特别是android的新手。正在制作一个应用程序，我希望我的程序启动相机拍摄图像，然后在我将用于检测面部的脸部周围绘制一个矩形窗口。现在这是我的代码：
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PointF;
import android.media.FaceDetector;
import android.media.FaceDetector.Face;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
public class MainActivity extends Activity {
final int CAMERA_PIC_REQUEST = 0;
private int imageWidth, imageHeight;
private int numberOfFace = 5;
private FaceDetector myFaceDetect;
private FaceDetector.Face[] myFace;
float myEyesDistance;
int numberOfFaceDetected;
Bitmap thumbnail = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button strt = (Button) findViewById(R.id.start_camera);
strt.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Intent camera_intent = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE);
startActivityForResult(camera_intent, CAMERA_PIC_REQUEST);
BitmapFactory.Options BitmapFactoryOptionsbfo = new BitmapFactory.Options();
BitmapFactoryOptionsbfo.inPreferredConfig = Bitmap.Config.RGB_565;
imageWidth = thumbnail.getWidth();
imageHeight = thumbnail.getHeight();
myFace = new FaceDetector.Face[numberOfFace];
myFaceDetect = new FaceDetector(imageWidth, imageHeight, numberOfFace);
numberOfFaceDetected = myFaceDetect.findFaces(thumbnail, myFace);
Canvas canvas = null;
canvas.drawBitmap(thumbnail, 0, 0, null);
Paint myPaint = new Paint();
myPaint.setColor(Color.GREEN);
myPaint.setStyle(Paint.Style.STROKE);
myPaint.setStrokeWidth(3);
for(int i=0; i < numberOfFaceDetected; i++)
{
Face face = myFace[i];
PointF myMidPoint = new PointF();
face.getMidPoint(myMidPoint);
myEyesDistance = face.eyesDistance();
canvas.drawRect(
(int)(myMidPoint.x - myEyesDistance),
(int)(myMidPoint.y - myEyesDistance),
(int)(myMidPoint.x + myEyesDistance),
(int)(myMidPoint.y + myEyesDistance),
myPaint);
}
}
});
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
switch(requestCode){
case 0:
if(resultCode==RESULT_OK){
thumbnail = (Bitmap) data.getExtras().get("data");
}
}
}
@Override
protected void onSaveInstanceState(Bundle outState) {
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
Logcat显示：
08-20 12:13:16.218: E/AndroidRuntime(26801): FATAL EXCEPTION: main
08-20 12:13:16.218: E/AndroidRuntime(26801): java.lang.RuntimeException: Unable to resume activity {com.mh9.makeover/com.mh9.makeover.MainActivity}: java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=0, result=-1, data=Intent { act=inline-data (has extras) }} to activity {com.mh9.makeover/com.mh9.makeover.MainActivity}: java.lang.NullPointerException
08-20 12:13:16.218: E/AndroidRuntime(26801): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2124)
08-20 12:13:16.218: E/AndroidRuntime(26801): at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2139)
08-20 12:13:16.218: E/AndroidRuntime(26801): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1672)
08-20 12:13:16.218: E/AndroidRuntime(26801): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
08-20 12:13:16.218: E/AndroidRuntime(26801): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
08-20 12:13:16.218: E/AndroidRuntime(26801): at android.os.Handler.dispatchMessage(Handler.java:99)
08-20 12:13:16.218: E/AndroidRuntime(26801): at android.os.Looper.loop(Looper.java:130)
08-20 12:13:16.218: E/AndroidRuntime(26801): at android.app.ActivityThread.main(ActivityThread.java:3687)
08-20 12:13:16.218: E/AndroidRuntime(26801): at java.lang.reflect.Method.invokeNative(Native Method)
08-20 12:13:16.218: E/AndroidRuntime(26801): at java.lang.reflect.Method.invoke(Method.java:507)
08-20 12:13:16.218: E/AndroidRuntime(26801): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
08-20 12:13:16.218: E/AndroidRuntime(26801): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
08-20 12:13:16.218: E/AndroidRuntime(26801): at dalvik.system.NativeStart.main(Native Method)
08-20 12:13:16.218: E/AndroidRuntime(26801): Caused by: java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=0, result=-1, data=Intent { act=inline-data (has extras) }} to activity {com.mh9.makeover/com.mh9.makeover.MainActivity}: java.lang.NullPointerException
08-20 12:13:16.218: E/AndroidRuntime(26801): at android.app.ActivityThread.deliverResults(ActivityThread.java:2536)
08-20 12:13:16.218: E/AndroidRuntime(26801): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2111)
08-20 12:13:16.218: E/AndroidRuntime(26801): ... 12 more
08-20 12:13:16.218: E/AndroidRuntime(26801): Caused by: java.lang.NullPointerException
08-20 12:13:16.218: E/AndroidRuntime(26801): at com.mh9.makeover.MainActivity.onActivityResult(MainActivity.java:78)
08-20 12:13:16.218: E/AndroidRuntime(26801): at android.app.Activity.dispatchActivityResult(Activity.java:3908)
08-20 12:13:16.218: E/AndroidRuntime(26801): at android.app.ActivityThread.deliverResults(ActivityThread.java:2532)
08-20 12:13:16.218: E/AndroidRuntime(26801): ... 13 more
现在我有两个问题。首先是为什么我得到这个例外是什么意思？纠正解释将不胜感激。第二个问题：我会完成我想做的事吗？我的意思是在拍摄并保存图像后，我想传递它以在脸部周围绘制一个颈椎窗！
答案 0 :(得分：3)
由于没有来自onActivityResult（）方法中相机意图的额外内容而遇到NullPointerException：
thumbnail = (Bitmap) data.getExtras().get("data");
这通常发生在某些（高分辨率）设备中，因为设备需要具有指定文件的摄像头意图，其中应存储捕获的图像。
而不是：
Intent camera_intent = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE);
startActivityForResult(camera_intent, CAMERA_PIC_REQUEST);
试试这个：
// create Intent to take a picture and return control to the calling application
Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
fileUri = getOutputMediaFileUri(MEDIA_TYPE_IMAGE); // create a file to save the image
intent.putExtra(MediaStore.EXTRA_OUTPUT, fileUri); // set the image file name
// start the image capture Intent
startActivityForResult(intent, CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE);
而不是onactivityresult方法：
if(resultCode==RESULT_OK){
thumbnail = (Bitmap) data.getExtras().get("data");
}
试试这个：
if (requestCode == CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE) {
if (resultCode == RESULT_OK) {
// Image captured and saved to fileUri specified in the Intent
Toast.makeText(this, "Image saved to:\n" +
data.getData(), Toast.LENGTH_LONG).show();
} else if (resultCode == RESULT_CANCELED) {
// User cancelled the image capture
} else {
// Image capture failed, advise user
}
}
有关详细信息，请访问Documentation
祝你好运！