下面开始实现一个闪屏的效果,首先自定义类继承于View,然后重写onDraw方法,之前使用onDraw方法可以绘图,但是只是绘制一次,那如何实现循环呢。很容易想到使用invalidate()这个方法,因为使用这个方法它就会调用onDraw方法,这样就形成了一个死循环,不断刷新绘制界面。当然还有一个postInvalidate().方法,它与invalidate()的区别在于它用于非UI的线程,invalidate()必须在UI线程使用。所以,代码可以这样写:
import java.util.Random; import android.content.Context; import android.graphics.Canvas; import android.view.View; class RenderView extends View { Random rand = new Random(); public RenderView(Context context) { super(context); } protected void onDraw(Canvas canvas) { canvas.drawRGB(rand.nextInt(256), rand.nextInt(256), rand.nextInt(256)); invalidate(); } }
import android.content.Context; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.graphics.RectF; import android.os.Bundle; import android.view.View; public class Test extends GraphicsActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(new SampleView(this)); } private static class SampleView extends View { //画笔 private Paint[] mPaints; //画笔 private Paint mFramePaint; //是否有圆心 private boolean[] mUseCenters; //矩形 private RectF[] mOvals; //矩形 private RectF mBigOval; //开始弧度 private float mStart; //增量弧度 private float mSweep; //索引 private int mBigIndex; //扫描增量 private static final float SWEEP_INC = 2; private static final float START_INC = 15; 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); } /** * @category * @param canvas * @param oval * @param useCenter * @param paint */ private void drawArcs(Canvas canvas, RectF oval, boolean useCenter, Paint paint) { //画矩形 canvas.drawRect(oval, mFramePaint); //画弧形 canvas.drawArc(oval, mStart, mSweep, useCenter, paint); } @Override protected void onDraw(Canvas canvas) { //设置背景色 canvas.drawColor(Color.WHITE); //画大矩形 drawArcs(canvas, mBigOval, mUseCenters[mBigIndex], mPaints[mBigIndex]); //画四个小矩形 for (int i = 0; i < 4; i++) { drawArcs(canvas, mOvals[i], mUseCenters[i], mPaints[i]); } /** * 计算弧度 */ mSweep += SWEEP_INC; if (mSweep > 360) { mSweep -= 360; mStart += START_INC; if (mStart >= 360) { mStart -= 360; } //变换 mBigIndex = (mBigIndex + 1) % mOvals.length; } //刷新 invalidate(); } } }效果如下:
android中关于绘制平面2D图形的类基本上都在android.graphics这个包中,比如常用的Paint、Path、Canvas、Rect、Bitmap、Color、Matrix、Point等等。这些虽然基础,但却是绘图重要的类,所以先要掌握好。