Android Button设置Background背景图片无效的处理方法

 android  Android Button设置Background背景图片无效的处理方法已关闭评论
4月 262021

测试在 activity_main.xml给button加背景图片

    android:textColor="#fff" />

发现模拟器里不起作用,奇怪了, 后来查了网上资料,发现需要修改下面的文件才可以。
在res/values/themes.xml 中:
<style name="Theme.UICustomViews" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
<style name="Theme.UICustomViews" parent="Theme.MaterialComponents.DayNight.NoActionBar.Bridge">

css中 border, margin, padding,Background,Font,属性简写速记说明

 css  css中 border, margin, padding,Background,Font,属性简写速记说明已关闭评论
9月 262016



Shorthand properties are CSS properties that let you set the values of several other CSS properties simultaneously. Using a shorthand property, a Web developer can write more concise and often more readable style sheets, saving time and energy.

The CSS specification defines shorthand properties to group the definition of common properties acting on the same theme. E. g. the CSSbackground property is a shorthand property that’s able to define the value of background-colorbackground-imagebackground-repeat, and background-position. Similarly, the most common font-related properties can be defined using the shorthand font, and the different margins around a box can be defined using the margin shorthand.

Tricky edge cases

Even if they are very convenient to use, there are a few edge cases to keep in mind when using them:

  1. A value which is not specified is set to its initial value. That sounds anecdotal, but it really means that it overrides previously set values. Therefore:

    background-color: red; background: url(images/bg.gif) no-repeat top right;

    will not set the color of the background to red but to background-color‘s default, transparent, as the second rule has precedence.

  2. Only the individual properties values can inherit. As missing values are replaced by their initial value, it is impossible to allow inheritance of individual properties by omitting them. The keyword inherit can be applied to a property, but only as a whole, not as a keyword for one value or another. That means that the only way to make some specific value to be inherited is to use the longhand property with the keywordinherit.
  3. Shorthand properties try not to force a specific order for the values of the properties they replace. This works well when these properties use values of different types, as the order has no importance, but this does not work as easily when several properties can have identical values. Handling of these cases are grouped in several categories:

    1. Shorthands handling properties related to edges of a box, like border-stylemargin or padding, always use a consistent 1-to-4-value syntax representing those edges:

      border1.png The 1-value syntax: border-width: 1em — The unique value represents all edges
      border2.png The 2-value syntax: border-width: 1em 2em — The first value represents the vertical, that is top and bottom, edges, the second the horizontal ones, that is the left and right ones.
      border3.png The 3-value syntax: border-width: 1em 2em 3em — The first value represents the top edge, the second, the horizontal, that is left and right, ones, and the third value the bottom edge

      The 4-value syntax: border-width: 1em 2em 3em 4em — The four values represent the top, right, bottom and left edges respectively, always in that order, that is clock-wise starting at the top (The initial letter of Top-Right-Bottom-Left matches the order of the consonant of the word trouble: TRBL)

    2. Similarly, shorthands handling properties related to corners of a box, like border-radius, always use a consistent 1-to-4-value syntax representing those corners:

      corner1.png The 1-value syntax: border-radius: 1em — The unique value represents all corners
      corner2.png The 2-value syntax: border-radius: 1em 2em — The first value represents the top left and bottom right corner, the second the top right and bottom left ones.
      corner3.png The 3-value syntax: border-radius: 1em 2em 3em — The first value represents the top left corner, the second the top right and bottom left ones, and the third value the bottom right corner

      The 4-value syntax: border-radius: 1em 2em 3em 4em — The four values represent the top left, top right, bottom right and bottom left corners respectively, always in that order, that is clock-wise starting at the top left.

Background properties

A background with the following properties:

background-color: #000; background-image: url(images/bg.gif); background-repeat: no-repeat; background-position: top right;

Can be shortened to just one declaration:

background: #000 url(images/bg.gif) no-repeat top right;

(The shorthand form is actually the equivalent of the longhand properties above plus background-attachment: scroll and, in CSS3, some additional properties.)

Font properties

The following declarations:

font-style: italic; font-weight: bold; font-size: .8em; line-height: 1.2; font-family: Arial, sans-serif;

can be shortened to the following:

font: italic bold .8em/1.2 Arial, sans-serif;

This shorthand declaration is actually equivalent to the longhand declarations above plus font-variant: normal and font-size-adjust: none (CSS2.0 / CSS3), font-stretch: normal (CSS3).

Border properties

With borders, the width, color, and style can be simplified into one declaration. For example,

border-width: 1px; border-style: solid; border-color: #000;

Can be written as

border: 1px solid #000;

Margin and Padding properties

Shorthand versions of margin and padding values work the same way. The following CSS declarations:

margin-top: 10px; margin-right: 5px; margin-bottom: 10px; margin-left: 5px;

are the same as the following declaration (note that the values are in clockwise order from top: top, right, bottom, then left (TRBL, the consonants in “trouble”))

margin: 10px 5px 10px 5px;