Android - Debugging Your App

Sometimes, your app will crash when testing it.

1. Setting Breakpoints

1. 
2. 
3. For lines containing lamda expressions, you will get a drop-down menu of options for what the breakpoint should effect:
   • Set the breakpoint for the initial code on the line ("Line").
   • Set the breakpoint to trigger when the lamda expression is executed ("{ updateButton() }").
   • Both("All").

2. Launching the Debugger

• This behaves a lot like when you normally run the app.
  • However, the app will run more slowly, and when the breakpoint is reached, your IDE window will open a Debug tool that shows you what is going on.
     

3. Examining Objects

• The middle of the Debug tool shows a "Variables" list.
  • This will contain local variables, field/properties of the current object, and other values that your code might be referencing.
• Simple types, like the Long startTimeMs, just show their value.
• More complex types, like AppCompatButton will show their type and can be explored in turn using the gray triangle to expand the object tree.
   

4. Stepping Through the Code

On the Top

• From left to right, these are:
  • Execute this statement and move into the next one.
  • Step into the function being called in this statement, if it is not an Android SDK function.
  • Step into the function being called in this statement, even if it is an Android SDK function.
  • Execute far enough to exit the function that we are in and then stop.

On the Left

• Of particular note:
  • The top-most button (green triangle) will start executing code until the next breakpoint or crash.
  • The red square terminates your process.
  • The fourth button (two-overlapping red dots) brings up a dialog box showing all of your breakpoints.

5. Where Did it Go Wrong?

Kotlin

Java

• This code compiles, because setText() on a Button has a variant that accepts an Int as a parameter.
  • We are passing an Int that represents the number of seconds.
     

• As it turns out, setText(Int) does not show that Int value as text in the Button.
  • Instead, Android is expecting that to be a reference to a string resource, such as R.string.elapsed.

Those R values are all Integers, and so many functions in the Android SDK that accept an Int are expecting a resource ID, not some arbitrary value as we are providing.

In particular, if you get crash with an android.content.res.Resouces$NotFoundException, there is a good chance you are passing in a value to a function that is not a valid resource ID.

Solution

• Convert the numeric value to a String.