Android事件分发07——TouchDelegate的使用与解析

Android事件分发07TouchDelegate的使用与解析
一TouchDelegate的简单使用
1 图示

2 activity_touch_delegate_demoxml

2 TouchDelegateDemoActivity

二TouchDelegate源码

三主要的小小分析
1 构造函数

2 MotionEventACTION_DOWN

3 MotionEventACTION_MOVE和MotionEventACTION_UP

4 MotionEventACTION_CANCEL

5 余下的处理

四流程图

Android事件分发07——TouchDelegate的使用与解析

TouchDelegate 这个类的作用就是增大我们控件的触摸区域。前面文章（Android事件分发05——View的onTouchEvent）中,我们在分析 onTouchEvent的时候，有个步骤是这样的：

判断有没有添加TouchDelegate代理，如果添加了代理，那么调用代理的onTouchEvent方法处理，如果这个方法返回true,那么就返回true,代表消费了事件，如果没有返回true,那么继续其他处理。

public boolean onTouchEvent(MotionEvent event) {

...
if (mTouchDelegate != null) {
if (mTouchDelegate.onTouchEvent(event)) {
return true;
}
}
...
}

一、TouchDelegate的简单使用

我们通过下面的小小例子来演示了TouchDelegate的简单使用。

1.1 图示

这里面我们实现的东西很简单，就是增大触摸区域：如图

1.2 activity_touch_delegate_demo.xml

activity_touch_delegate_demo.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.AppCompatButton
android:textAllCaps="false"
android:layout_centerInParent="true"
android:id="@+id/test_btn"
android:text="TouchDelegate测试"
android:layout_width="200dp"
android:layout_height="60dp" />
</RelativeLayout>

1.2 TouchDelegateDemoActivity

TouchDelegateDemoActivity

public class TouchDelegateDemoActivity extends BaseActivity {
private AppCompatButton testBtn;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_touch_delegate_demo);
testBtn = (AppCompatButton)findViewById(R.id.test_btn);
testBtn.setOnClickListener(mOnClickListener);
View parent = (View) testBtn.getParent();
parent.post(new Runnable() {
@Override
public void run() {
int offset = 200;
Rect rect = new Rect();
testBtn.getHitRect(rect);
rect.set(rect.left-offset, rect.top-offset, rect.right+offset, rect.bottom+offset);
TouchDelegate delegate = new TouchDelegate(rect,testBtn);
((View)testBtn.getParent()).setTouchDelegate(delegate);
}
});
}

private View.OnClickListener mOnClickListener = new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(TouchDelegateDemoActivity.this, "测试而已", Toast.LENGTH_SHORT).show();
}
};
}

二、TouchDelegate源码

public class TouchDelegate {

/**
* View that should receive forwarded touch events
* 代理的view
*/
private View mDelegateView;

/**
* Bounds in local coordinates of the containing view that should be mapped to the delegate
* view. This rect is used for initial hit testing.
* 触摸区域
*/
private Rect mBounds;

/**
* mBounds inflated to include some slop. This rect is to track whether the motion events
* should be considered to be be within the delegate view.
* 移动时候触摸区域，包含了误差
*/
private Rect mSlopBounds;

/**
* True if the delegate had been targeted on a down event (intersected mBounds).
* 标记 down 事件，是否落在了触摸区域内
*/
private boolean mDelegateTargeted;

/**
* The touchable region of the View extends above its actual extent.
*/
public static final int ABOVE = 1;

/**
* The touchable region of the View extends below its actual extent.
*/
public static final int BELOW = 2;

/**
* The touchable region of the View extends to the left of its
* actual extent.
*/
public static final int TO_LEFT = 4;

/**
* The touchable region of the View extends to the right of its
* actual extent.
*/
public static final int TO_RIGHT = 8;

private int mSlop;

/**
* Constructor
*
* @param bounds Bounds in local coordinates of the containing view that should be mapped to
*        the delegate view
* @param delegateView The view that should receive motion events
*/
public TouchDelegate(Rect bounds, View delegateView) {
mBounds = bounds;
//获取相对的触摸区域的误差值（就是在这个超过原来的触摸区域，只要超出值小于等于这个值，都算在触摸区域内）
mSlop = ViewConfiguration.get(delegateView.getContext()).getScaledTouchSlop();
mSlopBounds = new Rect(bounds);
mSlopBounds.inset(-mSlop, -mSlop);
mDelegateView = delegateView;
}

/**
* Will forward touch events to the delegate view if the event is within the bounds
* specified in the constructor.
*
* @param event The touch event to forward
* @return True if the event was forwarded to the delegate, false otherwise.
*/
public boolean onTouchEvent(MotionEvent event) {
int x = (int)event.getX();
int y = (int)event.getY();
boolean sendToDelegate = false;
boolean hit = true;
boolean handled = false;

switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
Rect bounds = mBounds;
//判断这个区域包含不包含这个点
if (bounds.contains(x, y)) {
mDelegateTargeted = true;
sendToDelegate = true;
}
break;
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_MOVE:
sendToDelegate = mDelegateTargeted;
if (sendToDelegate) {
Rect slopBounds = mSlopBounds;
//判断移动的点是否超出了范围
if (!slopBounds.contains(x, y)) {
hit = false;
}
}
break;
case MotionEvent.ACTION_CANCEL:
sendToDelegate = mDelegateTargeted;
mDelegateTargeted = false;
break;
}
if (sendToDelegate) {
final View delegateView = mDelegateView;
//判断移动的点是否没有超出了我们的范围
if (hit) {
// Offset event coordinates to be inside the target view
//没有超出，重新设置触摸的点，以确保我们下面调用代理的view的分发方法时，控件能够判断点是落在它上面的
event.setLocation(delegateView.getWidth() / 2, delegateView.getHeight() / 2);
} else {
// Offset event coordinates to be outside the target view (in case it does
// something like tracking pressed state)
int slop = mSlop;
//超出了，重新设置触摸的点，保证控件能判断点不是落在它上面
event.setLocation(-(slop * 2), -(slop * 2));
}
handled = delegateView.dispatchTouchEvent(event);
}
return handled;
}
}

三、主要的小小分析

主要说明一下，TouchDelegate的原理，其实很简单，就是：事件传递到我们的代理中来的时候，我们的判断点有木有落在我们指定的区域内，如果落在区域内，那么我们把点修改为控件中间的点（这样可以确保此控件为最合适的view）,如果点不在区域内，那么我们修改点击的点(这样可以确保此控件不是最合适的view)，通过判断要不要分发动作，如果需要那么我们就用代理的view来分发事件。

3.1 构造函数

首先来看看 60–67行：这里面是构造函数初始化部分

public TouchDelegate(Rect bounds, View delegateView) {
mBounds = bounds;
//获取相对的触摸区域的误差值（就是在这个超过原来的触摸区域，只要超出值小于等于这个值，都算在触摸区域内）
mSlop = ViewConfiguration.get(delegateView.getContext()).getScaledTouchSlop();
mSlopBounds = new Rect(bounds);
mSlopBounds.inset(-mSlop, -mSlop);
mDelegateView = delegateView;
}

mBounds这个使我们按下时候判断的区域

mSlopBounds这个是我们移动时候判断的区域

3.2 MotionEvent.ACTION_DOWN

case MotionEvent.ACTION_DOWN:
Rect bounds = mBounds;
//判断这个区域包含不包含这个点
if (bounds.contains(x, y)) {
//如果点在区域内，那么标记我们有代理
mDelegateTargeted = true;
//标记需要发送处理到代理
sendToDelegate = true;
}
break;

按下的时候，判断当前的点是不是落在我们的区域内，如果是，那么我们标记我们的初始值。

3.3 MotionEvent.ACTION_MOVE和MotionEvent.ACTION_UP

case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_MOVE:
sendToDelegate = mDelegateTargeted;
if (sendToDelegate) {//有代理
Rect slopBounds = mSlopBounds;
//判断移动的点是否超出了范围
if (!slopBounds.contains(x, y)) {
hit = false;
}
}
break;

判断有没有代理，有代理，点超出了范围，那么设置

hit = false;

。

3.4 MotionEvent.ACTION_CANCEL

case MotionEvent.ACTION_CANCEL:
//修改状态
sendToDelegate = mDelegateTargeted;
mDelegateTargeted = false;

3.5 余下的处理

if (sendToDelegate) {
final View delegateView = mDelegateView;
//判断移动的点是否没有超出了我们的范围
if (hit) {
// Offset event coordinates to be inside the target view
//没有超出，重新设置触摸的点，以确保我们下面调用代理的view的分发方法时，控件能够判断点是落在它上面的
event.setLocation(delegateView.getWidth() / 2, delegateView.getHeight() / 2);
} else {
// Offset event coordinates to be outside the target view (in case it does
// something like tracking pressed state)
int slop = mSlop;
//超出了，重新设置触摸的点，保证控件能判断点不是落在它上面
event.setLocation(-(slop * 2), -(slop * 2));
}
handled = delegateView.dispatchTouchEvent(event);
}

根据前面的动作处理以后的标记判断，时候需要代理来处理消息，如果需要返回false,，如果需要我们判断，点是否已经超出了触摸范围，更改点的位置，调用代理view的事件分发。

四、流程图