Reducing repetitive Android code

Question

How can I reduce the amount of repetitive code in my Android app? A lot of the code seems to be doing the same thing twice. I think that there is a more compact way to do this.

What are some ways that I can reduce lines of code in this program?
Is there a better way that I could write this program? I think that I am taking more steps than necessary.

The code is for this app.

package com.kerseykyle.easyhash;

import java.security.MessageDigest;

import android.os.Build;
import android.os.Bundle;
import android.annotation.TargetApi;
import android.app.Activity;
import android.content.Intent;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends Activity {

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

        Intent intent = getIntent();
        String action = intent.getAction();
        String type = intent.getType();

        if (Intent.ACTION_SEND.equals(action) && type != null) {
            if ("text/plain".equals(type)) {
                handleSendText(intent); // Handle text being sent
            } 
        } 

        EditText myTextBox = (EditText) findViewById(R.id.input);
        myTextBox.setSingleLine(true);
        myTextBox.addTextChangedListener(new TextWatcher() {

            public void afterTextChanged(Editable s) {
            }

            public void beforeTextChanged(CharSequence s, int start, int count,
                    int after) {
            }

            @TargetApi(Build.VERSION_CODES.HONEYCOMB)
            public void onTextChanged(CharSequence s, int start, int before,
                    int count) {

                String md5hash = CreateHash(s.toString(), "MD5");
                TextView md5 = (TextView) findViewById(R.id.md5);
                md5.setText(md5hash);
                md5.setTextIsSelectable(true);

                String sha1hash = CreateHash(s.toString(), "SHA-1");
                TextView sha1 = (TextView) findViewById(R.id.sha1);
                sha1.setText(sha1hash);
                sha1.setTextIsSelectable(true);


                String sha256hash = CreateHash(s.toString(), "SHA-256");
                TextView sha256 = (TextView) findViewById(R.id.sha256);
                sha256.setText(sha256hash);
                sha256.setTextIsSelectable(true);

                String sha512hash = CreateHash(s.toString(), "SHA-512");
                TextView sha512 = (TextView) findViewById(R.id.sha512);
                sha512.setText(sha512hash);
                sha512.setTextIsSelectable(true);
            }
        });

    }

    public static String CreateHash(String data, String function) {
        try {
            MessageDigest digest = MessageDigest.getInstance(function);
            byte[] hash = digest.digest(((String) data).getBytes("UTF-8"));
            StringBuffer hexString = new StringBuffer();

            for (int i = 0; i < hash.length; i++) {
                String hex = Integer.toHexString(0xff & hash[i]);
                if (hex.length() == 1)
                    hexString.append('0');
                hexString.append(hex);
            }

            return hexString.toString();
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }
    }

    public void Share() {

        TextView md5 = (TextView) findViewById(R.id.md5);
        md5.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                EditText myTextBox = (EditText) findViewById(R.id.input);
                String md5hash = CreateHash(myTextBox.getText().toString(),
                        "MD5");
                Intent sendIntent = new Intent();
                sendIntent.setAction(Intent.ACTION_SEND);
                sendIntent.putExtra(Intent.EXTRA_TEXT, md5hash);
                sendIntent.setType("text/plain");
                startActivity(sendIntent);

            }
        });

        TextView sha1 = (TextView) findViewById(R.id.sha1);
        sha1.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                EditText myTextBox = (EditText) findViewById(R.id.input);
                String sha1hash = CreateHash(myTextBox.getText().toString(),
                        "SHA-1");
                Intent sendIntent = new Intent();
                sendIntent.setAction(Intent.ACTION_SEND);
                sendIntent.putExtra(Intent.EXTRA_TEXT, sha1hash);
                sendIntent.setType("text/plain");
                startActivity(sendIntent);
            }
        });

        TextView sha256 = (TextView) findViewById(R.id.sha256);
        sha256.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                EditText myTextBox = (EditText) findViewById(R.id.input);
                String sha256hash = CreateHash(myTextBox.getText().toString(),
                        "SHA-256");
                Intent sendIntent = new Intent();
                sendIntent.setAction(Intent.ACTION_SEND);
                sendIntent.putExtra(Intent.EXTRA_TEXT, sha256hash);
                sendIntent.setType("text/plain");
                startActivity(sendIntent);
            }
        });

        TextView sha512 = (TextView) findViewById(R.id.sha512);
        sha512.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                EditText myTextBox = (EditText) findViewById(R.id.input);
                String sha512hash = CreateHash(myTextBox.getText().toString(),
                        "SHA-512");
                Intent sendIntent = new Intent();
                sendIntent.setAction(Intent.ACTION_SEND);
                sendIntent.putExtra(Intent.EXTRA_TEXT, sha512hash);
                sendIntent.setType("text/plain");
                startActivity(sendIntent);
            }
        });

        {
        }
    }


    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    void handleSendText(Intent intent) {
        String sharedText = intent.getStringExtra(Intent.EXTRA_TEXT);
        if (sharedText != null) {

            EditText input = (EditText) findViewById(R.id.input);
            input.setText(sharedText);

            String md5hash = CreateHash(sharedText, "MD5");
            TextView md5 = (TextView) findViewById(R.id.md5);
            md5.setText(md5hash);
            md5.setTextIsSelectable(true);

            String sha1hash = CreateHash(sharedText, "SHA-1");
            TextView sha1 = (TextView) findViewById(R.id.sha1);
            sha1.setText(sha1hash);
            sha1.setTextIsSelectable(true);


            String sha256hash = CreateHash(sharedText, "SHA-256");
            TextView sha256 = (TextView) findViewById(R.id.sha256);
            sha256.setText(sha256hash);
            sha256.setTextIsSelectable(true);

            String sha512hash = CreateHash(sharedText, "SHA-512");
            TextView sha512 = (TextView) findViewById(R.id.sha512);
            sha512.setText(sha512hash);
            sha512.setTextIsSelectable(true);

        }
    } 
}

Answer 1

This type of problem is conveniently solved with a Strategy Pattern. But, first things first:

• you should search for efficient ways to convert bytes to hexadecimal-string values. This is a great solution I like....
• Unless you have no choice (you are using Patterns/Matchers) you should always use StringBuilder instead of StringBuffer
• The method CreateHash should not have a capital-letter to start with, it should rather be createHash

As for the Strategy Pattern.... In this case, you can create a class that listens for the text change, and updates the signature in the linked TextView. The same class listens for on-click on the TextView too. The class could have the signature

public abstract class HashDigestDisplay implements TextWatcher, OnClickListener {
    private final TextView view;
    private final MessageDigest digest;

    public HashDigestDisplay (TextView target, String digestName) throws NoSuchAlgorithmException {
        this.view = target;
        this.digest = MessageDigest.getInstance(digestName);
        this.view.setOnClickListener(this);
    }

    public void afterTextChanged(Editable s) {
    }

    public void beforeTextChanged(CharSequence s, int start, int count,
            int after) {
    }

    private String myDigest(String input) {
        digest.reset(); 
        byte[] hash = digest.digest(input.getBytes("UTF-8"));
        return bytesToHex(hash);
    }

    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    public void onTextChanged(CharSequence s, int start, int before, int count) {
            view.setText(myDigest(s.toString()));
            view.setTextIsSelectable(true);
    }

    @Override
    public void onClick(View v) {
            // TODO Auto-generated method stub
            EditText myTextBox = (EditText) findViewById(R.id.input);
            String hash = myDigest(myTextBox.getText().toString());
            Intent sendIntent = new Intent();
            sendIntent.setAction(Intent.ACTION_SEND);
            sendIntent.putExtra(Intent.EXTRA_TEXT, hash);
            sendIntent.setType("text/plain");
            startActivity(sendIntent);

    }
}

You can see the pattern that is emerging above. Obviously there are issues in the onClick method, but this is from copy/pasting your code.

Now, what you do in your onCreate() setup method is simply:

myTextBox.addTextChangedListener(
    new HashDigestDisplay((TextView) findViewById(R.id.md5), "MD5"));
myTextBox.addTextChangedListener(
    new HashDigestDisplay((TextView) findViewById(R.id.sha1), "SHA-1"));
....

After that, the system should be self-managing.

You only have one copy of the code, and the only things different about it are the name of the Digest and the target of the TextView.