嗨，朋友，我正在处理一个应用程序。
在该应用程序中，当应用程序启动时，Pic应该会自动从相机中捕获。
我的代码是：
1.相机演示
public class CameraDemo extends Activity
{
private static final String TAG = "CameraDemo";
Camera camera;
Preview preview;
Button buttonClick;
Chronometer ch;
/** 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);
buttonClick = (Button) findViewById(R.id.buttonClick);
ch=(Chronometer)findViewById(R.id.chronometer1);
ch.start();
preview.camera.takePicture(shutterCallback,rawCallback,jpegCallback);
// If I write above code here it shows error.
buttonClick.setOnClickListener( new OnClickListener()
{
public void onClick(View v)
{
buttonClick.setVisibility(View.INVISIBLE);
preview.camera.takePicture(shutterCallback, rawCallback,jpegCallback);
// Here it works perfactly
Toast.makeText(CameraDemo.this,""+ch.getText(), Toast.LENGTH_LONG).show();
}
});
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/tmp/%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");
}
};
}
2. Preview.java
package com.example;
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;
@SuppressWarnings("deprecation")
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/tmp/%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 );
}
}
为此，我给出了以上许可：
<uses-permission android:name="android.permission.CAMERA" />我的错误日志是：
FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example/com.example.CameraDemo}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2343)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2395)
at android.app.ActivityThread.access$600(ActivityThread.java:162)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1364)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5371)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.CameraDemo.onCreate(CameraDemo.java:41)
at android.app.Activity.performCreate(Activity.java:5122)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1081)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2307)
... 11 more
我的问题是：
当我在按钮单击事件中使用此代码时，它可以正常工作。但是，当我启动应用程序图像时，需要自动捕获图像。
相同的代码在onCreate（）事件中不起作用，并且应用程序不幸地停止了。
请告诉这个解决方案。
谢谢。
最佳答案
呼叫时尚未创建您的SurfaceViewpreview.camera.takePicture(shutterCallback,rawCallback,jpegCallback);
所以当时相机是NULL。
尝试达成协议后再叫它。
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.camera);
preview = new Preview(this);
((FrameLayout) findViewById(R.id.preview)).addView(preview);
new java.util.Timer().schedule(
new java.util.TimerTask() {
@Override
public void run() {
// your code here
preview.camera.takePicture(shutterCallback,rawCallback,jpegCallback);
}
},
2000
);
}
这对我来说很完美...
希望它也对您有用。祝您好运:)