当我只在水平轴上捏时，我需要放大我的视图。我ScaleGestureDetector.getCurrentSpanX()在我的代码中实现了。从 API doc 它的作用是：
Return the average X distance between each of the pointers forming the gesture in progress through the focal point.
但仅适用于 API 级别 11 或更高级别。此类中的其他一些类似方法也需要 API 级别 11：
getCurrentSpanX ()
getCurrentSpanY ()
getPreviousSpanX ()
getPreviousSpanY ()
我想最好的解决方案是使用ScaleGestureDetectorAndroid 4.1.2（最新版本）中的类。你可以在这里找到它：
您将需要进行一些小的修改：
1）添加进口
import android.view.MotionEvent;
import android.view.ViewConfiguration;
2) 删除此行 (143 - 148)
/**
* Consistency verifier for debugging purposes.
*/
private final InputEventConsistencyVerifier mInputEventConsistencyVerifier =
InputEventConsistencyVerifier.isInstrumentationEnabled() ?
new InputEventConsistencyVerifier(this, 0) : null;
还有这个 (169 - 171)
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
}
瞧，享受您的新 ScaleGestureDetector！与 API 8 及更高版本兼容的完整源代码在这里：
/*
* Copyright (C) 2010 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package eu.bioport.tests;
import android.content.Context;
import android.util.FloatMath;
import android.view.MotionEvent;
import android.view.ViewConfiguration;
/**
* Detects scaling transformation gestures using the supplied {@link MotionEvent}s.
* The {@link OnScaleGestureListener} callback will notify users when a particular
* gesture event has occurred.
*
* This class should only be used with {@link MotionEvent}s reported via touch.
*
* To use this class:
* <ul>
* <li>Create an instance of the {@code ScaleGestureDetector} for your
* {@link View}
* <li>In the {@link View#onTouchEvent(MotionEvent)} method ensure you call
* {@link #onTouchEvent(MotionEvent)}. The methods defined in your
* callback will be executed when the events occur.
* </ul>
*/
public class ScaleGestureDetector {
private static final String TAG = "ScaleGestureDetector";
/**
* The listener for receiving notifications when gestures occur.
* If you want to listen for all the different gestures then implement
* this interface. If you only want to listen for a subset it might
* be easier to extend {@link SimpleOnScaleGestureListener}.
*
* An application will receive events in the following order:
* <ul>
* <li>One {@link OnScaleGestureListener#onScaleBegin(ScaleGestureDetector)}
* <li>Zero or more {@link OnScaleGestureListener#onScale(ScaleGestureDetector)}
* <li>One {@link OnScaleGestureListener#onScaleEnd(ScaleGestureDetector)}
* </ul>
*/
public interface OnScaleGestureListener {
/**
* Responds to scaling events for a gesture in progress.
* Reported by pointer motion.
*
* @param detector The detector reporting the event - use this to
* retrieve extended info about event state.
* @return Whether or not the detector should consider this event
* as handled. If an event was not handled, the detector
* will continue to accumulate movement until an event is
* handled. This can be useful if an application, for example,
* only wants to update scaling factors if the change is
* greater than 0.01.
*/
public boolean onScale(ScaleGestureDetector detector);
/**
* Responds to the beginning of a scaling gesture. Reported by
* new pointers going down.
*
* @param detector The detector reporting the event - use this to
* retrieve extended info about event state.
* @return Whether or not the detector should continue recognizing
* this gesture. For example, if a gesture is beginning
* with a focal point outside of a region where it makes
* sense, onScaleBegin() may return false to ignore the
* rest of the gesture.
*/
public boolean onScaleBegin(ScaleGestureDetector detector);
/**
* Responds to the end of a scale gesture. Reported by existing
* pointers going up.
*
* Once a scale has ended, {@link ScaleGestureDetector#getFocusX()}
* and {@link ScaleGestureDetector#getFocusY()} will return focal point
* of the pointers remaining on the screen.
*
* @param detector The detector reporting the event - use this to
* retrieve extended info about event state.
*/
public void onScaleEnd(ScaleGestureDetector detector);
}
/**
* A convenience class to extend when you only want to listen for a subset
* of scaling-related events. This implements all methods in
* {@link OnScaleGestureListener} but does nothing.
* {@link OnScaleGestureListener#onScale(ScaleGestureDetector)} returns
* {@code false} so that a subclass can retrieve the accumulated scale
* factor in an overridden onScaleEnd.
* {@link OnScaleGestureListener#onScaleBegin(ScaleGestureDetector)} returns
* {@code true}.
*/
public static class SimpleOnScaleGestureListener implements OnScaleGestureListener {
public boolean onScale(ScaleGestureDetector detector) {
return false;
}
public boolean onScaleBegin(ScaleGestureDetector detector) {
return true;
}
public void onScaleEnd(ScaleGestureDetector detector) {
// Intentionally empty
}
}
private final Context mContext;
private final OnScaleGestureListener mListener;
private float mFocusX;
private float mFocusY;
private float mCurrSpan;
private float mPrevSpan;
private float mInitialSpan;
private float mCurrSpanX;
private float mCurrSpanY;
private float mPrevSpanX;
private float mPrevSpanY;
private long mCurrTime;
private long mPrevTime;
private boolean mInProgress;
private int mSpanSlop;
public ScaleGestureDetector(Context context, OnScaleGestureListener listener) {
mContext = context;
mListener = listener;
mSpanSlop = ViewConfiguration.get(context).getScaledTouchSlop() * 2;
}
/**
* Accepts MotionEvents and dispatches events to a {@link OnScaleGestureListener}
* when appropriate.
*
* <p>Applications should pass a complete and consistent event stream to this method.
* A complete and consistent event stream involves all MotionEvents from the initial
* ACTION_DOWN to the final ACTION_UP or ACTION_CANCEL.</p>
*
* @param event The event to process
* @return true if the event was processed and the detector wants to receive the
* rest of the MotionEvents in this event stream.
*/
public boolean onTouchEvent(MotionEvent event) {
final int action = event.getActionMasked();
final boolean streamComplete = action == MotionEvent.ACTION_UP ||
action == MotionEvent.ACTION_CANCEL;
if (action == MotionEvent.ACTION_DOWN || streamComplete) {
// Reset any scale in progress with the listener.
// If it's an ACTION_DOWN we're beginning a new event stream.
// This means the app probably didn't give us all the events. Shame on it.
if (mInProgress) {
mListener.onScaleEnd(this);
mInProgress = false;
mInitialSpan = 0;
}
if (streamComplete) {
return true;
}
}
final boolean configChanged =
action == MotionEvent.ACTION_POINTER_UP ||
action == MotionEvent.ACTION_POINTER_DOWN;
final boolean pointerUp = action == MotionEvent.ACTION_POINTER_UP;
final int skipIndex = pointerUp ? event.getActionIndex() : -1;
// Determine focal point
float sumX = 0, sumY = 0;
final int count = event.getPointerCount();
for (int i = 0; i < count; i++) {
if (skipIndex == i) continue;
sumX += event.getX(i);
sumY += event.getY(i);
}
final int div = pointerUp ? count - 1 : count;
final float focusX = sumX / div;
final float focusY = sumY / div;
// Determine average deviation from focal point
float devSumX = 0, devSumY = 0;
for (int i = 0; i < count; i++) {
if (skipIndex == i) continue;
devSumX += Math.abs(event.getX(i) - focusX);
devSumY += Math.abs(event.getY(i) - focusY);
}
final float devX = devSumX / div;
final float devY = devSumY / div;
// Span is the average distance between touch points through the focal point;
// i.e. the diameter of the circle with a radius of the average deviation from
// the focal point.
final float spanX = devX * 2;
final float spanY = devY * 2;
final float span = FloatMath.sqrt(spanX * spanX + spanY * spanY);
// Dispatch begin/end events as needed.
// If the configuration changes, notify the app to reset its current state by beginning
// a fresh scale event stream.
final boolean wasInProgress = mInProgress;
mFocusX = focusX;
mFocusY = focusY;
if (mInProgress && (span == 0 || configChanged)) {
mListener.onScaleEnd(this);
mInProgress = false;
mInitialSpan = span;
}
if (configChanged) {
mPrevSpanX = mCurrSpanX = spanX;
mPrevSpanY = mCurrSpanY = spanY;
mInitialSpan = mPrevSpan = mCurrSpan = span;
}
if (!mInProgress && span != 0 &&
(wasInProgress || Math.abs(span - mInitialSpan) > mSpanSlop)) {
mPrevSpanX = mCurrSpanX = spanX;
mPrevSpanY = mCurrSpanY = spanY;
mPrevSpan = mCurrSpan = span;
mInProgress = mListener.onScaleBegin(this);
}
// Handle motion; focal point and span/scale factor are changing.
if (action == MotionEvent.ACTION_MOVE) {
mCurrSpanX = spanX;
mCurrSpanY = spanY;
mCurrSpan = span;
boolean updatePrev = true;
if (mInProgress) {
updatePrev = mListener.onScale(this);
}
if (updatePrev) {
mPrevSpanX = mCurrSpanX;
mPrevSpanY = mCurrSpanY;
mPrevSpan = mCurrSpan;
}
}
return true;
}
/**
* Returns {@code true} if a scale gesture is in progress.
*/
public boolean isInProgress() {
return mInProgress;
}
/**
* Get the X coordinate of the current gesture's focal point.
* If a gesture is in progress, the focal point is between
* each of the pointers forming the gesture.
*
* If {@link #isInProgress()} would return false, the result of this
* function is undefined.
*
* @return X coordinate of the focal point in pixels.
*/
public float getFocusX() {
return mFocusX;
}
/**
* Get the Y coordinate of the current gesture's focal point.
* If a gesture is in progress, the focal point is between
* each of the pointers forming the gesture.
*
* If {@link #isInProgress()} would return false, the result of this
* function is undefined.
*
* @return Y coordinate of the focal point in pixels.
*/
public float getFocusY() {
return mFocusY;
}
/**
* Return the average distance between each of the pointers forming the
* gesture in progress through the focal point.
*
* @return Distance between pointers in pixels.
*/
public float getCurrentSpan() {
return mCurrSpan;
}
/**
* Return the average X distance between each of the pointers forming the
* gesture in progress through the focal point.
*
* @return Distance between pointers in pixels.
*/
public float getCurrentSpanX() {
return mCurrSpanX;
}
/**
* Return the average Y distance between each of the pointers forming the
* gesture in progress through the focal point.
*
* @return Distance between pointers in pixels.
*/
public float getCurrentSpanY() {
return mCurrSpanY;
}
/**
* Return the previous average distance between each of the pointers forming the
* gesture in progress through the focal point.
*
* @return Previous distance between pointers in pixels.
*/
public float getPreviousSpan() {
return mPrevSpan;
}
/**
* Return the previous average X distance between each of the pointers forming the
* gesture in progress through the focal point.
*
* @return Previous distance between pointers in pixels.
*/
public float getPreviousSpanX() {
return mPrevSpanX;
}
/**
* Return the previous average Y distance between each of the pointers forming the
* gesture in progress through the focal point.
*
* @return Previous distance between pointers in pixels.
*/
public float getPreviousSpanY() {
return mPrevSpanY;
}
/**
* Return the scaling factor from the previous scale event to the current
* event. This value is defined as
* ({@link #getCurrentSpan()} / {@link #getPreviousSpan()}).
*
* @return The current scaling factor.
*/
public float getScaleFactor() {
return mPrevSpan > 0 ? mCurrSpan / mPrevSpan : 1;
}
/**
* Return the time difference in milliseconds between the previous
* accepted scaling event and the current scaling event.
*
* @return Time difference since the last scaling event in milliseconds.
*/
public long getTimeDelta() {
return mCurrTime - mPrevTime;
}
/**
* Return the event time of the current event being processed.
*
* @return Current event time in milliseconds.
*/
public long getEventTime() {
return mCurrTime;
}
}