9Patch图片介绍
9Patch图片是一种特殊的png图片,以.9.png结尾,它在原始的图片四周各添加一个宽度为1像素的像条,这4条线条决定了该图片的缩放规则、内容显示规则。
在Android Studio 上编辑.9.png,具体是在Android Studio上右键点击你要编辑的照片,选择Create 9-Patch file就可以进入编辑界面。
这就是9-Patch的编辑界面
Optional controls include:
- Zoom: Adjust the zoom level of the graphic in the drawing area.
- Patch scale: Adjust the scale of the images in the preview area.
- Show lock: Visualize the non-drawable area of the graphic on mouse-over.
- Show patches: Preview the stretchable patches in the drawing area (pink is a stretchable patch), as shown in figure 2, above.
- Show content: Highlight the content area in the preview images (purple is the area in which content is allowed), as shown in figure 2.
- Show bad patches: Adds a red border around patch areas that may produce artifacts in the graphic when stretched, as shown in figure 2. Visual coherence of your stretched image will be maintained if you eliminate all bad patches.
这3个从上到下依次是
- 纵向拉伸的预览
- 横线拉伸的预览
- 纵横向一起拉伸的预览
9Patch的规则：
-
上侧和左侧的黑色线段共同决定了图片的缩放区域
- 上侧的黑色线段为上边界绘制巨型,它覆盖的区域可以水平缩放。
- 左侧的黑色线段为左边界绘制巨型,它覆盖的区域可以纵向上缩放。
- 它们二者的交集区域可以在两个方向上缩放
-
下侧和右侧的黑色线段共同决定了图片的内容显示区域
- 以下侧的黑色线段为下边界绘制巨型
- 以右侧的黑色线段为右边界绘制巨型
- 它们二者的交集区域为内容显示区域
9Patch 相关文章
Android设计中如何切图.9.png（点9图）
转自: http://www.miued.com/2074/
在Android的设计过程中,为了适配不同的手机分辨率,图片大多需要拉伸或者压缩,这样就出现了可以任意调整大小的一种图片格式“.9.png”。这种图片是用于Android开发的一种特殊的图片格式,它的好处在于可以用简单的方式把一张图片中哪些区域可以拉伸,哪些区域不可以拉伸设定好,同时可以把显示内容区域的位置标示清楚。
本文结合一些具体的例子来看下.9.png的具体用法。
首先看下普通的.png资源与.9.png的资源区别：
普通的png资源就不多介绍了,可以明显看到.9.png的外围是有一些黑色的线条的,那这些线条是用来做什么的呢？我们来看下放大的图像：
放大后可以比较明显的看到上下左右分别有一个像素的黑色线段,这里分别标注了序号。简单来说,序号1和2标识了可以拉伸的区域,序号3和4标识了内容区域。当设定了按钮实际应用的宽和高之后,横向会拉伸1区域的像素,纵向会拉伸2区域的像素。如下图：
拉伸的含义应该比较容易理解,但是内容区域的标注有什么意义呢？我们来看下图：
这里程序设置的文字垂直居中,水平居左的对齐方式。对齐方式是没有问题的,但是对于这种大圆角同时又有些不规则边框的的图形来说,错误的标注方式会让排版看起来很混乱。所以我们需要修正内容区域的线段位置和长度。
把横向的内容区域缩短到圆角以内,纵向的内容区域控制在输入框的高度以内,这样文字就可以正常显示了。
这里还有一种特殊情况,就是本身是.9.png的资源,但是在修改过程中你希望这张.9.png不能被拉伸（在做皮肤的情况中有可能会遇到）,那怎么办呢？只要把拉伸区域的点点在透明像素的地方就可以了,这样拉伸的时候会拉伸透明部分的像素,而不会拉伸图像本身。如下图:
大家可以看到拉伸区域的黑点是可以不连续的。
说了半天.9.png的用法,那.9.png如何输出呢？有很多种方式可以输出.9.png,比如说用draw9patch.bat这个工具,或者简单一点,用photoshop直接输出。输出的方式是先输出普通的png资源,然后扩大画布大小,上下左右各空出一个像素,再用一个像素的铅笔工具（颜色选择纯黑色）,上下左右分别画点就可以了,保存的时候注意把后缀修改为.9.png。
有两点需要特别注意下：
1.最外围的一圈像素必须要么是纯黑色,要么是透明,一点点的半透明的像素都不可以有,比如说99%的黑色或者是1%的投影都不可以有;
2.文件的后缀名必须是.9.png,不能是.png或者是.9.png.png,这样的命名都会导致编译失败。
A simple guide to 9-patch for Android UI
转自:http://radleymarx.com/ux-dev/simple-guide-to-9-patch/
While I was working on my first Android app, I found 9-patch (aka 9.png) to be confusing and poorly documented. After a little while, I finally picked up on how it works and decided to throw together something to help others figure it out.
Basically, 9-patch uses png transparency to do an advanced form of 9-slice or scale9. The guides are straight, 1-pixel black lines drawn on the edge of your image that define the scaling and fill of your image. By naming your image file name.9.png, Android will recognize the 9.png format and use the black guides to scale and fill your bitmaps.
Here's a basic guide map:
9-patch-guides
As you can see, you have guides on each side of your image. The TOP and LEFT guides are for scaling your image (i.e. 9-slice), while the RIGHT and BOTTOM guides define the fill area.
The black guide lines are cut-off/removed from your image - they won't show in the app. Guides must only be one pixel wide, so if you want a 48x48 button, your png will actually be 50x50. Anything thicker than one pixel will remain part of your image. (My examples have 4-pixel wide guides for better visibility. They should really be only 1-pixel).
Your guides must be solid black (#000000). Even a slight difference in color (#000001) or alpha will cause it to fail and stretch normally. This failure won't be obvious either*, it fails silently! Yes. Really. Now you know.
Also you should keep in mind that remaining area of the one-pixel outline must be completely transparent. This includes the four corners of the image - those should always be clear. This can be a bigger problem than you realize. For example, if you scale an image in Photoshop it will add anti-aliased pixels which may include almost-invisible pixels which will also cause it to fail*. If you must scale in Photoshop, use the Nearest Neighbor setting in the Resample Image pulldown menu (at the bottom of the Image Size pop-up menu) to keep sharp edges on your guides.
This is actually a "fix" in the latest dev kit. Previously it would manifest itself as all of your other images and resources suddenly breaking, not the actually broken 9-patch image.
scalable-area
The TOP and LEFT guides are used to define the scalable portion of your image - LEFT for scaling height, TOP for scaling width. Using a button image as an example, this means the button can stretch horizontally and vertically within the black portion and everything else, such as the corners, will remain the same size. The allows you to have buttons that can scale to any size and maintain a uniform look.
It's important to note that 9-patch images don't scale down - they only scale up. So it's best to start as small as possible.
Also, you can leave out portions in the middle of the scale line. So for example, if you have a button with a sharp glossy edge across the middle, you can leave out a few pixels in the middle of the LEFT guide. The center horizontal axis of your image won't scale, just the parts above and below it, so your sharp gloss won't get anti-aliased or fuzzy.
Fill area guides are optional and provide a way define the area for stuff like your text label. Fill determines how much room there is within your image to place text, or an icon, or other things. 9-patch isn't just for buttons, it works for background images as well.
The above button & label example is exaggerated simply to explain the idea of fill - the label isn't completely accurate. To be honest, I haven't experienced how Android does multi-line labels since a button label is usually a single row of text.
Finally, here's a good demonstration of how scale and fill guides can vary, such as a LinearLayout with a background image & fully rounded sides:
With this example, the LEFT guide isn't used but we're still required to have a guide. The background image don't scale vertically; it just scales horizontally (based on the TOP guide). Looking at the fill guides, the RIGHT and BOTTOM guides extend beyond where they meet the image's curved edges. This allows me to place my round buttons close to the edges of the background for a tight, fitted look.
So that's it. 9-patch is super easy, once you get it. It's not a perfect way to do scaling, but the fill-area and multi-line scale-guides does offer more flexibility than traditional 9-slice and scale9. Give it a try and you'll figure it out quickly.
其他资料
Create resizable bitmaps (9-Patch files)
Drawables overview