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禁用ViewPager左右两侧拉到边界的渐变颜色

2014-05-11 21:10 330 查看

禁用ViewPager左右两侧拉到边界的渐变颜色

Android ViewPager在拖拽到左边和右边的时候，禁止显示***或者蓝色的渐变图片的解决方法

先说明哦，想看看院里的，从头开始看，否则，就拉到最下面啦。解决方案就在最下面。

修改前：

修改后：

先看下ViewPager中和这个颜色相关的代码：

private EdgeEffectCompat mLeftEdge;
private EdgeEffectCompat mRightEdge;

就是这俩货，导致的边界颜色。没办法，这货是private的，后面只能通过反射来得到了。

再看下draw()方法中的逻辑：

@Override
public void draw(Canvas canvas) {
super.draw(canvas);
boolean needsInvalidate = false;

final int overScrollMode = ViewCompat.getOverScrollMode(this);
if (overScrollMode == ViewCompat.OVER_SCROLL_ALWAYS ||
(overScrollMode == ViewCompat.OVER_SCROLL_IF_CONTENT_SCROLLS &&
mAdapter != null && mAdapter.getCount() > 1)) {
if (!mLeftEdge.isFinished()) {
final int restoreCount = canvas.save();
final int height = getHeight() - getPaddingTop() - getPaddingBottom();

canvas.rotate(270);
canvas.translate(-height + getPaddingTop(), 0);
mLeftEdge.setSize(height, getWidth());
needsInvalidate |= mLeftEdge.draw(canvas);
canvas.restoreToCount(restoreCount);
}
if (!mRightEdge.isFinished()) {
final int restoreCount = canvas.save();
final int width = getWidth();
final int height = getHeight() - getPaddingTop() - getPaddingBottom();
final int itemCount = mAdapter != null ? mAdapter.getCount() : 1;

canvas.rotate(90);
canvas.translate(-getPaddingTop(),
-itemCount * (width + mPageMargin) + mPageMargin);
mRightEdge.setSize(height, width);
needsInvalidate |= mRightEdge.draw(canvas);
canvas.restoreToCount(restoreCount);
}
} else {
mLeftEdge.finish();
mRightEdge.finish();
}

if (needsInvalidate) {
// Keep animating
invalidate();
}
}

在进行绘制渐变图片之前会判断是否已经finish,【if (!mLeftEdge.isFinished())】，如果我们能修改为finished状态，不就OK了吗？！经过测试，调用mLeftEdge.finish()和mRightEdge.finish()就能达到我们要的结果。但是悲催的是，draw()方法是随时随地都在调用的，所以要在一个在draw()方法之后调用，但是还得随时随地调用的方法才行。

好吧，先说点原理的东东。

ViewPager.javaàdraw()方法 à mRightEdge.draw(canvas);以及mLeftEdge.draw(canvas);à EdgeEffectCompat.javaà看下全部的代码吧：

public class EdgeEffectCompat {
private Object mEdgeEffect;

private static final EdgeEffectImpl IMPL;

static {
if (Build.VERSION.SDK_INT >= 14) { // ICS
IMPL = new EdgeEffectIcsImpl();
} else {
IMPL = new BaseEdgeEffectImpl();
}
}

interface EdgeEffectImpl {
public Object newEdgeEffect(Context context);
public void setSize(Object edgeEffect, int width, int height);
public boolean isFinished(Object edgeEffect);
public void finish(Object edgeEffect);
public boolean onPull(Object edgeEffect, float deltaDistance);
public boolean onRelease(Object edgeEffect);
public boolean onAbsorb(Object edgeEffect, int velocity);
public boolean draw(Object edgeEffect, Canvas canvas);
}

/**
* Null implementation to use pre-ICS
*/
static class BaseEdgeEffectImpl implements EdgeEffectImpl {
public Object newEdgeEffect(Context context) {
return null;
}

public void setSize(Object edgeEffect, int width, int height) {
}

public boolean isFinished(Object edgeEffect) {
return true;
}

public void finish(Object edgeEffect) {
}

public boolean onPull(Object edgeEffect, float deltaDistance) {
return false;
}

public boolean onRelease(Object edgeEffect) {
return false;
}

public boolean onAbsorb(Object edgeEffect, int velocity) {
return false;
}

public boolean draw(Object edgeEffect, Canvas canvas) {
return false;
}
}

static class EdgeEffectIcsImpl implements EdgeEffectImpl {
public Object newEdgeEffect(Context context) {
return EdgeEffectCompatIcs.newEdgeEffect(context);
}

public void setSize(Object edgeEffect, int width, int height) {
EdgeEffectCompatIcs.setSize(edgeEffect, width, height);
}

public boolean isFinished(Object edgeEffect) {
return EdgeEffectCompatIcs.isFinished(edgeEffect);
}

public void finish(Object edgeEffect) {
EdgeEffectCompatIcs.finish(edgeEffect);
}

public boolean onPull(Object edgeEffect, float deltaDistance) {
return EdgeEffectCompatIcs.onPull(edgeEffect, deltaDistance);
}

public boolean onRelease(Object edgeEffect) {
return EdgeEffectCompatIcs.onRelease(edgeEffect);
}

public boolean onAbsorb(Object edgeEffect, int velocity) {
return EdgeEffectCompatIcs.onAbsorb(edgeEffect, velocity);
}

public boolean draw(Object edgeEffect, Canvas canvas) {
return EdgeEffectCompatIcs.draw(edgeEffect, canvas);
}
}

/**
* Construct a new EdgeEffect themed using the given context.
*
* <p>Note: On platform versions that do not support EdgeEffect, all operations
* on the newly constructed object will be mocked/no-ops.</p>
*
* @param context Context to use for theming the effect
*/
public EdgeEffectCompat(Context context) {
mEdgeEffect = IMPL.newEdgeEffect(context);
}

/**
* Set the size of this edge effect in pixels.
*
* @param width Effect width in pixels
* @param height Effect height in pixels
*/
public void setSize(int width, int height) {
IMPL.setSize(mEdgeEffect, width, height);
}

/**
* Reports if this EdgeEffectCompat's animation is finished. If this method returns false
* after a call to {@link #draw(Canvas)} the host widget should schedule another
* drawing pass to continue the animation.
*
* @return true if animation is finished, false if drawing should continue on the next frame.
*/
public boolean isFinished() {
return IMPL.isFinished(mEdgeEffect);
}

/**
* Immediately finish the current animation.
* After this call {@link #isFinished()} will return true.
*/
public void finish() {
IMPL.finish(mEdgeEffect);
}

/**
* A view should call this when content is pulled away from an edge by the user.
* This will update the state of the current visual effect and its associated animation.
* The host view should always {@link android.view.View#invalidate()} if this method
* returns true and draw the results accordingly.
*
* @param deltaDistance Change in distance since the last call. Values may be 0 (no change) to
* 1.f (full length of the view) or negative values to express change
* back toward the edge reached to initiate the effect.
* @return true if the host view should call invalidate, false if it should not.
*/
public boolean onPull(float deltaDistance) {
return IMPL.onPull(mEdgeEffect, deltaDistance);
}

/**
* Call when the object is released after being pulled.
* This will begin the "decay" phase of the effect. After calling this method
* the host view should {@link android.view.View#invalidate()} if this method
* returns true and thereby draw the results accordingly.
*
* @return true if the host view should invalidate, false if it should not.
*/
public boolean onRelease() {
return IMPL.onRelease(mEdgeEffect);
}

/**
* Call when the effect absorbs an impact at the given velocity.
* Used when a fling reaches the scroll boundary.
*
* <p>When using a {@link android.widget.Scroller} or {@link android.widget.OverScroller},
* the method <code>getCurrVelocity</code> will provide a reasonable approximation
* to use here.</p>
*
* @param velocity Velocity at impact in pixels per second.
* @return true if the host view should invalidate, false if it should not.
*/
public boolean onAbsorb(int velocity) {
return IMPL.onAbsorb(mEdgeEffect, velocity);
}

/**
* Draw into the provided canvas. Assumes that the canvas has been rotated
* accordingly and the size has been set. The effect will be drawn the full
* width of X=0 to X=width, beginning from Y=0 and extending to some factor <
* 1.f of height.
*
* @param canvas Canvas to draw into
* @return true if drawing should continue beyond this frame to continue the
* animation
*/
public boolean draw(Canvas canvas) {
return IMPL.draw(mEdgeEffect, canvas);
}
}

à看完之后，下面进入到EdgeEffectCompatIcs.javaà好吧，再贴上完整的代码

class EdgeEffectCompatIcs {
public static Object newEdgeEffect(Context context) {
return new EdgeEffect(context);
}

public static void setSize(Object edgeEffect, int width, int height) {
((EdgeEffect) edgeEffect).setSize(width, height);
}

public static boolean isFinished(Object edgeEffect) {
return ((EdgeEffect) edgeEffect).isFinished();
}
public static void finish(Object edgeEffect) {
((EdgeEffect) edgeEffect).finish();
}

public static boolean onPull(Object edgeEffect, float deltaDistance) {
((EdgeEffect) edgeEffect).onPull(deltaDistance);
return true;
}

public static boolean onRelease(Object edgeEffect) {
EdgeEffect eff = (EdgeEffect) edgeEffect;
eff.onRelease();
return eff.isFinished();
}

public static boolean onAbsorb(Object edgeEffect, int velocity) {
((EdgeEffect) edgeEffect).onAbsorb(velocity);
return true;
}
public static boolean draw(Object edgeEffect, Canvas canvas) {
return ((EdgeEffect) edgeEffect).draw(canvas);
}
}

à下面进入到EdgeEffect.java中吧à如果你有闲情逸致的话，那就看下他的代码吧，都是这货在搞鬼。

下面就说正经的内容了，看看我的解决方案：

主要是在自定义的OnPageChangeListener里面。

先定义一下：

private EdgeEffectCompat leftEdge;
private EdgeEffectCompat rightEdge;

然后是构造中，通过反射得到对象：

try {
Field leftEdgeField = mViewPager.getClass().getDeclaredField("mLeftEdge");
Field rightEdgeField = mViewPager.getClass().getDeclaredField("mRightEdge");

Log.i("xinye", "=======leftEdgeField:" + leftEdgeField + ",rightEdgeField:" + rightEdgeField);
if(leftEdgeField != null && rightEdgeField != null){

leftEdgeField.setAccessible(true);
rightEdgeField.setAccessible(true);

leftEdge = (EdgeEffectCompat) leftEdgeField.get(mViewPager);
rightEdge = (EdgeEffectCompat) rightEdgeField.get(mViewPager);
Log.i("xinye", "=======OK啦，leftEdge:" + leftEdge + ",rightEdge:" + rightEdge);
}

} catch (Exception e) {
e.printStackTrace();
}

然后，就是最重要的了：

@Override
public void onPageScrolled(int position, floatpositionOffset, int positionOffsetPixels){

if(leftEdge != null && rightEdge != null){
leftEdge.finish();
rightEdge.finish();
leftEdge.setSize(0, 0);
rightEdge.setSize(0, 0);
}

好吧，完事了。做做看吧

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