Android事件分发07——TouchDelegate的使用与解析

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

<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。

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四、流程图