我一直在寻找一个如何在我的应用中实现个人资料图片更改的示例。我想允许人们使用Parse.com添加/更改他们的个人资料图片（类似于今天的所有社交媒体应用）。
例如： Twitter，Facebook，Instagram等等，它们都允许您拍摄/上传个人资料图片，并保存该图片，以后可以查看。
我没有找到任何材料来解决如何做这样的事情，似乎没有其他任何事情可以理解我在这里想要实现的目标：
An Image Downloaded From Parse Stay On Screen Even After You Exit And Reopen App?
到目前为止，在我的应用程序中，用户可以使用相机意图拍摄照片或从图库上传图像，该图像将在图像视图中完美显示。
问题是：当我退出并重新打开应用时，图片视图中的图片不再显示（它已消失）。
我该如何解决这个问题？
MainActivity：
public class MainActivity extends AppCompatActivity {
public static final int TAKE_PIC_REQUEST_CODE = 0;
public static final int CHOOSE_PIC_REQUEST_CODE = 1;
public static final int MEDIA_TYPE_IMAGE = 2;
private Uri mMediaUri;
private TextView mChangeProfilePic;
protected ImageView mPreviewImageView;
private Button mSaveChangesBtn;
public ImageView mProfilePic;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
//Initialize variables
mChangeProfilePic = (TextView) findViewById(R.id.changeProfileImageTxt);
mPreviewImageView = (ImageView) findViewById(R.id.profileImage);
mSaveChangesBtn = (Button) findViewById(R.id.saveProfileChangesBtn);
mSaveChangesBtn.setEnabled(false);
final Button mNextBtn = (Button) findViewById(R.id.NextBtn);
mNextBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intentNext = new Intent(MainActivity.this, SecondActivity.class);
startActivity(intentNext);
}
});
//Change profile image
//set onlClick to TextView
mChangeProfilePic.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(getApplicationContext(), "Change Pic Pressed", Toast.LENGTH_SHORT).show();
//show dialog
AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
builder.setTitle("Upload or Take a photo");
builder.setPositiveButton("Upload", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
//upload image
Intent choosePictureIntent = new Intent(Intent.ACTION_GET_CONTENT);
choosePictureIntent.setType("image/*");
startActivityForResult(choosePictureIntent, CHOOSE_PIC_REQUEST_CODE);
mSaveChangesBtn.setEnabled(true);
}
});
builder.setNegativeButton("Take Photo", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
//take photo
Intent takePicture = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
mMediaUri = getOutputMediaFileUri(MEDIA_TYPE_IMAGE);
if (mMediaUri == null) {
//display error
Toast.makeText(getApplicationContext(), "Sorry there was an error! Try again.", Toast.LENGTH_LONG).show();
mSaveChangesBtn.setEnabled(false);
} else {
takePicture.putExtra(MediaStore.EXTRA_OUTPUT, mMediaUri);
startActivityForResult(takePicture, TAKE_PIC_REQUEST_CODE);
mSaveChangesBtn.setEnabled(true);
}
}
});
AlertDialog dialog = builder.create();
dialog.show();
}
});//End change profile image onClick Listener
//Save profile changes button
//Also uploads content to parse and pulls it back same time
mSaveChangesBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//create parse object for image to upload
final ParseObject imageUpload = new ParseObject("ImageUploads");
try {
//convert image to bytes for upload.
byte[] fileBytes = FileHelper.getByteArrayFromFile(MainActivity.this, mMediaUri);
if (fileBytes == null) {
//there was an error
Toast.makeText(getApplicationContext(), "There was an error. Try again!", Toast.LENGTH_LONG).show();
mSaveChangesBtn.setEnabled(false);
} else {
fileBytes = FileHelper.reduceImageForUpload(fileBytes);
String fileName = FileHelper.getFileName(MainActivity.this, mMediaUri, "image");
final ParseFile file = new ParseFile(fileName, fileBytes);
imageUpload.saveEventually(new SaveCallback() {
@Override
public void done(ParseException e) {
if (e == null) {
imageUpload.put("imageContent", file);
imageUpload.saveInBackground(new SaveCallback() {
@Override
public void done(ParseException e) {
Toast.makeText(getApplicationContext(), "Success Uploading iMage!", Toast.LENGTH_LONG).show();
//Retrieve the recently saved image from Parse
queryParseProfileImages(imageUpload);
mSaveChangesBtn.setEnabled(false);
}
}
);
} else {
//there was an error
Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_LONG).show();
mSaveChangesBtn.setEnabled(false);
}
}
});
}
} catch (Exception e1) {
Toast.makeText(getApplicationContext(), e1.getMessage(), Toast.LENGTH_LONG).show();
}
}//End onClick(View v)
});//End onClick Listener
//This method queries for the most recent picture taken
ParseQuery<ParseObject> imagesQuery = new ParseQuery<>("ImageUploads");
imagesQuery.orderByDescending("createdAt");
imagesQuery.findInBackground(new FindCallback<ParseObject>() {
@Override
public void done(List<ParseObject> images, ParseException e) {
if(e == null){
//for (int i = 0; i < images.size(); i++) {
final String imgUrl = images.get(0).getParseFile("imageContent").getUrl();
mProfilePic = (ImageView) findViewById(R.id.profileImage);
Picasso.with(MainActivity.this).load(imgUrl).into(mProfilePic);
//}
//images.pinInBackground();
//profileImageId = profImgObj.getObjectId();
//Log.d(TAG, "The object id is: " + profileImageId);
}else{
Toast.makeText(MainActivity.this, e.getMessage(), Toast.LENGTH_LONG).show();
}
}
});
}//End onCreate
//Method containing ParseQuery to download/pull back the image that was uploaded to Parse
//Inside the Image View
private void queryParseProfileImages(final ParseObject imageUploadPassed) {
ParseFile userImageRetrievedObj = (ParseFile) imageUploadPassed.get("imageContent");
userImageRetrievedObj.getDataInBackground(new GetDataCallback() {
public void done(byte[] data, ParseException e) {
if (e == null) {
final String imgUrl = imageUploadPassed.getParseFile("imageContent").getUrl();
mProfilePic = (ImageView) findViewById(R.id.profileImage);
Picasso.with(MainActivity.this).load(imgUrl).into(mProfilePic);
imageUploadPassed.pinInBackground();
} else {
// something went wrong
}
}
});
}
//inner helper method
private Uri getOutputMediaFileUri(int mediaTypeImage) {
if (isExternalStorageAvailable()) {
//get the URI
//get external storage dir
File mediaStorageDir = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES), "UPLOADIMAGES");
//create subdirectore if it does not exist
if (!mediaStorageDir.exists()) {
//create dir
if (!mediaStorageDir.mkdirs()) {
return null;
}
}
//create a file name
//create file
File mediaFile = null;
Date now = new Date();
String timestamp = new SimpleDateFormat("yyyyMMdd_HHmmss", Locale.US).format(now);
String path = mediaStorageDir.getPath() + File.separator;
if (mediaTypeImage == MEDIA_TYPE_IMAGE) {
mediaFile = new File(path + "IMG_" + timestamp + ".jpg");
}
//return file uri
Log.d("UPLOADIMAGE", "FILE: " + Uri.fromFile(mediaFile));
return Uri.fromFile(mediaFile);
} else {
return null;
}
}
//check if external storage is mounted. helper method
private boolean isExternalStorageAvailable() {
String state = Environment.getExternalStorageState();
if (state.equals(Environment.MEDIA_MOUNTED)) {
return true;
} else {
return false;
}
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (resultCode == RESULT_OK) {
if (requestCode == CHOOSE_PIC_REQUEST_CODE) {
if (data == null) {
Toast.makeText(getApplicationContext(), "Image cannot be null!", Toast.LENGTH_LONG).show();
} else {
mMediaUri = data.getData();
//set previews
mPreviewImageView.setImageURI(mMediaUri);
//Bundle extras = data.getExtras();
//Log.e("URI", mMediaUri.toString());
//Bitmap bmp = (Bitmap) extras.get("data");
}
} else {
Intent mediaScanIntent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
mediaScanIntent.setData(mMediaUri);
sendBroadcast(mediaScanIntent);
//set previews
mPreviewImageView.setImageURI(mMediaUri);
}
} else if (resultCode != RESULT_CANCELED) {
Toast.makeText(getApplicationContext(), "Cancelled!", Toast.LENGTH_LONG).show();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.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();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
答案 0 :(得分：4)
首先，我必须说这是一个非常好的问题，我很高兴每个名声不好的人都会提出如此好的问题。
您遇到的问题基本上是Android Activity生命周期的问题。我猜，问题非常简单：我在您的活动onCreate()中看不到从Parse检索图像的地方：您的下载方法仅在onClickListener中调用。
所以我没有把它提到这里，而是将它提取到private方法，类似这样的东西：
修改
private void queryImagesFromParse(){
ParseQuery<ParseObject> imagesQuery = new ParseQuery<>("User");
imagesQuery.findInBackground(new FindCallback<ParseObject>() {
@Override
public void done(List<ParseObject> imagesItems, ParseException e) {
if(e == null){
ParseUser userCurrentOfParse = ParseUser.getCurrentUser();
if(userCurrentOfParse != null) {
//final String imgUrl = imageUploadPassed.getParseFile("imageContent").getUrl();
final String imgUrl = userCurrentOfParse.getParseFile("userProfilePics").getUrl();
mHomeProfilePic = (ImageView) findViewById(R.id.userHomeProfilePicImageView);
Picasso.with(HomeActivity.this).load(imgUrl).into(mHomeProfilePic);
//imageUploadPassed.pinInBackground();
// profileImageId = imageUploadPassed.getObjectId();
//Log.d(TAG, "The object id is: " + profileImageId);
}
}else{
Toast.makeText(HomeActivity.this, e.getMessage(), Toast.LENGTH_LONG).show();
}
}
});
}
（上面的代码只是为了给出一个粗略的想法，如果它编译我会感到惊讶。）
然后，您在onCreate()结束时调用此方法（onStart也可以正常工作，但我更喜欢onCreate()）。当然，你也可以从之前的地方调用这个方法（实际上，如果你真的extract方法Right-Click＆gt; Refractor＆gt; {{1} }）
顺便说一下，您使用Extract Method非常好，但最好使用Picasso的{{1}}对其进行初始化，以便Context代替Activity （应该快1 ns！）
编辑：还要确保图片正在Parse上的User表上传和查询，这样可以确保每个用户都能看到自己的图像（当前登录用户的图像）而不是每个上传下一张图像的其他用户。
希望它有所帮助！