android源码解析--switch
请不要问，为什么这一次突然说到switch了，我也不知道，可能是看到前面的文章了吧， android4.0新控件Switch方法解析，然后今天就看下switch的源码。
A Switch is a two-state toggle switch widget that can select between two options. The user may drag the "thumb" back and forth to choose the selected option, or simply tap to toggle as if it were a checkbox. The text property controls the text displayed in the label for the switch, whereas the off and on text controls the text on the thumb. Similarly, the textAppearance and the related setTypeface() methods control the typeface and style of label text, whereas the switchTextAppearance and the related seSwitchTypeface() methods control that of the thumb. See the Toggle Buttons guide.
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。文本属性设置显示在switch控件上面的文本，而on和off属性设置着"thumb"（滑动块）上面的文本。同样,textAppearance和相关setTypeface()方法设置文本的字体和风格,而switchTextAppearance和相关seSwitchTypeface()方法设置滑动块上面的文本属性。
详情请看切换按钮指南
看下里面的全局变量：
public class Switch extends CompoundButton {
private static final int TOUCH_MODE_IDLE = 0;
private static final int TOUCH_MODE_DOWN = 1;
private static final int TOUCH_MODE_DRAGGING = 2;
// Enum for the "typeface" XML parameter.
private static final int SANS = 1;
private static final int SERIF = 2;
private static final int MONOSPACE = 3;
private Drawable mThumbDrawable;
private Drawable mTrackDrawable;
private int mThumbTextPadding;
private int mSwitchMinWidth;
private int mSwitchPadding;
private CharSequence mTextOn;
private CharSequence mTextOff;
private int mTouchMode;
private int mTouchSlop;
private float mTouchX;
private float mTouchY;
private VelocityTracker mVelocityTracker = VelocityTracker.obtain();
private int mMinFlingVelocity;
private float mThumbPosition;
private int mSwitchWidth;
private int mSwitchHeight;
private int mThumbWidth; // Does not include padding
private int mSwitchLeft;
private int mSwitchTop;
private int mSwitchRight;
private int mSwitchBottom;
private TextPaint mTextPaint;
private ColorStateList mTextColors;
private Layout mOnLayout;
private Layout mOffLayout;
@SuppressWarnings("hiding")
private final Rect mTempRect = new Rect();
private static final int[] CHECKED_STATE_SET = {
R.attr.state_checked
};
switch类继承自CompoundButton，好吧，这个明天看一下。变量具体含义在下面方法里具体说明。
再看下构造方法：
/**
* Construct a new Switch with default styling.
*
* @param context The Context that will determine this widget's theming.
*/
public Switch(Context context) {
this(context, null);
}
/**
* Construct a new Switch with default styling, overriding specific style
* attributes as requested.
*
* @param context The Context that will determine this widget's theming.
* @param attrs Specification of attributes that should deviate from default styling.
*/
public Switch(Context context, AttributeSet attrs) {
this(context, attrs, com.android.internal.R.attr.switchStyle);
}
/**
* Construct a new Switch with a default style determined by the given theme attribute,
* overriding specific style attributes as requested.
*
* @param context The Context that will determine this widget's theming.
* @param attrs Specification of attributes that should deviate from the default styling.
* @param defStyle An attribute ID within the active theme containing a reference to the
* default style for this widget. e.g. android.R.attr.switchStyle.
*/
public Switch(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mTextPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
Resources res = getResources();
mTextPaint.density = res.getDisplayMetrics().density;
mTextPaint.setCompatibilityScaling(res.getCompatibilityInfo().applicationScale);
TypedArray a = context.obtainStyledAttributes(attrs,
com.android.internal.R.styleable.Switch, defStyle, 0);
mThumbDrawable = a.getDrawable(com.android.internal.R.styleable.Switch_thumb);
mTrackDrawable = a.getDrawable(com.android.internal.R.styleable.Switch_track);
mTextOn = a.getText(com.android.internal.R.styleable.Switch_textOn);
mTextOff = a.getText(com.android.internal.R.styleable.Switch_textOff);
mThumbTextPadding = a.getDimensionPixelSize(
com.android.internal.R.styleable.Switch_thumbTextPadding, 0);
mSwitchMinWidth = a.getDimensionPixelSize(
com.android.internal.R.styleable.Switch_switchMinWidth, 0);
mSwitchPadding = a.getDimensionPixelSize(
com.android.internal.R.styleable.Switch_switchPadding, 0);
int appearance = a.getResourceId(
com.android.internal.R.styleable.Switch_switchTextAppearance, 0);
if (appearance != 0) {
setSwitchTextAppearance(context, appearance);
}
a.recycle();
ViewConfiguration config = ViewConfiguration.get(context);
mTouchSlop = config.getScaledTouchSlop();
mMinFlingVelocity = config.getScaledMinimumFlingVelocity();
// Refresh display with current params
refreshDrawableState();
setChecked(isChecked());
}第一个和第二个构造方法实际上都是调用的第三个构造方法，但是关于AttributeSet的具体使用，这里也不详细叙，不了解的可以看一下android自定义视图属性(atts.xml，TypedArray)学习。
下面是一个通过指定TextAppearance资源设置switch文本属性（颜色、字体大小、风格、未选中颜色、选中颜色）的方法：
/**
* Sets the switch text color, size, style, hint color, and highlight color
* from the specified TextAppearance resource.
*/
public void setSwitchTextAppearance(Context context, int resid) {
TypedArray appearance =
context.obtainStyledAttributes(resid,
com.android.internal.R.styleable.TextAppearance);
ColorStateList colors;
int ts;
colors = appearance.getColorStateList(com.android.internal.R.styleable.
TextAppearance_textColor);
if (colors != null) {
mTextColors = colors;
} else {
// If no color set in TextAppearance, default to the view's textColor
mTextColors = getTextColors();
}
ts = appearance.getDimensionPixelSize(com.android.internal.R.styleable.
TextAppearance_textSize, 0);
if (ts != 0) {
if (ts != mTextPaint.getTextSize()) {
mTextPaint.setTextSize(ts);
requestLayout();
}
}
int typefaceIndex, styleIndex;
typefaceIndex = appearance.getInt(com.android.internal.R.styleable.
TextAppearance_typeface, -1);
styleIndex = appearance.getInt(com.android.internal.R.styleable.
TextAppearance_textStyle, -1);
setSwitchTypefaceByIndex(typefaceIndex, styleIndex);
appearance.recycle();
}关于TypeArray的学习，请参考android自定义视图属性(atts.xml，TypedArray)学习。
上面方法中调用了一个私有方法setSwitchTypefaceByIndex：
private void setSwitchTypefaceByIndex(int typefaceIndex, int styleIndex) {
Typeface tf = null;
switch (typefaceIndex) {
case SANS:
tf = Typeface.SANS_SERIF;
break;
case SERIF:
tf = Typeface.SERIF;
break;
case MONOSPACE:
tf = Typeface.MONOSPACE;
break;
}
setSwitchTypeface(tf, styleIndex);
}为什么要这样设计呢，在android自定义视图属性(atts.xml，TypedArray)学习里讲到，attrs.xml里面format格式就那几种，存不了复杂内容格式。
里面用到了setSwitchTypeface方法：
/**
* 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.
*/
public void setSwitchTypeface(Typeface tf, int style) {
if (style > 0) {
if (tf == null) {
tf = Typeface.defaultFromStyle(style);
} else {
tf = Typeface.create(tf, style);
}
setSwitchTypeface(tf);
// now compute what (if any) algorithmic styling is needed
int typefaceStyle = tf != null ? tf.getStyle() : 0;
int need = style & ~typefaceStyle;
mTextPaint.setFakeBoldText((need & Typeface.BOLD) != 0);
mTextPaint.setTextSkewX((need & Typeface.ITALIC) != 0 ? -0.25f : 0);
} else {
mTextPaint.setFakeBoldText(false);
mTextPaint.setTextSkewX(0);
setSwitchTypeface(tf);
}
}
设置在switch上面显示字体和风格，如果没有指定字体风格，字体会采用默认的倾斜加粗。
里面又用到了setSwitchTypeface方法：
/**
* Sets the typeface in which the text should be displayed on the switch.
* Note that not all Typeface families actually have bold and italic
* variants, so you may need to use
* {@link #setSwitchTypeface(Typeface, int)} to get the appearance
* that you actually want.
*
* @attr ref android.R.styleable#TextView_typeface
* @attr ref android.R.styleable#TextView_textStyle
*/
public void setSwitchTypeface(Typeface tf) {
if (mTextPaint.getTypeface() != tf) {
mTextPaint.setTypeface(tf);
requestLayout();
invalidate();
}
}
设置在switch上面显示的字体格式，应该注意并不是所有的字体集都含有粗体和倾斜，所以当需要时，可以调用setSwitchTypeface来设置自己的字体风格。
下面这四个方法就是设置和获取在on和off上面的字体：
* Returns the text displayed when the button is in the checked state.
*/
public CharSequence getTextOn() {
return mTextOn;
}
/**
* Sets the text displayed when the button is in the checked state.
*/
public void setTextOn(CharSequence textOn) {
mTextOn = textOn;
requestLayout();
}
/**
* Returns the text displayed when the button is not in the checked state.
*/
public CharSequence getTextOff() {
return mTextOff;
}
/**
* Sets the text displayed when the button is not in the checked state.
*/
public void setTextOff(CharSequence textOff) {
mTextOff = textOff;
requestLayout();
}
下面onMeasure方法，测量控件的宽高，供绘图时使用。
@Override
public void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
if (mOnLayout == null) {
mOnLayout = makeLayout(mTextOn);
}
if (mOffLayout == null) {
mOffLayout = makeLayout(mTextOff);
}
mTrackDrawable.getPadding(mTempRect);
final int maxTextWidth = Math.max(mOnLayout.getWidth(), mOffLayout.getWidth());
final int switchWidth = Math.max(mSwitchMinWidth,
maxTextWidth * 2 + mThumbTextPadding * 4 + mTempRect.left + mTempRect.right);
final int switchHeight = mTrackDrawable.getIntrinsicHeight();
mThumbWidth = maxTextWidth + mThumbTextPadding * 2;
switch (widthMode) {
case MeasureSpec.AT_MOST:
widthSize = Math.min(widthSize, switchWidth);
break;
case MeasureSpec.UNSPECIFIED:
widthSize = switchWidth;
break;
case MeasureSpec.EXACTLY:
// Just use what we were given
break;
}
switch (heightMode) {
case MeasureSpec.AT_MOST:
heightSize = Math.min(heightSize, switchHeight);
break;
case MeasureSpec.UNSPECIFIED:
heightSize = switchHeight;
break;
case MeasureSpec.EXACTLY:
// Just use what we were given
break;
}
mSwitchWidth = switchWidth;
mSwitchHeight = switchHeight;
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
final int measuredHeight = getMeasuredHeight();
if (measuredHeight < switchHeight) {
setMeasuredDimension(getMeasuredWidthAndState(), switchHeight);
}
}
里面用到了makeLayout方法：
private Layout makeLayout(CharSequence text) {
return new StaticLayout(text, mTextPaint,
(int) Math.ceil(Layout.getDesiredWidth(text, mTextPaint)),
Layout.Alignment.ALIGN_NORMAL, 1.f, 0, true);
}如果mOnLayout活着mOffLayout为空，就返回一个Layout。
下面响应拖拉事件，如果选中状态，显示选中文字，默认为on，否则显示off文字，默认为off。
@Override
public void onPopulateAccessibilityEvent(AccessibilityEvent event) {
super.onPopulateAccessibilityEvent(event);
if (isChecked()) {
CharSequence text = mOnLayout.getText();
if (TextUtils.isEmpty(text)) {
text = mContext.getString(R.string.switch_on);
}
event.getText().add(text);
} else {
CharSequence text = mOffLayout.getText();
if (TextUtils.isEmpty(text)) {
text = mContext.getString(R.string.switch_off);
}
event.getText().add(text);
}
}
下面就是onTouchEvent方法了：
@Override
public boolean onTouchEvent(MotionEvent ev) {
mVelocityTracker.addMovement(ev);
final int action = ev.getActionMasked();
switch (action) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
if (isEnabled() && hitThumb(x, y)) {
mTouchMode = TOUCH_MODE_DOWN;
mTouchX = x;
mTouchY = y;
}
break;
}
case MotionEvent.ACTION_MOVE: {
switch (mTouchMode) {
case TOUCH_MODE_IDLE:
// Didn't target the thumb, treat normally.
break;
case TOUCH_MODE_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
if (Math.abs(x - mTouchX) > mTouchSlop ||
Math.abs(y - mTouchY) > mTouchSlop) {
mTouchMode = TOUCH_MODE_DRAGGING;
getParent().requestDisallowInterceptTouchEvent(true);
mTouchX = x;
mTouchY = y;
return true;
}
break;
}
case TOUCH_MODE_DRAGGING: {
final float x = ev.getX();
final float dx = x - mTouchX;
float newPos = Math.max(0,
Math.min(mThumbPosition + dx, getThumbScrollRange()));
if (newPos != mThumbPosition) {
mThumbPosition = newPos;
mTouchX = x;
invalidate();
}
return true;
}
}
break;
}
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_CANCEL: {
if (mTouchMode == TOUCH_MODE_DRAGGING) {
stopDrag(ev);
return true;
}
mTouchMode = TOUCH_MODE_IDLE;
mVelocityTracker.clear();
break;
}
}
return super.onTouchEvent(ev);
}
里面使用hitThumb方法判断触发点是否在控件区域内：
/**
* @return true if (x, y) is within the target area of the switch thumb
*/
private boolean hitThumb(float x, float y) {
mThumbDrawable.getPadding(mTempRect);
final int thumbTop = mSwitchTop - mTouchSlop;
final int thumbLeft = mSwitchLeft + (int) (mThumbPosition + 0.5f) - mTouchSlop;
final int thumbRight = thumbLeft + mThumbWidth +
mTempRect.left + mTempRect.right + mTouchSlop;
final int thumbBottom = mSwitchBottom + mTouchSlop;
return x > thumbLeft && x < thumbRight && y > thumbTop && y < thumbBottom;
}如果是，把mTouchMode 设为TOUCH_MODE_DOWN。
然后执行：
case TOUCH_MODE_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
if (Math.abs(x - mTouchX) > mTouchSlop ||
Math.abs(y - mTouchY) > mTouchSlop) {
mTouchMode = TOUCH_MODE_DRAGGING;
getParent().requestDisallowInterceptTouchEvent(true);
mTouchX = x;
mTouchY = y;
return true;
}
break;
mTouchMode 被设为TOUCH_MODE_DRAGGING，在TOUCH_MODE_DRAGGING中有getThumbScrollRange方法：
private int getThumbScrollRange() {
if (mTrackDrawable == null) {
return 0;
}
mTrackDrawable.getPadding(mTempRect);
return mSwitchWidth - mThumbWidth - mTempRect.left - mTempRect.right;
}
判断滑动块的滑动距离。根据距离来判断是否需要切换。
在ACTION_CANCEL：中使用到了stopDrag方法
/**
* Called from onTouchEvent to end a drag operation.
*
* @param ev Event that triggered the end of drag mode - ACTION_UP or ACTION_CANCEL
*/
private void stopDrag(MotionEvent ev) {
mTouchMode = TOUCH_MODE_IDLE;
// Up and not canceled, also checks the switch has not been disabled during the drag
boolean commitChange = ev.getAction() == MotionEvent.ACTION_UP && isEnabled();
cancelSuperTouch(ev);
if (commitChange) {
boolean newState;
mVelocityTracker.computeCurrentVelocity(1000);
float xvel = mVelocityTracker.getXVelocity();
if (Math.abs(xvel) > mMinFlingVelocity) {
newState = xvel > 0;
} else {
newState = getTargetCheckedState();
}
animateThumbToCheckedState(newState);
} else {
animateThumbToCheckedState(isChecked());
}
}
用commitChange来判断event是弹起并且滑动块是否可以滑动。然后回调父类的onTouchEvent方法中的Action_Cancel部分：
private void cancelSuperTouch(MotionEvent ev) {
MotionEvent cancel = MotionEvent.obtain(ev);
cancel.setAction(MotionEvent.ACTION_CANCEL);
super.onTouchEvent(cancel);
cancel.recycle();
}
if (commitChange) {
boolean newState;
mVelocityTracker.computeCurrentVelocity(1000);
float xvel = mVelocityTracker.getXVelocity();
if (Math.abs(xvel) > mMinFlingVelocity) {
newState = xvel > 0;
} else {
newState = getTargetCheckedState();
}
animateThumbToCheckedState(newState);
} else {
animateThumbToCheckedState(isChecked());
}
这一块是根据滑动速度来判断状态是否进行切换。
private void animateThumbToCheckedState(boolean newCheckedState) {
// TODO animate!
//float targetPos = newCheckedState ? 0 : getThumbScrollRange();
//mThumbPosition = targetPos;
setChecked(newCheckedState);
}
private boolean getTargetCheckedState() {
return mThumbPosition >= getThumbScrollRange() / 2;
}
@Override
public void setChecked(boolean checked) {
super.setChecked(checked);
mThumbPosition = checked ? getThumbScrollRange() : 0;
invalidate();
}
所以当滑动速度大于mMinFlingVelocity或者滑动距离大于滑动块的1/2时，滑动块状态就会进行切换，然后控件重绘。
下面两个方法onLayout和onDrow设置重绘时候各个参数：
Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
mThumbPosition = isChecked() ? getThumbScrollRange() : 0;
int switchRight = getWidth() - getPaddingRight();
int switchLeft = switchRight - mSwitchWidth;
int switchTop = 0;
int switchBottom = 0;
switch (getGravity() & Gravity.VERTICAL_GRAVITY_MASK) {
default:
case Gravity.TOP:
switchTop = getPaddingTop();
switchBottom = switchTop + mSwitchHeight;
break;
case Gravity.CENTER_VERTICAL:
switchTop = (getPaddingTop() + getHeight() - getPaddingBottom()) / 2 -
mSwitchHeight / 2;
switchBottom = switchTop + mSwitchHeight;
break;
case Gravity.BOTTOM:
switchBottom = getHeight() - getPaddingBottom();
switchTop = switchBottom - mSwitchHeight;
break;
}
mSwitchLeft = switchLeft;
mSwitchTop = switchTop;
mSwitchBottom = switchBottom;
mSwitchRight = switchRight;
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
// Draw the switch
int switchLeft = mSwitchLeft;
int switchTop = mSwitchTop;
int switchRight = mSwitchRight;
int switchBottom = mSwitchBottom;
mTrackDrawable.setBounds(switchLeft, switchTop, switchRight, switchBottom);
mTrackDrawable.draw(canvas);
canvas.save();
mTrackDrawable.getPadding(mTempRect);
int switchInnerLeft = switchLeft + mTempRect.left;
int switchInnerTop = switchTop + mTempRect.top;
int switchInnerRight = switchRight - mTempRect.right;
int switchInnerBottom = switchBottom - mTempRect.bottom;
canvas.clipRect(switchInnerLeft, switchTop, switchInnerRight, switchBottom);
mThumbDrawable.getPadding(mTempRect);
final int thumbPos = (int) (mThumbPosition + 0.5f);
int thumbLeft = switchInnerLeft - mTempRect.left + thumbPos;
int thumbRight = switchInnerLeft + thumbPos + mThumbWidth + mTempRect.right;
mThumbDrawable.setBounds(thumbLeft, switchTop, thumbRight, switchBottom);
mThumbDrawable.draw(canvas);
// mTextColors should not be null, but just in case
if (mTextColors != null) {
mTextPaint.setColor(mTextColors.getColorForState(getDrawableState(),
mTextColors.getDefaultColor()));
}
mTextPaint.drawableState = getDrawableState();
Layout switchText = getTargetCheckedState() ? mOnLayout : mOffLayout;
canvas.translate((thumbLeft + thumbRight) / 2 - switchText.getWidth() / 2,
(switchInnerTop + switchInnerBottom) / 2 - switchText.getHeight() / 2);
switchText.draw(canvas);
canvas.restore();
}
获取控件距离右边距距离：
@Override
public int getCompoundPaddingRight() {
int padding = super.getCompoundPaddingRight() + mSwitchWidth;
if (!TextUtils.isEmpty(getText())) {
padding += mSwitchPadding;
}
return padding;
}
下面四个方法是
@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();
int[] myDrawableState = getDrawableState();
// Set the state of the Drawable
// Drawable may be null when checked state is set from XML, from super constructor
if (mThumbDrawable != null) mThumbDrawable.setState(myDrawableState);
if (mTrackDrawable != null) mTrackDrawable.setState(myDrawableState);
invalidate();
}
@Override
protected boolean verifyDrawable(Drawable who) {
return super.verifyDrawable(who) || who == mThumbDrawable || who == mTrackDrawable;
}
@Override
public void jumpDrawablesToCurrentState() {
super.jumpDrawablesToCurrentState();
mThumbDrawable.jumpToCurrentState();
mTrackDrawable.jumpToCurrentState();
}
}
drawableStateChanged方法：This function is called whenever the state of the view changes in such a way that it impacts the state of drawables being shown.当当前视图状态发改变时这个方法被调用。
onCreateDrawableState方法：为这个view生成一个新的Drawable状态。
verifyDrawable ：If your view subclass is displaying its own Drawable objects, it should override this function and return true for any Drawable it is displaying：如果你的视图是显示自己的子类Drawable对象,它对任何显示的Drawable对象应该重写这个函数返回true。
jumpDrawableToCurrentState():在与Switch相关的Drawable操作时调用 Drawable.jumpToCurrentState()这个方法。
初稿完成！终于可以吃饭了。。。
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