WheelView源码解析注释

Author: xiaosong520

app/src/main/java/com/bigkoo/pickerviewdemo/MainActivity.java

@@ -78,7 +78,7 @@ public void onClick(View v) {
     private void initTimePicker() {
         //控制时间范围(如果不设置范围，则使用默认时间1900-2100年，此段代码可注释)
         Calendar selectedDate = Calendar.getInstance();
-        /*selectedDate.set(2013,2,29);*/
+        selectedDate.set(2013,2,29);
         Calendar startDate = Calendar.getInstance();
         startDate.set(2013,1,23);
         Calendar endDate = Calendar.getInstance();

pickerview/build.gradle

@@ -12,8 +12,8 @@ android {
     defaultConfig {
         minSdkVersion 9
         targetSdkVersion 25
-        versionCode 11
-        versionName "3.0.7"
+        versionCode 12
+        versionName "3.0.8"
     }
     buildTypes {
         release {
@@ -39,7 +39,7 @@ publish {
     userOrg = 'contrarywind'//bintray.com 用户名/组织名 user/org name
     groupId = 'com.contrarywind'//JCenter上显示的路径 path
     artifactId = 'Android-PickerView'//项目名称 project name
-    publishVersion = '3.0.7'//版本号 version code
+    publishVersion = '3.0.8'//版本号 version code
     desc = 'this is a pickerview for android'//项目描述 description
     website = 'https://github.com/Contrarywind/Android-PickerView' //项目网址链接 link
 }

pickerview/src/main/java/com/bigkoo/pickerview/lib/SmoothScrollTimerTask.java

@@ -21,7 +21,7 @@ public final void run() {
         if (realTotalOffset == Integer.MAX_VALUE) {
             realTotalOffset = offset;
         }
-        //把要滚动的范围细分成十小份，按是小份单位来重绘
+        //把要滚动的范围细分成10小份，按10小份单位来重绘
         realOffset = (int) ((float) realTotalOffset * 0.1F);
 
         if (realOffset == 0) {

pickerview/src/main/java/com/bigkoo/pickerview/lib/WheelView.java

@@ -251,7 +251,7 @@ void smoothScroll(ACTION action) {
         cancelFuture();
         if (action == ACTION.FLING || action == ACTION.DAGGLE) {
             mOffset = (int) ((totalScrollY % itemHeight + itemHeight) % itemHeight);
-            if ((float) mOffset > itemHeight / 2.0F) {
+            if ((float) mOffset > itemHeight / 2.0F) {//如果超过Item高度的一半，滚动到下一个Item去
                 mOffset = (int) (itemHeight - (float) mOffset);
             } else {
                 mOffset = -mOffset;
@@ -606,13 +606,20 @@ public boolean onTouchEvent(MotionEvent event) {
                 break;
             //完成滑动，手指离开屏幕
             case MotionEvent.ACTION_UP:
+
             default:
-                if (!eventConsumed) {
+                if (!eventConsumed) {//屏幕点击或者拖拽事件
                     float y = event.getY();
-                    double l = Math.acos((radius - y) / radius) * radius;
-                    int circlePosition = (int) ((l + itemHeight / 2) / itemHeight);
-
+                    // 由于之前是有向右偏移90度，所以 实际弧度范围为α2 =π/2-α （α=[0,π]）
+                    // 根据cosα = sin(π/2-α)
+                    // (radius - y) / radius = sinα2 = sin(π/2-α) = cosα
+                    // arccos(cosα)= α
+                    // 所以 弧长 L = α*R
+                    double L = Math.acos((radius - y) / radius) * radius;
+                    //item0 有一半是在不可见区域，所以需要加上 itemHeight / 2
+                    int circlePosition = (int) ((L + itemHeight / 2) / itemHeight);
                     float extraOffset = (totalScrollY % itemHeight + itemHeight) % itemHeight;
+                    //已滑动的弧长值
                     mOffset = (int) ((circlePosition - itemsVisible / 2) * itemHeight - extraOffset);
 
                     if ((System.currentTimeMillis() - startTime) > 120) {