它与前置摄像头完美配合，但无法使用后置摄像头。
在IF语句中，条件必须是（cameraId＆lt; 1）对吗？我是对的吗？ 无法弄清楚导致错误的原因。
此外，当条件变为camId＆gt; 0，它给出了Toast消息。很明显，返回的值必须是0，如预期的那样。那为什么会导致错误？
这是我的代码和Logcat：
package com.iamtheonewhoknocks.toolkit;
import android.app.Activity;
import android.content.pm.PackageManager;
import android.hardware.Camera;
import android.hardware.Camera.CameraInfo;
import android.os.Bundle;
import android.util.Log;
import android.widget.FrameLayout;
import android.widget.Toast;
public class MagnifyActivity extends Activity { // same as MirrorActivity with
// different camPreview
// Fields -----------------------------------------------------------------
private Camera camera = null;
private MirrorViewmg camPreview = null;
private FrameLayout previewLayout = null;
private int cameraId = -1 ;
// Methods ----------------------------------------------------------------
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_magnify);
// Find out if we even have a camera
if (!getPackageManager()
.hasSystemFeature(PackageManager.FEATURE_CAMERA)) {
Toast.makeText(this, "No camera feature on this device",
Toast.LENGTH_SHORT).show();
} else {
// Get the ID of the back facing camera
cameraId = findFirstBackFacingCamera();
//Log.d(DEBUG_TAG,"value of cameraid=", cameraId);
// If we have a valid camera
if (cameraId < 1) {
// Get the preview frame and strip it of all of it's views
previewLayout = (FrameLayout) findViewById(R.id.camPreviewmg);
previewLayout.removeAllViews();
// Start the camera
startCameraInLayout(previewLayout, cameraId);
} else {
Toast.makeText(this, "No back facing camera found",
Toast.LENGTH_SHORT).show();
}
}
}
@Override
protected void onPause() {
if (camera != null) {
camera.release();
camera = null;
}
super.onPause();
}
@Override
protected void onResume() {
super.onResume();
if (camera == null && previewLayout != null) {
previewLayout.removeAllViews();
startCameraInLayout(previewLayout, cameraId);
}
}
private int findFirstBackFacingCamera() {
int foundId = -1;
int numCams = Camera.getNumberOfCameras();
for (int camId = 0; camId < numCams; camId++) {
// Get the camera information
CameraInfo info = new CameraInfo();
Camera.getCameraInfo(camId, info);
// Check to see if this is a back facing camera
if (info.facing == CameraInfo.CAMERA_FACING_BACK) {
foundId = camId;
break;
}
}
return foundId;
}
private void startCameraInLayout(FrameLayout layout, int cameraId) {
camera = Camera.open(cameraId);
if (camera != null) {
// Create a new MirrorView object and
// add the view to the FrameLayout
camPreview = new MirrorViewmg(this, camera);
layout.addView(camPreview);
}
}
/*
* @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the
* menu; this adds items to the action bar if it is present.
* getMenuInflater().inflate(R.menu.magnify, menu); return true; }
*/
}
日志：
04-23 21:56:36.885: D/AndroidRuntime(31421): Shutting down VM
04-23 21:56:36.885: W/dalvikvm(31421): threadid=1: thread exiting with uncaught exception (group=0x416b0d40)
04-23 21:56:36.889: E/AndroidRuntime(31421): FATAL EXCEPTION: main
04-23 21:56:36.889: E/AndroidRuntime(31421): Process: com.iamtheonewhoknocks.toolkit, PID: 31421
04-23 21:56:36.889: E/AndroidRuntime(31421): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.iamtheonewhoknocks.toolkit/com.iamtheonewhoknocks.toolkit.MagnifyActivity}: java.lang.NullPointerException
04-23 21:56:36.889: E/AndroidRuntime(31421): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
04-23 21:56:36.889: E/AndroidRuntime(31421): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2269)
04-23 21:56:36.889: E/AndroidRuntime(31421): at android.app.ActivityThread.access$800(ActivityThread.java:139)
04-23 21:56:36.889: E/AndroidRuntime(31421): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
04-23 21:56:36.889: E/AndroidRuntime(31421): at android.os.Handler.dispatchMessage(Handler.java:102)
04-23 21:56:36.889: E/AndroidRuntime(31421): at android.os.Looper.loop(Looper.java:136)
04-23 21:56:36.889: E/AndroidRuntime(31421): at android.app.ActivityThread.main(ActivityThread.java:5102)
04-23 21:56:36.889: E/AndroidRuntime(31421): at java.lang.reflect.Method.invokeNative(Native Method)
04-23 21:56:36.889: E/AndroidRuntime(31421): at java.lang.reflect.Method.invoke(Method.java:515)
04-23 21:56:36.889: E/AndroidRuntime(31421): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
04-23 21:56:36.889: E/AndroidRuntime(31421): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
04-23 21:56:36.889: E/AndroidRuntime(31421): at dalvik.system.NativeStart.main(Native Method)
04-23 21:56:36.889: E/AndroidRuntime(31421): Caused by: java.lang.NullPointerException
04-23 21:56:36.889: E/AndroidRuntime(31421): at com.iamtheonewhoknocks.toolkit.MirrorViewmg.<init>(MirrorViewmg.java:22)
04-23 21:56:36.889: E/AndroidRuntime(31421): at com.iamtheonewhoknocks.toolkit.MagnifyActivity.startCameraInLayout(MagnifyActivity.java:94)
04-23 21:56:36.889: E/AndroidRuntime(31421): at com.iamtheonewhoknocks.toolkit.MagnifyActivity.onCreate(MagnifyActivity.java:43)
04-23 21:56:36.889: E/AndroidRuntime(31421): at android.app.Activity.performCreate(Activity.java:5248)
04-23 21:56:36.889: E/AndroidRuntime(31421): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1110)
04-23 21:56:36.889: E/AndroidRuntime(31421): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2173)
04-23 21:56:36.889: E/AndroidRuntime(31421): ... 11 more
04-23 21:56:38.418: I/Process(31421): Sending signal. PID: 31421 SIG: 9
MainActivity.java
package com.iamtheonewhoknocks.toolkit;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageButton;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
flashlightButton();
calculatorButton();
mirrorButton();
converterButton();
mgglassButton();
timerButton();
}
private void flashlightButton() {
ImageButton flButton = (ImageButton) findViewById(R.id.flashButton);
flButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this,
FlashlightActivity.class));
}
});
}
private void calculatorButton() {
ImageButton flButton = (ImageButton) findViewById(R.id.calcButton);
flButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this,
CalculatorActivity.class));
}
});
}
private void mirrorButton() {
ImageButton mrButton = (ImageButton) findViewById(R.id.mirrorButton);
mrButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this,
MirrorActivity.class));
}
});
}
private void converterButton() {
ImageButton flButton = (ImageButton) findViewById(R.id.converterButton);
flButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this,
ConverterActivity.class));
}
});
}
private void mgglassButton() {
ImageButton mrButton = (ImageButton) findViewById(R.id.mglassButton);
mrButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this,
MagnifyActivity.class));
}
});
}
private void timerButton() {
ImageButton mrButton = (ImageButton) findViewById(R.id.timerButton);
mrButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this, TimerActivity.class));
}
});
}
/*
* @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; }
*/
}
答案 0 :(得分：0)
条件应为cameraid >= 0。