Android: Unfortunately MyApp has stoped

The Problem

Your application quit because an uncaught RuntimeException was thrown.
The most common of these is the NullPointerException.

How to solve it?

Every time an Android application crashes (or any Java application for that matter), a Stack trace is written to the console (in this case, logcat). This stack trace contains vital information for solving your problem.

Android Studio

In the bottom bar of the window, click on the Android button. Alternatively, you can press alt+6. Make sure your emulator or device is selected in the Devices panel. Next, try to find the stack trace, which is shown in red. There may be a lot of stuff logged into logcat, so you may need to scroll a bit. An easy way to find the stack trace is to clear the logcat (using the recycle bin on the right), and let the app crash again.

Eclipse

In the top right corner, click the DDMS button. If it is not there, you might need to add it first using the Open Perspective button to the left of the Java button. You will find the logcat pane at the bottom. First, make sure your device is selected in the topleft devices panel. Next, try to find the stack trace, which is shown in red. Again, there may be a lot of stuff logged into logcat, so you may need to scroll a bit. An easy way to find the stack trace here is to clear the logcat (using the clear log button on the top right), and let the app crash again. You should also click on the package name of your app, if it is not already selected. This will filter out only the log message made by your app.

I have found the stack trace, now what?
Yay! You're halfway to solving your problem.
You only need to find out what exactly made your application crash, by analyzing the stack trace.

I still can't solve my problem!
If you've found your Exception and the line where it occurred, and still cannot figure out how to fix it, don't hesitate to ask a question on StackOverflow.

Try to be as concise as possible: post the stack trace, and the relevant code (e.g. a few lines up to the line which threw the Exception).

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Android: How to get screen width and height

If you want the display dimensions in pixels you can use getSize:

Display display = getWindowManager().getDefaultDisplay();
Point size = new Point();
display.getSize(size);
int width = size.x;
int height = size.y;

If you're not in an Activity you can get the default Display via WINDOW_SERVICE:

WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
Display display = wm.getDefaultDisplay();

Before getSize was introduced (in API level 13), you could use the getWidth and getHeight methods that are now deprecated:

Display display = getWindowManager().getDefaultDisplay(); 
int width = display.getWidth();  // deprecated
int height = display.getHeight();  // deprecated

For the use case you're describing however, a margin/padding in the layout seems more appropriate.

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Android SDK installation doesn't find Java JDK

In order to fix this press Back when you get the notification and then Next. This time it will find the JDK.

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Proper use case for Android UserManager.isUserAGoat()

In the Android 4.2 API there's the UserManager class and the method:

public boolean isUserAGoat ()

From their source, it looks like the method returns false all the time:

/**
 * Used to determine whether the user making this call is subject to
 * teleportations.
 * @return whether the user making this call is a goat 
 */
public boolean isUserAGoat() {
    return false;
}

It looks like the method has no real use for us as developers. Someone has previously stated that it might be an Easter egg.

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Hide or close the Android Soft Keyboard

If you have in your layout a EditText and want to hide it with a Button then you can force Android to hide the virtual keyboard using the InputMethodManager, calling hideSoftInputFromWindow, passing in the token of the window containing your edit field.

EditText myEditText = (EditText) findViewById(R.id.myEditText);  
InputMethodManager imm = (InputMethodManager)getSystemService(
      Context.INPUT_METHOD_SERVICE);
imm.hideSoftInputFromWindow(myEditText.getWindowToken(), 0);

This will force the keyboard to be hidden in all situations. In some cases you will want to pass in InputMethodManager.HIDE_IMPLICIT_ONLY as the second parameter to ensure you only hide the keyboard when the user didn't explicitly force it to appear (by holding down menu).

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Android: "Debug certificate expired" Eclipse Plugins error

In order to fix the Debug certificate expired delete your debug certificate under ~/.android/debug.keystore on Linux and Mac OS X; the directory is something like %USERPROFILE%/.android on Windows.

The Eclipse plugin should then generate a new certificate when you next try to build a debug package. You may need to clean and then build to generate the certificate.

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How to: save activity state in Android App

I've been playing around with the Android SDK, and I am a little unclear on saving an application's state. So given this minor re-tooling of the 'Hello, Android' example:

package com.android.hello;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class HelloAndroid extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mTextView = new TextView(this);

        if (savedInstanceState == null) {
            mTextView.setText("Welcome to HelloAndroid!");
        } else {
            mTextView.setText("Welcome back.");
        }

        setContentView(mTextView);
    }

    private TextView mTextView = null;
}

I thought that might be all one needed to do for the simplest case, but it always gives me the first message, no matter how I navigate away from the app. I'm sure it's probably something simple like overriding onPause or something like that, but I've been poking away in the docs for 30 minutes or so and haven't found anything obvious, so would appreciate any help.

Answer:

You need to override onSaveInstanceState(Bundle savedInstanceState) and write the application state values you want to change to the Bundle parameter like this:

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
  super.onSaveInstanceState(savedInstanceState);
  // Save UI state changes to the savedInstanceState.
  // This bundle will be passed to onCreate if the process is
  // killed and restarted.
  savedInstanceState.putBoolean("MyBoolean", true);
  savedInstanceState.putDouble("myDouble", 1.9);
  savedInstanceState.putInt("MyInt", 1);
  savedInstanceState.putString("MyString", "Welcome back to Android");
  // etc.
}

The Bundle is essentially a way of storing a NVP ("Name-Value Pair") map, and it will get passed in to onCreate and also onRestoreInstanceState where you'd extract the values like this:

@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
  super.onRestoreInstanceState(savedInstanceState);
  // Restore UI state from the savedInstanceState.
  // This bundle has also been passed to onCreate.
  boolean myBoolean = savedInstanceState.getBoolean("MyBoolean");
  double myDouble = savedInstanceState.getDouble("myDouble");
  int myInt = savedInstanceState.getInt("MyInt");
  String myString = savedInstanceState.getString("MyString");
}

You did usually use this technique to store instance values for your application (selections, unsaved text, etc.).

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How do a lazzy load of images in ListView

This code hold the images

package com.wilson.android.library;

/*
 Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.
*/
import java.io.IOException;

public class DrawableManager {
    private final Map<String, Drawable> drawableMap;

    public DrawableManager() {
        drawableMap = new HashMap<String, Drawable>();
    }

    public Drawable fetchDrawable(String urlString) {
        if (drawableMap.containsKey(urlString)) {
            return drawableMap.get(urlString);
        }

        Log.d(this.getClass().getSimpleName(), "image url:" + urlString);
        try {
            InputStream is = fetch(urlString);
            Drawable drawable = Drawable.createFromStream(is, "src");


            if (drawable != null) {
                drawableMap.put(urlString, drawable);
                Log.d(this.getClass().getSimpleName(), "got a thumbnail drawable: " + drawable.getBounds() + ", "
                        + drawable.getIntrinsicHeight() + "," + drawable.getIntrinsicWidth() + ", "
                        + drawable.getMinimumHeight() + "," + drawable.getMinimumWidth());
            } else {
              Log.w(this.getClass().getSimpleName(), "could not get thumbnail");
            }

            return drawable;
        } catch (MalformedURLException e) {
            Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e);
            return null;
        } catch (IOException e) {
            Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e);
            return null;
        }
    }

    public void fetchDrawableOnThread(final String urlString, final ImageView imageView) {
        if (drawableMap.containsKey(urlString)) {
            imageView.setImageDrawable(drawableMap.get(urlString));
        }

        final Handler handler = new Handler() {
            @Override
            public void handleMessage(Message message) {
                imageView.setImageDrawable((Drawable) message.obj);
            }
        };

        Thread thread = new Thread() {
            @Override
            public void run() {
                //TODO : set imageView to a "pending" image
                Drawable drawable = fetchDrawable(urlString);
                Message message = handler.obtainMessage(1, drawable);
                handler.sendMessage(message);
            }
        };
        thread.start();
    }

    private InputStream fetch(String urlString) throws MalformedURLException, IOException {
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpGet request = new HttpGet(urlString);
        HttpResponse response = httpClient.execute(request);
        return response.getEntity().getContent();
    }
}

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