例子是一个原型操作， 所以特殊功能都可以基于此进行添加。
突出两点：
1： UI 布局
onMeasure 处理Header和Content的大小
onLayout 处理Header和Content的位置
实际下拉过程中， 是没有回调onLayout方法。
而是通过 mHeaderView.offsetTopAndBottom(3); 设置偏移位置。
通过invalidate();进行刷新。
PS:
offsetTopAndBottom方法设置View的位置， 不会造成View的重绘，代码里可以看见通过RenderNode.offsetTopAndBottom来实现的。（Draw绘制完的东西保存在RenderNode里面，所以位置的修改可以直接修改RenderNode）
invalidate 绘制当前的ViewTree， 这里的目的上让上面设置的RenderNode生效。
2： 事件传递
事件传递的关键是方法 canScrollVertically 的理解。
PS：
对于一些普通的布局， 例如 LinearLayout 是不能在其内部直接添加一个 ListView。
原因的话很简单 LinearLayout 没有重写 canScrollVertically 方法。
最开始就碰到canScrollVertically 这个问题困扰了两天。 后来读了源码， 才了解如果有特殊需求需要重写canScrollVertically .
package com.gank.demo.views.pulltorefresh;
import android.content.Context;
import android.graphics.Color;
import android.util.AttributeSet;
import android.util.Log;
import android.view.Gravity;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
/**
* Created by GankLi on 2016/6/20.
*/
public class UILayout extends ViewGroup {
private static final String TAG = "Gank";
private TextView mHeaderView;
private View mContentView;
private boolean mIsPulling = false;
private int mHeaderOffset = 0;
private static final float OFFSET_Y = 20.0f;
private float mBeginX;
private float mBeginY;
private int mTotal = 0;
public UILayout(Context context, AttributeSet attrs) {
super(context, attrs);
//Header
initHeaderVIew(context);
}
public UILayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
//Header
initHeaderVIew(context);
}
void initHeaderVIew(Context context){
mHeaderView = new TextView(context);
mHeaderView.setText("下拉刷新");
mHeaderView.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));
mHeaderView.setGravity(Gravity.CENTER);
mHeaderView.setBackgroundColor(Color.parseColor("#4b4b4b"));
addView(mHeaderView);
}
@Override
protected void onFinishInflate() {
int size = getChildCount();
Log.w(TAG, "Size: " + size);
for (int i = 0; i < size; i++) {
View child = getChildAt(i);
Log.w(TAG, "View: " + child);
if (!(child instanceof TextView)) {
mContentView = child;
}
}
super.onFinishInflate();
}
/**
* 设置 Head 和 Content 的大小
*/
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
Log.w(TAG, "---------------------Begin - onMeasure----------------------");
Log.w(TAG, "1: HSpec: " + MeasureSpec.toString(heightMeasureSpec) + " WSpec: " + MeasureSpec.toString(widthMeasureSpec) + " H: " + getMeasuredHeight() + " W: " + getMeasuredWidth());
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
Log.w(TAG, "2: HSpec: " + MeasureSpec.toString(heightMeasureSpec) + " WSpec: " + MeasureSpec.toString(widthMeasureSpec) + " H: " + getMeasuredHeight() + " W: " + getMeasuredWidth());
widthMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredWidth() - getPaddingRight() - getPaddingLeft(), MeasureSpec.EXACTLY);
heightMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredHeight() - getPaddingTop() - getPaddingBottom(), MeasureSpec.EXACTLY);
Log.w(TAG, "HSpec: " + MeasureSpec.toString(heightMeasureSpec) + " WSpec: " + MeasureSpec.toString(widthMeasureSpec) + " Head - HSpec: " + MeasureSpec.toString(MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED)));
mContentView.measure(widthMeasureSpec, heightMeasureSpec);
mHeaderView.measure(widthMeasureSpec, MeasureSpec
.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED));
Log.w(TAG, "---------------------End - onMeasure----------------------");
}
/**
* 设置 Head 和 Content 的位置
*/
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
Log.w(TAG, "=============Begin - onLayout=============");
Log.w(TAG, "changed: " + changed + "（" + l + "," + t + "） - (" + r + "," + b + ")");
if (mContentView == null) {
return;
}
int height = getMeasuredHeight();
int width = getMeasuredWidth();
Log.w(TAG, "H: " + height + " W: " + width);
Log.w(TAG, "mContentView: （0," + mHeaderOffset + "） - (" + width + "," + (height + mHeaderOffset) + ")");
Log.w(TAG, "mHeaderView: （0," + (mHeaderView.getMeasuredHeight() + mHeaderOffset) + "） - (" + width + "," + mHeaderOffset + ")");
mContentView.layout(0, mHeaderOffset, width, height + mHeaderOffset);
mHeaderView.layout(0, mHeaderOffset - mHeaderView.getMeasuredHeight(), width, mHeaderOffset);
Log.w(TAG, "=============End - onLayout=============");
}
/**
* 根据触摸， 显示下拉操作
*/
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
int action = ev.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN: //按下的时候，记录位置
mBeginX = ev.getX();
mBeginY = ev.getY();
mTotal = 0;
mIsPulling = false;
Log.w(TAG, "==ACTION_DOWN== (" + mBeginX + "," + mBeginY + ")");
super.dispatchTouchEvent(ev);
return true;
case MotionEvent.ACTION_MOVE: //
float offesty = ev.getY() - mBeginY;
if (!mIsPulling) {
if (offesty > OFFSET_Y) {
boolean canScrollUp = mContentView.canScrollVertically(-1);
if (canScrollUp) {//可以继续上滑
return super.dispatchTouchEvent(ev);
}else{//出发下拉逻辑
mIsPulling = true;
mHeaderOffset = (int) (offesty - OFFSET_Y);
mHeaderView.setVisibility(VISIBLE);
invalidate();
return true;
}
}
} else {//处理下拉操作
mHeaderOffset = (int) (offesty - OFFSET_Y);
mTotal += 3;
mHeaderView.offsetTopAndBottom(3);
mContentView.offsetTopAndBottom(3);
invalidate();
return true;
}
//Log.w(TAG, "====ACTION_MOVE==== (" + mBeginX + "," + mBeginY + ")" + " Offset: " + mHeaderOffset + " Pulling: " + mIsPulling);
return super.dispatchTouchEvent(ev);
case MotionEvent.ACTION_UP: //点击释放的时候， 下拉返回
mHeaderOffset = 0;
if (mIsPulling) {
mHeaderView.offsetTopAndBottom(-mTotal);
mContentView.offsetTopAndBottom(-mTotal);
invalidate();
mIsPulling = false;
return true;
}
Log.w(TAG, "==ACTION_UP== (" + ev.getX() + "," + ev.getY() + ")");
return super.dispatchTouchEvent(ev);
}
return super.dispatchTouchEvent(ev);
}
}
使用方式
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<com.gank.demo.views.pulltorefresh.UILayout
android:id="@+id/activity_pull"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/test"/>
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/test"/>
</LinearLayout>
</ScrollView>
</com.gank.demo.views.pulltorefresh.UILayout>
</FrameLayout>
