SurfaceView与普通View还有一个重要区别：View的绘图必须在UI线程中进行，但SurfaceView不存在这个问题，因为它是由SurfaceHolder来完成的。所以对于View组件，如果绘图时间过长，会阻塞UI主线程，而SurfaceHolder则会启动新的线程去更新SurfaceView的绘制，不会阻塞UI线程。
下面的程序是通过SurfaceView绘制正玄曲线和余玄曲线的示例，代码如下：
Activity：
package com.home.showwave;
import java.util.Timer;
import java.util.TimerTask;
import android.app.Activity;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.os.Bundle;
import android.view.SurfaceHolder;
import android.view.SurfaceHolder.Callback;
import android.view.SurfaceView;
import android.view.View;
public class ShowWaveActivity extends Activity {
private SurfaceHolder holder;
private SurfaceView surface;
private Paint paint;
private final int HEIGHT = 320;
// 要绘制的曲线的水平宽度
private final int WIDTH = 500;
// 离屏幕左边界的起始距离
private final int X_OFFSET = 5;
// 初始化X坐标
private int cx = X_OFFSET;
// 实际的Y轴的位置
private int centerY = HEIGHT / 2;
private Timer timer = new Timer();
private TimerTask task = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_show_wave);
// 获得SurfaceView对象
surface = (SurfaceView) findViewById(R.id.activity_show_wave_sv);
// 初始化SurfaceHolder对象
holder = surface.getHolder();
paint = new Paint();
paint.setColor(Color.GREEN);
paint.setStrokeWidth(3);
}
public void click(final View v) {
drawBackGround(holder);
cx = X_OFFSET;
if (task != null) {
task.cancel();
}
task = new TimerTask() {
@Override
public void run() {
// 根据是正玄还是余玄和X坐标确定Y坐标
int cy = v.getId() == R.id.activity_show_wave_btn_sin ? centerY
- (int) (100 * Math.sin((cx - 5) * 2 * Math.PI / 150))
: centerY
- (int) (100 * Math.cos((cx - 5) * 2 * Math.PI
/ 150));
Canvas canvas = holder.lockCanvas(new Rect(cx, cy - 2, cx + 2,
cy + 2));
// 根据Ｘ，Ｙ坐标画点
canvas.drawPoint(cx, cy, paint);
cx++;
// 超过指定宽度，线程取消，停止画曲线
if (cx > WIDTH) {
task.cancel();
task = null;
}
// 提交修改
holder.unlockCanvasAndPost(canvas);
}
};
timer.schedule(task, 0, 30);
holder.addCallback(new Callback() {
@Override
public void surfaceChanged(SurfaceHolder holder, int format,
int width, int height) {
drawBackGround(holder);
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
timer.cancel();
}
});
}
private void drawBackGround(SurfaceHolder holder) {
Canvas canvas = holder.lockCanvas();
// 绘制白色背景
canvas.drawColor(Color.WHITE);
Paint p = new Paint();
p.setColor(Color.BLACK);
p.setStrokeWidth(2);
// 绘制坐标轴
canvas.drawLine(X_OFFSET, centerY, WIDTH, centerY, p);
canvas.drawLine(X_OFFSET, 40, X_OFFSET, HEIGHT, p);
holder.unlockCanvasAndPost(canvas);
holder.lockCanvas(new Rect(0, 0, 0, 0));
holder.unlockCanvasAndPost(canvas);
}
}
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center_horizontal"
android:orientation="horizontal" >
<Button
android:id="@+id/activity_show_wave_btn_sin"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="click"
android:text="正玄曲线" />
<Button
android:id="@+id/activity_show_wave_btn_cos"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="click"
android:text="余玄曲线" />
</LinearLayout>
<SurfaceView
android:id="@+id/activity_show_wave_sv"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
