Reducing repetitive Android code

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) findV

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.

StackExchange Code Review Q#38132, answer score: 4