Cool Android Apis 整理（一）

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Foreword

Cool Android Apis

Dan Lew

Content

]Activity.startActivities()

Activity.startActivities()

Contex

ContextCompat

* Launch multiple new activities.  This is generally the same as calling
* {@link #startActivity(Intent)} for the first Intent in the array,
* that activity during its creation calling {@link #startActivity(Intent)}
* for the second entry, etc.  Note that unlike that approach, generally
* none of the activities except the last in the array will be created
* at this point, but rather will be created when the user first visits
* them (due to pressing back from the activity on top).

startActiviyies

Activity

TextUtils.isEmpty()

String

Html.fromHtml()

Html

linkView.setText(
Html.fromHtml(
"<b>fromHtml:</b>  \t Click " +
"<a href=\"http://oakzmm.com\">here</a> " +
"to visit my website "
)
);

TextView.setError()

View.isShown())

view.getVisibility() == View.VISIBLE

[code]editText = (EditText) findViewById(R.id.text);
System.out.println("------------------" + editText.isShown());
System.out.println("------------------" + (editText.getVisibility() == View.VISIBLE));
[/code]
log：

08-05 16:47:29.822  12720-12720/com.macouen.testdemo I/System.out﹕ ------------------false
08-05 16:47:29.822  12720-12720/com.macouen.testdemo I/System.out﹕ ------------------true

然而Google文档)：

[code]public boolean isShown ()                  Added in API level 1
Returns the visibility of this view and all of its ancestors
Returns
True if this view and all of its ancestors are VISIBLE
[/code]
摔！老老实实用 
view.getVisibility() == View.VISIBLE
 吧。

Build.VERSION_CODES
有些时候我们的app需要根据不同的SDK版本进行执行不同的操作

Example:

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
ActionBar actionBar = getActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
}

PhoneNumberUtils.convertKeypadLettersToDigits
这个方法简单粗暴，但是我没用过。这个方法会将输入的字母根据键盘上的映射转换为数字。

Translates any alphabetic letters (i.e. [A-Za-z]) in the specified phone number into the equivalent numeric digits, according to the phone keypad letter mapping described in ITU E.161 and ISO/IEC 9995-8.

所谓的ITU E.161 标准的键盘就是我们常用的T9键盘。也就是这样





ArgbEvaluator
!!重点这个方法简直不要太吊。。

ArgbEvaluator.evaluate(float fraction, Object startValue, Object endValue);
根据一个起始颜色值和一个结束颜色值以及一个偏移量生成一个新的颜色，分分钟实现类似于微信底部栏滑动颜色渐变。

这里提供另一个颜色渐变的版本

From Google Sample
SlidingTabsColors下的 
SlidingTabStrip.java


[code]/**
* Blend {@code color1} and {@code color2} using the given ratio.
*
* @param ratio of which to blend. 1.0 will return {@code color1}, 0.5 will give an even blend,
*              0.0 will return {@code color2}.
*/
private static int blendColors(int color1, int color2, float ratio) {
final float inverseRation = 1f - ratio;
float r = (Color.red(color1) * ratio) + (Color.red(color2) * inverseRation);
float g = (Color.green(color1) * ratio) + (Color.green(color2) * inverseRation);
float b = (Color.blue(color1) * ratio) + (Color.blue(color2) * inverseRation);
return Color.rgb((int) r, (int) g, (int) b);
}
[/code]
PS：这里说到ARGB，简单的提一下关于Alpha的问题 (和这个Tip并没有联系)。在Google I/O 2013大会上 
Romain Guy
 在
Android Graphics Performance
 这部分提到了
use alpha with care
 。具体的可以参考：

Android
Performance Case Study Follow-up
Best Practices for Using Alpha

Space
Added in API level 14

Space is a lightweight View subclass that may be used to create gaps between components in general purpose layouts.

最棒的一点是Space可以跳过 
Draw
 这个过程。

ValueAnimator.reverse()
之前见不少人提过这个方法，都是说可以顺畅的取消动画效果。文档中是这样说的。

Plays the ValueAnimator in reverse. If the animation is already running, it will stop itself and play backwards from the point reached when reverse was called. If the animation is not currently running, then it will start from the end and play backwards.
This behavior is only set for the current animation; future playing of the animation will use the default behavior of playing forward.

也就是说这个方法其实是反转动画，如果动画正在播放，这个方法停止动画，并从当前点往回播。如果动画已经播放完毕那就反过来一遍。那么也就是说 “顺畅的取消动画效果” ，是动画还在播放的是时候来调用
reverse
 这个方法。

待续。

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作者：Oak_Zmm

出处：http://oakzmm