我是Android编程新手。我需要使用OpenCV库打开相机，我已经关注了this视频教程。
但是，应用程序已在运行时停止在模拟器上，并且仅查看＆＃34; app_name已停止尝试再次打开的消息＆＃34;。有很多错误，我修复了很多错误，但我无法修复其他错误。这是我的logcat：
09-02 04:00:52.628 9058-9058/samaa.example.com.opencv249 E/AndroidRuntime: FATAL EXCEPTION: main Process: samaa.example.com.opencv249, PID: 9058
java.lang.RuntimeException: Unable to start activity ComponentInfo{samaa.example.com.opencv249/samaa.example.com.opencv249.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at samaa.example.com.opencv249.MainActivity.onCreate(MainActivity.java:55)
at android.app.Activity.performCreate(Activity.java:6679)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
这是我的主要活动：
package samaa.example.com.opencv249;
import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.SurfaceView;
import org.opencv.android.BaseLoaderCallback;
import org.opencv.android.CameraBridgeViewBase;
import org.opencv.android.JavaCameraView;
import org.opencv.android.OpenCVLoader;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
public class MainActivity extends AppCompatActivity implements CameraBridgeViewBase.CvCameraViewListener2 {
private static String TAG="MainActivity";
JavaCameraView javaCameraView;
Mat mRgba;
BaseLoaderCallback mLoaderCallBack = new BaseLoaderCallback(this) {
@Override
public void onManagerConnected(int status) {
switch (status){
case BaseLoaderCallback.SUCCESS: {
javaCameraView.enableView();
break;
}
default:{
super.onManagerConnected(status);
break;
}
}
}
};
static {
if (OpenCVLoader.initDebug()) {
Log.i(TAG, "successfull");
}
else {
Log.i(TAG,"failed");
}
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
javaCameraView = (javaCameraView).findViewById(R.id.java_camera_view);
javaCameraView.setVisibility(SurfaceView.VISIBLE);
javaCameraView.setCvCameraViewListener(this);
}
@Override
protected void onPause()
{
super.onPause();
if(javaCameraView != null)
javaCameraView.disableView();
}
@Override
protected void onDestroy()
{
super.onDestroy();
if(javaCameraView != null)
javaCameraView.disableView();
}
@Override
protected void onResume()
{
super.onResume();
javaCameraView.enableView();
/* if (OpenCVLoader.initDebug()) {
Log.i(TAG, "successfull");
mLoaderCallBack.onManagerConnected(LoaderCallbackInterface.SUCCESS);
}
else {
Log.i(TAG,"failed");
OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_2_4_2, this, mLoaderCallBack);
}*/
}
@Override
public void onCameraViewStarted(int width, int height) {
mRgba= new Mat(height,width, CvType.CV_8UC4);
}
@Override
public void onCameraViewStopped() {
mRgba.release();
}
@Override
public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
mRgba= inputFrame.rgba();
return mRgba;
}
private void requestRecordAudioPermission() {
//check API version, do nothing if API version < 23!
int currentapiVersion = android.os.Build.VERSION.SDK_INT;
if (currentapiVersion > android.os.Build.VERSION_CODES.LOLLIPOP){
if (ContextCompat.checkSelfPermission(this, Manifest.permission.RECORD_AUDIO) != PackageManager.PERMISSION_GRANTED) {
// Should we show an explanation?
if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.RECORD_AUDIO)) {
// Show an expanation to the user *asynchronously* -- don't block
// this thread waiting for the user's response! After the user
// sees the explanation, try again to request the permission.
} else {
// No explanation needed, we can request the permission.
ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.RECORD_AUDIO}, 1);
}
}
}
}
@Override
public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
switch (requestCode) {
case 1: {
// If request is cancelled, the result arrays are empty.
if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
// permission was granted, yay! Do the
// contacts-related task you need to do.
Log.d("Activity", "Granted!");
} else {
// permission denied, boo! Disable the
// functionality that depends on this permission.
Log.d("Activity", "Denied!");
finish();
}
return;
}
// other 'case' lines to check for other
// permissions this app might request
}
}
}
答案 0 :(得分：1)
您正尝试使用(javaCameraView).find从未初始化的视图中查找引用，因为您需要使用Casting，因此请使用
javaCameraView = (JavaCameraView)findViewById(R.id.java_camera_view);
//Casting,class name ^^^^^^^^^
// notice no dot(.) ^
而下面的语句会尝试从view对象中找到标识为java_camera_view的{{1}}，该对象尚未初始化
javaCameraView