Android4.0 Switch方法解析

就是很像开关的那种控件，它只有两个状态：on和off：在IOS中，有个UISwitch控件，其效果图，如下：

在android4.0里面，添加了一个和这个类似的控件：Switch，很形象，开关。效果图如下：

其类关系图如下：

java.lang.Object
	android.view.View
		android.widget.TextView
			android.widget.Button
				android.widget.CompoundButton
					android.widget.Switch

父类：compoundButton。

类的概述：

Switch是一个可以在两种状态切换的开关控件。用户可以拖动"thumb"来回选择，也可以像选择复选框一样点击切换Switch的状态。

主要方法：

Public Methods
int	getCompoundPaddingRight() Returns the right padding of the view, plus space for the right Drawable if any.
CharSequence	getTextOff() Returns the text displayed when the button is not in the checked state.
CharSequence	getTextOn() Returns the text displayed when the button is in the checked state.
void	jumpDrawablesToCurrentState() Call `Drawable.jumpToCurrentState()` on all Drawable objects associated with this view.
void	onMeasure(int widthMeasureSpec, int heightMeasureSpec) Measure the view and its content to determine the measured width and the measured height.
void	onPopulateAccessibilityEvent(AccessibilityEvent event) Called from `dispatchPopulateAccessibilityEvent(AccessibilityEvent)` giving a chance to this View to populate the accessibility event with its text content.
boolean	onTouchEvent(MotionEvent ev) Implement this method to handle touch screen motion events.
void	setChecked(boolean checked) Changes the checked state of this button.
void	setSwitchTextAppearance(Context context, int resid) Sets the switch text color, size, style, hint color, and highlight color from the specified TextAppearance resource.
void	setSwitchTypeface(Typeface tf, int style) Sets the typeface and style in which the text should be displayed on the switch, and turns on the fake bold and italic bits in the Paint if the Typeface that you provided does not have all the bits in the style that you specified.
void	setSwitchTypeface(Typeface tf) Sets the typeface in which the text should be displayed on the switch.
void	setTextOff(CharSequence textOff) Sets the text displayed when the button is not in the checked state.
void	setTextOn(CharSequence textOn) Sets the text displayed when the button is in the checked state.

getCompoundPaddingRight():没弄清楚什么意思。

在TextView中的源码：

[java] view plain copy

publicint getCompoundDrawablePadding() {
final Drawables dr = mDrawables;
return dr != null ? dr.mDrawablePadding : 0;
}

[java] view plain copy

publicint getCompoundDrawablePadding() {
final Drawables dr = mDrawables;
return dr != null ? dr.mDrawablePadding : 0;
}

jumpDrawableToCurrentState():在与Switch相关的Drawable操作时调用 Drawable.jumpToCurrentState()这个方法。

getTextOff()、getTextOn()、 setTextOff()、setTextOn()这四个方法比较简单，就是设定和获取非选中和选中状态下的文本值。

onMeasure():测量控件宽高，供绘图时使用。

onTouchEvent（MotionEvent ev）实现这一方法传递触摸屏运动事件。

setChecked()设置Switch的状态（选中，非选中）

setSwitchTextAppearance()设置字体大小

setSwitchTextTypefaces设置字体格式

看看google官方在/frameworks/base/core/res/res/values/styles.xml的一个定义：

[java] view plain copy

<style name="Widget.Holo.CompoundButton.Switch">
<item name="android:track">@android:drawable/switch_track_holo_dark</item>
<item name="android:thumb">@android:drawable/switch_inner_holo_dark</item>
<item name="android:switchTextAppearance">@android:style/TextAppearance.Holo.Widget.Switch</item>
<item name="android:textOn">@android:string/capital_on</item>
<item name="android:textOff">@android:string/capital_off</item>
<item name="android:thumbTextPadding">12dip</item>
<item name="android:switchMinWidth">96dip</item>
<item name="android:switchPadding">16dip</item>
</style>

[java] view plain copy

<style name="Widget.Holo.CompoundButton.Switch">
<item name="android:track">@android:drawable/switch_track_holo_dark</item>
<item name="android:thumb">@android:drawable/switch_inner_holo_dark</item>
<item name="android:switchTextAppearance">@android:style/TextAppearance.Holo.Widget.Switch</item>
<item name="android:textOn">@android:string/capital_on</item>
<item name="android:textOff">@android:string/capital_off</item>
<item name="android:thumbTextPadding">12dip</item>
<item name="android:switchMinWidth">96dip</item>
<item name="android:switchPadding">16dip</item>
</style>