我刚刚开始用 Java 编程，我需要一个简单的应用程序来显示相机、拍照并将图片数据发送到某个地方。
我一直在网上搜索，试图找到一个按预期工作的好相机教程，但显然它们都需要一些我还没有的内在知识。
On this https://stackoverflow.com/questions/2713165/take-and-save-picture-on-button-press页面上，commonsWare 指出了其中包含一些使用相机的示例代码的代码。我已经获取了 PictureDemo 代码并让它运行，没有错误。然而，它只会带来黑屏。我认为这是因为程序实际上并未激活主函数中的预览或相机，但每次我尝试添加我认为需要的代码时，我都会遇到异常。
所以我的问题是，我需要在主函数中添加什么才能让相机运行？或者是否有更好的教程，我可以看到用于启动相机的简单基本代码？
package assist.core;
import android.app.Activity;
import android.graphics.PixelFormat;
import android.hardware.Camera;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.KeyEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.Toast;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
public class MainActivity extends Activity
{
private SurfaceView preview = null;
private SurfaceHolder previewHolder = null;
private Camera camera = null;
private boolean inPreview = false;
/**
*
*/
@Override
public void onCreate(Bundle savedInstanceState)
{
//Call the parent class
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
preview = (SurfaceView) findViewById(R.id.preview);
previewHolder = preview.getHolder();
previewHolder.addCallback(surfaceCallback);
previewHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}
@Override
public void onResume() {
super.onResume();
//Get the camera instance
camera = CameraFinder.INSTANCE.open();
}
@Override
public void onPause() {
if (inPreview) {
camera.stopPreview();
}
camera.release();
camera = null;
inPreview = false;
super.onPause();
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_CAMERA || keyCode == KeyEvent.KEYCODE_SEARCH) {
if (inPreview) {
camera.takePicture(null, null, photoCallback);
inPreview = false;
}
return(true);
}
return(super.onKeyDown(keyCode, event));
}
private Camera.Size getBestPreviewSize(int width, int height, Camera.Parameters parameters) {
Camera.Size result = null;
for (Camera.Size size : parameters.getSupportedPreviewSizes()) {
if (size.width <= width && size.height <= height) {
if (result == null) {
result=size;
}
else {
int resultArea = result.width * result.height;
int newArea = size.width * size.height;
if (newArea > resultArea) {
result = size;
}
}
}
}
return(result);
}
SurfaceHolder.Callback surfaceCallback = new SurfaceHolder.Callback() {
public void surfaceCreated(SurfaceHolder holder) {
try {
camera.setPreviewDisplay(previewHolder);
}
catch (Throwable t) {
Log.e("MainActivity-surfaceCallback", "Exception in setPreviewDisplay()", t);
Toast.makeText(MainActivity.this, t.getMessage(), Toast.LENGTH_LONG).show();
}
}
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
Camera.Parameters parameters = camera.getParameters();
Camera.Size size = getBestPreviewSize(width, height, parameters);
if (size != null) {
parameters.setPreviewSize(size.width, size.height);
parameters.setPictureFormat(PixelFormat.JPEG);
camera.setParameters(parameters);
camera.startPreview();
inPreview = true;
}
}
public void surfaceDestroyed(SurfaceHolder holder) {
// no-op
}
};
Camera.PictureCallback photoCallback = new Camera.PictureCallback() {
public void onPictureTaken(byte[] data, Camera camera) {
new SavePhotoTask().execute(data);
camera.startPreview();
inPreview = true;
}
};
class SavePhotoTask extends AsyncTask<byte[], String, String> {
@Override
protected String doInBackground(byte[]... jpeg) {
File photo = new File(Environment.getExternalStorageDirectory(), "photo.jpg");
if(photo.exists()) {
photo.delete();
}
try {
FileOutputStream fos = new FileOutputStream(photo.getPath());
fos.write(jpeg[0]);
fos.close();
}
catch (java.io.IOException e) {
Log.e("MainActivity", "Exception in photoCallback", e);
}
return(null);
}
}
}
Update
至于我遇到的异常，如果我尝试像下面的代码那样创建 main 函数，
public void onCreate(Bundle savedInstanceState)
{
//Call the parent class
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
preview = (SurfaceView) findViewById(R.id.preview);
previewHolder = preview.getHolder();
previewHolder.addCallback(surfaceCallback);
previewHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
Camera.Parameters parameters = camera.getParameters();
parameters.setPictureFormat(PixelFormat.JPEG);
camera.setParameters(parameters);
try {
//Start the camera preview display
camera.setPreviewDisplay(previewHolder);
camera.startPreview();
}
catch (IOException ex) {
Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
}
}
我收到“应用程序意外停止。请重试。”我基本上是试图遵循以下步骤安卓文档 http://developer.android.com/reference/android/hardware/Camera.html#setPreviewDisplay(android.view.SurfaceHolder)指定。我还尝试在检索相机对象后将此代码放入 onResume 函数中，然后调用 this.onResume。
