Android onTouch事件

Question

我想要创建一个应用程序，在那里我可以改变GridLayout手势的颜色。GridLayout可以很好地处理以下代码：

@Override
public void onDraw(Canvas canvas) {
    if (touchOn) {
        canvas.drawColor(Color.RED);
    } else {
        canvas.drawColor(Color.GRAY);
    }
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    super.onTouchEvent(event);
    touchOn = true;
    invalidate();
    return true;
}

使用xml代码：

<GridLayout
    android:id="@+id/mygrid"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:columnCount="8"
    android:rowCount="8"
    android:layout_gravity="center"
    android:background="@android:color/background_light"
    android:layout_below="@+id/linearLayout3">
</GridLayout>

但我只能通过触摸网格来更改one手势的颜色。是否有MotionEvent或其他东西检测到我已经触摸了一个手势，并将(没有摘下手指)移动到下一个手势？这样我就可以用手指在网格上移动，颜色也会一个接一个地变化。

谢谢！

Answer 1

您可以通过在您的GestureDetector.OnGestureListener中实现MainActivity和GestureDetector.OnDoubleTapListener方法来检测手势，并更改每个手势的颜色：

public class MainActivity extends Activity implements 
        GestureDetector.OnGestureListener,
        GestureDetector.OnDoubleTapListener{

    private static final String DEBUG_TAG = "Gestures";
    private GestureDetectorCompat mDetector; 

    // Called when the activity is first created. 
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // Instantiate the gesture detector with the
        // application context and an implementation of
        // GestureDetector.OnGestureListener
        mDetector = new GestureDetectorCompat(this,this);
        // Set the gesture detector as the double tap
        // listener.
        mDetector.setOnDoubleTapListener(this);
    }

    @Override 
    public boolean onTouchEvent(MotionEvent event){ 
        this.mDetector.onTouchEvent(event);
        // Be sure to call the superclass implementation
        return super.onTouchEvent(event);
    }

    @Override
    public boolean onDown(MotionEvent event) { 
        Log.d(DEBUG_TAG,"onDown: " + event.toString()); 
        return true;
    }

    @Override
    public boolean onFling(MotionEvent event1, MotionEvent event2, 
            float velocityX, float velocityY) {
        Log.d(DEBUG_TAG, "onFling: " + event1.toString()+event2.toString());
        return true;
    }

    @Override
    public void onLongPress(MotionEvent event) {
        Log.d(DEBUG_TAG, "onLongPress: " + event.toString()); 
    }

    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX,
            float distanceY) {
        Log.d(DEBUG_TAG, "onScroll: " + e1.toString()+e2.toString());
        return true;
    }

    @Override
    public void onShowPress(MotionEvent event) {
        Log.d(DEBUG_TAG, "onShowPress: " + event.toString());
    }

    @Override
    public boolean onSingleTapUp(MotionEvent event) {
        Log.d(DEBUG_TAG, "onSingleTapUp: " + event.toString());
        return true;
    }

    @Override
    public boolean onDoubleTap(MotionEvent event) {
        Log.d(DEBUG_TAG, "onDoubleTap: " + event.toString());
        return true;
    }

    @Override
    public boolean onDoubleTapEvent(MotionEvent event) {
        Log.d(DEBUG_TAG, "onDoubleTapEvent: " + event.toString());
        return true;
    }

    @Override
    public boolean onSingleTapConfirmed(MotionEvent event) {
        Log.d(DEBUG_TAG, "onSingleTapConfirmed: " + event.toString());
        return true;
    }
}

你也可以在接触事件中跟踪运动。

您可以有一个基于运动的手势，它只是基于指针移动的距离和/或方向。但是速度往往是跟踪手势特征，甚至决定手势是否发生的决定性因素。为了简化速度计算，Android在Support中提供了VelocityTracker类和VelocityTrackerCompat类。VelocityTracker帮助您跟踪触摸事件的速度。这对于速度是手势标准的一部分的手势是有用的，比如放纵。

下面是一个例子。

public class MainActivity extends Activity {
    private static final String DEBUG_TAG = "Velocity";
        ...
    private VelocityTracker mVelocityTracker = null;
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int index = event.getActionIndex();
        int action = event.getActionMasked();
        int pointerId = event.getPointerId(index);

        switch(action) {
            case MotionEvent.ACTION_DOWN:
                if(mVelocityTracker == null) {
                    // Retrieve a new VelocityTracker object to watch the velocity of a motion.
                    mVelocityTracker = VelocityTracker.obtain();
                }
                else {
                    // Reset the velocity tracker back to its initial state.
                    mVelocityTracker.clear();
                }
                // Add a user's movement to the tracker.
                mVelocityTracker.addMovement(event);
                break;
            case MotionEvent.ACTION_MOVE:
                mVelocityTracker.addMovement(event);
                // When you want to determine the velocity, call 
                // computeCurrentVelocity(). Then call getXVelocity() 
                // and getYVelocity() to retrieve the velocity for each pointer ID. 
                mVelocityTracker.computeCurrentVelocity(1000);
                // Log velocity of pixels per second
                // Best practice to use VelocityTrackerCompat where possible.
                Log.d("", "X velocity: " + 
                        VelocityTrackerCompat.getXVelocity(mVelocityTracker, 
                        pointerId));
                Log.d("", "Y velocity: " + 
                        VelocityTrackerCompat.getYVelocity(mVelocityTracker,
                        pointerId));
                break;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                // Return a VelocityTracker object back to be re-used by others.
                mVelocityTracker.recycle();
                break;
        }
        return true;
    }
}

请参阅https://developer.android.com/training/gestures/detector.html

当用户在触摸屏上放置一个或多个手指，应用程序将该触摸模式解释为特定的手势时，就会出现“触摸手势”。相应地，手势检测有两个阶段：

• 收集关于触摸事件的数据。
• 对数据进行解释，看看它是否符合应用程序所支持的任何手势的标准。

和https://developer.android.com/training/gestures/movement.html#velocity

每当当前触点接触位置、压力或大小发生变化时，都会通过ACTION_MOVE事件触发新的ACTION_MOVE()。正如在检测公共手势中所描述的，所有这些事件都记录在onTouchEvent()的onTouchEvent参数中。