Android触摸事件

作者: Spirituality韬 | 来源:发表于2018-05-05 11:16 被阅读0次

布局原理介绍

Android中四大组件中Activity组件就是呈现的许多页面，其中Activity中嵌套很多控件，其中有RelativeLayout、ImageView等等，这些控件的基类都是View这个类，当然我们也知道ViewGroup继承View这个类，它可以看做一个控件的容器，比如RelativeLayout。

image

触摸事件的类型

接下来就看看触摸事件的类型
ACTION_DOWN：用户手指按下操作，往往也代表着一次触摸事件的开始。
ACTION_MOVE：用户手指在屏幕上移动，一般情况下的轻微移动都会触发一系列的移动事件。
ACTION_POINTER_DOWN：额外的手指按下操作。
ACTION_POINTER_UP：额外的手指的离开操作
ACTION_UP：用户手指离开屏幕的操作，一次抬起操作标志着一次触摸事件的结束

了解完这些触摸事件类型，接下来就来看看触摸事件的原理，它是怎么实现的

首先我们点击手机屏幕，假如点击的地方是一个嵌套的View，消息机制是怎么传递的呢？
MyView.java

public class MyView extends View {
private static final String TAG = "MyView";

public MyView(Context context) {
    super(context);
}

public MyView(Context context, @Nullable AttributeSet attrs) {
    super(context, attrs);
}

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
    switch (ev.getAction()){
        case MotionEvent.ACTION_DOWN:
            Log.i(TAG, "dispatchTouchEvent: ACTION_DOWN");
            break;
        case MotionEvent.ACTION_MOVE:
            Log.i(TAG, "dispatchTouchEvent: ACTION_MOVE");
            break;
        case MotionEvent.ACTION_UP:
            Log.i(TAG, "dispatchTouchEvent: ACTION_UP");
            break;
    }
    return super.dispatchTouchEvent(ev);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()){
        case MotionEvent.ACTION_DOWN:
            Log.i(TAG, "onTouchEvent: ACTION_DOWN");
            break;
        case MotionEvent.ACTION_MOVE:
            Log.i(TAG, "onTouchEvent: ACTION_MOVE");
            break;
        case MotionEvent.ACTION_UP:
            Log.i(TAG, "onTouchEvent: ACTION_UP");
            break;
    }
    return super.onTouchEvent(event);
}
}

MainActivity.java

public class MainActivity extends AppCompatActivity implements View.OnTouchListener, View.OnClickListener {

private static final String TAG = "MainActivity";
private MyView myView;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    myView = (MyView) findViewById(R.id.myView);
    myView.setOnClickListener(this);
    myView.setOnTouchListener(this);
}

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
    switch (ev.getAction()){
        case MotionEvent.ACTION_DOWN:
            Log.i(TAG, "dispatchTouchEvent: MainActivity ACTION_DOWN");
            break;
        case MotionEvent.ACTION_MOVE:
            Log.i(TAG, "dispatchTouchEvent: MainActivity ACTION_MOVE");
            break;
        case MotionEvent.ACTION_UP:
            Log.i(TAG, "dispatchTouchEvent: MainActivity ACTION_UP");
            break;
    }
    return super.dispatchTouchEvent(ev);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()){
        case MotionEvent.ACTION_DOWN:
            Log.i(TAG, "onTouchEvent: MainActivity ACTION_DOWN");
            break;
        case MotionEvent.ACTION_MOVE:
            Log.i(TAG, "onTouchEvent: MainActivity ACTION_MOVE");
            break;
        case MotionEvent.ACTION_UP:
            Log.i(TAG, "onTouchEvent: MainActivity ACTION_UP");
            break;
    }
    return super.onTouchEvent(event);
}

@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
    switch (motionEvent.getAction()){
        case MotionEvent.ACTION_DOWN:
            Log.i(TAG, "onTouch: myView ACTION_DOWN");
            break;
        case MotionEvent.ACTION_MOVE:
            Log.i(TAG, "onTouch: myView ACTION_MOVE");
            break;
        case MotionEvent.ACTION_UP:
            Log.i(TAG, "onTouch: myView ACTION_UP");
            break;
    }
    return false;
}

@Override
public void onClick(View view) {
    if (view.getId() == R.id.myView){
            Log.i(TAG, "onClick: myView");
    }
}
}

点击MyView区域

MainActivity: dispatchTouchEvent: MainActivity ACTION_DOWN
MyView: dispatchTouchEvent: ACTION_DOWN
MainActivity: onTouch: myView ACTION_DOWN
MyView: onTouchEvent: ACTION_DOWN
MainActivity: dispatchTouchEvent: MainActivity ACTION_UP
MyView: dispatchTouchEvent: ACTION_UP
MainActivity: onTouch: myView ACTION_UP
MyView: onTouchEvent: ACTION_UP
MainActivity: onClick: myView

由输出结果可知，dispatchTouchEvent消息是由外向里传递，onTouchEvent处理这个消息，其返回结果就是该消息是否被消费，super则是被消费。如果不消费则把事件返回到父级消费。
把MyView中onTouchEvent返回之改为false

MainActivity: dispatchTouchEvent: MainActivity ACTION_DOWN
MyView: dispatchTouchEvent: ACTION_DOWN
MainActivity: onTouch: myView ACTION_DOWN
MyView: onTouchEvent: ACTION_DOWN
MainActivity: onTouchEvent: MainActivity ACTION_DOWN
MainActivity: dispatchTouchEvent: MainActivity ACTION_UP
MainActivity: onTouchEvent: MainActivity ACTION_UP

下面在Activity中添加一个Layout布局，其中View就在这个布局上
MyLayout.java

public class MyLayout extends RelativeLayout {

private static final String TAG = "MyLayout";

public MyLayout(Context context) {
    super(context);
}

public MyLayout(Context context, AttributeSet attrs) {
    super(context, attrs);
}

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
    switch (ev.getAction()) {
        case MotionEvent.ACTION_DOWN:
            Log.e(TAG, "dispatchTouchEvent ACTION_DOWN");
            break;
        case MotionEvent.ACTION_MOVE:
            Log.e(TAG, "dispatchTouchEvent ACTION_MOVE");
            break;
        case MotionEvent.ACTION_UP:
            Log.e(TAG, "dispatchTouchEvent ACTION_UP");
            break;
        case MotionEvent.ACTION_CANCEL:
            Log.e(TAG, "dispatchTouchEvent ACTION_CANCEL");
            break;
        default:
            break;
    }
    return super.dispatchTouchEvent(ev);
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
    switch (ev.getAction()) {
        case MotionEvent.ACTION_DOWN:
            Log.e(TAG, "onInterceptTouchEvent ACTION_DOWN");
            break;
        case MotionEvent.ACTION_MOVE:
            Log.e(TAG, "onInterceptTouchEvent ACTION_MOVE");
            break;
        case MotionEvent.ACTION_UP:
            Log.e(TAG, "onInterceptTouchEvent ACTION_UP");
            break;
        default:
            break;
    }
    return true;
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            Log.e(TAG, "onTouchEvent ACTION_DOWN");
            break;
        case MotionEvent.ACTION_MOVE:
            Log.e(TAG, "onTouchEvent ACTION_MOVE");
            break;
        case MotionEvent.ACTION_UP:
            Log.e(TAG, "onTouchEvent ACTION_UP");
            break;
        case MotionEvent.ACTION_CANCEL:
            Log.e(TAG, "onTouchEvent ACTION_CANCEL");
            break;
        default:
            break;
    }
    return super.onTouchEvent(event);
}
}

onInterceptTouchEvent方式ViewGroup中特有的方法，意思很简单它的返回值就是决定是否拦截此触摸活动，点击View区域来看看输出结果。

dispatchTouchEvent: MainActivity ACTION_DOWN
MyLayout: dispatchTouchEvent ACTION_DOWN
MyLayout: onInterceptTouchEvent ACTION_DOWN
MyLayout: onTouchEvent ACTION_DOWN
MainActivity: onTouchEvent: MainActivity ACTION_DOWN
MainActivity: dispatchTouchEvent: MainActivity ACTION_UP
MainActivity: onTouchEvent: MainActivity ACTION_UP

由此结果可知，dispatchTouchEvent并没有传递到View，当然这个拦截的效果，再将返回值改为false

MainActivity: dispatchTouchEvent: MainActivity ACTION_DOWN
MyLayout: dispatchTouchEvent ACTION_DOWN
MyLayout: onInterceptTouchEvent ACTION_DOWN
MyView: dispatchTouchEvent: ACTION_DOWN
MainActivity: onTouch: myView ACTION_DOWN
MyView: onTouchEvent: ACTION_DOWN
MainActivity: dispatchTouchEvent: MainActivity ACTION_UP
MyLayout: dispatchTouchEvent ACTION_UP
MyLayout: onInterceptTouchEvent ACTION_UP
MyView: dispatchTouchEvent: ACTION_UP
MainActivity: onTouch: myView ACTION_UP
MyView: onTouchEvent: ACTION_UP
MainActivity: onClick: myView

结合onTouchEvent的讲解输出结果一目了然了。

源码分析

通过对源码的具体分析来验证以上的输出结果
View.java

public boolean dispatchTouchEvent(MotionEvent event) {
    ....
    if (onFilterTouchEventForSecurity(event)) {
        if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
            result = true;
        }
        //noinspection SimplifiableIfStatement
        ListenerInfo li = mListenerInfo;
        if (li != null && li.mOnTouchListener != null
                && (mViewFlags & ENABLED_MASK) == ENABLED
                && li.mOnTouchListener.onTouch(this, event)) {
            result = true;
        }
        if (!result && onTouchEvent(event)) {
            result = true;
        }
    }
    ....
    }

由上面代码逻辑可以知道首先执行li.mOnTouchListener.onTouch(this, event)，mOnTouchListener就是在Activity中设置的监听回调，如果onTouch返回值为true，显而易见dispatchTouchEvent就直接返回了不会往后执行onTouchEvent这个函数了。这也是为什么输出结果先执行onTouch而后执行onTouchEvent得原因，也是onTouch返回false，而执行onTouchEvent。

接下来看onTouchEvent

public boolean onTouchEvent(MotionEvent event) {
    ...
    if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
        switch (action) {
            case MotionEvent.ACTION_UP:
                 ...
                 if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
                        // This is a tap, so remove the longpress check
                        removeLongPressCallback();

                        // Only perform take click actions if we were in the pressed state
                        if (!focusTaken) {
                            // Use a Runnable and post this rather than calling
                            // performClick directly. This lets other visual state
                            // of the view update before click actions start.
                            if (mPerformClick == null) {
                                mPerformClick = new PerformClick();
                            }
                            if (!post(mPerformClick)) {
                                performClick();
                            }
                        }
                    }
              ...
    }
 }

mPerformClick 这个函数实现Runnable这个接口，回调li.mOnClickListener.onClick(this)方法。这也是onClick在ACTION_UP时最后调用的原因

Android触摸事件

布局原理介绍

触摸事件的类型

源码分析

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