活动被破坏后ImageView丢失图像

Question

我正在尝试创建一个应用程序，让用户可以选择要在其个人资料中显示的图片。我可以在imageview上浏览和设置他们选定的图像。但是一旦活动被破坏，图像就会丢失。我试图实现onSaveInstanceState，但它仍然是一样的。我想知道我是否正确使用它。我希望你能帮助像我这样的新手。提前致谢。下面是我使用的代码：

public class AccountFragment extends Fragment implements OnClickListener { 
private LoginDataBaseAdapter loginDataBaseAdapter; 
Bitmap image; 
Bitmap bitmap; 
String picture_location; 
TextView textTargetUri; 
ImageView targetImage; 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
      Bundle savedInstanceState) { 


     View rootView = inflater.inflate(R.layout.fragment_account, container, false); 


      textTargetUri = (TextView) rootView.findViewById(R.id.targeturi); 

      targetImage=(ImageView) rootView.findViewById(R.id.profpic); 

      targetImage.setOnClickListener(new ImageView.OnClickListener(){ 
      @Override 
      public void onClick(View arg0) { 
       Intent intent = new Intent(Intent.ACTION_PICK, 
       android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI); 
       startActivityForResult(intent, 0); 
      }}); 

      if (savedInstanceState != null) { 
       //if there is a bundle, use the saved image resource (if one is there) 
       image = savedInstanceState.getParcelable("BitmapImage"); 
       targetImage.setImageBitmap(image); 
       textTargetUri.setText(savedInstanceState.getString("path_to_picture")); 
      } 



     return rootView; 



    } 

    @Override 
    public void onSaveInstanceState(Bundle savedInstanceState){ 
     super.onSaveInstanceState(savedInstanceState); 
     savedInstanceState.putParcelable("BitmapImage", bitmap); 
     savedInstanceState.putString("path_to_picture", picture_location); 
    } 


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

     if (resultCode == Activity.RESULT_OK){ 
      Uri targetUri = data.getData(); 
      picture_location = targetUri.toString(); 
      textTargetUri.setText(targetUri.toString()); 
      Bitmap bitmap; 
      try { 
       bitmap = BitmapFactory.decodeStream(getActivity().getContentResolver().openInputStream(targetUri)); 
       targetImage.setImageBitmap(bitmap); 
      } 
      catch (FileNotFoundException e){ 
       e.printStackTrace(); 
      } 
     } 
    } 

    @Override 
    public void onClick(View arg0) { 
     // TODO Auto-generated method stub 

    }} 

顺便说一句，你可能已经注意到，而不是在OnCreate后使用onRestoreInstanceState，我试图用不同的方法。我从另一个问题找到了一个答案，你也可以在oncreate中实现它。我使用它，因为每当我声明函数onRestoreInstanceState我被要求删除@Override注释。

@Override 
protected void onRestoreInstanceState(Bundle savedInstanceState){  
      image = savedInstanceState.getParcelable("BitmapImage"); 
      targetImage.setImageBitmap(image); 
      textTargetUri.setText(savedInstanceState.getString("path_to_picture")); 
    } 

Answer 1

使用onSaveInstanceState和onCreate/onRestoreInstanceState用于短期活动状态保存 - 但不用于持久存储应用程序的数据。

你可以阅读有关的onSaveInstanceState here

你可以阅读有关持久性存储here

codeMagic使用SharedPrefs（见持久存储链接）为您的长期持久性存储建议。如果你想这样做，我会建议在你的onActivityResult方法中保存图像URI（链接有一个很好的例子），然后调用一个方法来读取SharedPref并加载你可以调用的图像onCreate以及onActivityResult。

您可能还希望将自己的图像/位图副本存储在应用程序自己的内部存储器中（请参阅持久存储链接）。

Answer 2

如果你没有完成的活动，您可以使用onSavedInstance()存储picture_location值，并将其绑定回无论是从picture_location值onCreate(SavedInst)/onRestore()。

Answer 3

如果位图实例状态不是建议的方式来保存所选图像的信息。

您可以在这里找到的解释：Handling configuration Changes

我广泛地在这里的博客上讲述它：Retain selected Image during Screen Rotation

下面我贴我的实现图示的解决方案：

1 - 创建一个片段，并对其进行配置保留在内存中

import android.graphics.Bitmap; 
import android.os.Bundle; 
import android.support.v4.app.Fragment; 

public class ImageRetainingFragment extends Fragment { 
    private Bitmap selectedImage; 

    @Override public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     // retain this fragment   
     setRetainInstance(true); 
} 

public void setImage(Bitmap selectedImage) { 
    this.selectedImage = selectedImage; 
} 

public Bitmap getImage() { 
    return this.selectedImage; 
} 
} 

2 - 在您的活动中使用它

private static final String FRAGMENT_NAME = "imageFragment"; 


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

    .... 

    initializeImageRetainingFragment(); 
    tryLoadImage(); 
} 


private void initializeImageRetainingFragment() { 
    // find the retained fragment on activity restarts  
    FragmentManager fragmentManager = getSupportFragmentManager(); 
    this.imageRetainingFragment = (ImageRetainingFragment) fragmentManager.findFragmentByTag(FRAGMENT_NAME); 
    // create the fragment and bitmap the first time 
    if (this.imageRetainingFragment == null) { 
     this.imageRetainingFragment = new ImageRetainingFragment(); 
     fragmentManager.beginTransaction() 
     // Add a fragment to the activity state. 
     .add(this.imageRetainingFragment, FRAGMENT_NAME) 
     .commit(); 
    } 
} 
private void tryLoadImage() { 
    if (this.imageRetainingFragment == null) { 
     return; 
    } 

    Bitmap selectedImage = this.imageRetainingFragment.getImage(); 
     if (selectedImage == null) { 
     return; 
     } 

     ImageView selectedImageView = (ImageView)findViewById(R.id.selectedImage); 
     selectedImageView.setImageBitmap(selectedImage); 
}