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
但是我在方法中出现错误
onActivityResult:,java.lang.NullPointerException: Attempt to invoke
virtual method ‘java.lang.Object
android.os.Bundle.get(java.lang.String)’ on a null object reference
这行给出了错误：
Bitmap imageBitmap = (Bitmap) extras.get("data");
当我注释掉这一行时,该应用程序将以某种方式工作：
takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, photoURI);
我的整个代码位于：
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中
<?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中
<?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="${applicationId}.fileprovider"
android:exported="false"
android:grantUriPermissions="true">
<meta-data
android:name="android.support.FILE_PROVIDER_PATHS"
android:resource="@xml/file_paths" />
</provider>
</application>
</manifest>
file_paths.xml
<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
<external-path name="images" path="."/>
<external-path name="external_files" path="."/>
</paths>
解决方法:
如下更改您的文件提供者
<provider
android:name="android.support.v4.content.FileProvider"
android:authorities="${applicationId}.fileprovider"
android:exported="false"
android:grantUriPermissions="true">
<meta-data
android:name="android.support.FILE_PROVIDER_PATHS"
android:resource="@xml/file_paths" />
</provider>
和你的file_path.xml如下
<?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>
对于图像捕获,请使用此意图
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内部,您需要按以下方式更改代码
@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;
}
}
}
而且,如果要从onActivityResult获取位图,则需要引用此链接Click here