滑动（平移）的实现方式
首先看一下有几种方式可以实现滑动效果，实际也就是平移。
通过layout实现
@Override
public boolean onTouchEvent(MotionEvent event) {
float x = event.getX();
float y = event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
lastX = x;
lastY = y;
break;
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_MOVE:
int offsetX = (int) (x - lastX);
int offsetY = (int) (y - lastY);
layout(getLeft() + offsetX, getTop() + offsetY,
getRight() + offsetX, getBottom() + offsetY);
break;
}
return true;
}
也可以简单封装成一个方法，实现X轴方向上的平移：
private void translateWithLayout(int deltaX) {
layout(getLeft() - deltaX, getTop(),
getRight() - deltaX, getBottom());
}
通过offset方法实现
@Override
public boolean onTouchEvent(MotionEvent event) {
float x = event.getX();
float y = event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
lastX = x;
lastY = y;
Log.d(TAG, "onTouchDown " + x + " " + y);
break;
case MotionEvent.ACTION_MOVE:
int offsetX = (int) (x - lastX);
int offsetY = (int) (y - lastY);
offsetLeftAndRight(offsetX);
offsetTopAndBottom(offsetY);
break;
case MotionEvent.ACTION_UP:
Log.d(TAG, "onTouchUp " + x + " " + y);
break;
}
return true;
}
可以封装成一个方法，实现X轴方向的平移：
private void translateWithOffset(int deltaX) {
offsetLeftAndRight(deltaX);
}
通过LayoutParams实现
private void translateWithParams(int deltaX) {
MarginLayoutParams layoutParams = (MarginLayoutParams) getLayoutParams();
layoutParams.leftMargin = getLeft() - deltaX;
setLayoutParams(layoutParams);
}
滑动冲突的解决方式
实际上所有的滑动冲突，都是两种解决思路，外部拦截和内部拦截。
下面举了一个实际例子，是在ScrollView的外部添加一个横向滑动效果。
布局文件如下：
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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=".MainActivity">
<com.one.view.OutsideView
app:layout_constraintTop_toTopOf="parent"
android:id="@+id/outside"
android:layout_marginTop="40dp"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<ScrollView
android:layout_gravity="center"
android:layout_width="wrap_content"
android:layout_height="100dp">
<TextView
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:textAlignment="center"
android:textSize="30sp"
android:text="HelloWorld1\nHelloWorld2\nHelloWorld3\nHelloWorld4\n"/>
</ScrollView>
</com.one.view.OutsideView>
<com.one.view.InsideView
app:layout_constraintTop_toBottomOf="@+id/outside"
android:layout_marginTop="40dp"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<com.one.view.MyScrollView
android:layout_gravity="center"
android:layout_width="wrap_content"
android:layout_height="100dp">
<TextView
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:textAlignment="center"
android:textSize="30sp"
android:text="HelloWorld1\nHelloWorld2\nHelloWorld3\nHelloWorld4\n"/>
</com.one.view.MyScrollView>
</com.one.view.InsideView>
</androidx.constraintlayout.widget.ConstraintLayout>
实现了一个这样的效果：
t1.png
外部拦截
外部拦截是通过重写父容器的onInterceptTouchEvent方法，根据需要返回是否拦截的决定。
// intercept from outside
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
int x = (int) event.getX();
int y = (int) event.getY();
boolean intercepted = false;
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
lastX = x;
lastY = y;
intercepted = false;
break;
case MotionEvent.ACTION_MOVE:
int deltaX = lastX - x;
int deltaY = lastY - y;
intercepted = (Math.abs(deltaX) - 10 > 0) && (Math.abs(deltaY) - 10 < 0);
break;
}
Log.d(TAG, "onInterceptTouchEvent " + intercepted
+ " x=" + event.getX() + " y=" + event.getY());
return intercepted;
}
接着在onTouchEvent方法中实现横向滑动效果：
@Override
public boolean onTouchEvent(MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_MOVE) {
int x = (int) event.getX();
int y = (int) event.getY();
int deltaX = lastX - x;
int deltaY = lastY - y;
Log.d(TAG, "onTouchEvent x=" + deltaX + " y=" + deltaY);
layout(getLeft() - deltaX, getTop(),
getRight() - deltaX, getBottom());
}
return true;
}
内部拦截
内部拦截方式稍微比较复杂，需要在父容器和子view中都添加逻辑代码。
首先在父容器中，对除了ACTION_DOWN之外的所有事件进行拦截。
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
int action = event.getAction();
int x = (int) event.getX();
int y = (int) event.getY();
if (action == MotionEvent.ACTION_DOWN) {
lastX = x;
lastY = y;
Log.d(TAG, "onInterceptTouchEvent ACTION_DOWN");
}
return (action != MotionEvent.ACTION_DOWN);
}
接着在onTouchEvent方法中实现一个横向平移。
@Override
public boolean onTouchEvent(MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_MOVE) {
int x = (int) event.getX();
int y = (int) event.getY();
int deltaX = lastX - x;
int deltaY = lastY - y;
Log.d(TAG, "onTouchEvent x=" + deltaX + " y=" + deltaY);
translateWithParams(deltaX);
}
return true;
}
比较复杂的逻辑是需要在子view中实现一个是否禁止拦截的判断：
// intercept from inside
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
int x = (int) event.getX();
int y = (int) event.getY();
boolean intercepted = false;
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
lastX = x;
lastY = y;
intercepted = false;
getParent().requestDisallowInterceptTouchEvent(true);
break;
case MotionEvent.ACTION_MOVE:
int deltaX = lastX - x;
int deltaY = lastY - y;
intercepted = (Math.abs(deltaX) - 10 > 0) && (Math.abs(deltaY) - 10 < 0);
if (intercepted) {
getParent().requestDisallowInterceptTouchEvent(false);
}
break;
default:
break;
}
Log.d(TAG, "dispatchTouchEvent " + intercepted
+ " x=" + event.getX() + " y=" + event.getY());
return super.dispatchTouchEvent(event);
}
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