App Crashing - Can't Find Reason

Question

After completing the "Build a Simple Android App" project, I'm attempting to create a similar, but a bit more complicated, app before I move on, so that I get used to the language more. My app is Doctor Who-themed, and while eventually it will be a shake-to-activate app similar to the sample app in the project on here, right now it still works with the click of a button because I need to be able to test it on an emulator.

The end goal for the app is to, when the device is shaken, choose one random number out of three (each corresponds to one of the New Who Doctors' Characters) and read that number to fade in an image of that Doctor. Directly after, it fades in a random quote from an array of quotes from that specific Doctor.

Currently, I'd gotten the app working to the point where, when I clicked the button, the app chose a Doctor, and a quote from the array for that Doctor, and was able to fade the quote in. In trying to implement the image fading in, I've done something that makes the app crash when I try to run it.

I'm sure it'll be some stupid mistake, but it would be fantastic if it could be found.

The project has four class files: MainActivity.java, DoctorWho.java, Nine.java, Ten.java, and Eleven.java. Nine, Ten, and Eleven are all nearly identical, just using different quotes. I'm not sure how much this crash encompasses, so I'll put most of the code here just in case.

MainActivity.java

private DoctorWho mDoctorWho = new DoctorWho();
private TextView mQuoteLabel;
private Button mGetQuoteButton;
private ImageView mImageView1;
private ImageView mImageView2;
private ImageView mImageView3;

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

    mQuoteLabel = (TextView) findViewById(R.id.quotePlace);
    mGetQuoteButton = (Button) findViewById(R.id.button1);
    mGetQuoteButton.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View arg0) {
            String quote = mDoctorWho.getDoctorQuote();
            mDoctorWho.animateDoctor();
            mQuoteLabel.setText(quote);
            animateQuoteIn();

        }
    });
}

private void animateQuoteIn() {
    AlphaAnimation fadeInAnimation = new AlphaAnimation(0, 1);
    fadeInAnimation.setDuration(1500);
    fadeInAnimation.setFillAfter(true);
    mQuoteLabel.setAnimation(fadeInAnimation);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

DoctorWho.java

private Nine mNine = new Nine();
private Ten mTen = new Ten();
private Eleven mEleven = new Eleven();
private ImageView mImageView1;

int randomNumber = 0;

public String getDoctorQuote() {
    String quote = "";

    // Choose a Random number out of three values
    Random randomGenerator = new Random();
    int randomNumber = randomGenerator.nextInt(3);

    // Use that value to choose which of the Doctors to get a quote from
    if (randomNumber == 0) {
        // Quote from Nine
        quote = mNine.getQuote();
    }
    else if (randomNumber == 1) {
        // Quote from Ten
        quote = mTen.getQuote();
    }
    else if (randomNumber == 2) {
        // Quote from Eleven
        quote = mEleven.getQuote();
    }
    else {
        quote = "Error";
    }
    return quote;
}

public void animateDoctor() {
    if (randomNumber == 0) {
        animateNinthDoctor();
    }
    else if (randomNumber == 1) {
        animateTenthDoctor();
    }
    else if (randomNumber == 2) {
        animateEleventhDoctor();
    }
}

private void animateNinthDoctor() {
    AlphaAnimation fadeInAnimation = new AlphaAnimation(0, 1);
    fadeInAnimation.setDuration(1500);
    fadeInAnimation.setFillAfter(true);
    mImageView1.setAnimation(fadeInAnimation);
}

private void animateTenthDoctor() {
    AlphaAnimation fadeInAnimation = new AlphaAnimation(0, 1);
    fadeInAnimation.setDuration(1500);
    fadeInAnimation.setFillAfter(true);
    mImageView1.setAnimation(fadeInAnimation);
}

private void animateEleventhDoctor() {
    AlphaAnimation fadeInAnimation = new AlphaAnimation(0, 1);
    fadeInAnimation.setDuration(1500);
    fadeInAnimation.setFillAfter(true);
    mImageView1.setAnimation(fadeInAnimation);
}

Nine.java (I've removed the quotes to make it a bit more condensed)

public String[] mNineQuotes = {
        "Quote",
        "Quote",
        "Quote" };

public String getQuote() {

    String quote = "";

    Random randomGenerator = new Random();
    int randomNumber = randomGenerator.nextInt(mNineQuotes.length);

    quote = mNineQuotes[randomNumber];

    return quote;
}

Answer 1 · 2013-12-12T20:08:05Z

December 12, 2013 8:08pm

There are a bunch of ways of going about getting it to work, so this is just one way that you could try.

In the MainActivity.onCreate method:

// ... Your other code ...

@Override
public void onClick(View arg0) {
      // Get a random quote number
      int quoteNumber = mDoctorWho.getQuoteNumber();

      // Display the quote and image that correspond to the quote number that we got above
      mQuoteLabel.setText(mDoctorWho.getDoctorQuote(quoteNumber));
      animateDoctor(mDoctorWho.getDoctorImage(quoteNumber));
   }

public void animateDoctor(Drawable doctorImage) {
   // Assign the image that we passed into this method to the image view
   mImageView1.setImageDrawable(doctorImage);

   // Do the animation
   AlphaAnimation fadeInAnimation = new AlphaAnimation(0, 1);
   fadeInAnimation.setDuration(1500);
   fadeInAnimation.setFillAfter(true);
   mImageView1.setAnimation(fadeInAnimation);
}

// ... Your other code ...

Then in the DoctorWho class:

// ...Your other code ...

// This method returns a random quote number between 0 and 2
public int getQuoteNumber() {
   Random randomGenerator = new Random();
   return randomGenerator.nextInt(3);
}

// This method returns the Doctor Who quote that corresponds to the specified number
public String getDoctorQuote(int quoteNumber) {
   // Use that value to choose which of the Doctors to get a quote from
    if (quoteNumber == 0) {
        // Quote from Nine
        quote = mNine.getQuote();
    }
    else if (quoteNumber == 1) {
        // Quote from Ten
        quote = mTen.getQuote();
    }
    else if (quoteNumber == 2) {
        // Quote from Eleven
        quote = mEleven.getQuote();
    }
    else {
        quote = "Error";
    }
    return quote;
}

// This method returns the Doctor Who image that corresponds to the specified quote number
public Drawable getDoctorImage(int quoteNumber) {
   if (quoteNumber == 0) {
      return R.drawable.ninthdoctor;
   }
   else if (quoteNumber == 1) {
      return R.drawable.tenthdoctor;
   }
   else if (quoteNumber == 2) {
      return R.drawable.eleventhdoctor;
   }
   else {
      // The program should never get here, but you have to return something or throw an exception, or else your program won't compile
      return null;
   }
}
// ... Your other code ...

If you do it like this, you'll only need one animateDoctor method. Since the only difference between the different doctor animations is the image, it'll be easier to pass the image in as a parameter to a single method, rather than have several different methods which are all the same except for the doctor image. My code may not be entirely correct, but that's kind of an overview of one way to do it.

Answer 2 · 2013-12-09T02:19:51Z

December 9, 2013 2:19am

It looks like your mImageView1 property in your DoctorWho class never gets assigned a value, so when you call mImageView1.setAnimation in your animate methods, you're calling a method on a null value. You should assign the DoctorWho.mImageView1 property before you start calling methods on your DoctorWho class.

If you look at the Console window in Eclipse, it'll show you which line of code is causing the crash.

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App Crashing - Can't Find Reason

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