使用SurfaceView绘制动态图像 图片看不了？点击切换HTTP 返回上层

实例 SurfaceViewDrawDemo 绘制的是一幅静态图像，而使用 SurfaceView 可以绘制动态图像。

绘制动态图像的过程应该在一个单独的线程中完成，而不应该在主线程中进行。实例 SurfaceViewDynDrawDemo 演示了使用 SurfaceView 组件绘制动态图像的过程。

该实例修改自 Android SDK 提供的实例，绘制的是类似于 Windows 中的变幻线屏保的效果，运行效果如图 1 所示。
实例 SurfaceViewDynDrawDemo 的布局文件 main.xml 内容如下：

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<?xml version="1.0" encoding="utf-8"?>   <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="fill_parent"     android:layout_height="fill_parent"     android:orientation="vertical">       <TextView         android:layout_width="fill_parent"         android:layout_height="wrap_content"         android:text="@string/hello" />       <SurfaceView         android:id="@+id/surfaceViewl"         android:layout_width="fill_parent"         android:layout_height="fill_parent" />     </LinearLayout>

实例 SurfaceViewDynDrawDemo 的主 Activity 为 SurfaceViewDynDrawDemoActivity，其代码如下：

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import android.app.Activity; import android.graphics.Canvas; import android.graphics.Paint; import android.os.Bundle; import android.util.Log; import android.view.SurfaceHolder; import android.view.SurfaceView;   public class SurfaceViewDynDrawDemoActivity extends Activity {     private SurfaceView mySurfaceView;     private DrawingThread mDrawingThread;     SurfaceHolder surfaceHolder;       /**      * Called when the activity is first created.      */     @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.main);         mySurfaceView = (SurfaceView) findViewById(R.id.surfaceViewl);         surfaceHolder = mySurfaceView.getHolder();         surfaceHolder.addCallback(new SurfaceHolder.Callback() {               @Override             public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {                 // TODO Auto-generated method stub             }               @Override             public void surfaceCreated(SurfaceHolder holder) {                 // TODO Auto-generated method stub                 mDrawingThread = new DrawingThread();                 mDrawingThread.mSurface = surfaceHolder;                 mDrawingThread.start();             }               @Override             public void surfaceDestroyed(SurfaceHolder holder) {                 // TODO Auto-generated method stub                 mDrawingThread.mQuit = true;             }         });     }       static final class MovingPoint {         float x, y, dx, dy;           void init(int width, int height, float minStep) {             x = (float) ((width - 1) * Math.random());             y = (float) ((height - 1) * Math.random());             dx = (float) (Math.random() * minStep * 2) + 1;             dy = (float) (Math.random() * minStep * 2) + 1;         }           float adjDelta(float cur, float minStep, float maxStep) {             cur += (Math.random() * minStep) - (minStep / 2);             if (cur < 0 && cur > -minStep) cur = -minStep;             if (cur >= 0 && cur < minStep) cur = minStep;             if (cur > maxStep) cur = maxStep;             if (cur < -maxStep) cur = -maxStep;             return cur;         }           void step(int width, int height, float minStep, float maxStep) {             x += dx;             if (x <= 0 || x >= (width - 1)) {                 if (x <= 0) x = 0;                 else if (x >= (width - 1)) x = width - 1;                 dx = adjDelta(-dx, minStep, maxStep);             }             y += dy;             if (y <= 0 || y >= (height - 1)) {                 if (y <= 0) y = 0;                 else if (y >= (height - 1)) y = height - 1;                 dy = adjDelta(-dy, minStep, maxStep);             }         }     }       class DrawingThread extends Thread {         // These are protected by the Thread's lock         SurfaceHolder mSurface;         boolean mRunning;         boolean mActive;         boolean mQuit;         // Internal state         int mLineWidth;         float mMinStep;         float mMaxStep;           boolean mInitialized = false;         final MovingPoint mPoint1 = new MovingPoint();         final MovingPoint mPoint2 = new MovingPoint();           static final int NUM_OLD = 100;         int mNum0ld = 0;         final float[] m0ld = new float[NUM_OLD * 4];         final int[] m01dColor = new int[NUM_OLD];         int mBrightLine = 0;           // X is red, Y is blue         final MovingPoint mColor = new MovingPoint();           final Paint mBackground = new Paint();         final Paint mForeground = new Paint();           int makeGreen(int index) {             int dist = Math.abs(mBrightLine - index);             if (dist > 10) return 0;             return (255 - (dist * (255 / 10))) << 8;         }           @Override         public void run() {             mLineWidth = (int) (getResources().getDisplayMetrics().density * 1.5);             if (mLineWidth < 1) mLineWidth = 1;             mMinStep = mLineWidth * 2;             mMaxStep = mMinStep * 3;               mBackground.setColor(0xff000000);             mForeground.setColor(0xff00ffff);             mForeground.setAntiAlias(false);             mForeground.setStrokeWidth(mLineWidth);               while (true) {                 if (mQuit) {                     return;                 }                 // Lock the canvas for drawing                 Canvas canvas = mSurface.lockCanvas();                 if (canvas == null) {                     Log.i("WindowSurface", "Failure locking canvas");                     continue;                 }                   // Update graphics                 if (!mInitialized) {                     mInitialized = true;                     mPoint1.init(canvas.getWidth(), canvas.getHeight(), mMinStep);                     mPoint2.init(canvas.getWidth(), canvas.getHeight(), mMinStep);                     mColor.init(127, 127, 1);                 } else {                     mPoint1.step(canvas.getWidth(), canvas.getHeight(), mMinStep, mMaxStep);                     mPoint2.step(canvas.getWidth(), canvas.getHeight(), mMinStep, mMaxStep);                     mColor.step(127, 127, 1, 3);                 }                 mBrightLine += 2;                 if (mBrightLine > (NUM_OLD * 2)) {                     mBrightLine = -2;                 }                   // Clear background                 canvas.drawColor(mBackground.getColor());                 // Draw old lines                 for (int i = mNum0ld - 1; i >= 0; i--) {                     mForeground.setColor(m01dColor[i] | makeGreen(i));                     mForeground.setAlpha(((NUM_OLD - i) * 255) / NUM_OLD);                     int p = i * 4;                     canvas.drawLine(m0ld[p], m0ld[p + 1], m0ld[p + 2], m0ld[p + 3], mForeground);                 }                 // Draw new line                 int red = (int) mColor.x + 128;                 if (red > 255) red = 255;                 int blue = (int) mColor.y + 128;                 if (blue > 255) blue = 255;                 int color = 0xff000000 | (red << 16) | blue;                 mForeground.setColor(color | makeGreen(-2));                 canvas.drawLine(mPoint1.x, mPoint1.y, mPoint2.x, mPoint2.y, mForeground);                   // Add in the new line                 if (mNum0ld > 1) {                     System.arraycopy(m0ld, 0, m0ld, 4, (mNum0ld - 1) * 4);                     System.arraycopy(m01dColor, 0, m01dColor, 1, mNum0ld - 1);                 }                 if (mNum0ld < NUM_OLD) mNum0ld++;                 m0ld[0] = mPoint1.x;                 m0ld[1] = mPoint1.y;                 m0ld[2] = mPoint2.x;                 m0ld[3] = mPoint2.y;                 m01dColor[0] = color;                 // All done                 mSurface.unlockCanvasAndPost(canvas);             }         }     } }

需要注意的是，就像前面所提到的，绘制动态图像的过程必须在一个单独的线程中完成，而不能在主线程中进行。在该实例中，绘图过程是在 DrawingThread 中完成的。