【转】Android SwitchButton（滑动开关）

时间：2015-02-13 16:01:23 阅读：215 评论：0 收藏：0 [点我收藏+]

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原文网址：http://blog.csdn.net/wangjinyu501/article/details/27961303

版本：1.0

日期：2014.5.17 2014.6.1

在介绍SwitchButton之前，先来看一下系统Button是如何实现的。源码如下：

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@RemoteView
public class Button extends TextView {
public Button(Context context) {
this(context, null);
}
public Button(Context context, AttributeSet attrs) {
this(context, attrs, com.android.internal.R.attr.buttonStyle);
}
public Button(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
@Override
public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
super.onInitializeAccessibilityEvent(event);
event.setClassName(Button. class.getName());
}
@Override
public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
super.onInitializeAccessibilityNodeInfo(info);
info.setClassName(Button. class.getName());
}
}

是直接继承于TextView，所不同的是在构造方法中添加了Button的样式，并且在初始化可见性方面交由Button类自己来处理。虽然Button的实现比较简单，但是它的子类并不是这样。看一下：

直接子类只有有一个，CompoundButton。它是一个抽象类，而实现这个类的控件正是CheckBox, RadioButton, Switch, ToggleButton这四个，所以先重点说一下它。源码如下：

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/**
*
* A button with two states, checked and unchecked. When the button is pressed
* or clicked, the state changes automatically.
*
*
* XML attributes
*
* See {@link android.R.styleable#CompoundButton
* CompoundButton Attributes}, {@link android.R.styleable#Button Button
* Attributes}, {@link android.R.styleable#TextView TextView Attributes}, {@link
* android.R.styleable #View View Attributes}
*
*/
public abstract class CompoundButton extends Button implements Checkable {
private boolean mChecked ;
private int mButtonResource ;
private boolean mBroadcasting ;
private Drawable mButtonDrawable;
private OnCheckedChangeListener mOnCheckedChangeListener;
private OnCheckedChangeListener mOnCheckedChangeWidgetListener ;
private static final int[] CHECKED_STATE_SET = {
R.attr.state_checked
};
public CompoundButton(Context context) {
this(context, null);
}
public CompoundButton(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public CompoundButton(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
TypedArray a =
context.obtainStyledAttributes(
attrs, com.android.internal.R.styleable.CompoundButton, defStyle, 0);
Drawable d = a.getDrawable(com.android.internal.R.styleable.CompoundButton_button);
if (d != null ) {
setButtonDrawable(d);
}
boolean checked = a
.getBoolean(com.android.internal.R.styleable.CompoundButton_checked, false);
setChecked(checked);
a.recycle();
}
public void toggle() {
setChecked(! mChecked);
}
@Override
public boolean performClick() {
/*
* XXX: These are tiny, need some surrounding ‘expanded touch area‘,
* which will need to be implemented in Button if we only override
* performClick()
*/
/* When clicked, toggle the state */
toggle();
return super .performClick();
}
@ViewDebug.ExportedProperty
public boolean isChecked() {
return mChecked ;
}
/**
* Changes the checked state of this button.
*
* @param checked true to check the button, false to uncheck it
*/
public void setChecked(boolean checked) {
if (mChecked != checked) {
mChecked = checked;
refreshDrawableState();
notifyViewAccessibilityStateChangedIfNeeded(
AccessibilityEvent.CONTENT_CHANGE_TYPE_UNDEFINED );
// Avoid infinite recursions if setChecked() is called from a listener
if (mBroadcasting ) {
return;
}
mBroadcasting = true ;
if (mOnCheckedChangeListener != null) {
mOnCheckedChangeListener.onCheckedChanged(this, mChecked);
}
if (mOnCheckedChangeWidgetListener != null) {
mOnCheckedChangeWidgetListener .onCheckedChanged(this, mChecked);
}
mBroadcasting = false ;
}
}
/**
* Register a callback to be invoked when the checked state of this button
* changes.
*
* @param listener the callback to call on checked state change
*/
public void setOnCheckedChangeListener(OnCheckedChangeListener listener) {
mOnCheckedChangeListener = listener;
}
/**
* Register a callback to be invoked when the checked state of this button
* changes. This callback is used for internal purpose only.
*
* @param listener the callback to call on checked state change
* @hide
*/
void setOnCheckedChangeWidgetListener(OnCheckedChangeListener listener) {
mOnCheckedChangeWidgetListener = listener;
}
/**
* Interface definition for a callback to be invoked when the checked state
* of a compound button changed.
*/
public static interface OnCheckedChangeListener {
/**
* Called when the checked state of a compound button has changed.
*
* @param buttonView The compound button view whose state has changed.
* @param isChecked The new checked state of buttonView.
*/
void onCheckedChanged(CompoundButton buttonView, boolean isChecked);
}
/**
* Set the background to a given Drawable, identified by its resource id.
*
* @param resid the resource id of the drawable to use as the background
*/
public void setButtonDrawable(int resid) {
if (resid != 0 && resid == mButtonResource ) {
return;
}
mButtonResource = resid;
Drawable d = null;
if (mButtonResource != 0) {
d = getResources().getDrawable(mButtonResource );
}
setButtonDrawable(d);
}
/**
* Set the background to a given Drawable
*
* @param d The Drawable to use as the background
*/
public void setButtonDrawable(Drawable d) {
if (d != null ) {
if (mButtonDrawable != null) {
mButtonDrawable.setCallback(null);
unscheduleDrawable( mButtonDrawable);
}
d.setCallback( this);
d.setVisible(getVisibility() == VISIBLE, false);
mButtonDrawable = d;
setMinHeight(mButtonDrawable .getIntrinsicHeight());
}
refreshDrawableState();
}
@Override
public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
super.onInitializeAccessibilityEvent(event);
event.setClassName(CompoundButton.class .getName());
event.setChecked( mChecked);
}
@Override
public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
super.onInitializeAccessibilityNodeInfo(info);
info.setClassName(CompoundButton.class .getName());
info.setCheckable( true);
info.setChecked( mChecked);
}
@Override
public int getCompoundPaddingLeft() {
int padding = super.getCompoundPaddingLeft();
if (!isLayoutRtl()) {
final Drawable buttonDrawable = mButtonDrawable;
if (buttonDrawable != null) {
padding += buttonDrawable.getIntrinsicWidth();
}
}
return padding;
}
@Override
public int getCompoundPaddingRight() {
int padding = super.getCompoundPaddingRight();
if (isLayoutRtl()) {
final Drawable buttonDrawable = mButtonDrawable;
if (buttonDrawable != null) {
padding += buttonDrawable.getIntrinsicWidth();
}
}
return padding;
}
/**
* @hide
*/
@Override
public int getHorizontalOffsetForDrawables() {
final Drawable buttonDrawable = mButtonDrawable ;
return (buttonDrawable != null) ? buttonDrawable.getIntrinsicWidth() : 0;
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
final Drawable buttonDrawable = mButtonDrawable ;
if (buttonDrawable != null) {
final int verticalGravity = getGravity() & Gravity.VERTICAL_GRAVITY_MASK ;
final int drawableHeight = buttonDrawable.getIntrinsicHeight();
final int drawableWidth = buttonDrawable.getIntrinsicWidth();
int top = 0;
switch (verticalGravity) {
case Gravity.BOTTOM :
top = getHeight() - drawableHeight;
break;
case Gravity.CENTER_VERTICAL :
top = (getHeight() - drawableHeight) / 2;
break;
}
int bottom = top + drawableHeight;
int left = isLayoutRtl() ? getWidth() - drawableWidth : 0;
int right = isLayoutRtl() ? getWidth() : drawableWidth;
buttonDrawable.setBounds(left, top, right, bottom);
buttonDrawable.draw(canvas);
}
}
@Override
protected int[] onCreateDrawableState(int extraSpace) {
final int [] drawableState = super.onCreateDrawableState(extraSpace + 1);
if (isChecked()) {
mergeDrawableStates(drawableState, CHECKED_STATE_SET);
}
return drawableState;
}
@Override
protected void drawableStateChanged() {
super.drawableStateChanged();
if (mButtonDrawable != null) {
int[] myDrawableState = getDrawableState();
// Set the state of the Drawable
mButtonDrawable.setState(myDrawableState);
invalidate();
}
}
@Override
protected boolean verifyDrawable(Drawable who) {
return super .verifyDrawable(who) || who == mButtonDrawable;
}
@Override
public void jumpDrawablesToCurrentState() {
super.jumpDrawablesToCurrentState();
if (mButtonDrawable != null) mButtonDrawable.jumpToCurrentState();
}
static class SavedState extends BaseSavedState {
boolean checked ;
/**
* Constructor called from {@link CompoundButton#onSaveInstanceState()}
*/
SavedState(Parcelable superState) {
super(superState);
}
/**
* Constructor called from {@link #CREATOR}
*/
private SavedState(Parcel in) {
super(in);
checked = (Boolean)in.readValue( null);
}
@Override
public void writeToParcel(Parcel out, int flags) {
super.writeToParcel(out, flags);
out.writeValue( checked);
}
@Override
public String toString() {
return "CompoundButton.SavedState{"
+ Integer.toHexString(System.identityHashCode(this))
+ " checked=" + checked + "}" ;
}
public static final Parcelable.Creator<SavedState> CREATOR
= new Parcelable.Creator<SavedState>() {
public SavedState createFromParcel(Parcel in) {
return new SavedState(in);
}
public SavedState[] newArray(int size) {
return new SavedState[size];
}
};
}
@Override
public Parcelable onSaveInstanceState() {
// Force our ancestor class to save its state
setFreezesText( true);
Parcelable superState = super.onSaveInstanceState();
SavedState ss = new SavedState(superState);
ss. checked = isChecked();
return ss;
}
@Override
public void onRestoreInstanceState(Parcelable state) {
SavedState ss = (SavedState) state;
super.onRestoreInstanceState(ss.getSuperState());
setChecked(ss. checked);
requestLayout();
}
}

先从构造方法开始，在构造方法中，

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public CompoundButton(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
TypedArray a =
context.obtainStyledAttributes(
attrs, com.android.internal.R.styleable.CompoundButton, defStyle, 0);
Drawable d = a.getDrawable(com.android.internal.R.styleable.CompoundButton_button);
if (d != null ) {
setButtonDrawable(d);
}
boolean checked = a
.getBoolean(com.android.internal.R.styleable.CompoundButton_checked, false);
setChecked(checked);
a.recycle();
}

先是从attrs中读取定义的属性，一个是Drawable用于设置背景；一个是布尔类型变量用于判断是否check过。设置背景使用的是setButtonDrawable()方法，代码如下：

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/**
* Set the background to a given Drawable
*
* @param d The Drawable to use as the background
*/
public void setButtonDrawable(Drawable d) {
if (d != null ) {
if (mButtonDrawable != null) {
mButtonDrawable.setCallback(null);
unscheduleDrawable( mButtonDrawable);
}
d.setCallback( this);
d.setVisible(getVisibility() == VISIBLE, false);
mButtonDrawable = d;
setMinHeight(mButtonDrawable .getIntrinsicHeight());
}
refreshDrawableState();
}

这个方法写的就比较完善，可以作为一个学习的典范。首先判断传递过来的Drawable是否为空，如果不为空并且默认的Drawable也不为空，那么取消默认Drawable的callback，然后调用unscheduleDrawable方法。这个方法代码如下：

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/**
* Unschedule any events associated with the given Drawable. This can be
* used when selecting a new Drawable into a view, so that the previous
* one is completely unscheduled.
*
* @param who The Drawable to unschedule.
*
* @see #drawableStateChanged
*/
public void unscheduleDrawable(Drawable who) {
if (mAttachInfo != null && who != null) {
mAttachInfo.mViewRootImpl .mChoreographer.removeCallbacks(
Choreographer.CALLBACK_ANIMATION, null, who);
}
}

从方法注释中可以看出它的用途，正是更换Drawable时候使用的。接下来开始重新设置Drawable，包括回调、可见性、最小高度。最后调用refreshDrawableState()方法，这个是View类的方法，用于更新Drawable状态。

然后再回过头看一下setChecked(checked)方法，这个用于设置check，也就是button的点击状态。代码如下：

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/**
* Changes the checked state of this button.
*
* @param checked true to check the button, false to uncheck it
*/
public void setChecked( boolean checked) {
if (mChecked != checked) {
mChecked = checked;
refreshDrawableState();
notifyViewAccessibilityStateChangedIfNeeded(
AccessibilityEvent.CONTENT_CHANGE_TYPE_UNDEFINED );
// Avoid infinite recursions if setChecked() is called from a listener
if (mBroadcasting ) {
return;
}
mBroadcasting = true ;
if (mOnCheckedChangeListener != null) {
mOnCheckedChangeListener.onCheckedChanged(this, mChecked);
}
if (mOnCheckedChangeWidgetListener != null) {
mOnCheckedChangeWidgetListener .onCheckedChanged(this, mChecked);
}
mBroadcasting = false ;
}
}

在这个方法中多出了一个接口，这个接口真是check的一个回调接口，代码如下：

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/**
* Interface definition for a callback to be invoked when the checked state
* of a compound button changed.
*/
public static interface OnCheckedChangeListener {
/**
* Called when the checked state of a compound button has changed.
*
* @param buttonView The compound button view whose state has changed.
* @param isChecked The new checked state of buttonView.
*/
void onCheckedChanged(CompoundButton buttonView, boolean isChecked);
}

这种回调接口在Android中处处可见，之前的文章也有介绍过。但是在上面的方法，它使用了一个mBroadcasting变量，进而巧妙地避免了重复递归的问题，大家自己感受一下。

然后就是ondraw()方法了，把之前的drawable画出来。代码如下：

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@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
final Drawable buttonDrawable = mButtonDrawable ;
if (buttonDrawable != null) {
final int verticalGravity = getGravity() & Gravity.VERTICAL_GRAVITY_MASK ;
final int drawableHeight = buttonDrawable.getIntrinsicHeight();
final int drawableWidth = buttonDrawable.getIntrinsicWidth();
int top = 0;
switch (verticalGravity) {
case Gravity.BOTTOM :
top = getHeight() - drawableHeight;
break;
case Gravity.CENTER_VERTICAL :
top = (getHeight() - drawableHeight) / 2;
break;
}
int bottom = top + drawableHeight;
int left = isLayoutRtl() ? getWidth() - drawableWidth : 0;
int right = isLayoutRtl() ? getWidth() : drawableWidth;
buttonDrawable.setBounds(left, top, right, bottom);
buttonDrawable.draw(canvas);
}
}

看得出来，在onDrawable()方法中，最主要的部分还是如何确定上下左右四个参数。确定完后就可以画出来了。但是，CompoundButton是一个抽象类，并不能直接使用，那看一下它的子类是如何实现的：

1、CheckBox

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public class CheckBox extends CompoundButton {
public CheckBox(Context context) {
this(context, null);
}
public CheckBox(Context context, AttributeSet attrs) {
this(context, attrs, com.android.internal.R.attr.checkboxStyle);
}
public CheckBox(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
@Override
public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
super.onInitializeAccessibilityEvent(event);
event.setClassName(CheckBox. class.getName());
}
@Override
public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
super.onInitializeAccessibilityNodeInfo(info);
info.setClassName(CheckBox. class.getName());
}
}

和Button的实现差不多，使用了一个自己的样式。并且也是重写了那两个方法。再来看一下RadioButton，

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public class RadioButton extends CompoundButton {
public RadioButton(Context context) {
this(context, null);
}
public RadioButton(Context context, AttributeSet attrs) {
this(context, attrs, com.android.internal.R.attr.radioButtonStyle);
}
public RadioButton(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
/**
* {@inheritDoc}
*
* If the radio button is already checked, this method will not toggle the radio button.
*/
@Override
public void toggle() {
// we override to prevent toggle when the radio is already
// checked (as opposed to check boxes widgets)
if (!isChecked()) {
super.toggle();
}
}
@Override
public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
super.onInitializeAccessibilityEvent(event);
event.setClassName(RadioButton. class.getName());
}
@Override
public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
super.onInitializeAccessibilityNodeInfo(info);
info.setClassName(RadioButton. class.getName());
}
}

和CheckBox实现差不多，区别在于多重写了一个方法，用于防止按钮被重复点击。另外还有ToggleButton以及Switch，前者实现也比较简单，后者稍微麻烦了一些，感兴趣可以自己分析。

最后切入正题，看看滑动Button要如何实现呢？首先看一下效果图：

图1-1

图1-2

图1-1所示的滑动Button实现的思路是这样的，背景图片有开和关的文字，一个按钮在其上面左右滑动，遮住相应的部分，使其在一个位置时候只能看到一个开关。

如图1-3，在实现的时候，先画一个开关背景图片只，然后在其上面画一个按钮，滑动开关的时候对上面的按钮进行处理即可。

准备：

1、按钮图片

2、背景图片

编码：

在自定义滑动按钮控件的时候，可以有多种选择，可以继承于Button，也可以继承于Button的子类，也可以继承于View类等。我们知道滑动按钮是一个很简单的控件，就是左右滑动改变显示内容，不需要其他的额外东西在里面，所以直接继承于View来实现即可。如果继承于系统的一些控件，那么有很多东西用不到，会造成浪费。

1、定义一个类继承于View，初始化构造方法，在构造方法中加载图片及其信息。

2、重写onMeasure()方法，计算控件的大小。

3、重写onTouchEvent()方法，对滑动事件进行判别处理。

4、定义接口，实现回调。

5、重写onDraw()方法，动态画出按钮。

代码如下：

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