为什么会出现空指针异常？相机应用

Question

我收到以下崩溃报告

Failure delivering result ResultInfo{who=null, request=1, result=-1, data=Intent { act=inline-data dat=content://media/external/images/media/3322 (has extras) }} to activity {com.example.instareport/com.example.instareport.MainActivity}: java.lang.NullPointerException

我的 fragment_main.xml 看起来像这样

<RelativeLayout 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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.instareport.MainActivity$PlaceholderFragment" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

    <ImageView 
        android:layout_height="wrap_content" 
        android:layout_width="wrap_content" 
        android:visibility="visible"
        android:id="@+id/imageView1" />
</RelativeLayout>

我的 MainActivity 类在下面

public class MainActivity extends Activity {

    static final int REQUEST_IMAGE_CAPTURE = 1;
    private ImageView mImageView;
    private Bitmap  imageBitmap;

    private void dispatchTakePictureIntent() {
        Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        if (takePictureIntent.resolveActivity(getPackageManager()) != null) {
            startActivityForResult(takePictureIntent, REQUEST_IMAGE_CAPTURE);
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == REQUEST_IMAGE_CAPTURE && resultCode == RESULT_OK) {
            super.onActivityResult(requestCode, resultCode, data);
            Bundle extras = data.getExtras();
            imageBitmap = (Bitmap) extras.get("data");
            mImageView.setImageBitmap(imageBitmap);
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mImageView = (ImageView)findViewById(R.id.imageView1);
        if (savedInstanceState == null) {
            getFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment()).commit();
        }
        dispatchTakePictureIntent();
    }

    @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;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container,
                    false);
            return rootView;
        }
    }

}

基本上，当应用程序启动时，它应该调用相机应用程序，因为它有一个意图，当我按下快门按钮时，我按下确定（接受图像），然后它开始崩溃.

我尝试在下一行插入断点，这就是代码抛出异常的地方

mImageView.setImageBitmap(imageBitmap);

为什么会这样？我尝试从官方 Android 网站和 Android 教程的角度关注 Android 教程。

谢谢

已编辑。

这里是日志猫

07-17 21:16:12.131: W/dalvikvm(21693): threadid=1: thread exiting with uncaught exception (group=0x41522438)
07-17 21:16:12.191: E/AndroidRuntime(21693): FATAL EXCEPTION: main
07-17 21:16:12.191: E/AndroidRuntime(21693): java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1, result=-1, data=Intent { act=inline-data dat=content://media/external/images/media/3322 (has extras) }} to activity {com.example.instareport/com.example.instareport.MainActivity}: java.lang.NullPointerException
07-17 21:16:12.191: E/AndroidRuntime(21693):    at android.app.ActivityThread.deliverResults(ActivityThread.java:3205)
07-17 21:16:12.191: E/AndroidRuntime(21693):    at android.app.ActivityThread.handleSendResult(ActivityThread.java:3248)
07-17 21:16:12.191: E/AndroidRuntime(21693):    at android.app.ActivityThread.access$1100(ActivityThread.java:138)
07-17 21:16:12.191: E/AndroidRuntime(21693):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1252)
07-17 21:16:12.191: E/AndroidRuntime(21693):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-17 21:16:12.191: E/AndroidRuntime(21693):    at android.os.Looper.loop(Looper.java:137)
07-17 21:16:12.191: E/AndroidRuntime(21693):    at android.app.ActivityThread.main(ActivityThread.java:4911)
07-17 21:16:12.191: E/AndroidRuntime(21693):    at java.lang.reflect.Method.invokeNative(Native Method)
07-17 21:16:12.191: E/AndroidRuntime(21693):    at java.lang.reflect.Method.invoke(Method.java:511)
07-17 21:16:12.191: E/AndroidRuntime(21693):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
07-17 21:16:12.191: E/AndroidRuntime(21693):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
07-17 21:16:12.191: E/AndroidRuntime(21693):    at dalvik.system.NativeStart.main(Native Method)
07-17 21:16:12.191: E/AndroidRuntime(21693): Caused by: java.lang.NullPointerException
07-17 21:16:12.191: E/AndroidRuntime(21693):    at com.example.instareport.MainActivity.onActivityResult(MainActivity.java:66)
07-17 21:16:12.191: E/AndroidRuntime(21693):    at android.app.Activity.dispatchActivityResult(Activity.java:5492)
07-17 21:16:12.191: E/AndroidRuntime(21693):    at android.app.ActivityThread.deliverResults(ActivityThread.java:3201)
07-17 21:16:12.191: E/AndroidRuntime(21693):    ... 11 more

Answer 1

public class MainActivity extends Activity {

    static final int REQUEST_IMAGE_CAPTURE = 1;
    private ImageView mImageView;
    private Bitmap imageBitmap;

    private void dispatchTakePictureIntent() {
        Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        if (takePictureIntent.resolveActivity(getPackageManager()) != null) {
            startActivityForResult(takePictureIntent, REQUEST_IMAGE_CAPTURE);
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == REQUEST_IMAGE_CAPTURE && resultCode == RESULT_OK) {
            super.onActivityResult(requestCode, resultCode, data);
            Bundle extras = data.getExtras();
            imageBitmap = (Bitmap) extras.get("data");
            // imageBitmap = (Bitmap) data.getExtras().get("data");
            mImageView.setImageBitmap(imageBitmap);
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mImageView = (ImageView) findViewById(R.id.imageView1);
        dispatchTakePictureIntent();
    }

    @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;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }



}

删除fragment_main.xml。并编辑activity_main.xml：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.instareport.MainActivity"
    tools:ignore="MergeRootFrame" >

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

如果您检索的位图是可以接受的，那么就这样做。如果它的尺寸太小，你可以在这里得到更好的解决方案http://pastebin.com/NF9yu0sa

Answer 2

您确定是 null 还是 data 或 extras？ （如果没有，请快速检查）。 另外，你试过没有“超级”行吗？

抱歉，我还不能做 cmets。

Answer 3

NullPointer 异常的原因是你没有初始化 Bitmap 变量。您的代码可能是这样的：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mImageView = (ImageView)findViewById(R.id.imageView1);
    bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.imageView1);
    ****Rest of your code ********
    }