*1.ViewPortHandler 主要包含当前chart的value的视图信息，比如offsets，缩放的比例，平移的累计量，每一个ChartView都会持有一个ViewPortHandler，它作为一个中间件，连接chartView，Transformer，Axis，ChartTouchListener等。
2.它最重要的一个成员变量是mMatrixTouch,缩放的比例，平移的累计量都放在其中。
1.简单描述其作用
举个简单的例子：在进行了缩放之后是如何刷新界面的，代码如下
首先在ChartTouchListener处理手势：
public class BarLineChartTouchListener extends ChartTouchListener{
private Matrix mMatrix = new Matrix();
@Override
public boolean onTouch(View view, MotionEvent event) {
switch (event.getAction() & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_MOVE:
//1.计算缩放比例,操作mMatrix，t代表缩放中心点
mMatrix.postScale(scaleX, scaleY, t.x, t.y);
break;
}
//更新ViewPortHandler的matrix，refresh方法会刷新界面
mMatrix = mChart.getViewPortHandler().refresh(mMatrix, mChart, true);
return true;
}
}
public Matrix refresh(Matrix newMatrix, View chart, boolean invalidate) {
mMatrixTouch.set(newMatrix);
// make sure scale and translation are within their bounds
limitTransAndScale(mMatrixTouch, mContentRect);
if (invalidate)
chart.invalidate();
newMatrix.set(mMatrixTouch);
return newMatrix;
}
最后在chartView的ondraw方法中会获取ViewPortHandler中Matrix的信息重新渲染，这个流程后面会详细的讲解。
2.主要成员变量
protected final Matrix mMatrixTouch = new Matrix();//处理touch event的矩阵
protected RectF mContentRect = new RectF(); //value的绘制区域，去掉offset，坐标轴等
3.主要成员方法
//每次进行手势操作后，调用此方法，刷新view
public Matrix refresh(Matrix newMatrix, View chart, boolean invalidate){
mMatrixTouch.set(newMatrix);
//边界检测
limitTransAndScale(mMatrixTouch, mContentRect);
if (invalidate)
chart.invalidate();
newMatrix.set(mMatrixTouch);
return newMatrix;
}
//检测是否超出了最大
public void limitTransAndScale(Matrix matrix, RectF content) {
matrix.getValues(matrixBuffer);
//获取累计的transX，scaleX
float curTransX = matrixBuffer[Matrix.MTRANS_X];
float curScaleX = matrixBuffer[Matrix.MSCALE_X];
//获取累计的transY，scaleY
float curTransY = matrixBuffer[Matrix.MTRANS_Y];
float curScaleY = matrixBuffer[Matrix.MSCALE_Y];
// min scale-x is 1f
mScaleX = Math.min(Math.max(mMinScaleX, curScaleX), mMaxScaleX);
// min scale-y is 1f
mScaleY = Math.min(Math.max(mMinScaleY, curScaleY), mMaxScaleY);
float width = 0f;
float height = 0f;
if (content != null) {
width = content.width();
height = content.height();
}
//计算最大的transX，比如没有缩放的情况下，mScaleX = 1，最大transX为0，缩放2倍，最大transX为一个chartWidth
float maxTransX = -width * (mScaleX - 1f);
mTransX = Math.min(Math.max(curTransX, maxTransX - mTransOffsetX), mTransOffsetX);
//计算最大的transY
float maxTransY = height * (mScaleY - 1f);
mTransY = Math.max(Math.min(curTransY, maxTransY + mTransOffsetY), -mTransOffsetY);
matrixBuffer[Matrix.MTRANS_X] = mTransX;
matrixBuffer[Matrix.MSCALE_X] = mScaleX;
matrixBuffer[Matrix.MTRANS_Y] = mTransY;
matrixBuffer[Matrix.MSCALE_Y] = mScaleY;
matrix.setValues(matrixBuffer);
}
//计算好offset之后重新设置mContentRect
public void restrainViewPort(float offsetLeft, float offsetTop, float offsetRight,
float offsetBottom) {
mContentRect.set(offsetLeft, offsetTop, mChartWidth - offsetRight, mChartHeight
- offsetBottom);
}
//缩放
public void zoom(float scaleX, float scaleY, float x, float y, Matrix outputMatrix) {
outputMatrix.reset();
outputMatrix.set(mMatrixTouch);
outputMatrix.postScale(scaleX, scaleY, x, y);
}
//平移
public void translate(final float[] transformedPts, Matrix outputMatrix) {
outputMatrix.reset();
outputMatrix.set(mMatrixTouch);
final float x = transformedPts[0] - offsetLeft();
final float y = transformedPts[1] - offsetTop();
outputMatrix.postTranslate(-x, -y);
}
4.ViewPortHandler的初始化
在chartView中的onSizeChange方法中得到view的宽高后设置ViewPortHandler的mContent
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
if (w > 0 && h > 0 && w < 10000 && h < 10000) {
mViewPortHandler.setChartDimens(w, h);
} else {
if (mLogEnabled)
Log.w(LOG_TAG, "*Avoiding* setting chart dimens! width: " + w + ", height: " + h);
}
// This may cause the chart view to mutate properties affecting the view port --
// lets do this before we try to run any pending jobs on the view port itself
notifyDataSetChanged();
...
super.onSizeChanged(w, h, oldw, oldh);
}
上面的代码初步设置了宽高了之后，还要给X，Y轴等留出位置，所以要重新设置left，top，right，bottom，这是在ChartView中的这个方法处理的
@Override
public void calculateOffsets() {
float offsetLeft = 0f, offsetRight = 0f, offsetTop = 0f, offsetBottom = 0f;
if (mXAxis.isEnabled() && mXAxis.isDrawLabelsEnabled()) {
float xLabelHeight = mXAxis.mLabelRotatedHeight + mXAxis.getYOffset();
offsetBottom += xLabelHeight;
}
if (mAxisLeft.isEnabled() && mAxisLeft.isDrawLabelsEnabled()) {
float longestYLabelWidth = mAxisLeft.getRequiredWidthSpace(mAxisRendererLeft.getPaintAxisLabels());
offsetLeft += longestYLabelWidth;
}
offsetTop += getExtraTopOffset();
offsetRight += getExtraRightOffset();
offsetBottom += getExtraBottomOffset();
offsetLeft += getExtraLeftOffset();
float minOffset = Utils.convertDpToPixel(mMinOffset);
mViewPortHandler.restrainViewPort(
Math.max(minOffset, offsetLeft),
Math.max(minOffset, offsetTop),
Math.max(minOffset, offsetRight),
Math.max(minOffset, offsetBottom));
prepareOffsetMatrix();
prepareValuePxMatrix();
Log.e(TAG, "1.3: notifyDataChanged :计算offsets，本质就是根据设置的offset重新设置mViewHandler的content区域");
Log.e(TAG, "1.4:notifyDataChanged :调用prepareOffsetMatrix 和 prepareValuePxMatrix 初始化左右两个y轴的transformer的offsetMatrix和valueToPxMatrix,这一步很重要");
}
