我是JAVA的新手，我正在尝试使用Google培训文档学习android开发。我写了一些使用此培训的代码module
这基本上是调用相机意图 - ＆gt;单击图像，然后将图像写入外部存储（SD卡）的外部根目录。使用代码我可以使用现有的相机应用程序成功点击照片，我可以查看缩略图，但当我尝试导航到文件夹（有我的包名称）时，我不是能够查看通过应用程序点击的图像，即包含我的包名称的文件夹，但其中没有图像文件。
从下面的代码可以看出，我已经实现了createImageFile（）函数来创建外部存储中的图像文件，并且在addListenerOnButton（）函数内部我已经将createImageFile（）的返回值赋给了照片uri 。这不会创建一个图像文件吗？或者我错过了介于两者之间的任何步骤。我研究了一下，发现“write（）”方法应该实现，以便将图像数据写入由createImageFile（）函数创建的文件路径，但由于我是新手，我试过但我无法想象我应该在哪里实现write（）方法以及应该将哪些数据传递给它。
以下是我的代码 -
package com.app.simple.simplecamera;
import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.net.Uri;
import android.os.Environment;
import android.provider.MediaStore;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.support.v4.content.FileProvider;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.ImageView;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import java.io.FileOutputStream;
import java.io.IOException;
import android.widget.Toast;
import static android.app.Activity.RESULT_OK;
/**
* A placeholder fragment containing a simple view.
*/
public class MainActivityFragment extends Fragment {
public MainActivityFragment() {
}
/**creating View instance*/
View rootview;
/**setting image capture intent to 1**/
static final int REQUEST_IMAGE_CAPTURE = 1;
//static final int RESULT_OK = 1;
Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
Context context;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
/**instantiating rootview to infalter,so that whenever
* fragment is inflated the camera fucntion will be called**/
rootview = inflater.inflate(R.layout.fragment_main, container, false);
/**calling the public funtion addlistenerbutton so as to invoke camera intent**/
addListenerOnButton();
// getActivity().setResult(RESULT_OK);
/**return the rootview instance whenever oncreate function is invoked in fragment**/
return rootview;
}
/**setting image capture intent to 1**/
//static final int REQUEST_IMAGE_CAPTURE = 1;
//static final int RESULT_OK = 1;
//Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
/**public function for registering button action**/
/**public void addListenerOnButton(){*/
String mCurrentPhotoPath;
public File createImageFile() throws IOException{
//create a timestamp for the file
String timestamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
//the filename should be as below
String imageFileName = "JPEG" + timestamp + "_";
/**assiging a directory to store the file
here the getExternalFilesDir is accessed via the getActivity()(since it's inside a fragement
and DIRECTORY_PICTURES on the device is allocated for storage**/
File storageDir = getActivity().getExternalFilesDir(Environment.DIRECTORY_PICTURES);
//a temp file is created
File image = File.createTempFile(
imageFileName, /* prefix */
".jpg", /* suffix */
storageDir /* directory */
);
mCurrentPhotoPath = "file:" + image.getAbsolutePath();
//FileOutputStream out = new FileOutputStream(image);
//out.write(mCurrentPhotoPath.getBytes());
//galleryAddPic();
return image;
}
public void addListenerOnButton(){
/**creating a button instance and assiging it to the
* oncreateview function via the rootview object*/
Button button = (Button) rootview.findViewById(R.id.button);
/**setOnClickListener contains the camera action within it**/
button.setOnClickListener(new View.OnClickListener(){
/**onClick fucntion to invoke the exisitng camera app via the camera intent**/
public void onClick(View v) {
/*Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);*/
/**if camera exists, which is checked by the getpackagemanager fucntion, then capture image**/
if (takePictureIntent.resolveActivity(getActivity().getPackageManager()) != null) {
//startActivityForResult(takePictureIntent, REQUEST_IMAGE_CAPTURE);
Context context = getContext().getApplicationContext();
// Create the File where the photo should go
File photoFile = null;
try{
photoFile = createImageFile();
}
catch (IOException ex){
// Error occurred while creating the File
Toast toast = Toast.makeText(context, "There was a problem saving the photo...", Toast.LENGTH_SHORT);
toast.show();
}
// File pictureFile = createPhotoFile();
// Continue only if the File was successfully created
if (photoFile != null){
//Uri photoURI = FileProvider.getUriForFile(this, "com.app.simple.simplecamera.fileprovider", photoFile);
Uri photoURI = FileProvider.getUriForFile(context, "com.app.simple.simplecamera.fileprovider", photoFile);
takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, photoURI);
//getActivity().setResult(RESULT_OK,takePictureIntent);
startActivityForResult(takePictureIntent, REQUEST_IMAGE_CAPTURE);
//startActivityForResult(takePictureIntent, RESULT_OK)
}
}
}
});
}
@Override
///**overriding the onactivityresult method so that it creates a tumbnail
// * it takes int he request_image_capture value from addlistenronbutton method
// * result code formthe camera activity inside the addlistneronbiutton method
// * and data from the intent that invokes the camera and takes picture**/
public void onActivityResult(int requestCode, int resultCode, Intent data){
/**checking if request i simagecapture and result is ok**/
if (requestCode == REQUEST_IMAGE_CAPTURE && resultCode == RESULT_OK){
Bundle extras = data.getExtras();
/**creating a data bundle with teh object extra**/
Bundle extras = data.getExtras();
/**creating bitmap from the captured image data which is etched from
* the intent data inside addlistneronbutton**/
Bitmap imageBitmap = (Bitmap) extras.get("data");
/**creating a placeholder for the image thumbnail using the Imageview instance and the corresponding xml image placeholder "result"
* refer the fragment xml for the image placeholder**/
ImageView imageView = (ImageView)rootview.findViewById(R.id.result);
imageView.setImageBitmap(imageBitmap);
}
}
}
编辑 - 我忘了提到onActivityResult（）在'boolean android.graphics.Bitmap.compress
上抛出一个空指针异常以下是我的堆栈跟踪 - AndroidRuntime：FATAL EXCEPTION：主要 处理：com.app.simple.simplecamera，PID：641 java.lang.RuntimeException：将结果ResultInfo {who = null，request = 65537，result = -1，data = null}传递给activity {com.app.simple.simplecamera / com.app.simple.simplecamera.MainActivity}： java.lang.NullPointerException：尝试在空对象引用上调用虚方法'boolean android.graphics.Bitmap.compress（android.graphics.Bitmap $ CompressFormat，int，java.io.OutputStream）' 在android.app.ActivityThread.deliverResults（ActivityThread.java:3948） 在android.app.ActivityThread.handleSendResult（ActivityThread.java:3991） 在android.app.ActivityThread.-wrap16（ActivityThread.java） 在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1542） 在android.os.Handler.dispatchMessage（Handler.java:111） 在android.os.Looper.loop（Looper.java:207） 在android.app.ActivityThread.main（ActivityThread.java:5769） at java.lang.reflect.Method.invoke（Native Method） 在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:789） 在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:679） 引起：java.lang.NullPointerException：尝试在空对象引用上调用虚方法'boolean android.graphics.Bitmap.compress（android.graphics.Bitmap $ CompressFormat，int，java.io.OutputStream）' 在com.app.simple.simplecamera.MainActivityFragment.onActivityResult（MainActivityFragment.java:176） 在android.support.v4.app.FragmentActivity.onActivityResult（FragmentActivity.java:175） 在android.app.Activity.dispatchActivityResult（Activity.java:6845） 在android.app.ActivityThread.deliverResults（ActivityThread.java:3944） 在android.app.ActivityThread.handleSendResult（ActivityThread.java:3991） 在android.app.ActivityThread.-wrap16（ActivityThread.java） 在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1542） 在android.os.Handler.dispatchMessage（Handler.java:111） 在android.os.Looper.loop（Looper.java:207） 在android.app.ActivityThread.main（ActivityThread.java:5769） at java.lang.reflect.Method.invoke（Native Method） 在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:789） 在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:679） I /处理：发送信号。 PID：641 SIG：9 断开与目标VM的连接，地址：'localhost：8600'，transport：'socket'