我非常关注TicTacToeLib资源中的示例代码，以及如何在名为Android Application Development的书中显示位图的示例。我正在做他们正在做的所有相同的事情，唯一的区别是我使用的是SurfaceView而不是视图。谁能告诉我我做错了什么？最终目标是手动显示相机的预览图像，并在其上方显示图像。
抱歉，我忘了包含问题所在。 onDraw方法永远不会被调用。而且我的印象是它应该由invalidate方法调用。其次，lockCanvas（）方法返回一个NULL画布。即使我修改代码后不使用SurfaceHolder中的PUSH_BUFFER常量（我已编辑了此修正的代码）。
package com.test.combine;
import android.content.res.XmlResourceParser;
import android.app.Activity;
import android.content.Context;
import android.hardware.Camera;
import android.hardware.Camera.Size;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.Window;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.util.AttributeSet;
import java.io.IOException;
import android.util.Log;
import java.util.List;
public class CombineTestActivity extends Activity
{
private Preview mPreview;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Hide the window title.
requestWindowFeature(Window.FEATURE_NO_TITLE);
// Create our Preview view and set it as the content of our activity.
mPreview = new Preview(this);
setContentView(mPreview);
}
}
// ----------------------------------------------------------------------
class Preview extends SurfaceView implements SurfaceHolder.Callback {
private SurfaceHolder mHolder;
private Camera mCamera;
private Paint mPaint;
private Canvas canvas;
private Bitmap currentprev;
private Picture mPicture;
private Camera.PreviewCallback mPrevCallback = new Camera.PreviewCallback()
{
public void onPreviewFrame( byte[] data, Camera Cam ) {
Log.d("CombineTestActivity", "Preview registered");
Log.d("CombineTestActivity", "Data length = "
+ data.length );
// currentprev = BitmapFactory.decodeByteArray( data, 0,
// data.length );
currentprev = BitmapFactory.decodeResource( getResources(),
R.drawable.creature00 );
if( currentprev == null )
Log.d("CombineTestActivity", "currentprev is null" );
Log.d("CombineTestActivity", "Preview Finished" );
invalidate();
}
};
private OnTouchListener mCorkyListener = new OnTouchListener() {
public boolean onTouch(View v, MotionEvent me) {
Log.d("CombineTestActivity", "touch registered" );
mCamera.takePicture( null, null, mPicCallback );
return false;
}
};
private Camera.PictureCallback mPicCallback = new Camera.PictureCallback() {
public void onPictureTaken( byte[] data, Camera mCamera ) {
Log.d("CombineTestActivity", "picture method run" );
}
};
Preview(Context context) {
super(context);
// Install a SurfaceHolder.Callback so we get notified when the
// underlying surface is created and destroyed.
mPicture = new Picture();
mHolder = getHolder();
mHolder.addCallback(this);
mHolder.setType(SurfaceHolder.SURFACE_TYPE_NORMAL);
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
canvas = mHolder.lockCanvas();
if(canvas==null)
Log.d( "CombineTestActivity", "canvas is null in constructor");
this.setOnTouchListener( mCorkyListener );
invalidate();
}
@Override
protected void onDraw( Canvas mCanvas ) {
if( mCanvas == null )
Log.e("CombineTestActivity", "canvas is null" );
if( currentprev == null ) {
Log.e("CombineTestActivity", "currentprev is null" );
return;
}
mCanvas.drawBitmap( currentprev, 0.0f, 0.0f, mPaint );
Log.d("CombineTestActivity", "exiting onDraw" );
}
public void surfaceCreated(SurfaceHolder holder) {
// The Surface has been created, acquire the camera and tell it where
// to draw.
mCamera = Camera.open();
mCamera.setPreviewCallback( mPrevCallback );
/*
try {
mCamera.setPreviewDisplay(holder);
} catch (IOException exception) {
mCamera.release();
mCamera = null;
// TODO: add more exception handling logic here
}
*/
}
public void surfaceDestroyed(SurfaceHolder holder) {
// Surface will be destroyed when we return, so stop the preview.
// Because the CameraDevice object is not a shared resource, it's very
// important to release it when the activity is paused.
mCamera.stopPreview();
mCamera.release();
mCamera = null;
}
private Size getOptimalPreviewSize(List<Size> sizes, int w, int h) {
final double ASPECT_TOLERANCE = 0.05;
double targetRatio = (double) w / h;
if (sizes == null) return null;
Size optimalSize = null;
double minDiff = Double.MAX_VALUE;
int targetHeight = h;
// Try to find an size match aspect ratio and size
for (Size size : sizes) {
double ratio = (double) size.width / size.height;
if (Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE) continue;
if (Math.abs(size.height - targetHeight) < minDiff) {
optimalSize = size;
minDiff = Math.abs(size.height - targetHeight);
}
}
// Cannot find the one match the aspect ratio, ignore the requirement
if (optimalSize == null) {
minDiff = Double.MAX_VALUE;
for (Size size : sizes) {
if (Math.abs(size.height - targetHeight) < minDiff) {
optimalSize = size;
minDiff = Math.abs(size.height - targetHeight);
}
}
}
return optimalSize;
}
public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
// Now that the size is known, set up the camera parameters and begin
// the preview.
Camera.Parameters parameters = mCamera.getParameters();
List<Size> sizes = parameters.getSupportedPreviewSizes();
if( sizes.isEmpty() )
Log.d( "CameraTestActivity", "sizes null");
else
Log.d( "CameraTestActivity", "sizes not null");
Size optimalSize = getOptimalPreviewSize(sizes, w, h);
if( optimalSize == null )
Log.d( "CameraTestActivity", "optimalSize null");
else
Log.d( "CameraTestActivity", "optimalSize not null");
parameters.setPreviewSize(optimalSize.width, optimalSize.height);
if( parameters == null )
Log.d( "CameraTestActivity", "parameters null" );
else
Log.d( "CameraTestActivity", "parameters not null" );
mCamera.setParameters(parameters);
mCamera.startPreview();
}
}
答案 0 :(得分：0)
我显然找到了解决方案。虽然SurfaceView继承自View，但它并不像View那样调用onDraw。至于为什么lockCanvas不工作，我仍然不知道。