Question

我有一项活动可以打开另一项活动来获取下载图片。图片返回到我原来的活动并在imageView中休息。这很好。如何保存图像，以便用户稍后返回或杀死应用程序时图像仍然存在。我知道我应该使用共享首选项来获取图像路径而不是保存图像本身，但我不知道该怎么做。

主要活动

public class MainActivity extends Activity {

  private static final int REQUEST_CODE = 1;
  private Bitmap bitmap;
  Button button;
  ImageView imageView;
  String selectedImagePath;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    button=(Button) findViewById(R.id.click);
    imageView=(ImageView) findViewById(R.id.image);
    imageView.setOnLongClickListener(new View.OnLongClickListener() {
        @Override
        public boolean onLongClick(View v) {
            Switch();
            return true;
        }
    });
  }

  public void Switch(){
    imageView = (ImageView) findViewById(R.id.image);
    Intent intent = new Intent(Intent.ACTION_PICK, MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
    startActivityForResult(intent, REQUEST_CODE);
  }

  @Override
  protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode==REQUEST_CODE&&resultCode== Activity.RESULT_OK){
      try {
        Uri selectedImage = data.getData();
        String[] filePathColumn = {MediaStore.Images.Media.DATA};
        Cursor cursor = getContentResolver().query(selectedImage, filePathColumn, null, null, null);
        cursor.moveToFirst();
        int columnIndex = cursor.getColumnIndex(filePathColumn[0]);
        String filePath = cursor.getString(columnIndex);
        Log.v("roni", filePath);
        cursor.close();
        if(bitmap != null && !bitmap.isRecycled())
          {
            bitmap = null;
          }
        bitmap = BitmapFactory.decodeFile(filePath);
        //imageView.setBackgroundResource(0);
        imageView.setImageBitmap(bitmap);
        } catch (Exception e){
          e.printStackTrace();
        }
      }
  }

  @Override
  protected void onPause() {
    super.onPause();
     save();
  }

  public void save() {
    SharedPreferences sp = getSharedPreferences("AppSharedPref", 1); // Open SharedPreferences with name AppSharedPref
    SharedPreferences.Editor editor = sp.edit();
    editor.putString("ImagePath", selectedImagePath); // Store selectedImagePath with key "ImagePath". This key will be then used to retrieve data.
    editor.commit();
  }

  @Override
  protected void onResume() {
    super.onResume();
    restore();
  }

  public void restore(){
    SharedPreferences sp = getSharedPreferences("AppSharedPref", 1);
    selectedImagePath = sp.getString("ImagePath", "");
    bitmap = BitmapFactory.decodeFile(selectedImagePath);
    imageView.setImageBitmap(bitmap);
  }
}

ViewActivity

public class ViewActivity extends ActionBarActivity {
ImageButton imageViews;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_view);
    imageViews = (ImageButton) findViewById(R.id.image);
    Intent intent = getIntent();
    Uri data = intent.getData();
    if (intent.getType().indexOf("image/") != -1)
    {
        imageViews.setImageURI(data);
    }
}

Answer 1

Write方法将Bitmap编码为字符串base64

public static String encodeToBase64(Bitmap image) {
    Bitmap immage = image;
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    immage.compress(Bitmap.CompressFormat.PNG, 100, baos);
    byte[] b = baos.toByteArray();
    String imageEncoded = Base64.encodeToString(b, Base64.DEFAULT);

    Log.d("Image Log:", imageEncoded);
    return imageEncoded;
}

在此方法中传递 yourBitmap ，例如您偏好中的encodeTobase64

        SharedPreferences myPrefrence = getPreferences(MODE_PRIVATE);
        SharedPreferences.Editor editor = myPrefrence.edit();
        editor.putString("namePreferance", itemNAme);
        editor.putString("imagePreferance", encodeToBase64(yourBitmap));
        editor.commit();

当您想要显示图像时，只需使用Bitmap方法将其转换为decodeToBase64

public static Bitmap decodeToBase64(String input) {
    byte[] decodedByte = Base64.decode(input, 0);
    return BitmapFactory.decodeByteArray(decodedByte, 0, decodedByte.length);
}

这里是再次获取Bitmap的代码

SharedPreferences myPrefrence = getPreferences(MODE_PRIVATE);
String imageS = myPrefrence.getString("imagePreferance", "");
Bitmap imageB; 
if(!imageS.equals("")) imageB = decodeToBase64(imageS);

但在我看来，你应该只保留共享首选项的位图路径。

Answer 2

以下是我使用的内容：

public class AppPrefrances {
protected static AppPrefrances INSTANCE;
private static SharedPreferences prefs;

public static AppPrefrances getInstance(Context context) {
    if (INSTANCE == null) {
        INSTANCE = new AppPrefrances();
        prefs = PreferenceManager.getDefaultSharedPreferences(context);
    }

    return INSTANCE;
}

public void setPath(String path) {
    prefs.edit().putString("path", path).apply();
}

public String getPath() {
    return prefs.getString("path", "-1");
}
}

现在在你的onActivityResult：

AppPrefrances.getInstance(getApplicationContext()).setPath(file_path);

然后在onCreate中，检查：

String check= AppPrefrances.getInstance(getApplicationContext()).setPath();
if(check!=null&&!check.equals("-1")){
imageView.setImageUri(Uri.parse(check));
}

Answer 3

#EliaszKubala,it my code.

这里错误：无法恢复活动{com.example.thang.sdcardimagesactivity / com.example

 @Override
protected void onPause() {
    super.onPause();
    save();
}
public void save(){
    SharedPreferences sp = getSharedPreferences("AppSharedPref", 1); // Open SharedPreferences with name AppSharedPref
    SharedPreferences.Editor editor = sp.edit();
    editor.putString("ImagePath", "abc");
    editor.putString("ImagePath", encodeTobase64(bitmap)); // Store selectedImagePath with key "ImagePath". This key will be then used to retrieve data.
    editor.commit();
}

@Override
protected void onResume() {
    super.onResume();
    restore();
}
public void restore(){
    SharedPreferences sp = getSharedPreferences("AppSharedPref", 1);
    selectedImagePath = sp.getString("ImagePath", "abc");
    bitmap = decodeToBase64(selectedImagePath);
    imageView.setImageBitmap(bitmap);
}
public static String encodeTobase64(Bitmap image) {
    Bitmap immage = image;
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    immage.compress(Bitmap.CompressFormat.PNG, 100, baos);
    byte[] b = baos.toByteArray();
    String imageEncoded = Base64.encodeToString(b, Base64.DEFAULT);

    Log.d("Image Log:", imageEncoded);
    return imageEncoded;
}
public static Bitmap decodeToBase64(String input) {
    byte[] decodedByte = Base64.decode(input, 0);
    return BitmapFactory.decodeByteArray(decodedByte, 0, decodedByte.length);
}

如何使用共享首选项将图像保存到ImageView

3 个答案: