我的画廊意图不显示图像？为什么？

Question

这是将图像插入数据库的代码。问题是当使用函数“requestWritePermission（）;”时然后我不能从另一个进入这个活动但是当我删除这个功能..这个活动开始但是当点击上传图片按钮它进入画廊但没有显示图像..我没有得到它。请帮忙。

package com.example.tariqziad.myapplication;

import android.Manifest;
import android.annotation.TargetApi;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.os.Build;
import android.provider.MediaStore;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.File;

import okhttp3.MediaType;
import okhttp3.MultipartBody;
import okhttp3.RequestBody;
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;

import static android.R.attr.id;

public class ImageUpload extends AppCompatActivity {

    Button uploadbutton, insertbutton;
    ImageView imageView;
    String mediaPath;
    private static final int WRITE_PERMISSION = 0x01;
    private static final int PICK_IMAGE = 100;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_image_upload);
        //requestWritePermission();


        uploadbutton= (Button)findViewById(R.id.upload);
        insertbutton= (Button)findViewById(R.id.insert);

        insertbutton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                uploadpic();
            }
        });


        uploadbutton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Intent galleryIntent = new Intent(Intent.ACTION_PICK,
                        android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
                startActivityForResult(galleryIntent,PICK_IMAGE);

            }
        });

        imageView=(ImageView)findViewById(R.id.imageview);
    }


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

        try {
            // When an Image is picked
            if (requestCode == 0 && resultCode == RESULT_OK && null != data) {

                // Get the Image from data
                Uri selectedImage = data.getData();
                String[] filePathColumn = {MediaStore.Images.Media.DATA};

                Cursor cursor = getContentResolver().query(selectedImage, filePathColumn, null, null, null);
                assert cursor != null;
                cursor.moveToFirst();

                int columnIndex = cursor.getColumnIndex(filePathColumn[0]);
                mediaPath = cursor.getString(columnIndex);
                // Set the Image in ImageView for Previewing the Media
                imageView.setImageBitmap(BitmapFactory.decodeFile(mediaPath));
                cursor.close();
            } else {
                Toast.makeText(this, "You haven't picked Image/Video", Toast.LENGTH_LONG).show();
            }
        } catch (Exception e) {
            Toast.makeText(this, "Something went wrong", Toast.LENGTH_LONG).show();
        }

    }

    private void uploadpic() {
        File file = new File(mediaPath);

        RequestBody requestBody = RequestBody.create(MediaType.parse("*/*"), file);
        MultipartBody.Part fileToUpload = MultipartBody.Part.createFormData("file", file.getName(), requestBody);
        RequestBody filename = RequestBody.create(MediaType.parse("text/plain"), file.getName());
        SchoolInterfaces t=SchoolApi.getClient().create(SchoolInterfaces.class);
        Call<ImageResponse> call=t.uploadFile(fileToUpload,filename);
        call.enqueue(new Callback<ImageResponse>() {
            @Override
            public void onResponse(Call<ImageResponse> call, Response<ImageResponse> response) {
                ImageResponse serverResponse = response.body();
                if (serverResponse != null) {
                    if (serverResponse.getSuccess()) {
                      /* Intent intent=new Intent(PostArea.this,SellerActivity.class);
                       intent.putExtra("id",id);
                       startActivity(intent); */
                        //finish();
                    } else {
                        Toast.makeText(getApplicationContext(), serverResponse.getMessage(),Toast.LENGTH_SHORT).show();
                    }
                } else {
                    assert serverResponse != null;
                    Log.v("Response", serverResponse.toString());
                }
            }

            @Override
            public void onFailure(Call<ImageResponse> call, Throwable t) {

            }
        });
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
        if(requestCode == WRITE_PERMISSION){
            if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {

                Toast.makeText(this, "You must allow permission write external storage to your mobile device.", Toast.LENGTH_SHORT).show();

            }
        }
    }

    @TargetApi(Build.VERSION_CODES.M)
    private void requestWritePermission() {
        if (checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, WRITE_PERMISSION);
        }
    }

}