当我仅在水平轴上捏时，我需要放大视图。我在代码中实现了ScaleGestureDetector.getCurrentSpanX()。从API doc开始它的作用是：
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 ()
答案 0 :(得分：5)
我想最好的解决方案是使用Android 4.1.2（最新版本）中的ScaleGestureDetector类。你可以在这里找到它：
您需要做一些小修改：
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;
和这（169 - 171）
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
}
瞧，享受你的新ScaleGestureDetector吧！与API 8及更高版本兼容的完整源代码如下：
/*
* 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;
}
}