When you create a new project in Android Studio almost all your project files are inside the src directory, including resources and the manifest file. For the most part, you should need to modify only the files under the src directory. More information about the Gradle project structure is available in the Gradle Plugin User Guide.
In Android Studio, chose “File” → “Import Project” and select the folder of the sample, exercise or solution project. Android Studio may ask you to choose the type of project you are importing. If this is the case, make sure to choose “Import project from external model” and select the “Gradle” option.
You can define view widths and heights and font sizes using px, dp or sp.
px
Pixels
Corresponds to actual pixels on the screen.
dp or dip
Density-independent Pixels
An abstract unit that is based on the physical density of the screen. These units are relative to a 160 dpi screen, so one dp is one pixel on a 160 dpi screen. The ratio of dp-to-pixel will change with the screen density, but not necessarily in direct proportion. Note: The compiler accepts both "dip" and "dp", though "dp" is more consistent with "sp".
sp or sip
Scale-independent Pixels
This is like the dp unit, but it is also scaled by the user's font size preference. It is recommend you use this unit when specifying font sizes, so they will be adjusted for both the screen density and user's preference.
Tip: Try to never use anything but sp or dp unless you absolutely have to. Using sp and dp will make your Android applications compatible with multiple screen densities and resolutions.
You can resize your graphical resources with the following ratio table, or use our handy online calculator:
| mdpi | hdpi | xhdpi | xxhdpi |
|---|---|---|---|
| 2 | 3 | 4 | 6 |
Context is an interface to global information about an application environment. This is an abstract class whose implementation is provided by the Android system. It allows access to application-specific resources and classes, as well as up-calls for application-level operations such as launching activities, broadcasting and receiving intents, etc. Both the Application class and the Activity class implement the Context interface. The Application instance is tied to the lifecycle of the application, while the Activity instance is tied to the lifecycle of an Activity. Thus, they have access to different information about the application environment. You normally use the Activity context for view-related actions and the Application context generally should only be used if you need a context whose lifecycle is separate from the current context, that is tied to the lifetime of the process rather than the current component.
You can add messages that appear in Logcat with some different methods in android.util.Log:
Log.d("MyTag", "message saved as draft");To log exceptions:
Log.e("MyTag", "message draft could not be saved", exception);A toast provides simple feedback about an operation in a small popup. It only fills the amount of space required for the message and the current activity remains visible and interactive. For example, navigating away from an email before you send it triggers a "Draft saved" toast to let you know that you can continue editing later. Toasts automatically disappear after a timeout.
First, instantiate a Toast object with one of the makeText() methods. This method takes three parameters: a context, the text message, and the duration for the toast. It returns a properly initialized Toast object. You can display the toast notification with show(), as shown in the following example:
Toast.makeText(this, "Message saved as draft.", Toast.LENGTH_LONG).show();If user response to a status message is required, consider instead using a Notification.