画弧

画图主要是在View的onDraw(Canvas canvas)操作

该例中的drawPict不起作用

package com.example.androidtest;import android.os.Bundle;import android.app.Activity;import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.graphics.Picture;import android.graphics.Rect;import android.graphics.RectF;import android.graphics.drawable.Drawable;import android.util.AttributeSet;import android.view.View;import android.view.ViewGroup;import android.view.ViewParent;class PictureLayout extends ViewGroup{private final Picture mPicture = new Picture();public PictureLayout(Context context){super(context);}public PictureLayout(Context context, AttributeSet attrs){super(context, attrs);}protected void onLayout(boolean changed, int l, int t, int r, int b){final int count = super.getChildCount();for (int i = 0; i < count; i++) {final View child = getChildAt(i);if (child.getVisibility() != GONE) {final int childLeft = getPaddingLeft();final int childTop = getPaddingTop();child.layout(childLeft, childTop, childLeft + child.getMeasuredWidth(), childTop + child.getMeasuredHeight());}}}public void addView(View child){if (getChildCount() > 1) {throw new IllegalStateException("PictureLayout can host only direct child");}super.addView(child);}public void addView(View child, int index){if (getChildCount() > 1) {throw new IllegalStateException("PictureLayout can host only one direct child");}super.addView(child, index);}public void addView(View child, LayoutParams params){if (getChildCount() > 1) {throw new IllegalStateException("PictureLayout can host only one direct child");}super.addView(child, params);}public void addView(View child, int index, LayoutParams params){if (getChildCount() > 1) {throw new IllegalStateException("PictureLayout can host only one direct child");}super.addView(child, index, params);}protected LayoutParams generateDefaultParams(){return new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);}protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec){final int count = getChildCount();int maxHeight = 0;int maxWidth = 0;for (int i = 0; i < count; i++) {final View child = getChildAt(i);if (child.getVisibility() != GONE) {measureChild(child, widthMeasureSpec, heightMeasureSpec);}}maxWidth += getPaddingLeft() + getPaddingRight();maxHeight += getPaddingTop() + getPaddingBottom();Drawable drawable = getBackground();if (drawable != null) {maxHeight = Math.max(maxHeight, drawable.getMinimumHeight());maxWidth = Math.max(maxWidth, drawable.getMinimumWidth());}setMeasuredDimension(resolveSize(maxWidth, widthMeasureSpec), resolveSize(maxHeight, heightMeasureSpec));}private void drawPict(Canvas canvas, int x, int y, int w, int h, float sx, float sy){canvas.save();canvas.translate(x, y);canvas.clipRect(0, 0, w, h);canvas.scale(0.5f, 0.5f);canvas.scale(sx,  sy, w, h);canvas.drawPicture(mPicture);canvas.restore();}protected void dispatchDraw(Canvas canvas){super.dispatchDraw(mPicture.beginRecording(getWidth(), getHeight()));mPicture.endRecording();int x = getWidth() / 2;int y = getHeight() / 2;if (false) {drawPict(canvas, 0, 0, x, y, 1, 1);drawPict(canvas, x, 0, x, y, -1, 1);drawPict(canvas, 0, y, x, y, 1, -1);drawPict(canvas, x, y, x, y, -1, -1);}}public ViewParent invalidateChildParent(int[] location, Rect dirty){location[0] = getLeft();location[1] = getTop();dirty.set(0, 0, getWidth(), getHeight());return getParent();}}class GraphicsActivity extends Activity{private static final boolean TEST_PICTURE = false;protected void onCreate(Bundle savedInstanceState){super.onCreate(savedInstanceState);}public void setContentView(View view){if (TEST_PICTURE) {ViewGroup vg = new PictureLayout(this);vg.addView(view);view = vg;}super.setContentView(view);}}public class MainActivity extends GraphicsActivity {@Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);             setContentView(new SampleView(this));       }   private static class SampleView extends View{private Paint[] mPaints;private Paint mFramePaint;private boolean[] mUseCenters;private RectF[] mOvals;private RectF mBigOval;private float mStart;private float mSweep;private int mBigIndex;private static final float SWEEP_INC = 2;private static final float START_INC = 2;public SampleView(Context context){super(context);mPaints = new Paint[4];mUseCenters = new boolean[4];mOvals = new RectF[4];mPaints[0] = new Paint();mPaints[0].setAntiAlias(true);mPaints[0].setStyle(Paint.Style.FILL);mPaints[0].setColor(0x88ff0000);mUseCenters[0] = false;mPaints[1] = new Paint(mPaints[0]);mPaints[1].setColor(0x8800ff00);mUseCenters[1] = true;mPaints[2] = new Paint(mPaints[0]);mPaints[2].setStyle(Paint.Style.STROKE);mPaints[2].setStrokeWidth(4);mPaints[2].setColor(0x880000ff);mUseCenters[2] = false;mPaints[3] = new Paint(mPaints[2]);mPaints[3].setColor(0x88888888);mUseCenters[3] = true;mBigOval = new RectF(40, 10, 280, 250);mOvals[0] = new RectF(10, 270, 70, 330);mOvals[1] = new RectF(90, 270, 150, 330);mOvals[2] = new RectF(170, 270, 230, 330);mOvals[3] = new RectF(250, 270, 310, 330);mFramePaint = new Paint();mFramePaint.setAntiAlias(true);mFramePaint.setStyle(Paint.Style.STROKE);mFramePaint.setStrokeWidth(0);}private void drawArcs(Canvas canvas, RectF oval, boolean useCenter, Paint paint){canvas.drawRect(oval, mFramePaint);canvas.drawArc(oval, mStart, mSweep, useCenter, paint);}protected void onDraw(Canvas canvas){canvas.drawColor(Color.WHITE);drawArcs(canvas, mBigOval, mUseCenters[mBigIndex], mPaints[mBigIndex]);for (int i = 0; i < 4; i++) {drawArcs(canvas, mOvals[i], mUseCenters[i], mPaints[i]);}mSweep += SWEEP_INC;if (mSweep > 360) {mSweep -= 360;mStart += START_INC;if (mStart >= 360) {mStart -= 360;}mBigIndex = (mBigIndex + 1) % mOvals.length;}invalidate();}}}