Question

我在这里关注相机上的Android开发人员教程：https://developer.android.com/training/camera/photobasics#java

但是我在方法中出错

onActivityResult：，java.lang.NullPointerException：尝试调用虚方法'java.lang.Object 空对象引用上的android.os.Bundle.get（java.lang.String）'

此行显示错误：

Bitmap imageBitmap = (Bitmap) extras.get("data");

以某种方式，当我注释掉这一行时，该应用程序便可以工作了：

takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, photoURI);

我的整个代码位于此处： https://github.com/europa9/EanScannerForAndroid

MainActivity.java

package one.askit.eanscanner;

import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.icu.text.SimpleDateFormat;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.provider.MediaStore;
import android.support.v4.content.FileProvider;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import java.io.File;
import java.io.IOException;
import java.util.Date;

public class MainActivity extends AppCompatActivity {
    static final int REQUEST_IMAGE_CAPTURE = 1;
    static final int REQUEST_TAKE_PHOTO = 1;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Permission
        checkPermissionExternalRead();
        checkPermissionExternalWrite();
        checkPermissionCamera();

        // Listeners
        listeners();

        FrameLayout frameLayoutCameraPreview = findViewById(R.id.frameLayoutCameraPreview);
        frameLayoutCameraPreview.setVisibility(View.GONE);

    }

    /*- Check permission Read ------------------------------------------------------------------- */
    // Pops up message to user for reading
    private void checkPermissionExternalRead(){
        int MY_PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE = 1;
        if (checkSelfPermission(android.Manifest.permission.READ_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {

            // Should we show an explanation?
            if (shouldShowRequestPermissionRationale(
                    android.Manifest.permission.READ_EXTERNAL_STORAGE)) {
                // Explain to the user why we need to read the contacts
            }

            requestPermissions(new String[]{android.Manifest.permission.READ_EXTERNAL_STORAGE},
                    MY_PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE);

            // MY_PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE is an
            // app-defined int constant that should be quite unique

            return;
        }
    } // checkPermissionRead

    /*- Check permission Write ------------------------------------------------------------------ */
    // Pops up message to user for writing
    private void checkPermissionExternalWrite(){
        int MY_PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE = 1;
        if (checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {

            // Should we show an explanation?
            if (shouldShowRequestPermissionRationale(
                    android.Manifest.permission.WRITE_EXTERNAL_STORAGE)) {
                // Explain to the user why we need to read the contacts
            }

            requestPermissions(new String[]{android.Manifest.permission.WRITE_EXTERNAL_STORAGE},
                    MY_PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE);

            // MY_PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE is an
            // app-defined int constant that should be quite unique

            return;
        }
    } // checkPermissionWrite

    /*- Check permission Camera ----------------------------------------------------------------- */
    public void checkPermissionCamera(){
        int MY_PERMISSIONS_REQUEST_CAMERA = 1;
        if (checkSelfPermission(Manifest.permission.CAMERA)
                != PackageManager.PERMISSION_GRANTED) {

            // Should we show an explanation?
            if (shouldShowRequestPermissionRationale(
                    Manifest.permission.CAMERA)) {
                // Explain to the user why we need to read the contacts
            }

            requestPermissions(new String[]{android.Manifest.permission.CAMERA},
                    MY_PERMISSIONS_REQUEST_CAMERA);

            // MY_PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE is an
            // app-defined int constant that should be quite unique

            return;
        }
    } // checkPermissionInternalRead


    public void listeners(){
        Button buttonScan = findViewById(R.id.buttonScan);
        buttonScan.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                buttonScanClicked();
            }
        });

    }
    public void buttonScanClicked(){
        // Scan text
        TextView TextViewScan = findViewById(R.id.TextViewScan);
        TextViewScan.setText("Now scanning");

        // Take picture
        dispatchTakePictureIntent();
    }

    private void dispatchTakePictureIntent() {
        Intent picIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE).addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);

        String file_path = Environment.getExternalStorageDirectory().toString() +
                "/" + this.getResources().getString(R.string.app_name);

        File dir = new File(file_path);
        if (!dir.exists())
            dir.mkdirs();
        // IMAGE_PATH = new File(dir, mContext.getResources().getString(R.string.app_name) + AppConstants.USER_ID + System.currentTimeMillis() + ".png");

        File IMAGE_PATH = new File(dir, this.getResources().getString(R.string.app_name) + System.currentTimeMillis() + ".png");

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            picIntent.putExtra(MediaStore.EXTRA_OUTPUT, FileProvider.getUriForFile(this, this.getPackageName() + ".fileprovider", IMAGE_PATH));
        }
        else {
            picIntent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(IMAGE_PATH));
        }

        startActivityForResult(picIntent, REQUEST_TAKE_PHOTO);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == REQUEST_IMAGE_CAPTURE && resultCode == RESULT_OK) {
            Bundle extras = data.getExtras();
            if (extras != null) {
                //Do your logic
                Bitmap imageBitmap = (Bitmap) extras.get("data");
                ImageView imageViewScanPreview = findViewById(R.id.imageViewScanPreview);
                imageViewScanPreview.setImageBitmap(imageBitmap);
            } else {
                //Do something else
                Toast.makeText(this, "Its null!", Toast.LENGTH_LONG).show();
            }

        }
    }

}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <FrameLayout
        android:id="@+id/frameLayoutCameraPreview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1" />

    <ImageView
        android:id="@+id/imageViewScanPreview"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:srcCompat="?attr/colorAccent" />

    <TextView
        android:id="@+id/TextViewScan"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Doint nothing"></TextView>

    <Button
        android:id="@+id/buttonScan"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="Scan" />
</LinearLayout>

AndroidManifest.xml

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

    <uses-feature android:name="android.hardware.camera" android:required="true" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <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"
        android:theme="@style/AppTheme">
        <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" />
        </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="images" path="."/>
    <external-path name="external_files" path="."/>
</paths>

Answer 1

像下面一样更改您的file provider

    <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" />
    </provider>

您的 file_path.xml 如下所示

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <external-path name="images" path="."/>

    <external-path name="external_files" path="."/>

</paths>

要进行图像捕获，请使用此Intent

  Intent picIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE).addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);


        String file_path = Environment.getExternalStorageDirectory().toString() +
                "/" + mContext.getResources().getString(R.string.app_name);

        File dir = new File(file_path);
        if (!dir.exists())
            dir.mkdirs();
       // IMAGE_PATH = new File(dir, mContext.getResources().getString(R.string.app_name) + AppConstants.USER_ID + System.currentTimeMillis() + ".png");

        IMAGE_PATH = new File(dir, mContext.getResources().getString(R.string.app_name) + System.currentTimeMillis() + ".png");

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            picIntent.putExtra(MediaStore.EXTRA_OUTPUT, FileProvider.getUriForFile(mContext, mContext.getPackageName()+".fileprovider", IMAGE_PATH));
        }
        else {
            picIntent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(IMAGE_PATH));
        }

        ((Activity) mContext).startActivityForResult(picIntent, CAMERA_REQUEST);

在onActivityREsult内，您需要按照以下步骤更改代码

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

        int cropperType = 1;
        if (requestCode == REQUEST_IMAGE_CAPTURE) {

            switch (resultCode) {
                case Activity.RESULT_OK:

                     String imagePAth= Uri.fromFile(IMAGE_PATH);
                GlideApp.with(this).load(imagePAth).diskCacheStrategy(DiskCacheStrategy.ALL).skipMemoryCache(false).
                        placeholder(R.drawable.default_picture).error(R.drawable.default_picture).dontAnimate().into(YOUR_IMAGEVIEW);

                    break;
                case Activity.RESULT_CANCELED:

                    break;
            }
        }

    }

如果您想要Bitmap中的onActivityResult，则需要引用此链接Click here

Answer 2

有多种方法可以从相机接收位图。

您正在尝试从不存在的其他内容中获取位图。由于将空值强制转换为位图，因此错误发生在访问数据时而非您尝试使用位图时。

如果您通过takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, photoURI);提供输出URI，则大多数Android手机会将照片存储在该URI上，并且您必须通过存储在其中的文件访问位图。如果删除URI，则在Intent中会在照片中提供额外的图片，这就是为什么如果删除该行，代码就起作用的原因。

相机“位图imageBitmap =（Bitmap）extras.get（“ data”）;“给出Nullpointer错误

2 个答案: