Question

我正在尝试编写我的第一个Android应用程序，这将涉及拍照并用它做事。

我在线查看了几个教程之后将一些代码放在一起，但是只要点击按钮就会得到以下NullPointerException：

10-03 14:48:00.284 26310-26310/org.broadinstitute.jsnap E/MainActivity: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.XmlResourceParser android.content.pm.ProviderInfo.loadXmlMetaData(android.content.pm.PackageManager, java.lang.String)' on a null object reference
10-03 14:48:00.293 26310-26310/org.broadinstitute.jsnap E/MYAPP: exception
                                                                 java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.XmlResourceParser android.content.pm.ProviderInfo.loadXmlMetaData(android.content.pm.PackageManager, java.lang.String)' on a null object reference
                                                                     at android.support.v4.content.FileProvider.parsePathStrategy(FileProvider.java:583)
                                                                     at android.support.v4.content.FileProvider.getPathStrategy(FileProvider.java:557)
                                                                     at android.support.v4.content.FileProvider.getUriForFile(FileProvider.java:399)
                                                                     at org.broadinstitute.jsnap.MainActivity.takePhoto(MainActivity.java:54)
                                                                     at org.broadinstitute.jsnap.MainActivity.access$000(MainActivity.java:24)
                                                                     at org.broadinstitute.jsnap.MainActivity$1.onClick(MainActivity.java:43)
                                                                     at android.view.View.performClick(View.java:6205)
                                                                     at android.widget.TextView.performClick(TextView.java:11103)
                                                                     at android.view.View$PerformClick.run(View.java:23653)
                                                                     at android.os.Handler.handleCallback(Handler.java:751)
                                                                     at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                     at android.os.Looper.loop(Looper.java:154)
                                                                     at android.app.ActivityThread.main(ActivityThread.java:6682)
                                                                     at java.lang.reflect.Method.invoke(Native Method)
                                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)
                                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)

我不太确定如何解决。这是我的相关代码：

清单：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="org.broadinstitute.jsnap">

    <uses-permission android:name="android.permission.CAMERA" />
    <uses-feature android:name="android.hardware.camera" android:required="true"/>
    <uses-feature android:name="android.hardware.camera.autofocus" />
    <uses-feature android:name="android.hardware.camera.flash" android:required="false"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        >
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <provider
            android:name="android.support.v4.content.FileProvider"
            android:authorities="${applicationId}.fileprovider"
            android:exported="false"
            android:grantUriPermissions="true">
            <meta-data
                android:name="android.support.FILE_PROVIDER_PATHS"
                android:resource="@xml/file_paths"></meta-data>
        </provider>
    </application>

</manifest>

file_paths.xml

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <external-path name="jsnap_images" path="Android/data/org.broadinstitute.jsnap/files/Pictures" />
</paths>

和MainActivity：

package org.broadinstitute.jsnap;

import android.app.Activity;
import android.content.ContentResolver;
import android.content.Intent;
import android.graphics.Bitmap;
import android.net.Uri;
import android.os.Build;
import android.os.Environment;
import android.provider.MediaStore;
import android.support.v4.content.FileProvider;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;
import java.io.File;
import java.io.IOException;
import java.util.jar.Manifest;


public class MainActivity extends Activity {
    private static String logtag = "MainActivity";
    private static int TAKE_PICTURE = 1;
    private static final String AUTHORITY = "org.broadinstitute.jsnap.provider";
    private static final String PHOTOS="photos";
    private static final String FILENAME="jsnap_test.jpeg";
    Uri imageURI;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button cameraButton = (Button)(findViewById(R.id.cam_button));
        cameraButton.setOnClickListener(cameraListener);

    }
    private View.OnClickListener cameraListener = new View.OnClickListener() {
        public void onClick(View v) {
            try {
                takePhoto(v);
            } catch (Exception e) {
                Log.e(logtag, e.toString());
            }
        }
    };
    private void takePhoto(View v){
        Intent intent = new Intent("android.media.action.IMAGE_CAPTURE");
        File photo = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES), FILENAME);
        imageURI=FileProvider.getUriForFile(this, AUTHORITY, photo);
        intent.putExtra(MediaStore.EXTRA_OUTPUT, imageURI);
        // TAKE_PICTURE is a request code saying we want to use the rear-facing camera.
        startActivityForResult(intent, TAKE_PICTURE);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent intent) {
        super.onActivityResult(requestCode, resultCode, intent);

        if(resultCode == Activity.RESULT_OK) {
            Uri selectedImage = imageURI;
            getContentResolver().notifyChange(selectedImage, null);

            ImageView imageView = (ImageView)findViewById(R.id.image_camera);
            ContentResolver cr = getContentResolver();
            Bitmap bitmap;

            try {
                bitmap = MediaStore.Images.Media.getBitmap(cr, selectedImage);
                imageView.setImageBitmap(bitmap);
                Toast.makeText(MainActivity.this, selectedImage.toString(), Toast.LENGTH_SHORT).show();
            } catch(Exception e) {
                Log.e(logtag, e.toString());
            }
        }
    }
}

非常感谢任何帮助。

Answer 1

首先，这个：

android:authorities="${applicationId}.fileprovider"

与此不匹配：

private static final String AUTHORITY = "org.broadinstitute.jsnap.provider";

在两个地方使用相同的算法。因此，将第二行替换为：

private static final String AUTHORITY = BuildConfig.APPLICATION_ID+".fileprovider";

这会让你超越NullPointerException。

第二，这：

File photo = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES), FILENAME);

与此不匹配：

<external-path name="jsnap_images" path="Android/data/org.broadinstitute.jsnap/files/Pictures" />

由于我不知道哪些是您真正想要的，我不能建议修复。

Answer 2

我知道这是一个非常老的问题，但这是供将来的观众使用的答案。因此，我遇到了类似的问题，经过研究，我找到了这种方法的替代方法。

您的意图在这里例如：从路径中查看图像

 val intent = Intent()
 intent.setAction(Intent.ACTION_VIEW)
 val file = File(currentUri)
 intent.setFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION)
 val contentURI = getContentUri(context!!, file.absolutePath)
 intent.setDataAndType(contentURI,"image/*")
 startActivity(intent)

下面的主要功能

private fun getContentUri(context:Context, absPath:String):Uri? {
        val cursor = context.getContentResolver().query(
            MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
            arrayOf<String>(MediaStore.Images.Media._ID),
            MediaStore.Images.Media.DATA + "=? ",
            arrayOf<String>(absPath), null)
        if (cursor != null && cursor.moveToFirst())
        {
            val id = cursor.getInt(cursor.getColumnIndex(MediaStore.MediaColumns._ID))
            return Uri.withAppendedPath(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, Integer.toString(id))
        }
        else if (!absPath.isEmpty())
        {
            val values = ContentValues()
            values.put(MediaStore.Images.Media.DATA, absPath)
            return context.getContentResolver().insert(
                MediaStore.Images.Media.EXTERNAL_CONTENT_URI, values)
        }
        else
        {
            return null
        }
    }

FileProvider.getUriForFile返回NullPointerException

2 个答案: