Java Android自定义摄像头,获取空指针异常?
我是android编码的新手,我在android开发者网站上,他们正在解释如何创建自定义相机。我所有的东西都和他们在网站上的一模一样,但我一直在mCamera.setPreviewDisplay(holder)上得到空指针;-第31行:CameraPreview.java 以下是activity_main.xml:Java Android自定义摄像头,获取空指针异常?,java,android,android-camera,Java,Android,Android Camera,我是android编码的新手,我在android开发者网站上,他们正在解释如何创建自定义相机。我所有的东西都和他们在网站上的一模一样,但我一直在mCamera.setPreviewDisplay(holder)上得到空指针;-第31行:CameraPreview.java 以下是activity_main.xml: <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tool
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<FrameLayout
android:id="@+id/camera_preview"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_weight="1"/>
</LinearLayout>
CameraPreview.java:
package com.example.customcamera;
import java.io.IOException;
import android.content.Context;
import android.hardware.Camera;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
/** A basic Camera preview class */
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
private SurfaceHolder mHolder;
private Camera mCamera;
private String TAG = "CameraPreview";
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());
}
}
}
getCameraInstance
状态返回c;//如果摄像机不可用,则返回null
。它是否返回null
?您检查过这个吗?您确定mHolder不为null吗?如果mHolder为null,那么当它调用getHolder()时,它将返回null?它为什么要这样做?是的,刚刚检查过。我使用日志来跟踪,它不会抛出任何异常。注意:我正在调试我的Nexus 7I,我刚刚发现我需要指定它使用的摄像头,因为Nexus 7没有背面摄像头,它会自动返回null,并且不会引发任何异常。我必须更新清单以支持api 9,但没关系。谢谢!:)
package com.example.customcamera;
import java.io.IOException;
import android.content.Context;
import android.hardware.Camera;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
/** A basic Camera preview class */
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
private SurfaceHolder mHolder;
private Camera mCamera;
private String TAG = "CameraPreview";
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());
}
}
}