Afficher une image du téléphone dans un imageView

public class MainActivity extends Activity {
  ImageView mImageView;
 //File imgFile = new  File("/sdcard/Selfie_Time/image.jpg");
 String path = Environment.getExternalStorageDirectory()+ "/Selfie_Time/image.jpg";
 File imgFile = new File(path);


 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  
  
  mImageView = (ImageView) findViewById(R.id.image);
  Button bt=(Button)findViewById(R.id.get);
  
  bt.setOnClickListener(new OnClickListener() {
            
     @Override
     public void onClick(View v) {
     image(v);
       
       }});
  
 }
 
 public void image(View v){
  
  
  if(imgFile.exists())
  {
     Bitmap myBitmap = BitmapFactory.decodeFile(imgFile.getAbsolutePath());
     //ImageView imageView=(ImageView)findViewById(R.id.imageView);
     mImageView.setImageBitmap(myBitmap);
  }
 }

<LinearLayout xmlns:android="[http://schemas.android.com/apk/res/android]"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"  >

   
    
     <Button
            android:id="@+id/get"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Aperçu" />
     
      <ImageView
        android:id="@+id/image"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="[http://schemas.android.com/apk/res/android]"
    package="com.example.testsixteen"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="15"
        android:targetSdkVersion="15" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>