Android Studio failed to convert drawable into a drawable

<uses-sdk android:minSdkVersion="4" />
// 
<uses-sdk android:minSdkVersion="8" />

		Drawable dr = getResources().getDrawable(R.drawable.algebra);
		int h = dr.getIntrinsicHeight();
		int w = dr.getIntrinsicWidth();

		Bitmap ball = BitmapFactory.decodeResource(getResources(), R.drawable.algebra);
		int _nWidth = ball.getWidth();
		int _nHeight = ball.getHeight();

import android.os.Build.VERSION;
//
int nSdkVersion = Integer.parseInt(Build.VERSION.SDK);
int nApiVersion = VERSION.SDK;

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="//schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <TextView
        android:id="@+id/idLabel"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Enter word"/>
    <EditText
        android:id="@+id/idEntry"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:background="@android:drawable/editbox_background"
        android:layout_below="@id/idLabel"/>
    <Button
        android:id="@+id/idOk"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/idEntry"
        android:layout_alignParentRight="true"
        android:layout_marginLeft="10dip"
        android:text="OK" />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_toLeftOf="@id/idOk"
        android:layout_alignTop="@id/idOk"
        android:text="Cancel" />
</RelativeLayout>

 android:layout_height="wrap_content" android:onClick="@string/clickHandler">

myClickHandler

	public void myClickHandler(View view) {
		switch (view.getId()) {
		// open new class as activity
		case R.id.btnOpenClass: {
				Intent pictureActivity = new Intent(getBaseContext(),
						MyClass.class);
				startActivity(pictureActivity);
		}
		break;			
			
		case R.id.btnAbout: {
			//aboutDialogCreate();
		}
			break;
			
		// open url	
		 case R.id.btnHome: {
		 String url = "//android.okhelp.cz/";
		 Intent i = new Intent(Intent.ACTION_VIEW);
		 i.setData(Uri.parse(url));
		 startActivity(i);
		 }break;

		}

	}// end myClickHandler

// listener .. if click on button will scrolling to mTextView bottom
private OnClickListener mButtonListener = new OnClickListener() {
	    public void onClick(View v) {
	      // do something when the button is clicked
	    int nBottom =	mTextView.getBottom();
	    hScrollView.scrollTo(0, nBottom);
	    }
	};