Android ListView下拉顶部图片变大

在git上查看牛人的代码，发现是反编译别人的代码，还没加注释，代码也没有完全编译完整，所以这里我做的简单的注释，仅供学习.

PullToZoomListView

变量说明

这里变量包含了：自定义返回动画加速度、自定义动画线程、头部图片view，最后的y坐标，做好的比例，做大的比例等。

private static final String TAG = "PullToZoomListView";

private static final int INVALID_VALUE = -1;//重置值

//自定义加速度动画
private static final Interpolator sInterpolator = new Interpolator() {
public float getInterpolation(float interpolator) {
float f = interpolator - 1.0F;
return 1.0F + f * (f * (f * (f * f)));
}
};
private int mActivePointerId = INVALID_VALUE;//当前手指的Id
private FrameLayout mHeaderContainer;//头部
private int mHeaderHeight;//头部图片的高度
private ImageView mHeaderImage;//头部图片
float mLastMotionY = INVALID_VALUE;//最后y坐标
float mLastScale = INVALID_VALUE;//最后的比例
float mMaxScale = INVALID_VALUE;//最大的比例
private OnScrollListener mOnScrollListener;//滑动监听
private ScalingRunnalable mScalingRunnalable;//动画线程
private int mScreenHeight;//屏幕高度
private ImageView mShadow;//阴影遮罩

自定义View初始化：设置了头部的头部和遮罩并且设置了监听。

/**
* 初始化
* @param paramContext
*/
private void init(Context paramContext) {
DisplayMetrics metrics = new DisplayMetrics();
((Activity) paramContext).getWindowManager().getDefaultDisplay().getMetrics(metrics);

this.mScreenHeight = metrics.heightPixels;//屏幕高度赋值
this.mHeaderContainer = new FrameLayout(paramContext);//头部
this.mHeaderImage = new ImageView(paramContext);//头部图片
int screenWidth = metrics.widthPixels;//屏幕宽度

//设置头部View的样式 设置屏幕宽度，最大样式高度为屏幕高度的9/16
setHeaderViewSize(screenWidth, (int) (9.0F * (screenWidth / 16.0F)));

this.mShadow = new ImageView(paramContext);//遮罩
FrameLayout.LayoutParams layoutParams =
new FrameLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
ViewGroup.LayoutParams.MATCH_PARENT);
layoutParams.gravity = Gravity.CENTER;
this.mShadow.setLayoutParams(layoutParams);//设置遮罩样式
//头部添加View
this.mHeaderContainer.addView(this.mHeaderImage);
this.mHeaderContainer.addView(this.mShadow);
//添加头部
addHeaderView(this.mHeaderContainer);
//初始化返回动画
this.mScalingRunnalable = new ScalingRunnalable();
//设置监听
super.setOnScrollListener(this);
}

开启动画：判断当前的头部布局底部的位置–是否大于图片的初始化高度。

/**
* 开启动画
*/
private void endScraling() {
if (this.mHeaderContainer.getBottom() >= this.mHeaderHeight) {
Log.d(TAG, "this.mScalingRunnalable.startAnimation(200L)");
this.mScalingRunnalable.startAnimation(200L);
}
}

多指触碰时将第0个手指赋值。

/**
* 多点触碰的时候按下,当第0个有手指抬起，再次有手指按下后，将按下的事件的手指指针作为当前手指指针
*
* @param motionEvent
*/
private void onSecondaryPointerUp(MotionEvent motionEvent) {
Log.d(TAG, "onSecondaryPointerUp motionEvent.getPointerId(0) = " + motionEvent.getPointerId(0));
Log.d(TAG, "onSecondaryPointerUp this.mActivePointerId = " + this.mActivePointerId);
if (motionEvent.getPointerId(0) == this.mActivePointerId) {
this.mLastMotionY = motionEvent.getY(0);
this.mActivePointerId = motionEvent.getPointerId(0);
}
Log.d(TAG, "onSecondaryPointerUp mLastMotionY = " + mLastMotionY);
Log.d(TAG, "onSecondaryPointerUp mActivePointerId = " + mActivePointerId);
}

重置所有的数据

/**
* 重置所有数据
*/
private void reset() {
this.mActivePointerId = INVALID_VALUE;
this.mLastMotionY = INVALID_VALUE;
this.mMaxScale = INVALID_VALUE;
this.mLastScale = INVALID_VALUE;
}

向上滚动时修改布局样式

@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
Log.d(TAG, "onScroll");

float bottomSpacing = this.mHeaderHeight - this.mHeaderContainer.get
f25c
Bottom();
Log.d(TAG, "onScroll bottomSpacing = " + bottomSpacing);

if ((bottomSpacing > 0.0F) && (bottomSpacing < this.mHeaderHeight)) {//如果是向上滑动
int toUpScroll = (int) (0.65D * bottomSpacing);
this.mHeaderImage.scrollTo(0, -toUpScroll);
Log.d(TAG, "onScroll 向上滑动  toUpScroll = " + toUpScroll);
} else if (this.mHeaderImage.getScrollY() != 0) {
Log.d(TAG, "onScroll this.mHeaderImage.getScrollY() = " + this.mHeaderImage.getScrollY());
this.mHeaderImage.scrollTo(0, 0);
}
if (this.mOnScrollListener != null) {
this.mOnScrollListener.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount);
}
}

不同事件处理，修改布局样式

@Override
public boolean onTouchEvent(MotionEvent motionEvent) {
switch (motionEvent.getAction() & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_OUTSIDE:
case MotionEvent.ACTION_DOWN:
if (!this.mScalingRunnalable.mIsFinished) {
this.mScalingRunnalable.abortAnimation();
}
this.mLastMotionY = motionEvent.getY();
//获取第一个手指指针的ID
this.mActivePointerId = motionEvent.getPointerId(0);
this.mMaxScale = (this.mScreenHeight / this.mHeaderHeight);
this.mLastScale = (this.mHeaderContainer.getBottom() / this.mHeaderHeight);
Log.d(TAG, "onTouchEvent  ACTION_DOWN mLastMotionY = " + mLastMotionY);
Log.d(TAG, "onTouchEvent  ACTION_DOWN mActivePointerId = " + mActivePointerId);
Log.d(TAG, "onTouchEvent  ACTION_DOWN mMaxScale = " + mMaxScale);
Log.d(TAG, "onTouchEvent  ACTION_DOWN mLastScale = " + mLastScale);
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG, "onTouchEvent ACTION_MOVE mActivePointerId" + mActivePointerId);
//获取当前id的手机指针
int pointer = motionEvent.findPointerIndex(this.mActivePointerId);
//判断指针不为空
if (pointer == INVALID_VALUE) {
Log.e(TAG, "Invalid pointerId=" + this.mActivePointerId + " in onTouchEvent");
} else {
//如果开始没有赋值，则需要赋值
if (this.mLastMotionY == INVALID_VALUE) {
this.mLastMotionY = motionEvent.getY(pointer);
}
if (this.mHeaderContainer.getBottom() >= this.mHeaderHeight) {
//获取头部样式
ViewGroup.LayoutParams headerParams = this.mHeaderContainer.getLayoutParams();

float currentScale = ((motionEvent.getY(pointer) - this.mLastMotionY + this.mHeaderContainer.getBottom())
/ this.mHeaderHeight - this.mLastScale)
/ 2.0F + this.mLastScale;
if ((this.mLastScale <= 1.0D) && (currentScale < this.mLastScale)) {
//最后比例小于默认并且当前的比例要小于上次的比例，则修改头部的高度
headerParams.height = this.mHeaderHeight;
this.mHeaderContainer.setLayoutParams(headerParams);
return super.onTouchEvent(motionEvent);
} else {
//否则，将当前的比例赋值为最后一次的比例
this.mLastScale = Math.min(Math.max(currentScale, 1.0F), this.mMaxScale);
headerParams.height = ((int) (this.mHeaderHeight * this.mLastScale));
//判断修改后的高度小于屏幕的高度
if (headerParams.height < this.mScreenHeight) {
this.mHeaderContainer.setLayoutParams(headerParams);
}
//记录最后的y坐标
this.mLastMotionY = motionEvent.getY(pointer);
return true;
}
}
this.mLastMotionY = motionEvent.getY(pointer);
}
break;
case MotionEvent.ACTION_UP:
Log.d(TAG, "onTouchEvent  ACTION_UP 重置");
//重置
reset();
//当手指起来的时候，结算拉伸，判断是否开启动画
endScraling();
break;
case MotionEvent.ACTION_CANCEL:
int actionIndex = motionEvent.getActionIndex();//获取当前最上层的指针
this.mLastMotionY = motionEvent.getY(actionIndex);//获取最后的y坐标
this.mActivePointerId = motionEvent.getPointerId(actionIndex);//获取最上层指针的手指
Log.d(TAG, "onTouchEvent  ACTION_CANCEL  actionIndex = " + actionIndex + " mLastMotionY = " + mLastMotionY + " mActivePointerId = " + mActivePointerId);
break;
case MotionEvent.ACTION_POINTER_DOWN:
//当第二个手指按下或者放开触发这个事件
onSecondaryPointerUp(motionEvent);
this.mLastMotionY = motionEvent.getY(motionEvent.findPointerIndex(this.mActivePointerId));
Log.d(TAG, "onTouchEvent_Po  ACTION_POINTER_DOWN mLastMotionY = " + mLastMotionY);
break;
case MotionEvent.ACTION_POINTER_UP:
//当第二个手指按下或者放开
Log.d(TAG, "onTouchEvent_Po  ACTION_POINTER_UP ");
break;
}
return super.onTouchEvent(motionEvent);
}

向上返回时的动画

/**
* 向上返回的动画
*/
class ScalingRunnalable implements Runnable {
long mDuration;//持续时间
boolean mIsFinished = true;//是否结束
float mScale;//比例
long mStartTime;//开始时间

ScalingRunnalable() {
}

/**
* 中止动画
*/
public void abortAnimation() {
this.mIsFinished = true;
}

/**
* 是否中止
*
* @return
*/
public boolean isFinished() {
return this.mIsFinished;
}

public void run() {
Log.d(TAG, "ScalingRunnalable mIsFinished = " + this.mIsFinished + " this.mScale = " + this.mScale);
float currentScale;
ViewGroup.LayoutParams mHeaderContainerParams;//头部样式
//判断是否中止和已经滑动超过的默认大小
if ((!this.mIsFinished) && (this.mScale > 1.0D)) {
float currentTime = ((float) SystemClock.currentThreadTimeMillis() - (float) this.mStartTime) / (float) this.mDuration;
currentScale = this.mScale - (this.mScale - 1.0F) * PullToZoomListView.sInterpolator.getInterpolation(currentTime);
Log.d(TAG, "ScalingRunnalable currentTime = " + currentTime + " currentScale = " + currentScale);

mHeaderContainerParams = PullToZoomListView.this.mHeaderContainer.getLayoutParams();
if (currentScale > 1.0F) {
Log.d(TAG, "ScalingRunnalable currentScale > 1.0  -- 修改头部高度");
mHeaderContainerParams.height = PullToZoomListView.this.mHeaderHeight;
mHeaderContainerParams.height = ((int) (currentScale * PullToZoomListView.this.mHeaderHeight));
PullToZoomListView.this.mHeaderContainer.setLayoutParams(mHeaderContainerParams);
PullToZoomListView.this.post(this);//循环执行
} else {
Log.d(TAG, "ScalingRunnalable currentScale < 1.0  -- 中止");
this.mIsFinished = true;
}
}
}

public void startAnimation(long paramLong) {
Log.d(TAG, "ScalingRunnalable 开始执行动画");
this.mStartTime = SystemClock.currentThreadTimeMillis();
this.mDuration = paramLong;
this.mScale = ((float) (PullToZoomListView.this.mHeaderContainer.getBottom()) / PullToZoomListView.this.mHeaderHeight);
this.mIsFinished = false;
Log.d(TAG, "ScalingRunnalable this.mStartTime = " + this.mStartTime);
Log.d(TAG, "ScalingRunnalable this.mDuration = " + this.mDuration);
Log.d(TAG, "ScalingRunnalable this.mScale = " + this.mScale);
Log.d(TAG, "ScalingRunnalable this.mIsFinished = " + this.mIsFinished);
PullToZoomListView.this.post(this);
}
}