android - 尝试打开前置摄像头时出现异常

Question

我无法获得前置摄像头（摄像头ID 1）。当我尝试运行以下代码时，屏幕上会出现open cam #1 failed。

附上一个片段。任何帮助将不胜感激（我在nexus 4上尝试）。

Tester.java

package com.example.cam;

import java.util.HashMap;
import java.util.Iterator;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.pm.PackageManager;
import android.hardware.Camera;
import android.os.Bundle;
import android.view.Menu;
import android.widget.Toast;

public class Tester extends Activity {
    private static final int[] camIds = { Camera.CameraInfo.CAMERA_FACING_BACK, Camera.CameraInfo.CAMERA_FACING_FRONT };
    @SuppressLint("UseSparseArrays")
    private final HashMap<Integer, Camera> camMap = new HashMap<Integer, Camera>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        return true;
    }

    @Override
    protected void onResume() {
        super.onResume();
        if (!checkCameraHardware())
            finish();
        getCameras();
        releaseCamera();
    }

    @Override
    protected void onPause() {
        super.onPause();
        releaseCamera();
    }

    @Override
    protected void onStop() {
        super.onStop();
        releaseCamera();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        releaseCamera();
    }

    private final void doToast(final String message) {
        Toast.makeText(this, message, Toast.LENGTH_SHORT).show();
    }

    private final void getCameras() {
        for (int camId : camIds)
            try {
                camMap.put(camId, Camera.open(camId));
                doToast("open cam #" + camId + " succeeded");
            } catch (Exception e) {
                doToast("open cam #" + camId + " failed");
            }
    }

    private final void releaseCamera() {
        final Iterator<Integer> iter = camMap.keySet().iterator();
        while (iter.hasNext())
            camMap.remove(iter.next()).release();
    }

    private final boolean checkCameraHardware() {
        if (getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA))
            return camIds.length <= Camera.getNumberOfCameras(); 
        else
            return false;
    }
}

的AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.cam"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="19"
        android:targetSdkVersion="19" />

    <uses-permission android:name="android.permission.CAMERA" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.RECORD_AUDIO" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
    <uses-permission android:name="android.permission.CAPTURE_AUDIO_OUTPUT" />
    <uses-permission android:name="android.permission.CAPTURE_SECURE_VIDEO_OUTPUT" />
    <uses-permission android:name="android.permission.CAPTURE_VIDEO_OUTPUT" />
    <uses-permission android:name="android.permission.FLASHLIGHT" />

    <uses-feature
        android:name="android.hardware.camera"
        android:required="true" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.cam.Tester"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>    
</manifest>