再也不信网上流传的方法了！！android创建组件的真正写法！

摘要: android创建组件的真正写法

http://blog.csdn.net/jincf2011/article/details/6344678 气死我了 这货博客坑死大爷了大爷弄了两天各种毛病

一看官网原来这玩意儿不是这么写的

官网教程：

All of the view classes defined in the Android framework extend

View

. Your custom view can also extend

View

directly, or you can save time by extending one of the existing view subclasses, such as

Button

.
To allow the Android Developer Tools to interact with your view, at a minimum you must provide a constructor that takes a

Context

and an

AttributeSet

object as parameters. This constructor allows the layout editor to create and edit an instance of your view.

class PieChart extends View {
public PieChart(Context context, AttributeSet attrs) {
super(context, attrs);
}
}

Define Custom Attributes

To add a built-in

View

to your user interface, you specify it in an XML element and control its appearance and behavior with element attributes. Well-written custom views can also be added and styled via XML. To enable this behavior in your custom view, you must:

Define custom attributes for your view in a

<declare-styleable>

resource element

Specify values for the attributes in your XML layout

Retrieve attribute values at runtime

Apply the retrieved attribute values to your view

This section discusses how to define custom attributes and specify their values. The next section deals with retrieving and applying the values at runtime.
To define custom attributes, add

<declare-styleable>

resources to your project. It's customary to put these resources into a

res/values/attrs.xml

file. Here's an example of an

attrs.xml

file:

<resources>
<declare-styleable name="PieChart">
<attr name="showText" format="boolean" />
<attr name="labelPosition" format="enum">
<enum name="left" value="0"/>
<enum name="right" value="1"/>
</attr>
</declare-styleable>
</resources>

This code declares two custom attributes,

showText

and

labelPosition

, that belong to a styleable entity named

PieChart

. The name of the styleable entity is, by convention, the same name as the name of the class that defines the custom view. Although it's not strictly necessary to follow this convention, many popular code editors depend on this naming convention to provide statement completion.
Once you define the custom attributes, you can use them in layout XML files just like built-in attributes. The only difference is that your custom attributes belong to a different namespace. Instead of belonging to the

http://schemas.android.com/apk/res/android

namespace, they belong to

http://schemas.android.com/apk/res/[your package name]

. For example, here's how to use the attributes defined for

PieChart

:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:custom="http://schemas.android.com/apk/res/com.example.customviews">
<com.example.customviews.charting.PieChart
custom:showText="true"
custom:labelPosition="left" />
</LinearLayout>

In order to avoid having to repeat the long namespace URI, the sample uses an

xmlns

directive. This directive assigns the alias

custom

to the namespace

http://schemas.android.com/apk/res/com.example.customviews

. You can choose any alias you want for your namespace.
Notice the name of the XML tag that adds the custom view to the layout. It is the fully qualified name of the custom view class. If your view class is an inner class, you must further qualify it with the name of the view's outer class. further. For instance, the

PieChart

class has an inner class called

PieView

. To use the custom attributes from this class, you would use the tag

com.example.customviews.charting.PieChart$PieView

.

Apply Custom Attributes

When a view is created from an XML layout, all of the attributes in the XML tag are read from the resource bundle and passed into the view's constructor as an

AttributeSet

. Although it's possible to read values from the

AttributeSet

directly, doing so has some disadvantages:

Resource references within attribute values are not resolved

Styles are not applied

Instead, pass the

AttributeSet

to

, int, int)]obtainStyledAttributes()

. This method passes back a

TypedArray

array of values that have already been dereferenced and styled.
The Android resource compiler does a lot of work for you to make calling

, int, int)]obtainStyledAttributes()

easier. For each

<declare-styleable>

resource in the res directory, the generated R.java defines both an array of attribute ids and a set of constants that define the index for each attribute in the array. You use the predefined constants to read the attributes from the

TypedArray

. Here's how the

PieChart

class reads its attributes:

public PieChart(Context context, AttributeSet attrs) {
super(context, attrs);
TypedArray a = context.getTheme().obtainStyledAttributes(
attrs,
R.styleable.PieChart,
0, 0);

try {
mShowText = a.getBoolean(R.styleable.PieChart_showText, false);
mTextPos = a.getInteger(R.styleable.PieChart_labelPosition, 0);
} finally {
a.recycle();
}
}

Note that

TypedArray

objects are a shared resource and must be recycled after use.
太长了是吧 简单说一下：

自定义组件NewView继承一个View类

重写构造函数

public NewView(Context context) {
this(context,null);
}
public NewView(Context context, AttributeSet attrs) {
super(context, attrs);
}

为了专业一点 让xml文件能配置这个组件 ，需要在values下的attrs.xml中定义一下自定义组件的参数

<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="NewView">
<attr name="pressedIcon" format="reference" />
<attr name="buttonIcon" format="reference"/>
<attr name="text" format="string"/>
<attr name="iconSize" format="dimension"/>
<attr name="textSize" format="dimension"/>
</declare-styleable>
</resources>

reference 代表引用资源文件 string代表字符 color 代表颜色 dimension代表大小

好了现在可以在布局文件中引入这个组件了

<com.xxx.app.view.NewView
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
app:text="@string/main_one"
app:iconSize="20dp"/>

app代表属性的namespace，如果用android studio的话

根元素加上

xmlns:app="http://schemas.android.com/apk/res-auto"

如果是eclipse 需要替换成

xmlns:app="http://schemas.android.com/apk/res/包名"

然后我们在构造函数中处理这些传入的参数

TypedArray a = context.getTheme().obtainStyledAttributes(attrs, R.styleable.NewView, 0, 0);
try{
CharSequence text = a.getText(R.styleable.NewView_text);
}finally{
a.recycle();
}

取到的参数怎么处理 就不用说了哈