see #setSystemUiVisibility(int)
*/
public static final int SYSTEM_UI_FLAG_LOW_PROFILE = 0x00000001;

從這一段介紹看出，這個常量是在setSystemUiVisibility傳入的參數，竟然涉及到了沉浸式模式：用在遊戲，電子書閱讀或者任何「身臨其境」的應用，而在一般的系統瀏覽器中被認為是太分心的。這個留在下一篇博客細說吧，還打算封一個工具庫。

好的，內容非常的多，但不怎麼常用。

人往高處走，水往低處流。

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