使用 SurfaceView 绘图需要为 SurfaceView 对象添加 SurfaceHoloder.Callback 接口,并在该接口的 surfaceCreated() 方法中通过 lockCanvas() 方法获取 Canvas 对象,以此保证当获取 Canvas 时,SurfaceView 对象可用。
当绘图工作完成后,通过 SurfaceHoloder.unlockCanvas-AndPost() 方法将绘制的图像显示出来,并释放 Canvas 对象。
实例 SurfaceViewDrawDemo 演示了使用 SurfaceView 组件绘制静态图像的过程,其绘制的内容与《Android使用Bitmap绘图实例》教程中绘制的内容完全相同。
通过该实例,我们可以清楚地认识到使用 SurfaceView 绘图与使用 View 绘图的不同之处,该实例运行效果如图 1 所示。
图 1SurfaceView 绘图效果
实例 SurfaceViewDrawDemo 使用的布局文件 main.xml 内容如下:
<?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>
在 LinearLayout 布局中添加了一个 SurfaceView 组件,通过该组件进行绘图。
实例 SurfaceViewDrawDemo 的主 Activity 为 SurfaceDrawDemoActivity,其代码如下:
import android.app.Activity;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.RectF;
import android.os.Bundle;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
public class SurfaceDrawDemoActivity extends Activity {
private SurfaceView mySurfaceView;
private float[] mPts;
private static final float SIZE = 300;
private static final int SEGS = 32;
private static final int X = 0;
private static final int Y = 1;
/**
* Called when the activity is first created.
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
buildPoints();
mySurfaceView = (SurfaceView) findViewById(R.id.surfaceView1);
SurfaceHolder 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) {
//必须在该方法中获取Canvas对象,才能保证SurfaceView可用
Canvas canvas = holder.lockCanvas(); //获得canvas对象
//使用Canvas绘图
//画布移动到(10, 10)位置
canvas.translate(10, 10);
//画布使用白色填充
canvas.drawColor(Color.WHITE);
//创建红色画笔,使用单像素宽度,绘制直线
Paint paint = new Paint();
paint.setColor(Color.RED);
paint.setStrokeWidth(0);
canvas.drawLines(mPts, paint);
//创建蓝色画笔,宽度为3,绘制相关点
paint.setColor(Color.BLUE);
paint.setStrokeWidth(3);
canvas.drawPoints(mPts, paint);
//创建Path,并沿着path显示文字信息
RectF rect = new RectF(10, 250, 290, 480);
Path path = new Path();
path.addArc(rect, -180, 180);
paint.setTextSize(18);
paint.setColor(Color.BLUE);
canvas.drawTextOnPath("在SurfaceView中使用Canvas对象绘制静态图实例", path, 0,
0, paint);
holder.unlockCanvasAndPost(canvas); //释放canvas对象
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
// TODO Auto-generated method stub
}
});
}
private void buildPoints() {
//生成一系列点
final int ptCount = (SEGS + 1) * 2;
mPts = new float[ptCount * 2];
float value = 0;
final float delta = SIZE / SEGS;
for (int i = 0; i <= SEGS; i++) {
mPts[i * 4 + X] = SIZE - value;
mPts[i * 4 + Y] = 0;
mPts[i * 4 + X + 2] = 0;
mPts[i * 4 + Y + 2] = value;
value += delta;
}
}
}