简单讲解下，不去管绘制阴影的部分，其实折叠就是：
1、初始化转换点，这里注释说的很清楚，大家最好在纸上绘制下，标一下每个变量。
2、为matrix.setPolyToPoly
3、绘制时使用该matrix，且clipRect控制显示区域（这个区域也很简单，原图的第一块到最后一块），最好就是绘制bitmap了。
阴影这里大家可以换个明亮点的图片去看看~~
五、FoldLayout的实现
1、实现
我们的想法是这样的，我们的FoldLayout只能有一个直接子元素，当然这个子元素可以是RelativeLayout什么的，可以很复杂。然后只要外层套了我们的FoldLayout，就能实现折叠效果。
那么也就是说，我们的FoldLayout折叠效果展示的是它的子元素的“样子”，那么如何或者这个“样子”呢？
大家都知道，我们的ViewGroup有个方法叫做：dispatchDraw(Canvas)主要用来绘制子元素，我们可以对这个canvas进行设置matrix，以及重复调用dispatchDraw(Canvas)来实现类似上篇博客最后的效果，这样就完成了我们的可行性的分析。
package com.zhy.view;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.LinearGradient;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.Shader.TileMode;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;
public class FoldLayout extends ViewGroup
{
private static final int NUM_OF_POINT = 8;
/**
* 图片的折叠后的总宽度
*/
private float mTranslateDis;
protected float mFactor = 0.6f;
private int mNumOfFolds = 8;
private Matrix[] mMatrices = new Matrix[mNumOfFolds];
private Paint mSolidPaint;
private Paint mShadowPaint;
private Matrix mShadowGradientMatrix;
private LinearGradient mShadowGradientShader;
private float mFlodWidth;
private float mTranslateDisPerFlod;
public FoldLayout(Context context)
{
this(context, null);
}
public FoldLayout(Context context, AttributeSet attrs)
{
super(context, attrs);
for (int i = 0; i < mNumOfFolds; i++)
{
mMatrices[i] = new Matrix();
}
mSolidPaint = new Paint();
mShadowPaint = new Paint();
mShadowPaint.setStyle(Style.FILL);
mShadowGradientShader = new LinearGradient(0, 0, 0.5f, 0, Color.BLACK,
Color.TRANSPARENT, TileMode.CLAMP);
mShadowPaint.setShader(mShadowGradientShader);
mShadowGradientMatrix = new Matrix();
this.setWillNotDraw(false);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
{
View child = getChildAt(0);
measureChild(child, widthMeasureSpec, heightMeasureSpec);
setMeasuredDimension(child.getMeasuredWidth(),
child.getMeasuredHeight());
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b)
{
View child = getChildAt(0);
child.layout(0, 0, child.getMeasuredWidth(), child.getMeasuredHeight());
mBitmap = Bitmap.createBitmap(getMeasuredWidth(), getMeasuredHeight(),
Config.ARGB_8888);
mCanvas.setBitmap(mBitmap);
updateFold();
}
private void updateFold()
{
int w = getMeasuredWidth();
int h = getMeasuredHeight();
mTranslateDis = w * mFactor;
mFlodWidth = w / mNumOfFolds;
mTranslateDisPerFlod = mTranslateDis / mNumOfFolds;
int alpha = (int) (255 * (1 - mFactor));
mSolidPaint.setColor(Color.argb((int) (alpha * 0.8F), 0, 0, 0));
mShadowGradientMatrix.setScale(mFlodWidth, 1);
mShadowGradientShader.setLocalMatrix(mShadowGradientMatrix);
mShadowPaint.setAlpha(alpha);
float depth = (float) (Math.sqrt(mFlodWidth * mFlodWidth
- mTranslateDisPerFlod * mTranslateDisPerFlod) / 2);
float[] src = new float[NUM_OF_POINT];
float[] dst = new float[NUM_OF_POINT];
for (int i = 0; i < mNumOfFolds; i++)
{
mMatrices[i].reset();
src[0] = i * mFlodWidth;
src[1] = 0;
src[2] = src[0] + mFlodWidth;
src[3] = 0;
src[4] = src[2];
src[5] = h;
src[6] = src[0];
src[7] = src[5];
boolean isEven = i % 2 == 0;
dst[0] = i * mTranslateDisPerFlod;
dst[1] = isEven ? 0 : depth;
dst[2] = dst[0] + mTranslateDisPerFlod;
dst[3] = isEven ? depth : 0;
dst[4] = dst[2];
dst[5] = isEven ? h - depth : h;
dst[6] = dst[0];
dst[7] = isEven ? h : h - depth;
for (int y = 0; y < 8; y++)
{
dst[y] = Math.round(dst[y]);
}
mMatrices[i].setPolyToPoly(src, 0, dst, 0, src.length >> 1);
}
}
private Canvas mCanvas = new Canvas();
private Bitmap mBitmap;
private boolean isReady;
@Override
protected void dispatchDraw(Canvas canvas)
{
if (mFactor == 0)
return;
if (mFactor == 1)
{
super.dispatchDraw(canvas);
return;
}
for (int i = 0; i < mNumOfFolds; i++)
{
canvas.save();
canvas.concat(mMatrices[i]);
canvas.clipRect(mFlodWidth * i, 0, mFlodWidth * i + mFlodWidth,
getHeight());
if (isReady)
{
canvas.drawBitmap(mBitmap, 0, 0, null);
} else
{
// super.dispatchDraw(canvas);
super.dispatchDraw(mCanvas);
canvas.drawBitmap(mBitmap, 0, 0, null);
isReady = true;
}
canvas.translate(mFlodWidth * i, 0);
if (i % 2 == 0)
{
canvas.drawRect(0, 0, mFlodWidth, getHeight(), mSolidPaint);
} else
{
canvas.drawRect(0, 0, mFlodWidth, getHeight(), mShadowPaint);
}
canvas.restore();
}
}
//...dispatchDraw
public void setFactor(float factor)
{
this.mFactor = factor;
updateFold();
invalidate();
}
public float getFactor()
{
return mFactor;
}
}
