本文实例为大家分享了scrollView实现顶部图片下拉放大的具体代码，供大家参考，具体内容如下
之前的scrollView顶部图片下拉放大在之后的项目用到了几次，但没次都写在Activity中很麻烦，也不方便复用。这几天有空，所以重新使用自定义scrollView的方法实现这个效果。原理和之前的基本是一致的，所以也不多说了，直接上代码。
代码语言：javascript复制package com.example.myapplication.dropzoom;
import android.animation.ObjectAnimator;
import android.animation.ValueAnimator;
import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ScrollView;
/**
* Created by Liujinhua on 2016/3/25.
* 下拉放大scrollView
*/
public class DropZoomScrollView extends ScrollView implements View.OnTouchListener {
// 记录首次按下位置
private float mFirstPosition = 0;
// 是否正在放大
private Boolean mScaling = false;
private View dropZoomView;
private int dropZoomViewWidth;
private int dropZoomViewHeight;
public DropZoomScrollView(Context context) {
super(context);
}
public DropZoomScrollView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public DropZoomScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
protected void onFinishInflate() {
super.onFinishInflate();
init();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
private void init() {
setOverScrollMode(OVER_SCROLL_NEVER);
if (getChildAt(0) != null) {
ViewGroup vg = (ViewGroup) getChildAt(0);
if (vg.getChildAt(0) != null) {
dropZoomView = vg.getChildAt(0);
setOnTouchListener(this);
}
}
}
@Override
public boolean onTouch(View v, MotionEvent event) {
if (dropZoomViewWidth <= 0 || dropZoomViewHeight <= 0) {
dropZoomViewWidth = dropZoomView.getMeasuredWidth();
dropZoomViewHeight = dropZoomView.getMeasuredHeight();
}
switch (event.getAction()) {
case MotionEvent.ACTION_UP:
//手指离开后恢复图片
mScaling = false;
replyImage();
break;
case MotionEvent.ACTION_MOVE:
if (!mScaling) {
if (getScrollY() == 0) {
mFirstPosition = event.getY();// 滚动到顶部时记录位置，否则正常返回
} else {
break;
}
}
int distance = (int) ((event.getY() - mFirstPosition) * 0.6); // 滚动距离乘以一个系数
if (distance < 0) { // 当前位置比记录位置要小，正常返回
break;
}
// 处理放大
mScaling = true;
setZoom(1 distance);
return true; // 返回true表示已经完成触摸事件，不再处理
}
return false;
}
// 回弹动画 (使用了属性动画)
public void replyImage() {
final float distance = dropZoomView.getMeasuredWidth() - dropZoomViewWidth;
// 设置动画
ValueAnimator anim = ObjectAnimator.ofFloat(0.0F, 1.0F).setDuration((long) (distance * 0.7));
anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
float cVal = (Float) animation.getAnimatedValue();
setZoom(distance - ((distance) * cVal));
}
});
anim.start();
}
//缩放
public void setZoom(float s) {
if (dropZoomViewHeight <= 0 || dropZoomViewWidth <= 0) {
return;
}
ViewGroup.LayoutParams lp = dropZoomView.getLayoutParams();
lp.width = (int) (dropZoomViewWidth s);
lp.height = (int) (dropZoomViewHeight * ((dropZoomViewWidth s) / dropZoomViewWidth));
dropZoomView.setLayoutParams(lp);
}
} 使用的时候也十分的简单
代码语言：javascript复制<?xml version="1.0" encoding="utf-8"?
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
<com.example.myapplication.dropzoom.DropZoomScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:src="@drawable/bg" /
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:src="@drawable/home_bg" /
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:src="@drawable/home_bg" /
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:src="@drawable/home_bg" /
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:src="@drawable/home_bg" /
</LinearLayout
</com.example.myapplication.dropzoom.DropZoomScrollView
</LinearLayout 以上就是本文的全部内容，希望对大家的学习有所帮助。
