我正在创建一个Android应用程序，需要我创建相机预览的位图，以便我可以平均预览中心的像素。然而，无论相机指向什么，该应用程序始终返回0, 0, 0作为屏幕中心9x9平均像素的RGB值。预览.java和主要的java文件都在那里。这是Android的问题（如果是，有没有解决方法），还是我的代码有问题？谢谢！（如果代码稍微有点乱，请见谅）
（这是主要的Java文件）
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.hardware.Camera;
import android.hardware.Camera.PictureCallback;
import android.hardware.Camera.ShutterCallback;
import android.os.Bundle;
import android.util.Log;
import android.view.Display;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
import android.widget.FrameLayout;
public class CameraTest2Activity extends Activity {
private static final String TAG = "ZTG";
Camera camera;
Preview preview;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
preview = new Preview(this);
((FrameLayout) findViewById(R.id.preview)).addView(preview);
final Button button = (Button) findViewById(R.id.bFire);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
long timeAtStart = System.currentTimeMillis();
TextView rgbDisplay = (TextView) findViewById(R.id.RGBText);
Display display = getWindowManager().getDefaultDisplay();
int width = display.getWidth();
int height = display.getHeight();
Log.d(TAG, "Width and Height Retrieved As: " + width + ", " + height);
Bitmap b = Bitmap.createBitmap(width, height, Bitmap.Config. RGB_565);
Canvas c = new Canvas(b);
Preview view = (Preview) ((ViewGroup) findViewById(R.id.preview)).getChildAt(0);
view.draw(c);
String hexValue;
int centerX = (display.getWidth() / 2);
int centerY = (display.getHeight() / 2);
int test;
//test = b.getPixel(240, 350);
int sampleWidth = 9;
int sampleHeight = 9;
int[] pixels = new int[sampleWidth * sampleHeight];
b.getPixels(pixels, 0, 9, centerX - 4, centerY - 4, sampleWidth, sampleHeight);
int l = 0;
int tempNum;
int tempBlue;
int tempRed;
int tempGreen;
int blue = 0; //Color.blue(test);
int red = 0; //Color.red(test);
int green = 0; // Color.green(test);
test = 0;
Log.d("lookingFor", "test: " + pixels[1]);
while(l < 81){
tempNum = (Integer) pixels[l];
Log.d("lookingFor", "Pixel Num: " + Color.blue(tempNum));
tempBlue = Color.blue(tempNum);
tempRed = Color.red(tempNum);
tempGreen = Color.green(tempNum);
Log.d("lookingFor", "current Blue: " + tempBlue);
blue = blue + tempBlue;
Log.d("lookingFor", "added blue: " + blue);
red = red + tempRed;
green = green + tempGreen;
l = l + 1; //test g
}
Log.v("lookingFor", blue + " " + red + " " + green);
blue = blue / 81;
red = red / 81;
green = green / 81;
hexValue = Integer.toHexString(test);
Log.d(TAG, "pixel at (" + centerX + ", " + centerY + " succesfully retreived! with value of: " + test);
Log.d(TAG, "and an Hex value of: " + hexValue);
// blue = Color.blue(test);
// red = Color.red(test);
// green = Color.green(test);
//this is a modification
Log.d(TAG, "RGB COLOR! R:" + red + " G:" + green + " B:" + blue);
long timeAtEnd = System.currentTimeMillis();
long totalTime = timeAtEnd - timeAtStart;
Log.d(TAG, "Fetching the color took " + totalTime + " milliseconds");
rgbDisplay.setText("R:" + red + " G:" + green + " B:" + blue);
}
});
Log.d(TAG, "onCreate'd");
}
ShutterCallback shutterCallback = new ShutterCallback() {
public void onShutter() {
Log.d(TAG, "onShutter'd");
}
};
/** Handles data for raw picture */
PictureCallback rawCallback = new PictureCallback() {
public void onPictureTaken(byte[] data, Camera camera) {
Log.d(TAG, "onPictureTaken - raw");
}
};
/** Handles data for jpeg picture */
PictureCallback jpegCallback = new PictureCallback() {
public void onPictureTaken(byte[] data, Camera camera) {
FileOutputStream outStream = null;
try {
// write to local sandbox file system
// outStream =
// CameraDemo.this.openFileOutput(String.format("%d.jpg",
// System.currentTimeMillis()), 0);
// Or write to sdcard
outStream = new FileOutputStream(String.format(
"/sdcard/%d.jpg", System.currentTimeMillis()));
outStream.write(data);
outStream.close();
Log.d(TAG, "onPictureTaken - wrote bytes: " + data.length);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
}
Log.d(TAG, "onPictureTaken - jpeg");
}
};
}
（这是主要的Java文件）
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.hardware.Camera;
import android.hardware.Camera.PreviewCallback;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
class Preview extends SurfaceView implements SurfaceHolder.Callback {
private static final String TAG = "Preview";
SurfaceHolder mHolder;
public Camera camera;
Preview(Context context) {
super(context);
// Install a SurfaceHolder.Callback so we get notified when the
// underlying surface is created and destroyed.
mHolder = getHolder();
mHolder.addCallback(this);
mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}
public void surfaceCreated(SurfaceHolder holder) {
// The Surface has been created, acquire the camera and tell it where
// to draw.
camera = Camera.open();
try {
camera.setPreviewDisplay(holder);
camera.setPreviewCallback(new PreviewCallback() {
public void onPreviewFrame(byte[] data, Camera arg1) {
/*FileOutputStream outStream = null;
try {
outStream = new FileOutputStream(String.format(
"/sdcard/%d.jpg", System.currentTimeMillis()));
outStream.write(data);
outStream.close();
Log.d(TAG, "onPreviewFrame - wrote bytes: "
+ data.length);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
}*/
Preview.this.invalidate();
}
});
} catch (IOException e) {
e.printStackTrace();
}
}
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.
camera.stopPreview();
camera = null;
}
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 = camera.getParameters();
parameters.setPreviewSize(w, h);
camera.setParameters(parameters);
camera.startPreview();
}
@Override
public void draw(Canvas canvas) {
super.draw(canvas);
Paint p = new Paint(Color.RED);
Log.d(TAG, "draw");
canvas.drawText("PREVIEW", canvas.getWidth() / 2,
canvas.getHeight() / 2, p);
}
}