What s tools context in Android layout files

Question

Starting with a recent new version of ADT  I ve noticed this new attribute on the layout XML files  for example    lt LinearLayout xmlns android  http   schemas android com apk res android      xmlns tools  http   schemas android com tools      android orientation  vertical      android layout width  fill parent      android layout height  fill parent      tools context   MainActivity    gt    What is  tools context  used for   How does it even know the exact path to the activity that is written there  Does it look at the package of the app  inside the manifest   Is it limited to classes that extend Context or only activities   Is it usable for ListView items etc

User · Answer

tools context    is one of the Design Attributes that can facilitate layout creation in XML in the development framework  This attribute is used to show the development framework what activity class is picked for implementing the layout  Using    tools context     Android Studio chooses the necessary theme for the preview automatically   If you   d like to know more about some other attributes and useful tools for Android app development  take a look at this review  http   cases azoft com 4-must-know-tools-for-effective-android-development

User · Answer

This is the activity the tools UI editor uses to render your layout preview  It is documented here       This attribute declares which activity this layout is associated with by default  This enables features in the editor or layout preview that require knowledge of the activity  such as what the layout theme should be in the preview and where to insert onClick handlers when you make those from a quickfix

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That attribute is basically the persistence for the  Associated Activity  selection above the layout   At runtime  a layout is always associated with an activity  It can of course be associated with more than one  but at least one  In the tool  we need to know about this mapping  which at runtime happens in the other direction  an activity can call setContentView layout  to display a layout  in order to drive certain features   Right now  we re using it for one thing only  Picking the right theme to show for a layout  since the manifest file can register themes to use for an activity  and once we know the activity associated with the layout  we can pick the right theme to show for the layout   In the future  we ll use this to drive additional features - such as rendering the action bar  which is associated with the activity   a place to add onClick handlers  etc   The reason this is a tools  namespace attribute is that this is only a designtime mapping for use by the tool  The layout itself can be used by multiple activities fragments etc  We just want to give you a way to pick a designtime binding such that we can for example show the right theme  you can change it at any time  just like you can change our listview and fragment bindings  etc    Here s the full changeset which has more details on this   And yeah  the link Nikolay listed above shows how the new configuration chooser looks and works  One more thing  The  tools  namespace is special  The android packaging tool knows to ignore it  so none of those attributes will be packaged into the APK  We re using it for extra metadata in the layout  It s also where for example the attributes to suppress lint warnings are stored -- as tools ignore

User · Answer

This is best solution   https   developer android com studio write tool-attributes  This is design attributes we can set activty context in xml like   tools context   activity ActivityName    Adapter   tools context  com PackegaName AdapterName      You can navigate to java class when clicking on the marked icon and tools have more features like  tools text    tools visibility    tools listItems     for recycler view    etx

User · Answer

According to the Android Tools Project Site   tools context    This attribute is typically set on the root element in a layout XML file  and records which activity the layout is associated with  at designtime  since obviously a layout can be used by more than one layout   This will for example be used by the layout editor to guess a default theme  since themes are defined in the Manifest and are associated with activities  not layouts  You can use the same dot prefix as in manifests to just specify the activity class without the full application package name as a prefix      lt android support v7 widget GridLayout     xmlns android  http   schemas android com apk res android          xmlns tools  http   schemas android com tools      tools context   MainActivity  gt      Used by  Layout editors in Studio  amp  Eclipse  Lint

User · Answer

tools context   MainActivity  thisline is used in xml file which indicate that which java source file is used to access this xml file  it means show this xml preview for perticular java files

User · Answer

lt androidx constraintlayout widget ConstraintLayout     xmlns android  http   schemas android com apk res android      xmlns tools  http   schemas android com tools      xmlns app  http   schemas android com apk res-auto      android layout width  match parent      android layout height  match parent      tools context   MainActivity  gt         more views   lt  androidx constraintlayout widget ConstraintLayout gt    In the above code  the basic need of tools context is to tell which activity or fragment the layout file is associated with by default  So  you can specify the activity class name using the same dot prefix as used in Manifest file   By doing so  the Android Studio will choose the necessary theme for the preview automatically and you don   t have to do the preview settings manually  As we all know that a layout file can be associated with several activities but the themes are defined in the Manifest file and these themes are associated with your activity  So  by adding tools context in your layout file  the Android Studio preview will automatically choose the necessary theme for you

User · Answer

1 Description  tools  context    activity name  it won t be packaged into the apk  Only ADT Layout Editor in your current Layout file set corresponding rendering context  show your current Layout in rendering the context is the activity name corresponds to the activity  if the activity in the manifest file set a Theme  then ADT Layout Editor will render your current Layout according to the Theme Means that if you set the MainActivity set a Theme  The Light  the other   then you see in visual layout manager o background control of what should be the Theme  The Light looks like Only to show you what you see is what you get results   Some people see will understand some  some people see the also don t know  I ll add a few words of explanation   2 Sample     Take a simple tools text  for example  some more image  convenient to further understand the tools context    lt TextView     android id    id text1      android layout width  wrap content      android layout height  wrap content      android text  sample name1    gt    lt TextView     android id    id text2      android layout width  wrap content      android layout height  wrap content      tools text  sample name2    gt         TextView1 adopted the android  text  and use the  tools text in the TextView2  on the right side of the Layout editor will display the sample name1  the sample name2 two font  if after you run the code to compile  generated apk  terminal display only the sample name1  does not show the sample name2 the words  You can try to run  see how the effect    3 Specific description  1 The tools  context    activity name  it won t be packaged into the apk understanding  the equivalent of this is commented  the compiled no effect    2 Only ADT Layout Editor  i e   for the above icon on the right side of the simulator  in the current Layout file set corresponding rendering context  the Layout of the current XML in rendering the context is the activity name corresponds to the activity  if the activity in the manifest file set a Theme  then ADT Layout Editor will render your current Layout according to the Theme Means that if you set the MainActivity set a Theme  The Light can also be  other   understand  you added tools  context    activity name   the XML layout is rendering specified activity  establishes a Theme in the manifest file  pictured above right simulator Theme style will also follow changes corresponding to the Theme    4 summary  To sum up  these properties mainly aimed at above the right tools  the simulator debugging time display status  and compile doesn t work

User · Answer

This attribute helps to get the best knowledge of the activity associated with your layout  This is also useful when you have to add onClick handlers on a view using QuickFix   tools context   MainActivity

[android] What's "tools:context" in Android layout files?

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