最近在做一款音乐剪切小工具， 需要用到一个范围选取的控件。没有合适的系统控件只能自定义一个。
效果图：
test.gif
源码：
https://github.com/zyl409214686/CustomRangeSeekBar
实现思路
- 构造方法中初始化paint以及自定义属性等其他参数。
- 重写
onMeasure方法确定view大小。 - 重写
onSizeChanged方法初始化进度条rectF类对象。 - 重写
onDraw方法绘画出进度以及滑块和进度文字并将需要改变的参数改为变量。 - 重写
onTouchEvent处理检测点击滑块，以及相应的滑块的滑动和触发重绘等。
实现过程
1)初始化自定义属性以及需要的各个参数。
public CustomRangeSeekBar(Context context, AttributeSet attrs) {
super(context, attrs);
TypedArray a = getContext().obtainStyledAttributes(attrs, R.styleable.CustomRangeSeekBar, 0, 0);
this.mAbsoluteMinValue = new Float(a.getFloat(R.styleable.CustomRangeSeekBar_absoluteMin, (float) 0.0));
this.mAbsoluteMaxValue = new Float(a.getFloat(R.styleable.CustomRangeSeekBar_absolutemMax, (float) 100.0));
mThumbImage = BitmapFactory.decodeResource(getResources(), a.getResourceId(R.styleable.CustomRangeSeekBar_thumbImage, R.mipmap.btn_seekbar_normal));
mProgressBarBg = BitmapFactory.decodeResource(getResources(), a.getResourceId(R.styleable.CustomRangeSeekBar_progressBarBg, R.mipmap.seekbar_bg));
mProgressBarSelBg = BitmapFactory.decodeResource(getResources(), a.getResourceId(R.styleable.CustomRangeSeekBar_progressBarSelBg, R.mipmap.seekbar_sel_bg));
mBetweenAbsoluteValue = a.getFloat(R.styleable.CustomRangeSeekBar_betweenAbsoluteValue, 0);
mProgressTextFormat = a.getInt(R.styleable.CustomRangeSeekBar_progressTextFormat, HINT_FORMAT_NUMBER);
mWordSize = a.getDimension(R.styleable.CustomRangeSeekBar_progressTextSize, 16);
mPaint.setTextSize(mWordSize);
mThumbWidth = mThumbImage.getWidth();
mThumbHalfWidth = 0.5f * mThumbWidth;
mThumbHalfHeight = 0.5f * mThumbImage.getHeight();
mProgressBarHeight = 0.3f * mThumbHalfHeight;
mWidthPadding = mThumbHalfHeight;
Paint.FontMetrics metrics = mPaint.getFontMetrics();
mWordHeight = (int) (metrics.descent - metrics.ascent);
setPercentMinValue(0.0);
setPercentMaxValue(100.0);
a.recycle();
}
2)重写onSizeChanged（）方法中初始化进度条以及进度条被选中状态的矩形区域。
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
mProgressBarRect = new RectF(mWidthPadding, mWordHeight + 0.5f * (h - mWordHeight - mProgressBarHeight),
w - mWidthPadding, mWordHeight + 0.5f*(h - mWordHeight + mProgressBarHeight));
mProgressBarSelRect = new RectF(mProgressBarRect);
}
3)重写onMeasure方法，设置view宽高。
View高度 = 滑块高度+进度文字高度。
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int width = MIN_WIDTH;
if (MeasureSpec.UNSPECIFIED != MeasureSpec.getMode(widthMeasureSpec)) {
width = MeasureSpec.getSize(widthMeasureSpec);
}
int height = mThumbImage.getHeight() + mWordHeight;
if (MeasureSpec.UNSPECIFIED != MeasureSpec.getMode(heightMeasureSpec)) {
height = Math.min(height, MeasureSpec.getSize(heightMeasureSpec));
}
setMeasuredDimension(width, height);
}
4)重写onDraw() 绘制进度、被选中范围进度、两个滑块以及两个滑块对应的进度文字。
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
// draw seek bar background line
mPaint.setStyle(Style.FILL);
canvas.drawBitmap(mProgressBarBg, null, mProgressBarRect, mPaint);
// draw seek bar active range line
mProgressBarSelRect.left = percentToScreen(mPercentMinValue);
mProgressBarSelRect.right = percentToScreen(mPercentMaxValue);
//canvas.drawBitmap(mProgressBarSelBg, mWidthPadding, 0.5f * (getHeight() - mProgressBarHeight), mPaint);
canvas.drawBitmap(mProgressBarSelBg, null, mProgressBarSelRect, mPaint);
// draw minimum thumb
drawThumb(percentToScreen(mPercentMinValue), Thumb.MIN.equals(mPressedThumb), canvas);
// draw maximum thumb
drawThumb(percentToScreen(mPercentMaxValue), Thumb.MAX.equals(mPressedThumb), canvas);
mPaint.setColor(Color.rgb(255, 165, 0));
// mPaint.setTextSize(DensityUtils.dp2px(getContext(), 16));
drawThumbMinText(percentToScreen(mPercentMinValue), getSelectedAbsoluteMinValue(), canvas);
drawThumbMaxText(percentToScreen(mPercentMaxValue), getSelectedAbsoluteMaxValue(), canvas);
}
5)重写onTouchEvent ()
@Override
public boolean onTouchEvent(MotionEvent event) {
if (!mIsEnable)
return true;
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
mPressedThumb = evalPressedThumb(event.getX());
if (Thumb.MIN.equals(mPressedThumb)) {
if (mThumbListener != null)
mThumbListener.onClickMinThumb(getSelectedAbsoluteMaxValue(), getSelectedAbsoluteMinValue());
}
if (Thumb.MAX.equals(mPressedThumb)) {
if (mThumbListener != null)
mThumbListener.onClickMaxThumb();
}
invalidate();
//Intercept parent TouchEvent
if (getParent() != null) {
getParent().requestDisallowInterceptTouchEvent(true);
}
break;
case MotionEvent.ACTION_MOVE:
if (mPressedThumb != null) {
float eventX = event.getX();
float maxValue = percentToAbsoluteValue(mPercentMaxValue);
float minValue = percentToAbsoluteValue(mPercentMinValue);
float eventValue = percentToAbsoluteValue(screenToPercent(eventX));
if (Thumb.MIN.equals(mPressedThumb)) {
minValue = eventValue;
if (mBetweenAbsoluteValue>0 && maxValue - minValue <= mBetweenAbsoluteValue)
minValue = new Float((maxValue - mBetweenAbsoluteValue));
setPercentMinValue(absoluteValueToPercent(minValue));//Notice01
if (mThumbListener != null)
mThumbListener.onMinMove(getSelectedAbsoluteMaxValue(), getSelectedAbsoluteMinValue());
} else if (Thumb.MAX.equals(mPressedThumb)) {
maxValue = eventValue;
if (mBetweenAbsoluteValue>0 && maxValue - minValue <= mBetweenAbsoluteValue)
maxValue = new Float(minValue + mBetweenAbsoluteValue);
setPercentMaxValue(absoluteValueToPercent(maxValue));
if (mThumbListener != null)
mThumbListener.onMaxMove(getSelectedAbsoluteMaxValue(), getSelectedAbsoluteMinValue());
}
}
//Intercept parent TouchEvent
if (getParent() != null) {
getParent().requestDisallowInterceptTouchEvent(true);
}
break;
case MotionEvent.ACTION_UP:
if (Thumb.MIN.equals(mPressedThumb)) {
if (mThumbListener != null)
mThumbListener.onUpMinThumb(getSelectedAbsoluteMaxValue(), getSelectedAbsoluteMinValue());
}
if (Thumb.MAX.equals(mPressedThumb)) {
if (mThumbListener != null)
mThumbListener.onUpMaxThumb();
}
//Intercept parent TouchEvent
if (getParent() != null) {
getParent().requestDisallowInterceptTouchEvent(true);
}
break;
case MotionEvent.ACTION_CANCEL:
if (Thumb.MIN.equals(mPressedThumb)) {
if (mThumbListener != null)
mThumbListener.onUpMinThumb(getSelectedAbsoluteMaxValue(), getSelectedAbsoluteMinValue());
}
if (Thumb.MAX.equals(mPressedThumb)) {
if (mThumbListener != null)
mThumbListener.onUpMaxThumb();
}
mPressedThumb = null;
//Intercept parent TouchEvent
if (getParent() != null) {
getParent().requestDisallowInterceptTouchEvent(true);
}
break;
}
return true;
}
evalPressedThumb()方法为检测事件源是否为滑块（左or右or不在滑块上）。其他还要一些转换的方法percentToAbsoluteValue为进度条比例值转换为具体值、
percentToAbsoluteValue为进度条的比例值转换到具体值、screenToPercent为view中具体像素转换为进度中的进度条的比例值。
滑动事件处理逻辑，当检测到滑动的为min滑块（左测滑块）时，看注释Notice01 代码 setPercentMinValue(absoluteValueToPercent(minValue)); 将绝对值转换为进度条比例，然后设置进去，看此方法。
public void setPercentMinValue(double value) {
mPercentMinValue = Math.max(0d, Math.min(1d, Math.min(value, mPercentMaxValue)));
invalidate();
}
将比例值设置进去并调用了重绘，其他逻辑都大同小异，具体可以看上面留的github源码。
注意事项
事件处理的结尾需要增加对父容器view拦截的阻止。getParent().requestDisallowInterceptTouchEvent(true);不然滑动过程事件被父容器拦截而出现滑动不顺畅的情况。
`
