Question

我有以下情况，这完全拉我的头发：我正在写一个类来管理Android相机，它扩展了Activity。在该课程内，我有以下代码。会发生什么事情，我总是得到零点异常 - 它的力量接近小朋友 - 在行中说：

startActivityForResult(intent, 0);

但是我得到System.out.println（“intent not null”）;在LogCat中打印好了......

LogCat说：

03-08 22:46:38.584: ERROR/AndroidRuntime(1079): java.lang.NullPointerException
03-08 22:46:38.584: ERROR/AndroidRuntime(1079):     at android.app.Activity.startActivityForResult(Activity.java:2749)
03-08 22:46:38.584: ERROR/AndroidRuntime(1079):     at com.test.cameratest.startCameraActivity(cameratest.java:39)

在清单中我有：

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera"/>
<activity android:name=".cameratest" />

那么，我做错了什么？为什么startActivityForResult总是抛出空？？

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

/** As per suggestion tried to change the method from protected to private or public
but still have the same problem */
protected void startCameraActivity()
{
   String path = (new StringBuilder()).append(Environment.getExternalStorageDirectory()).append("/images/test.jpg").toString();

    System.out.println("started");

    File file = new File(path);

    System.out.println(path);

    Uri outputFileUri = Uri.fromFile(file);

    Intent intent = new Intent("android.media.action.IMAGE_CAPTURE");

    intent.putExtra("output", outputFileUri);
    /** Removed as per suggestion 
    if (intent!=null)
    {
        System.out.println("intent not null");
            **startActivityForResult(intent, 0);**
    }
    */    

    **startActivityForResult(intent, 0);** <== null pointer exception
}

编辑：

根据建议，我在Android 2.1r2框架的Activity.java上查看了第2749行，这里是代码：

public void startActivityForResult(Intent intent, int requestCode) {
        if (mParent == null) {

               **** Line 2749 is the folowing                
               Instrumentation.ActivityResult ar =
                mInstrumentation.execStartActivity(
                    this, mMainThread.getApplicationThread(), mToken, this,
                    intent, requestCode);
               ****

            if (ar != null) {
                mMainThread.sendActivityResult(
                    mToken, mEmbeddedID, requestCode, ar.getResultCode(),
                    ar.getResultData());
            }
            if (requestCode >= 0) {
                // If this start is requesting a result, we can avoid making
                // the activity visible until the result is received.  Setting
                // this code during onCreate(Bundle savedInstanceState) or onResume() will keep the
                // activity hidden during this time, to avoid flickering.
                // This can only be done when a result is requested because
                // that guarantees we will get information back when the
                // activity is finished, no matter what happens to it.
                mStartedActivity = true;
            }
        } else {
            mParent.startActivityFromChild(this, intent, requestCode);
        }
    }

第2749行用双**标记但是，我没有看到该代码存在问题

EDITED

忘了解释我怎么称呼它：

cameratest cam = new cameratest();
cam.startCameraActivity();

Answer 1

尝试Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);

我认为这些常量字符串的引用在它们的值为时必然是相等的。

Answer 2

以下文章提供了此问题的解决方法，不仅适用于三星设备（我在HTC Desire Z运行模块化Android 2.3.7上有相同的问题）：

http://kevinpotgieter.wordpress.com/2011/03/30/null-intent-passed-back-on-samsung-galaxy-tab/

我意识到这很尴尬，但它确实有效。总而言之，它建议放弃尝试获取原始意图，并告诉如何获取处理捕获的照片。

Android：startActivityForResult始终为null并强制关闭我的应用

2 个答案: