该库被使用较多&＃xff0c;而其manual又较为简单。所以决定分析一下&＃xff0c;先从几个问题入手&＃xff1a;

icon怎么做到随着下拉的进行而联动旋转的&＃xff1f;

通过关系图发现我们所有用到的组件都继承自PullToRefreshBase
对&＃xff0c;它就是分析的出发点&＃xff1a;

1. 类PullToRefreshBase

onTouchEvent(MotionEvent event) –MotionEvent.ACTION_MOVE – >
pullEvent()

newScrollValue &＃61; Math.round(Math.min(initialMotionValue - lastMotionValue, 0) / FRICTION);itemDimension &＃61; getHeaderSize();

看的出&＃xff0c;将初始位置减去当前移动到的位置 得到位置增量 再除一个摩擦系数(FRICTION)&＃xff0c;接着

float scale &＃61; Math.abs(newScrollValue) / (float) itemDimension;
/* 中间省略一些代码 */
mHeaderLayout.onPull(scale);

通过header和footer的宽/高度来计算得到一个scale&＃xff0c;并调用mHeaderLayout的方法。

注:
1.如果对 PullToRefreshScrollView组件中的xml参数有疑问,一定要看看PullToRefreshBase.init(Context context, AttributeSet attrs)中利用这些参数都干了些啥。

2. LoadingLayout&＃xff1f;

在PullToRefreshBase.createLoadingLayout()方法会根据传递的参数&＃xff08;flip or rotate&＃xff09;来创建相应的LoadingLayout&＃xff0c;LoadingLayout其有两个子类&＃xff1a;RotateLoadingLayout 和 FlipLoadingLayout 分别代表了两种下拉时候所执行的动画所在&＃xff0c;这个时候基本上有谱了。

下来将1.说的地方串联起来 &＃xff0c;mHeaderLayout从怎么产生的&＃xff1f;

PullToRefreshBase.init()–>createLoadingLayout() –>AnimationStyle.createLoadingLayout()–>RotateLoadingLayout or FlipLoadingLayout.

也就是mHeaderLayout 就是 RotateLoadingLayout or FlipLoadingLayout的对象。

下拉时默认的动画如何替换为自己定义的

以RotateLoadingLayout为例&＃xff0c;只需要在两处地方替换自己的实现就可以了。

public class RotateLoadingLayout extends LoadingLayout {static final int ROTATION_ANIMATION_DURATION &＃61; 1200;private final Animation mRotateAnimation;private final Matrix mHeaderImageMatrix;private float mRotationPivotX, mRotationPivotY;private final boolean mRotateDrawableWhilePulling;public RotateLoadingLayout(Context context, Mode mode, Orientation scrollDirection, TypedArray attrs) {super(context, mode, scrollDirection, attrs);mRotateDrawableWhilePulling &＃61; attrs.getBoolean(R.styleable.PullToRefresh_ptrRotateDrawableWhilePulling, true);mHeaderImage.setScaleType(ScaleType.MATRIX);mHeaderImageMatrix &＃61; new Matrix();mHeaderImage.setImageMatrix(mHeaderImageMatrix);/*** mRotateAnimation 是在手下拉结束后 加载中的动画效果&＃xff0c;* 可以替换为自己的动画*/mRotateAnimation &＃61; new RotateAnimation(0, 720, Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF,0.5f);mRotateAnimation.setInterpolator(ANIMATION_INTERPOLATOR);mRotateAnimation.setDuration(ROTATION_ANIMATION_DURATION);mRotateAnimation.setRepeatCount(Animation.INFINITE);mRotateAnimation.setRepeatMode(Animation.RESTART);}public void onLoadingDrawableSet(Drawable imageDrawable) {if (null !&＃61; imageDrawable) {mRotationPivotX &＃61; Math.round(imageDrawable.getIntrinsicWidth() / 2f);mRotationPivotY &＃61; Math.round(imageDrawable.getIntrinsicHeight() / 2f);}}protected void onPullImpl(float scaleOfLayout) {/*** 这个函数里是下拉过程中的联动动画&＃xff0c;* 这里根据scaleOfLayout提供的值来在不同阶段展现不同的效果动画*/float angle;if (mRotateDrawableWhilePulling) {angle &＃61; scaleOfLayout * 90f;} else {angle &＃61; Math.max(0f, Math.min(180f, scaleOfLayout * 360f - 180f));}mHeaderImageMatrix.setRotate(angle, mRotationPivotX, mRotationPivotY);mHeaderImage.setImageMatrix(mHeaderImageMatrix);}&＃64;Overrideprotected void refreshingImpl() {mHeaderImage.startAnimation(mRotateAnimation);}&＃64;Overrideprotected void resetImpl() {mHeaderImage.clearAnimation();resetImageRotation();}private void resetImageRotation() {if (null !&＃61; mHeaderImageMatrix) {mHeaderImageMatrix.reset();mHeaderImage.setImageMatrix(mHeaderImageMatrix);}}&＃64;Overrideprotected void pullToRefreshImpl() {// NO-OP}&＃64;Overrideprotected void releaseToRefreshImpl() {// NO-OP}&＃64;Overrideprotected int getDefaultDrawableResId() {return R.drawable.default_ptr_rotate;}}