我一直在尝试创建一个相机预览，它在预览中显示一个带有多个透明图像的 View Pager。但是，我收到了这个错误：
05-10 03:31:23.614: E/AndroidRuntime(674): FATAL EXCEPTION: main
05-10 03:31:23.614: E/AndroidRuntime(674): java.lang.NullPointerException
05-10 03:31:23.614: E/AndroidRuntime(674): at com.android.gs1.MainActivity$CameraPreview.surfaceCreated(MainActivity.java:102)
05-10 03:31:23.614: E/AndroidRuntime(674): at android.view.SurfaceView.updateWindow(SurfaceView.java:562)
05-10 03:31:23.614: E/AndroidRuntime(674): at android.view.SurfaceView.access$000(SurfaceView.java:82)
05-10 03:31:23.614: E/AndroidRuntime(674): at android.view.SurfaceView$3.onPreDraw(SurfaceView.java:171)
05-10 03:31:23.614: E/AndroidRuntime(674): at android.view.ViewTreeObserver.dispatchOnPreDraw(ViewTreeObserver.java:590)
05-10 03:31:23.614: E/AndroidRuntime(674): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1596)
05-10 03:31:23.614: E/AndroidRuntime(674): at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2418)
05-10 03:31:23.614: E/AndroidRuntime(674): at android.os.Handler.dispatchMessage(Handler.java:99)
05-10 03:31:23.614: E/AndroidRuntime(674): at android.os.Looper.loop(Looper.java:137)
05-10 03:31:23.614: E/AndroidRuntime(674): at android.app.ActivityThread.main(ActivityThread.java:4340)
05-10 03:31:23.614: E/AndroidRuntime(674): at java.lang.reflect.Method.invokeNative(Native Method)
05-10 03:31:23.614: E/AndroidRuntime(674): at java.lang.reflect.Method.invoke(Method.java:511)
05-10 03:31:23.614: E/AndroidRuntime(674): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
05-10 03:31:23.614: E/AndroidRuntime(674): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
05-10 03:31:23.614: E/AndroidRuntime(674): at dalvik.system.NativeStart.main(Native Method)
这是我的代码：
package com.android.gs1;
import java.io.IOException;
import android.os.Bundle;
import android.os.Parcelable;
import android.app.Activity;
import android.content.Context;
import android.hardware.Camera;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.Toast;
public class MainActivity extends Activity {
ViewPager vp;
Camera mCamera;
SurfaceHolder mHolder;
static int j;
private vpAdapter myAdapter;
CameraPreview preview;
public static void passPageNumber(int i){
j = i;
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toast.makeText(getApplicationContext(), "Swipe Left or Right to Select an Option", Toast.LENGTH_LONG).show();
vp = (ViewPager) findViewById(R.id.viewpager);
myAdapter = new vpAdapter();
preview = new CameraPreview(getApplicationContext(), mCamera);
((LinearLayout) findViewById(R.id.preview)).addView(preview);
vp.setAdapter(myAdapter);
}
private class CameraPreview extends SurfaceView implements SurfaceHolder.Callback{
private final String TAG = null;
public CameraPreview(Context context, Camera camera) {
super(context);
// TODO Auto-generated constructor stub
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);
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
// TODO Auto-generated method stub
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());
}
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
// TODO Auto-generated method stub
try {
mCamera = Camera.open();
mCamera.setPreviewDisplay(holder);
mCamera.startPreview();
} catch (IOException e) {
Log.d(TAG, "Error setting camera preview: " + e.getMessage());
}
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
// TODO Auto-generated method stub
}
}
private class vpAdapter extends PagerAdapter{
@Override
public int getCount() {
// TODO Auto-generated method stub
return 5;
}
@Override
public boolean isViewFromObject(View view, Object object) {
// TODO Auto-generated method stub
return view == ((LinearLayout)object);
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
// TODO Auto-generated method stub
((ViewPager)container).removeView((LinearLayout)object);
}
@Override
public void finishUpdate(ViewGroup container) {
// TODO Auto-generated method stub
}
@Override
public Object instantiateItem(View container, int position) {
// TODO Auto-generated method stub
LayoutInflater inflater = (LayoutInflater)container.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View v = null;
switch(position){
case 0:
v = inflater.inflate(R.layout.first, null);
break;
case 1:
v = inflater.inflate(R.layout.second, null);
break;
case 2:
v = inflater.inflate(R.layout.third, null);
break;
case 3:
v = inflater.inflate(R.layout.fourth, null);
break;
case 4:
v = inflater.inflate(R.layout.fifth, null);
break;
}
((ViewPager)container).addView(v, 0);
return v;
}
@Override
public void startUpdate(ViewGroup container) {
// TODO Auto-generated method stub
}
@Override
public Parcelable saveState() {
// TODO Auto-generated method stub
return null;
}
}
}
这是我的xml
<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"
tools:context=".MainActivity"
android:background="#545454" >
<android.support.v4.view.ViewPager
android:id="@+android:id/viewpager"
android:layout_width="0dip"
android:layout_height="wrap_content"
android:layout_weight="0.49" />
<LinearLayout
android:id="@+id/preview"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
</LinearLayout>
</LinearLayout>
viewpager 还有五个 xml。它们看起来都像这样，但名称和 ID 不同。
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
>
<ImageView
android:id="@+id/image1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:adjustViewBounds="false"
android:contentDescription="@string/description_image_1"
android:scaleType="fitXY"
android:src="@drawable/first" />
</LinearLayout>
非常感谢
编辑：有人问我代码的最终工作版本。这里是：
public class MainActivity extends Activity {
ViewPager vp;
vpAdapter myAdapter;
Camera camera = null;
SurfaceHolder previewHolder = null;
private SurfaceView preview = null;
private boolean inPreview = false;
private boolean cameraConfigured = false;
public static String[] arrayURL;
public static boolean urlsPassed;
private View mContentView;
private View mLoadingView;
private int mShortAnimationDuration;
@SuppressWarnings("deprecation")
@SuppressLint("NewApi")
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.activity_main);
Toast.makeText(getApplicationContext(), "Swipe Left or Right to Select an Option", Toast.LENGTH_SHORT).show();
//NEW CODE
mContentView = findViewById(R.id.content);
mLoadingView = findViewById(R.id.loading_spinner);
mContentView.setVisibility(View.GONE);
mShortAnimationDuration = getResources().getInteger(
android.R.integer.config_shortAnimTime);
//NEW CODE
preview=(SurfaceView)findViewById(R.id.preview);
preview.setZOrderOnTop(false);
previewHolder=preview.getHolder();
previewHolder.addCallback(surfaceCallback);
previewHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}
private void crossfade() {
// Set the content view to 0% opacity but visible, so that it is visible
// (but fully transparent) during the animation.
mContentView.setAlpha(0f);
mContentView.setVisibility(View.VISIBLE);
// Animate the content view to 100% opacity, and clear any animation
// listener set on the view.
mContentView.animate()
.alpha(1f)
.setDuration(mShortAnimationDuration)
.setListener(null);
// Animate the loading view to 0% opacity. After the animation ends,
// set its visibility to GONE as an optimization step (it won't
// participate in layout passes, etc.)
mLoadingView.animate()
.alpha(0f)
.setDuration(mShortAnimationDuration)
.setListener(new AnimatorListenerAdapter() {
@Override
public void onAnimationEnd(Animator animation) {
mLoadingView.setVisibility(View.GONE);
}
});
}
public static void assignURL(String[] urls){
arrayURL = urls;
}
public static void urlsPassed(boolean transfer){
urlsPassed = transfer;
}
@Override
public void onResume() {
super.onResume();
camera=Camera.open();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public void onPause() {
if (inPreview) {
camera.stopPreview();
}
camera.release();
camera=null;
inPreview=false;
super.onPause();
}
private Camera.Size getBestPreviewSize(int width, int height,Camera.Parameters parameters) {
Camera.Size result=null;
for (Camera.Size size : parameters.getSupportedPreviewSizes()) {
if (size.width<=width && size.height<=height) {
if (result==null) {
result=size;
}
else {
int resultArea=result.width*result.height;
int newArea=size.width*size.height;
if (newArea>resultArea) {
result=size;
}
}
}
}
return(result);
}
private void initPreview(int width, int height) {
if (camera!=null && previewHolder.getSurface()!=null) {
try {
camera.setPreviewDisplay(previewHolder);
}
catch (Throwable t) {
Log.e("PreviewDemo-surfaceCallback",
"Exception in setPreviewDisplay()", t);
Toast
.makeText(MainActivity.this, t.getMessage(), Toast.LENGTH_LONG)
.show();
}
if (!cameraConfigured) {
Camera.Parameters parameters=camera.getParameters();
Camera.Size size=getBestPreviewSize(width, height,
parameters);
if (size!=null) {
parameters.setPreviewSize(size.width, size.height);
camera.setParameters(parameters);
cameraConfigured=true;
}
}
}
}
private void startPreview() {
if (cameraConfigured && camera!=null) {
camera.startPreview();
inPreview=true;
crossfade();
if(urlsPassed){
myAdapter = new vpAdapter(this, arrayURL);
vp = (ViewPager) findViewById(R.id.viewpager);
vp.setAdapter(myAdapter);
vp.setCurrentItem(0);
}
}
}
SurfaceHolder.Callback surfaceCallback=new SurfaceHolder.Callback() {
@Override
public void surfaceCreated(SurfaceHolder holder) {
// no-op -- wait until surfaceChanged()
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,int height) {
Camera.Parameters parameters = camera.getParameters();
parameters.setFocusMode(Camera.Parameters.FOCUS_MODE_AUTO);
camera.setParameters(parameters);
initPreview(width, height);
startPreview();
camera.autoFocus(null);
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
// no-op
}
};
}