自定义控件1.官方文档翻译

Android offers a sophisticated and powerful componentized model for
building your UI, based on the fundamental layout classes: View and
ViewGroup.
To start with, the platform includes a variety of prebuilt View and ViewGroup
subclasses — called widgets and layouts, respectively — that you can use to
construct your UI.

Android提供了一种精致的且强大的组件化模型用于构建你的UI, 这种模型基于基本的类: View 和 ViewGroup.
平台包括了大量的预置的View(视图)和ViewGroup (视图)组子类--分别称为控件和布局, 这些类可以用来构建你的UI.

A partial list of available widgets includes Button,
TextView,
EditText,
ListView,
CheckBox,
RadioButton,
Gallery,
Spinner,
and the more special-purpose AutoCompleteTextView,
ImageSwitcher,
and TextSwitcher.

部分可用的控件包括 ... , 还有一些特殊用途的控件比如: ... .

Among the layouts available are LinearLayout,
FrameLayout,
RelativeLayout,
and others. For more examples, see Common
Layout Objects.

可用的布局有: ... 等等, 更多的例子请参考:

If none of the prebuilt widgets or layouts meets your needs, you can
create your own View subclass. If you only need to make small adjustments to an
existing widget or layout, you can simply subclass the widget or layout and
override its methods.

如果预置的控件和视图都不满足你的需求, 你可以创建你自己的视图子类. 如果你只是需要在已有的控件或者布局上做一些微调, 你只需继承它,
并且重写它的方法即可.

Creating your own View subclasses gives you precise control over the
appearance and function of a screen element. To give an idea of the control you
get with custom views, here are some examples of what you could do with
them:

创建你自己的视图类, 你可以精确的控制一个屏幕元素的外观和功能. 这里有一些例子,
可以让你精确的控制自定义的视图:

• You could create a completely custom-rendered View type, for example a
  "volume control" knob rendered using 2D graphics, and which resembles an analog
  electronic control.  你可以创建一个完全自定义风格的视图类型, 比如, 使用2D图形创建声音控制手柄, 就像电子控制的那样.
• You could combine a group of View components into a new single component,
  perhaps to make something like a ComboBox (a combination of popup list and free
  entry text field), a dual-pane selector control (a left and right pane with a
  list in each where you can re-assign which item is in which list), and so on. 
  你可以把一些组件组合起来成为一个新的组件,  就像ComboBox, 一个选择控制器, 等等
• You could override the way that an EditText component is rendered on the
  screen (the Notepad
  Tutorial uses this to good effect, to create a lined-notepad page). 
  你可以覆盖一个View在屏幕上的渲染方式, the Notepad
  Tutorial 就使用了这种方式, 创建了一种带下划线的显示页面.
• You could capture other events like key presses and handle them in some
  custom way (such as for a game).  你可以捕获别的一些事件, 比如键盘按下, 自定义处理方式.

The Basic Approach

基本方法

Here is a high level overview of what you need to know to get started in
creating your own View components:

这里高度概括了一些步骤, 教你如何创建你的自定义组件.

1. Extend an existing View
   class or subclass with your own class.   继承View类或其子类
2. Override some of the methods from the superclass. The superclass methods to
   override start with ‘on‘, for example, onDraw(),
   onMeasure(),
   and onKeyDown().
   This is similar to the on... events in Activity
   or ListActivity
   that you override for lifecycle and other functionality hooks.   重写父类的一些方法.
   这些方法一般以 on 开头. 比如: ... , 这和你在activity中重写的生命周期方法等一些钩子功能的方法很类似.
3. Use your new extension class. Once completed, your new extension class can
   be used in place of the view upon which it was based.  使用你自己的类, 一旦创建,
   你的这些类可以用在任何父类可以使用的地方.

Tip: Extension classes can be defined as inner classes inside the activities
that use them. This is useful because it controls access to them but isn‘t
necessary (perhaps you want to create a new public View for wider use in your
application).

Tip: 子类可以定义为使用它的activity的内部类.这样方便控制访问, 但是这不是必须的.

Fully Customized Components

完全自定义的组件可以用来创建任何你想要的图形组件. 也许是一个像电压表的图形计量器, 或者想卡拉OK里面显示歌词的小球随着音乐滚动. 无论怎样,
内置的组件或者他们的组合是无法满足你的需求的.

Fortunately, you can easily create components that look and behave in any way
you like, limited perhaps only by your imagination, the size of the screen, and
the available processing power (remember that ultimately your application might
have to run on something with significantly less power than your desktop
workstation).

幸运的是,
你可以以你自己的要求轻松地创建完全属于自己的组件，你会发现不够用的只是你的想象力、屏幕的尺寸和处理器的性能（记住你的应用程序最后只会在那些性能低于桌面电脑的平台上面运行）。

To create a fully customized component:

要创建完全自定义组件:

1. The most generic view you can extend is, unsurprisingly, View, so
   you will usually start by extending this to create your new super component. 
   毫无疑问, 最普通的视图类就是View, 你需要继承它.
2. You can supply a constructor which can take attributes and parameters from
   the XML, and you can also consume your own such attributes and parameters
   (perhaps the color and range of the VU meter, or the width and damping of the
   needle, etc.)  重写一个构造方法, 这个构造方法必须可以把xml文件中的属性和值做为方法参数传入, 你也可以在xml文件中自己定义属性和值.
3. You will probably want to create your own event listeners, property
   accessors and modifiers, and possibly more sophisticated behavior in your
   component class as well.  你可能创建自己的事件监听器, 属性访问器和修改器, 或许是控制更加复杂精致的行为的代码.
4. You will almost certainly want to override onMeasure() and are also likely
   to need to override onDraw() if you want the component to show something. While
   both have default behavior, the default onDraw() will do nothing, and the
   default onMeasure() will always set a size of 100x100 — which is probably not
   what you want.  一般来说, 你需要重写 onMeasure() 方法, 同样的, 如果你想要在控件上显示一些东西的话, 也需要重写
   onDraw() . 这两个方法都有默认行为, onDraw() 方法什么也不做, 而onMeasure()方法会默认把大小设置成 100x100,
   这个数值或许不是你想要的.
5. Other on... methods may also be overridden as required.  需要的话, 重写其他的以 on
   开头的方法.

Extend onDraw() and onMeasure()

The onDraw() method delivers you a Canvas
upon which you can implement anything you want: 2D graphics, other standard or
custom components, styled text, or anything else you can think of.

onDraw() 方法会传递进来一个 Canvas(画布) 对象, 在这个画布上, 你可以绘制任何2D图形, 包括其他的标准或者自定义组件,
有样式的文字, 或者任何你可以想到的东西.

Note: This does not apply to 3D graphics. If you want to use 3D graphics, you
must extend SurfaceView
instead of View, and draw from a separate thread. See the GLSurfaceViewActivity
sample for details.

这里不适用3D图形.如果你想使用3D图形, 你必须继承 SurfaceView, 而不是View, 并且要在新线程里绘制.

onMeasure() is a little more involved. onMeasure() is a critical piece of the
rendering contract between your component and its container. onMeasure() should
be overridden to efficiently and accurately report the measurements of its
contained parts. This is made slightly more complex by the requirements of
limits from the parent (which are passed in to the onMeasure() method) and by
the requirement to call the setMeasuredDimension() method with the measured
width and height once they have been calculated. If you fail to call this method
from an overridden onMeasure() method, the result will be an exception at
measurement time.

onMeasure() 更复杂一点. 它是组件和其容器之间的渲染的决定性部分. 重写 onMeasure()
时要有效地精确地计算出它包含的内容的尺寸.这有点小麻烦，因为我们不但要考虑父类的限制（通过onMeasure（）传过来的），同时我们应该知道一旦测量宽度和高度出来后，就要立即调用setMeasuredDimension(int
measuredWidth, int measuredHeight) 方法, 把测量好的宽和高设置进去. 如果重写的onMeasure方法里没有调用这个方法,
在测量时会抛异常.

At a high level, implementing onMeasure() looks something like this:

概括说来, 实现 onMeasure 会做以下这些事情:

1. The overridden onMeasure() method is called with width and height measure
   specifications (widthMeasureSpec and heightMeasureSpec parameters, both are
   integer codes representing dimensions) which should be treated as requirements
   for the restrictions on the width and height measurements you should produce. A
   full reference to the kind of restrictions these specifications can require can
   be found in the reference documentation under View.onMeasure(int,
   int) (this reference documentation does a pretty good job of explaining the
   whole measurement operation as well).  
   重载的onMeasure（）方法会被调用，高度和宽度参数同时也会涉及到（widthMeasureSpec
   和heighMeasureSpec两个参数都是整数类型），同时你应该考虑你产品的尺寸限制。这里详细的内容可以参考View.onMeasure(int,
   int) （这个连接内容详细的解释了整个measurement操作）。
2. Your component‘s onMeasure() method should calculate a measurement width and
   height which will be required to render the component. It should try to stay
   within the specifications passed in, although it can choose to exceed them (in
   this case, the parent can choose what to do, including clipping, scrolling,
   throwing an exception, or asking the onMeasure() to try again, perhaps with
   different measurement
   specifications). 你的组件要通过onMeasure（）计算得到必要的measurement长度和宽度从而来显示你的组件，它应该与规格保持一致，尽管它可以实现一些规格以外的功能（在这个例子里，父类能够选择做什么，包括剪切、滑动、提交异常或者用不同的参数又一次调用onMeasure（）函数）。
3. Once the width and height are calculated, the setMeasuredDimension(int
   width, int height) method must be called with the calculated measurements.
   Failure to do this will result in an exception being
   thrown. 一旦高度和宽度计算出来之后，必须调用setMeasuredDimension(int width, int
   height)，否则就会导致异常。

----------------------

protected void onMeasure (int
widthMeasureSpec, int heightMeasureSpec)

Measure the view and its content to determine the measured width and the
measured height. This method is invoked by measure(int,
int) and should be overriden by subclasses to provide accurate and efficient
measurement of their contents.

测量view和它里面的内容, 从而确定测量之后的宽度和高度. 这个方法由 measure() 方法调用, 子类应该重写他, 提供精确有效的尺寸.

CONTRACT: When overriding this method, you must call setMeasuredDimension(int,
int) to store the measured width and height of this view. Failure to do so
will trigger an IllegalStateException, thrown by measure(int,
int). Calling the superclass‘ onMeasure(int,
int) is a valid use.

约定: 重写这个方法时, 你一定要调用 setMeasuredDimension(int, int) 方法, 用来保存测量之后的宽和高.
否则会抛异常

The base class implementation of measure defaults to the background size,
unless a larger size is allowed by the MeasureSpec. Subclasses should override
onMeasure(int,
int) to provide better measurements of their content.

父类中的实现只是设置了默认的背景大小, 子类要提供更好的测量尺寸.

If this method is overridden, it is the subclass‘s responsibility to make
sure the measured height and width are at least the view‘s minimum height and
width (getSuggestedMinimumHeight()
and getSuggestedMinimumWidth()).

如果子类重写了这个方法, 子类就要负责保证测量后的宽和高要至少要为view对象最小的宽和高.

Parameters

----------------------

Here‘s a summary of some of the other standard methods that the framework
calls on views:

这里总结了框架会在view上调用的一些其他标准的方法

A Custom View Example

The CustomView sample in the API
Demos provides an example of a customized View. The custom View is defined
in the LabelView
class.

API Demos 里的CustomView sample 提供了自定义视图的例子. LabelView类定义了自定义视图.

The LabelView sample demonstrates a number of different aspects of custom
components:

LabelView的例子展示了自定义组件的方方面面:

• Extending the View class for a completely custom component.
• Parameterized constructor that takes the view inflation parameters
  (parameters defined in the XML). Some of these are passed through to the View
  superclass, but more importantly, there are some custom attributes defined and
  used for LabelView.
• Standard public methods of the type you would expect to see for a label
  component, for example setText(), setTextSize(), setTextColor() and so on.
• An overridden onMeasure method to determine and set the rendering size of
  the component. (Note that in LabelView, the real work is done by a private
  measureWidth() method.)
• An overridden onDraw() method to draw the label onto the provided
  canvas.

You can see some sample usages of the LabelView custom View in custom_view_1.xml
from the samples. In particular, you can see a mix of both android: namespace
parameters and custom app: namespace parameters. These app: parameters are the
custom ones that the LabelView recognizes and works with, and are defined in a
styleable inner class inside of the samples R resources definition
class.

你可以在 xxx 里找到一些 LV的用法. 需要注意的是, 在这个xml文件里, 你可以看到安卓的名称空间和自定义的名称空间混合使用. 以
app开头的参数是自定义的, LV工作需要依赖这些参数, 这些参数会被定义为 R 文件中的 styleable 内部类.

Compound Controls

合成控件

如果你不想完全自定义组件, 而是想把几个已有控件组合成一个可重用的组件, 那么就可以创建一个组合控件. 概括的说,
这就是把一些原子性的控件做合成了一个控件. 比如说, 选择框可以认为是一个单行的et和一个相邻的带弹出列表的按钮的组合.

In Android, there are actually two other Views readily available to do this:
Spinner
and AutoCompleteTextView,
but regardless, the concept of a Combo Box makes an easy-to-understand
example.

事实上, 在android中, 还有另外两个视图也是这样: , 但是cb更容易理解.

To create a compound component: 要创建组合控件:

To create a compound component:

1. The usual starting point is a Layout of some kind, so create a class that
   extends a Layout. Perhaps in the case of a Combo box we might use a LinearLayout
   with horizontal orientation. Remember that other layouts can be nested inside,
   so the compound component can be arbitrarily complex and structured. Note that
   just like with an Activity, you can use either the declarative (XML-based)
   approach to creating the contained components, or you can nest them
   programmatically from your code.  通常要从Layout类开始, 创建一个类, 继承一种Layout
2. In the constructor for the new class, take whatever parameters the
   superclass expects, and pass them through to the superclass constructor first.
   Then you can set up the other views to use within your new component; this is
   where you would create the EditText field and the PopupList. Note that you also
   might introduce your own attributes and parameters into the XML that can be
   pulled out and used by your constructor.
3. You can also create listeners for events that your contained views might
   generate, for example, a listener method for the List Item Click Listener to
   update the contents of the EditText if a list selection is made.
4. You might also create your own properties with accessors and modifiers, for
   example, allow the EditText value to be set initially in the component and query
   for its contents when needed.
5. In the case of extending a Layout, you don‘t need to override the onDraw()
   and onMeasure() methods since the layout will have default behavior that will
   likely work just fine. However, you can still override them if you need to.
6. You might override other on... methods, like onKeyDown(), to perhaps choose
   certain default values from the popup list of a combo box when a certain key is
   pressed.

To summarize, the use of a Layout as the basis for a Custom Control has a
number of advantages, including:

• You can specify the layout using the declarative XML files just like with an
  activity screen, or you can create views programmatically and nest them into the
  layout from your code.
• The onDraw() and onMeasure() methods (plus most of the other on... methods)
  will likely have suitable behavior so you don‘t have to override them.
• In the end, you can very quickly construct arbitrarily complex compound
  views and re-use them as if they were a single component.

Examples of Compound Controls

In the API Demos project that comes with the SDK, there are two List examples
— Example 4 and Example 6 under Views/Lists demonstrate a SpeechView which
extends LinearLayout to make a component for displaying Speech quotes. The
corresponding classes in the sample code are List4.java and
List6.java.

Modifying an Existing View Type

For example, the SDK includes a NotePad
application in the samples. This demonstrates many aspects of using the
Android platform, among them is extending an EditText View to make a lined
notepad. This is not a perfect example, and the APIs for doing this might change
from this early preview, but it does demonstrate the principles.

If you haven‘t done so already, import the NotePad sample into Eclipse (or
just look at the source using the link provided). In particular look at the
definition of MyEditText in the NoteEditor.javafile.

Some points to note here

1. The Definition

   The class is defined with the following line:
   public static class
   MyEditText extends EditText

   • It is defined as an inner class within the NoteEditor activity, but it is
     public so that it could be accessed as NoteEditor.MyEditText from outside of the
     NoteEditor class if desired.
   • It is static, meaning it does not generate the so-called "synthetic methods"
     that allow it to access data from the parent class, which in turn means that it
     really behaves as a separate class rather than something strongly related to
     NoteEditor. This is a cleaner way to create inner classes if they do not need
     access to state from the outer class, keeps the generated class small, and
     allows it to be used easily from other classes.
   • It extends EditText, which is the View we have chosen to customize in this
     case. When we are finished, the new class will be able to substitute for a
     normal EditText view.
2. Class Initialization
   
   As always, the super is called first. Furthermore, this is not a default
   constructor, but a parameterized one. The EditText is created with these
   parameters when it is inflated from an XML layout file, thus, our constructor
   needs to both take them and pass them to the superclass constructor as
   well.
3. Overridden Methods
   
   In this example, there is only one method to be overridden: onDraw() — but
   there could easily be others needed when you create your own custom
   components.

   For the NotePad sample, overriding the onDraw() method allows us to paint the
   blue lines on the EditText view canvas (the canvas is passed into the overridden
   onDraw() method). The super.onDraw() method is called before the method ends.
   The superclass method should be invoked, but in this case, we do it at the end
   after we have painted the lines we want to include.

4. Use the Custom Component
   
   We now have our custom component, but how can we use it? In the NotePad
   example, the custom component is used directly from the declarative layout, so
   take a look at note_editor.xml in the res/layout folder.

   <view
   class="com.android.notepad.NoteEditor$MyEditText"
     id="@+id/note"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:background="@android:drawable/empty"
   android:padding="10dip"
   android:scrollbars="vertical"
   android:fadingEdge="vertical"/>

   • The custom component is created as a generic view in the XML, and the class
     is specified using the full package. Note also that the inner class we defined
     is referenced using the NoteEditor$MyEditText notation which is a standard way
     to refer to inner classes in the Java programming language.

     If your custom View component is not defined as an inner class, then you can,
     alternatively, declare the View component with the XML element name, and exclude
     the class attribute. For example:

     <com.android.notepad.MyEditText
     id="@+id/note"
       ...
     />

     Notice that the MyEditText class is now a separate class file. When the class
     is nested in the NoteEditor class, this technique will not work.

   • The other attributes and parameters in the definition are the ones passed
     into the custom component constructor, and then passed through to the EditText
     constructor, so they are the same parameters that you would use for an EditText
     view. Note that it is possible to add your own parameters as well, and we will
     touch on this again below.

And that‘s all there is to it. Admittedly this is a simple case, but that‘s
the point — creating custom components is only as complicated as you need it to
be.

A more sophisticated component may override even more on... methods and
introduce some of its own helper methods, substantially customizing its
properties and behavior. The only limit is your imagination and what you need
the component to do.

来自为知笔记(Wiz)