How to clear or hide an ImageView in Android

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="//schemas.android.com/apk/res/android"
      package="com.example.my_packag"
      android:versionCode="1"
      android:versionName="1.0">
    <uses-sdk android:minSdkVersion="7" />

    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".MainClass"
                  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>

int nf = Math.round(5.789f);
System.out.print(nf); // 6

float f = 28.611f; 
int n3 = Math.round(f);
System.out.println(n3); // 29

double d = 1234.56;
long lon = Math.round(d);
System.out.println(lon); // 1235

int diff = 90 - 40;
// float fDeleni = diff / 10; // error code
float fDeleni = (float)diff / 10.f; // ok
int nRound = Math.round(fDeleni);


// Caution:
int n2 = (int) 8.999f;
System.out.println(n2); // 8

• is sett debug mode on device?


• enabled debugging over USB?


• is device right connected?


• have you downloaded and instaled drivers for your device on PC?


• For Windows //developer.android.com/sdk/win-usb.html


• try disconnect and connect USB cable


• try do restart Android Studio

Context context = thisClass.this;
Drawable image = ImageOperations(context,
"//www.okhelp.cz/images/android/ad_4.png"
,"image.jpg");
ImageView imgView;
imgView = (ImageView)findViewById(R.id.idImageView);
imgView.setImageDrawable(image);

	private Drawable ImageOperations(Context ctx, String url, String saveFilename) {
		try {
			InputStream is = (InputStream) this.fetch(url);
			Drawable d = Drawable.createFromStream(is, "src");
			return d;
		} catch (MalformedURLException e) {
			e.printStackTrace();
			return null;
		} catch (IOException e) {
			e.printStackTrace();
			return null;
		}
	}

	public Object fetch(String address) throws MalformedURLException,IOException {
		URL url = new URL(address);
		Object content = url.getContent();
		return content;
	}

// MainActivity.java
//  myButton.setOnClickListener
Intent binary = new Intent(getApplicationContext(),Calculate.class);
	Bundle b = new Bundle();
	b.putString("prvni_label", "Decimal");
	b.putString("druhy_label", "Binary");
	b.putString("mode", "binary_to_decimal");
        binary.putExtras(b);
	startActivityForResult(binary, 0);
						
// in Calculate.java onCreate

   TextView mTextView1 = (TextView)findViewById(R.id.textView1);
   TextView mTextView2 = (TextView)findViewById(R.id.textView2);    
     Bundle _bundle = getIntent().getExtras();
		mTextView1.setText(_bundle.getString("prvni_label"));
		mTextView2.setText(_bundle.getString("druhy_label"));

//.................. HOW OPEN START NEW ACTIVITY WITHOUT A PARAMETER .........................

startActivity(new Intent(ThisActivity.this, NewActivity.class));