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Android自定义View的事件分发流程

news 2025/7/14 12:25:58

Android的事件分发机制遵循责任链模式，事件从Activity开始，依次经过ViewGroup和View，每个层级都有机会处理事件。

事件分发流程

1. 事件分发的主要方法

// 事件分发入口
public boolean dispatchTouchEvent(MotionEvent event)// 拦截事件（ViewGroup独有）
public boolean onInterceptTouchEvent(MotionEvent event)// 处理事件
public boolean onTouchEvent(MotionEvent event)

2. 完整的事件分发流程

Activity.dispatchTouchEvent()
↓
ViewGroup.dispatchTouchEvent()
↓
ViewGroup.onInterceptTouchEvent() // 决定是否拦截
↓
View.dispatchTouchEvent()
↓
View.onTouchEvent()
↓
Activity.onTouchEvent() // 如果所有View都不处理

3. 自定义View中的事件处理

基本事件处理

public class CustomView extends View {@Overridepublic boolean onTouchEvent(MotionEvent event) {switch (event.getAction()) {case MotionEvent.ACTION_DOWN:// 手指按下handleActionDown(event);return true; // 返回true表示消费事件case MotionEvent.ACTION_MOVE:// 手指移动handleActionMove(event);return true;case MotionEvent.ACTION_UP:// 手指抬起handleActionUp(event);return true;}return super.onTouchEvent(event);}private void handleActionDown(MotionEvent event) {// 记录起始位置mStartX = event.getX();mStartY = event.getY();}private void handleActionMove(MotionEvent event) {// 计算移动距离float deltaX = event.getX() - mStartX;float deltaY = event.getY() - mStartY;// 执行相应的操作performMove(deltaX, deltaY);}private void handleActionUp(MotionEvent event) {// 完成操作performAction();}
}

自定义ViewGroup的事件处理

public class CustomViewGroup extends ViewGroup {@Overridepublic boolean onInterceptTouchEvent(MotionEvent event) {switch (event.getAction()) {case MotionEvent.ACTION_DOWN:// 记录初始触摸点mInitialTouchX = event.getX();mInitialTouchY = event.getY();break;case MotionEvent.ACTION_MOVE:// 计算移动距离float deltaX = Math.abs(event.getX() - mInitialTouchX);float deltaY = Math.abs(event.getY() - mInitialTouchY);// 如果水平移动距离大于阈值，拦截事件if (deltaX > mTouchSlop && deltaX > deltaY) {return true; // 拦截事件，自己处理}break;}return super.onInterceptTouchEvent(event);}@Overridepublic boolean onTouchEvent(MotionEvent event) {switch (event.getAction()) {case MotionEvent.ACTION_DOWN:return true;case MotionEvent.ACTION_MOVE:// 处理滑动逻辑handleScroll(event);return true;case MotionEvent.ACTION_UP:// 处理释放逻辑handleRelease(event);return true;}return super.onTouchEvent(event);}
}

4. 事件分发的重要原则

返回值含义

true: 消费事件，事件不会继续传递

false: 不消费事件，事件继续向下传递

拦截机制

onInterceptTouchEvent() 只在ViewGroup中存在

返回true表示拦截子View的事件

拦截后，子View不会再收到后续事件

5. 实际应用示例

拖拽View的实现

public class DraggableImageView extends ImageView {private float mLastTouchX;private float mLastTouchY;private boolean mIsDragging = false;@Overridepublic boolean onTouchEvent(MotionEvent event) {switch (event.getAction()) {case MotionEvent.ACTION_DOWN:mLastTouchX = event.getX();mLastTouchY = event.getY();mIsDragging = false;return true;case MotionEvent.ACTION_MOVE:float deltaX = event.getX() - mLastTouchX;float deltaY = event.getY() - mLastTouchY;// 判断是否开始拖拽if (!mIsDragging && (Math.abs(deltaX) > 10 || Math.abs(deltaY) > 10)) {mIsDragging = true;}if (mIsDragging) {// 移动ViewsetTranslationX(getTranslationX() + deltaX);setTranslationY(getTranslationY() + deltaY);}mLastTouchX = event.getX();mLastTouchY = event.getY();return true;case MotionEvent.ACTION_UP:if (!mIsDragging) {// 执行点击事件performClick();}mIsDragging = false;return true;}return super.onTouchEvent(event);}
}

6. 调试技巧

@Override
public boolean dispatchTouchEvent(MotionEvent event) {Log.d("TouchEvent", "dispatchTouchEvent: " + event.getAction());boolean result = super.dispatchTouchEvent(event);Log.d("TouchEvent", "dispatchTouchEvent result: " + result);return result;
}@Override
public boolean onTouchEvent(MotionEvent event) {Log.d("TouchEvent", "onTouchEvent: " + event.getAction());boolean result = super.onTouchEvent(event);Log.d("TouchEvent", "onTouchEvent result: " + result);return result;
}