我是一名Android新手，正在尝试实施自定义相机应用。
我跟着这里的turotial： http://developer.android.com/guide/topics/media/camera.html
但每次我尝试启动应用程序时都会崩溃。
我的代码发布在下面：
MainActivity
import android.app.Activity;
import android.hardware.Camera;
import android.os.Bundle;
import android.view.Menu;
import android.widget.FrameLayout;
public class MainActivity extends Activity {
private Camera mCamera;
private CameraPreview mPreview;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mCamera = getCameraInstance();
// Create our Preview view and set it as the content of our activity.
mPreview = new CameraPreview(this, mCamera);
FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
preview.addView(mPreview);
}
public static Camera getCameraInstance(){
Camera c = null;
try {
c = Camera.open(); // attempt to get a Camera instance
}
catch (Exception e){
// Camera is not available (in use or does not exist)
}
return c; // returns null if camera is unavailable
}
@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;
}
}
CameraPreview类
package com.studio9ja.smileycamera;
import java.io.IOException;
import android.content.Context;
import android.hardware.Camera;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.Toast;
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
private SurfaceHolder mHolder;
private Camera mCamera;
private String TAG;
public CameraPreview(Context context, Camera camera) {
super(context);
mCamera = camera;
// Install a SurfaceHolder.Callback so we get notified when the
// underlying surface is created and destroyed.
mHolder = getHolder();
mHolder.addCallback(this);
// deprecated setting, but required on Android versions prior to 3.0
mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}
public void surfaceCreated(SurfaceHolder holder) {
// The Surface has been created, now tell the camera where to draw the preview.
try {
mCamera.setPreviewDisplay(holder);
mCamera.startPreview();
} catch (IOException e) {
Log.d(TAG, "Error setting camera preview: " + e.getMessage());
}
}
public void surfaceDestroyed(SurfaceHolder holder) {
// empty. Take care of releasing the Camera preview in your activity.
}
public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
// If your preview can change or rotate, take care of those events here.
// Make sure to stop the preview before resizing or reformatting it.
if (mHolder.getSurface() == null){
// preview surface does not exist
return;
}
// stop preview before making changes
try {
mCamera.stopPreview();
} catch (Exception e){
// ignore: tried to stop a non-existent preview
}
// set preview size and make any resize, rotate or
// reformatting changes here
// start preview with new settings
try {
mCamera.setPreviewDisplay(mHolder);
mCamera.startPreview();
} catch (Exception e){
Log.d(TAG, "Error starting camera preview: " + e.getMessage());
}
}
}
main_activity.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<FrameLayout
android:id="@+id/camera_preview"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_weight="1"
/>
<Button
android:id="@+id/button_capture"
android:text="Capture"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
/>
</LinearLayout>
我的Logcat
07-27 17:49:30.928: I/SurfaceView(2348): visibleChanged -- surfaceCreated
07-27 17:49:30.928: I/SurfaceView(2348): finishedDrawing
07-27 17:49:30.931: D/AndroidRuntime(2348): Shutting down VM
07-27 17:49:30.931: W/dalvikvm(2348): threadid=1: thread exiting with uncaught exception (group=0x410839a8)
07-27 17:49:30.932: E/AndroidRuntime(2348): FATAL EXCEPTION: main
07-27 17:49:30.932: E/AndroidRuntime(2348): java.lang.NullPointerException
07-27 17:49:30.932: E/AndroidRuntime(2348): at com.studio9ja.smileycamera.CameraPreview.surfaceCreated(CameraPreview.java:34)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.view.SurfaceView.updateWindow(SurfaceView.java:606)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.view.SurfaceView.access$000(SurfaceView.java:88)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.view.SurfaceView$3.onPreDraw(SurfaceView.java:183)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.view.ViewTreeObserver.dispatchOnPreDraw(ViewTreeObserver.java:692)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2123)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1139)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4879)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:776)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.view.Choreographer.doCallbacks(Choreographer.java:579)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.view.Choreographer.doFrame(Choreographer.java:548)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:762)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.os.Handler.handleCallback(Handler.java:725)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.os.Handler.dispatchMessage(Handler.java:92)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.os.Looper.loop(Looper.java:153)
07-27 17:49:30.932: E/AndroidRuntime(2348): at android.app.ActivityThread.main(ActivityThread.java:5297)
07-27 17:49:30.932: E/AndroidRuntime(2348): at java.lang.reflect.Method.invokeNative(Native Method)
07-27 17:49:30.932: E/AndroidRuntime(2348): at java.lang.reflect.Method.invoke(Method.java:511)
07-27 17:49:30.932: E/AndroidRuntime(2348): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
07-27 17:49:30.932: E/AndroidRuntime(2348): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
07-27 17:49:30.932: E/AndroidRuntime(2348): at dalvik.system.NativeStart.main(Native Method)
07-27 17:49:30.982: D/dalvikvm(2348): threadid=11: interp stack at 0x5e19a000
07-27 17:49:32.808: I/Process(2348): Sending signal. PID: 2348 SIG: 9
我还在manifest.xml中添加了以下权限
<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
任何帮助将不胜感激
答案 0 :(得分：0)
你的相机可能是空的。你应该打印例外，如果有一个只是要看，并记录以确保相机仍然不是空的：
/** A safe way to get an instance of the Camera object. */
public static Camera getCameraInstance(){
Camera c = null;
try {
c = Camera.open(); // attempt to get a Camera instance
}
catch (Exception e){
e.printstacktrace();
}
return c; // returns null if camera is unavailable
}
然后在调用预览之前检查以确保它不为空：
if(mCamera!=null){
mPreview = new CameraPreview(this, mCamera);
FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
preview.addView(mPreview);
}