最近跟着《Android進階之光》複習了自定義view，就來個自定義ViewGroup實例詳解，運用了很多view相關的知識：
1、事件分發 與 滑動衝突解決
2、view的滑動，包括scrollBy、scrollTo、sroller
3、view的繪製流程：measure、layout、draw（這裏不涉及）
HorizontalView：橫向滑動的viewGroup，gif不會製作，你就想象成viewPager那種效果。
1、直接上 HorizontalView的代碼，裏面有詳細的註釋：
/**
* 自定義viewGroup
* 可橫向滑動的viewGroup，類似viewPager
*/
public class HorizontalView extends ViewGroup {
private static final String TAG = "hfy:HorizontalView";
/**
* 滑動輔助對象
*/
private Scroller mScroller;
/**
* 速度追蹤器
*/
private VelocityTracker mVelocityTracker;
/**
* 記錄父view在攔截之前的x、y
*/
private int mLastXIntercept;
private int mLastYIntercept;
/**
* 記錄 父view 攔截時及之後的 開始的觸摸x、y
*/
private int mLastX;
private int mLastY;
/**
* 當前的展示的子view下標
*/
private int index;
/**
* 觸摸橫向移動距離
*/
private int offsetXTotal;
/**
* 滑動小於 子view 寬度的一半
*/
private boolean isScrollLessHalfWidth;
public HorizontalView(Context context) {
super(context);
init();
}
public HorizontalView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public HorizontalView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
private void init() {
mScroller = new Scroller(getContext());
mVelocityTracker = VelocityTracker.obtain();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
//測量子view
measureChildren(widthMeasureSpec, heightMeasureSpec);
//處理AT_MOST，寬：子view的寬和，高：第一個view的高
if (getChildCount() == 0) {
setMeasuredDimension(0, 0);
} else if (widthMode == MeasureSpec.AT_MOST && heightMode == MeasureSpec.AT_MOST) {
int childCount = getChildCount();
View firstChild = getChildAt(0);
setMeasuredDimension(childCount * firstChild.getMeasuredWidth(), firstChild.getMeasuredHeight());
} else if (widthMode == MeasureSpec.AT_MOST) {
int childCount = getChildCount();
View firstChild = getChildAt(0);
setMeasuredDimension(childCount * firstChild.getMeasuredWidth(), heightSize);
} else if (heightMode == MeasureSpec.AT_MOST) {
View firstChild = getChildAt(0);
setMeasuredDimension(widthSize, firstChild.getMeasuredHeight());
}
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
int childCount = getChildCount();
View child;
int left = 0;
//子view的佈局
for (int i = 0; i < childCount; i++) {
child = getChildAt(i);
if ((child.getVisibility() != GONE)) {
int width = child.getMeasuredWidth();
int height = child.getMeasuredHeight();
child.layout(left, 0, left + width, height);
left += width;
}
}
}
@Override
public boolean onInterceptTouchEvent(MotionEvent motionEvent) {
//解決滑動衝突
boolean isIntercept = false;
int x = (int) motionEvent.getX();
int y = (int) motionEvent.getY();
switch (motionEvent.getAction()) {
case MotionEvent.ACTION_DOWN:
mLastXIntercept = x;
mLastYIntercept = y;
break;
case MotionEvent.ACTION_MOVE:
//是橫向的滑動
boolean isHorizontal = Math.abs(x - mLastXIntercept) > Math.abs(y - mLastYIntercept);
if (isHorizontal) {
//此處一旦攔截，後面的ACTION就不會在調用onInterceptTouchEvent
isIntercept = true;
}
break;
case MotionEvent.ACTION_UP:
break;
}
Log.i(TAG, "onInterceptTouchEvent: isIntercept：" + isIntercept);
//此處要記錄下 攔截時的 開始的 觸摸點（僅用於下面onTouchEvent處理滑動使用）
mLastX = mLastXIntercept;
mLastY = mLastYIntercept;
mLastXIntercept = x;
mLastYIntercept = y;
return isIntercept;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int x = (int) event.getX();
int y = (int) event.getY();
int childMeasuredWidth = getChildAt(0).getMeasuredWidth();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
//因在onInterceptTouchEvent中ACTION_DOWN返回false，所以這裏不會走到。
break;
case MotionEvent.ACTION_MOVE:
//觸摸事件添加的速度追蹤器，用於在UP時計算速度
mVelocityTracker.addMovement(event);
int offsetX = x - mLastX;
offsetXTotal += offsetX;
isScrollLessHalfWidth = Math.abs(offsetXTotal) < childMeasuredWidth / 2;
////滑動於子view 寬度的一半
if (isScrollLessHalfWidth) {
//使所有子view進行水平滑動
scrollBy(-offsetX, 0);
} else {
//滑動大於子view 寬度的一半，就直接 自動地 平滑地 完整地 滑過去。
if (offsetXTotal > 0) {
//不是第一個，就右滑，這裏用To，因爲子view的左邊緣要滑到屏幕右邊，負值表示子view要右滑（要理解mScrollX）
if (index > 0) {
smoothScrollTo(childMeasuredWidth * (--index), 0);
}
} else if (index < (getChildCount() - 1)) {
//左滑
smoothScrollTo(childMeasuredWidth * (++index), 0);
}
offsetXTotal = 0;
}
break;
case MotionEvent.ACTION_UP:
//滑動沒有子view寬度一半 或者 第一個view右滑、最後的view左滑，那麼 手指擡起時就滑回原位
if (offsetXTotal > 0 && index == 0
|| offsetXTotal < 0 && index == (getChildCount() - 1)) {
smoothScrollTo(childMeasuredWidth * (index), 0);
} else if (isScrollLessHalfWidth) {
mVelocityTracker.computeCurrentVelocity(1000);
float xVelocity = mVelocityTracker.getXVelocity();
Log.i(TAG, "onTouchEvent: xVelocity=" + xVelocity);
if (Math.abs(xVelocity) > 50) {
//不是 第一個view右滑、最後的view左滑，也沒有滑過寬度一半，但 速度很快，也 完整地 自動滑動過去。
if (xVelocity > 0) {
if (index > 0) {
smoothScrollTo(childMeasuredWidth * (--index), 0);
}
} else {
if (index < (getChildCount() - 1)) {
smoothScrollTo(childMeasuredWidth * (++index), 0);
}
}
} else {
//滑動沒有子view寬度一半，速度也不快，那麼 手指擡起時 也 滑回原位
smoothScrollTo(childMeasuredWidth * (index), 0);
}
}
//擡起 把橫向滑動距離 置爲0
offsetXTotal = 0;
mVelocityTracker.clear();
break;
}
//這裏需要記錄上次的move的位置，因爲scrollBy使所有字view滑動，本身不動，MotionEvent是一直改變的。
mLastX = x;
mLastY = y;
Log.i(TAG, "onTouchEvent: index=" + index);
return true;
}
@Override
public void computeScroll() {
if (mScroller.computeScrollOffset()) {
scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
invalidate();
}
}
/**
* 彈性滑動到某一位置
*
* @param destX 目標X
* @param destY 目標Y
*/
public void smoothScrollTo(int destX, int destY) {
int scrollX = getScrollX();
int scrollY = getScrollY();
int offsetX = destX - scrollX;
int offsetY = destY - scrollY;
mScroller.startScroll(scrollX, scrollY, offsetX, offsetY, 600);
invalidate();
}
}
2、然後在xm使用，l如圖：
我們自定義的HorizontalView裏面放了3個ListView
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".CustomViewGroupActivity">
<com.hfy.demo00.logic.customview.HorizontalView
android:layout_width="match_parent"
android:layout_height="match_parent">
<ListView
android:id="@+id/lv_00"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/colorAccent">
</ListView>
<ListView
android:id="@+id/lv_01"
android:layout_width="match_parent"
android:layout_height="match_parent">
</ListView>
<ListView
android:id="@+id/lv_02"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/colorPrimary">
</ListView>
</com.hfy.demo00.logic.customview.HorizontalView>
</RelativeLayout>
3、Activtiy對3個listView初始化，如下：
public class CustomViewGroupActivity extends AppCompatActivity {
private ListView listView00;
private ListView listView01;
private ListView listView02;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_custom_view_group);
initView();
}
private void initView() {
listView00 = (ListView) findViewById(R.id.lv_00);
listView01 = (ListView) findViewById(R.id.lv_01);
listView02 = (ListView) findViewById(R.id.lv_02);
String[] strs1 = {"1","2","4","5","6","1","2","4","5","6","1","2","4","5","6"};
String[] strs2 = {"A","B","C","D","E","A","B","C","D","E","A","B","C","D","E"};
String[] strs3 = {"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o"};
ArrayAdapter adapter1 = new ArrayAdapter<String>(this, R.layout.support_simple_spinner_dropdown_item ,strs1);
listView00.setAdapter(adapter1);
ArrayAdapter adapter2 = new ArrayAdapter<String>(this, R.layout.support_simple_spinner_dropdown_item ,strs2);
listView01.setAdapter(adapter2);
ArrayAdapter adapter3 = new ArrayAdapter<String>(this, R.layout.support_simple_spinner_dropdown_item ,strs3);
listView02.setAdapter(adapter3);
}
}