接触到一个需求扫一维码的时候很难扫到，后来测试发现，是自动对焦问题。
zxing的自动对焦线程始终都在执行，但是硬件无法支持连续自动对焦，而只在扫描界面启动后进行一次对焦，而我们在扫码的时候不可能保证在同一距离下扫码。
解决方案：
1在 AutoFocusManager类中加入
//在这里插入代码片AutoStopTask autoStopTask;
public class AutoStopTask extends AsyncTask<Object, Object, Object>{
@Override
protected Object doInBackground(Object... params) {
try {
Thread.sleep(AUTO_FOCUS_INTERVAL_MS);
} catch (InterruptedException e) {
// continue
}
synchronized (AutoFocusManager.this) {
start();
}
return null;
}
}
2在 onAutoFocus方法中加上
@Override
public synchronized void onAutoFocus(boolean success, Camera theCamera) {
if (success) {
//自动对焦
outstandingTask = new AutoFocusTask();
outstandingTask.executeOnExecutor(Executors.newCachedThreadPool());
autoStopTask = new AutoStopTask();
autoStopTask.executeOnExecutor(Executors.newCachedThreadPool());
}
}
3在stop方法添加以下代码 线程也需要每次都停止
if(autoStopTask != null){
autoStopTask.cancel(true);
autoStopTask = null;
}
总结：原理就是利用单次自动对焦设备每次启动都会执行自动对焦的特点，重复启动关闭自动对焦功能，以达到连续自动对焦的目的。
完整类
/*
* Copyright (C) 2012 ZXing authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.xxx.zxing.camera;//你的包名
import android.annotation.SuppressLint;
import android.content.Context;
import android.content.SharedPreferences;
import android.hardware.Camera;
import android.os.AsyncTask;
import android.preference.PreferenceManager;
import android.util.Log;
import com.xxx.zxing.android.PreferencesActivity;
import java.util.ArrayList;
import java.util.Collection;
import java.util.concurrent.Executors;
import java.util.concurrent.RejectedExecutionException;
/**
* 自动聚焦
* @author qichunjie
*
*/
final class AutoFocusManager implements Camera.AutoFocusCallback {
private static final String TAG = AutoFocusManager.class.getSimpleName();
private static final long AUTO_FOCUS_INTERVAL_MS = 2000L;
private static final Collection<String> FOCUS_MODES_CALLING_AF;
static {
FOCUS_MODES_CALLING_AF = new ArrayList<String>(2);
FOCUS_MODES_CALLING_AF.add(Camera.Parameters.FOCUS_MODE_AUTO);
FOCUS_MODES_CALLING_AF.add(Camera.Parameters.FOCUS_MODE_MACRO);
}
private boolean stopped;
private boolean focusing;
private final boolean useAutoFocus;
private final Camera camera;
private AsyncTask<?,?,?> outstandingTask;
AutoFocusManager(Context context, Camera camera) {
this.camera = camera;
SharedPreferences sharedPrefs = PreferenceManager.getDefaultSharedPreferences(context);
String currentFocusMode = camera.getParameters().getFocusMode();
useAutoFocus =
sharedPrefs.getBoolean(PreferencesActivity.KEY_AUTO_FOCUS, true) &&
FOCUS_MODES_CALLING_AF.contains(currentFocusMode);
Log.i(TAG, "Current focus mode '" + currentFocusMode + "'; use auto focus? " + useAutoFocus);
start();
}
@Override
public synchronized void onAutoFocus(boolean success, Camera theCamera) {
focusing = false;
autoFocusAgainLater();
// if (success) {//自动对焦
// outstandingTask = new AutoFocusTask();
outstandingTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
// outstandingTask.executeOnExecutor(Executors.newCachedThreadPool());
// autoStopTask = new AutoStopTask();
autoStopTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
// autoStopTask.executeOnExecutor(Executors.newCachedThreadPool());
// }
}
@SuppressLint("NewApi")
private synchronized void autoFocusAgainLater() {
if (!stopped && outstandingTask == null) {
AutoFocusTask newTask = new AutoFocusTask();
try {
newTask.execute();
outstandingTask = newTask;
} catch (RejectedExecutionException ree) {
Log.w(TAG, "Could not request auto focus", ree);
}
}
}
synchronized void start() {
if (useAutoFocus) {
outstandingTask = null;
if (!stopped && !focusing) {
try {
camera.autoFocus(this);
focusing = true;
} catch (RuntimeException re) {
// Have heard RuntimeException reported in Android 4.0.x+; continue?
Log.w(TAG, "Unexpected exception while focusing", re);
// Try again later to keep cycle going
autoFocusAgainLater();
}
}
}
}
private synchronized void cancelOutstandingTask() {
if (outstandingTask != null) {
if (outstandingTask.getStatus() != AsyncTask.Status.FINISHED) {
outstandingTask.cancel(true);
}
outstandingTask = null;
}
}
synchronized void stop() {
stopped = true;
// if (useAutoFocus) {
// cancelOutstandingTask();
// // Doesn't hurt to call this even if not focusing
// try {
// camera.cancelAutoFocus();
// } catch (RuntimeException re) {
// // Have heard RuntimeException reported in Android 4.0.x+; continue?
// Log.w(TAG, "Unexpected exception while cancelling focusing", re);
// }
// }
if(autoStopTask != null){
//
autoStopTask.cancel(true);
autoStopTask = null;
}
}
private final class AutoFocusTask extends AsyncTask<Object,Object,Object> {
@Override
protected Object doInBackground(Object... voids) {
try {
Thread.sleep(AUTO_FOCUS_INTERVAL_MS);
} catch (InterruptedException e) {
// continue
}
synchronized (AutoFocusManager.this) {
start();
}
return null;
}
}
AutoStopTask autoStopTask;
public class AutoStopTask extends AsyncTask<Object, Object, Object>{
@Override
protected Object doInBackground(Object... params) {
try {
Thread.sleep(AUTO_FOCUS_INTERVAL_MS);
} catch (InterruptedException e) {
// continue
}
synchronized (AutoFocusManager.this) {
// stop();
start();
}
return null;
}
}
}