我是android开发的绝对初学者，我想制作相机On / Off应用程序，但我得到错误。所以请帮助我。
package com.vikram.flashcamera;
import android.app.Activity;
import android.content.Context;
import android.content.pm.PackageManager;
import android.hardware.Camera;
import android.hardware.Camera.Parameters;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class MainActivity extends Activity {
private boolean isLighOn = false;
private Camera camera;
private Button button;
@Override
protected void onStop() {
super.onStop();
if(camera != null) {
camera.release();
}
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = (Button) findViewById(R.id.buttonClick);
Context context = this;
PackageManager pm = context.getPackageManager();
if(!pm.hasSystemFeature(PackageManager.FEATURE_CAMERA)) {
Log.e("err", "Device has no camera!");
return;
}
camera = Camera.open();
final Parameters p = camera.getParameters();
button.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
if(isLighOn) {
Log.i("info", "torch is turn off!");
p.setFlashMode(Parameters.FLASH_MODE_OFF);
camera.setParameters(p);
camera.stopPreview();
isLighOn = false;
}
else {
Log.i("info", "torch is turn on!");
p.setFlashMode(Parameters.FLASH_MODE_TORCH);
camera.setParameters(p);
camera.startPreview();
isLighOn = true;
}
}
});
}
}
我的logCat错误如下所示。
08-25 15:50:41.932: E/Trace(878): error opening trace file: No such file or directory (2)
08- 5 15:50:42.453: D/AndroidRuntime(878): Shutting down VM
08-25 15:50:42.463: W/dalvikvm(878): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
08-25 15:50:42.473: E/AndroidRuntime(878): FATAL EXCEPTION: main
08-25 15:50:42.473: E/AndroidRuntime(878): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.vikram.flashcamera/com.vikram.flashcamera.MainActivity}: java.lang.NullPointerException
08-25 15:50:42.473: E/AndroidRuntime(878): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
08-25 15:50:42.473: E/AndroidRuntime(878): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
08-25 15:50:42.473: E/AndroidRuntime(878): at android.app.ActivityThread.access$600(ActivityThread.java:130)
08-25 15:50:42.473: E/AndroidRuntime(878): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
08-25 15:50:42.473: E/AndroidRuntime(878): at android.os.Handler.dispatchMessage(Handler.java:99)
08-25 15:50:42.473: E/AndroidRuntime(878): at android.os.Looper.loop(Looper.java:137)
08-25 15:50:42.473: E/AndroidRuntime(878): at android.app.ActivityThread.main(ActivityThread.java:4745)
08-25 15:50:42.473: E/AndroidRuntime(878): at java.lang.reflect.Method.invokeNative(Native Method)
08-25 15:50:42.473: E/AndroidRuntime(878): at java.lang.reflect.Method.invoke(Method.java:511)
08-25 15:50:42.473: E/AndroidRuntime(878): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
08-25 15:50:42.473: E/AndroidRuntime(878): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-25 15:50:42.473: E/AndroidRuntime(878): at dalvik.system.NativeStart.main(Native Method)
08-25 15:50:42.473: E/AndroidRuntime(878): Caused by: java.lang.NullPointerException
08-25 15:50:42.473: E/AndroidRuntime(878): at com.vikram.flashcamera.MainActivity.onCreate(MainActivity.java:44)
08-25 15:50:42.473: E/AndroidRuntime(878): at android.app.Activity.performCreate(Activity.java:5008)
08-25 15:50:42.473: E/AndroidRuntime(878): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
08-25 15:50:42.473: E/AndroidRuntime(878): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
08-25 15:50:42.473: E/AndroidRuntime(878): ... 11 more
08-25 18:03:08.543: E/Trace(900): error opening trace file: No such file or directory (2)
08-25 18:03:09.122: D/AndroidRuntime(900): Shutting down VM
08-25 18:03:09.122: W/dalvikvm(900): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
08-25 18:03:09.132: E/AndroidRuntime(900): FATAL EXCEPTION: main
08-25 18:03:09.132: E/AndroidRuntime(900): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.vikram.flashcamera/com.vikram.flashcamera.MainActivity}: java.lang.NullPointerException
08-25 18:03:09.132: E/AndroidRuntime(900): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
08-25 18:03:09.132: E/AndroidRuntime(900): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
08-25 18:03:09.132: E/AndroidRuntime(900): at android.app.ActivityThread.access$600(ActivityThread.java:130)
08-25 18:03:09.132: E/AndroidRuntime(900): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
08-25 18:03:09.132: E/AndroidRuntime(900): at android.os.Handler.dispatchMessage(Handler.java:99)
08-25 18:03:09.132: E/AndroidRuntime(900): at android.os.Looper.loop(Looper.java:137)
08-25 18:03:09.132: E/AndroidRuntime(900): at android.app.ActivityThread.main(ActivityThread.java:4745)
08-25 18:03:09.132: E/AndroidRuntime(900): at java.lang.reflect.Method.invokeNative(Native Method)
08-25 18:03:09.132: E/AndroidRuntime(900): at java.lang.reflect.Method.invoke(Method.java:511)
08-25 18:03:09.132: E/AndroidRuntime(900): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
08-25 18:03:09.132: E/AndroidRuntime(900): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-25 18:03:09.132: E/AndroidRuntime(900): at dalvik.system.NativeStart.main(Native Method)
08-25 18:03:09.132: E/AndroidRuntime(900): Caused by: java.lang.NullPointerException
08-25 18:03:09.132: E/AndroidRuntime(900): at com.vikram.flashcamera.MainActivity.onCreate(MainActivity.java:44)
08-25 18:03:09.132: E/AndroidRuntime(900): at android.app.Activity.performCreate(Activity.java:5008)
08-25 18:03:09.132: E/AndroidRuntime(900): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
08-25 18:03:09.132: E/AndroidRuntime(900): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
08-25 18:03:09.132: E/AndroidRuntime(900): ... 11 more
08-25 18:03:11.613: I/Process(900): Sending signal. PID: 900 SIG: 9
08-25 18:33:52.222: E/Trace(929): error opening trace file: No such file or directory (2)
08-25 18:33:52.813: D/AndroidRuntime(929): Shutting down VM
08-25 18:33:52.813: W/dalvikvm(929): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
08-25 18:33:52.833: E/AndroidRuntime(929): FATAL EXCEPTION: main
08-25 18:33:52.833: E/AndroidRuntime(929): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.vikram.flashcamera/com.vikram.flashcamera.MainActivity}: java.lang.NullPointerException
08-25 18:33:52.833: E/AndroidRuntime(929): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
08-25 18:33:52.833: E/AndroidRuntime(929): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
08-25 18:33:52.833: E/AndroidRuntime(929): at android.app.ActivityThread.access$600(ActivityThread.java:130)
08-25 18:33:52.833: E/AndroidRuntime(929): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
08-25 18:33:52.833: E/AndroidRuntime(929): at android.os.Handler.dispatchMessage(Handler.java:99)
08-25 18:33:52.833: E/AndroidRuntime(929): at android.os.Looper.loop(Looper.java:137)
08-25 18:33:52.833: E/AndroidRuntime(929): at android.app.ActivityThread.main(ActivityThread.java:4745)
08-25 18:33:52.833: E/AndroidRuntime(929): at java.lang.reflect.Method.invokeNative(Native Method)
08-25 18:33:52.833: E/AndroidRuntime(929): at java.lang.reflect.Method.invoke(Method.java:511)
08-25 18:33:52.833: E/AndroidRuntime(929): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
08-25 18:33:52.833: E/AndroidRuntime(929): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-25 18:33:52.833: E/AndroidRuntime(929): at dalvik.system.NativeStart.main(Native Method)
08-25 18:33:52.833: E/AndroidRuntime(929): Caused by: java.lang.NullPointerException
08-25 18:33:52.833: E/AndroidRuntime(929): at com.vikram.flashcamera.MainActivity.onCreate(MainActivity.java:44)
08-25 18:33:52.833: E/AndroidRuntime(929): at android.app.Activity.performCreate(Activity.java:5008)
08-25 18:33:52.833: E/AndroidRuntime(929): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
08-25 18:33:52.833: E/AndroidRuntime(929): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
08-25 18:33:52.833: E/AndroidRuntime(929): ... 11 more
08-25 18:38:52.904: I/Process(929): Sending signal. PID: 929 SIG: 9
答案 0 :(得分：1)
由于您的AVD没有拿到相机，我认为这可能对您有所帮助： Enable Camera in AVD
答案 1 :(得分：0)
您的错误跟踪显示您Activity的第44行发生了异常。通过计算您发布的代码行，这似乎是Camera.open()。根据文档，如果设备没有后置摄像头，则返回null。如果它在模拟器上，这可能是有意义的。