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AndroidStudio ConstrainLayout not working

I am beginner in android studio and having headache with this if someone could help me am i missing something?.... I have problem with Constraint layout, the problem is i put some element(ImageView, Button it does not mater) in layout and constraint it to parent but when I run it in emulator it just is not showing. also it is not showing me those buttons under elements connect BaseLine and remove Constrains for that element.
"screenShot":
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<ImageView
android:id="#+id/imageView"
android:layout_width="343dp"
android:layout_height="118dp"
android:layout_marginTop="10dp"
android:scaleType="centerCrop"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_c`enter code here`onstraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:srcCompat="#tools:sample/backgrounds/scenic[7]" />
</android.support.constraint.ConstraintLayout>

when i run it in emulator it just is not showing
The problem is here :
tools:srcCompat="#tools:sample/backgrounds/scenic[7]"
You need to understand what tools is, so I recommend to you to read a little bit the documentation.
Just a note of it :
It's a namespace that enable design-time features (such as which layout to show in a fragment) or compile-time behaviors (such as which shrinking mode to apply to your XML resources). When you build your app, the build tools remove these attributes so there is no effect on your APK size or runtime behavior.
Instead you have to use to show it on the emulator.
app:srcCompat="#drawable/your_drawable"
Note: remember to add : xmlns:app="http://schemas.android.com/apk/res-auto"

I found the solution.it's difrent in new Android Studio 3.4, You have to Right click on element and option Show Base Line is there now.

Text in XML Graphical Layout appears as strange characters

I am having issues viewing text in the graphical layout section of my android applications. This is consistently happening across many projects, new and old. See the link for visual example: http://i.imgur.com/OwENudf.jpg
The button in the image should say 'test' but instead its two boxes. Sometimes it appears as an open bracket, [
Background- I was having issues with eclipse/android sdk not creating the R.java file when a new project was created so I uninstalled the sdk and then reinstalled it. The R.java file builds fine now but the text in the graphic layouts is all strange characters.
Any idea what I can do to fix this?
The XML has one warning, which is 'Hardcoded string "test", should use #string resource"
I don't think this is the issue because I have had this error before on working applications.
EDIT:
XML code-
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginLeft="18dp"
android:text="test" />
</RelativeLayout>

I believe you are having font issues with your emulator. It can't find appropriate characters to display. You may need to reinstall that.

Ok so I searched and I think it will fix your problem (and it was too long to post it as a comment).
Go to the platforms folder where android-sdk is installed (C:\Program Files (x86)\Android\android-sdk\platforms).
Then go to the folders you're currenlty building your projects with then go to data/fonts (i.e C:\Program Files (x86)\Android\android-sdk\platforms\android-8\data\fonts) and take a look at the file fonts.xml. Also, may a ttf file disappeared when you updated your ADT (which seems odd).
You can find here an example. Read this carefully before trying to modify these files.
I hope this will solve your problem. If not, I have really no idea about what to do.

Why the ImageView class is not found?

i'm having troubles with creating the first android app (Silent Toggle Mode from the pdf "Android.Application.Development.for.For.Dummies" ) with inserting an Imageview in the main.xml file, when I go to the graphical layout, the image isn't showing itself and this error appears:"The following classes could not be found:
- ImageView (Change to android.widget.ImageView, Fix Build Path, Edit XML)"
this is my xml code
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:contentDescription="#string/hello_world"
android:orientation="vertical"
tools:context=".MainActivity" >
<EditText android:id="#+id/edit_message"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:hint="#string/edit_message" />
<ImageView
android:id="#+id/phone_icon"
android:contentDescription="#string/description"
android:layout_width="wrap_content"
android:scaleType="fitXY"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:src="#drawable/phone_on" />
<Button
android:id="#+id/toggleButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/ToggleSilentMode" />
</LinearLayout>
thanks

This is one issue that I have also run across recently. It was sort of a misleading error to me and kept me stumped for around 30 minutes this morning. It isn't that Android cannot find the class. It is that it is having trouble importing the image source file.
Now the reason that it is having trouble finding the image is because I did not copy the source image into the directory correctly. I have chosen to drag the source file from another folder directory into the appropriate locations. In the process, it did not copy the file over properly. Or it copied it over as just a link to the other resource.
As a result Android does not know what to do with the resource and throws that odd error. In order to resolve this problem, you need to delete the old image sources and then replace them with direct full copies of their equivalents. Then you should see this error go away and the application working as expected from the xml layout code.

I faced the same problem once. To get it out, I replaced all the existing images, now it worked.

I had the same issue, when added a new ImageView in my xml with an image src.
I tried to open this image with Photoshop and get an "module format error". So the image was corrupted. The problem was solved creating a new image similar to the first one.
Hope it works :)

Drawable not showing up

I have a fairly simple xml file that has an image button in it. The image shows up fine on the Graphical Layout xml designer, shows up fine when I run a development build, but as soon as I create the signed apk file and run it, the image no longer shows up. It's just an empty button. I can't think of a reason why, any ideas? The xml file looks like this:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/navigation_root"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<TextView
android:id="#+id/navigation_text"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="5dp"
android:text="TextView"
android:textAppearance="?android:attr/textAppearanceLarge" />
<SeekBar
android:id="#+id/navigation_seekbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:layout_weight="1"
android:padding="5dp" />
<LinearLayout
android:id="#+id/linearLayout1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="5dp" >
<ImageButton
android:id="#+id/part_select_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="#drawable/chapter_select" />
<Button
android:id="#+id/navigation_ok_button"
android:layout_width="75dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:text="#string/ok" />
<Button
android:id="#+id/navigation_cancel_button"
android:layout_width="75dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:text="#string/cancel" />
</LinearLayout>
</LinearLayout>
The image #drawable/chapter_select is a fairly small (41*41) png file that is in the res/drawable folder.

Seems like this is a bug with android, where sometimes the first image in the drawable folder doesn't show up. Added a dummy image called aaaa.png to the drawable folder and problem was solved. Found the answer here: ImageButton does not display a particular drawable

One of the reason is:
If you are using Vector file as a drawableLeft or drawableRight (or drawableStart or drawableEnd) in layout.xml, then you have to use androidx.appcompat.widget.AppCompatButton (formerly android.support.v7.widget.AppCompatButton) instead of Button.
Simple View like Button or Textview doesn't support Vector file as a drawableLeft or drawableRight (or drawableStart or drawableEnd) in my case.

Had the same issue and resolved it by removing all special characters. In my case it was dashes '-' in the filename:
background-720.png => background.png.

try to put the image in drawable-hdpi and drawable-mdpi folder
depends on what device you run you app , the image is searched in these folders...
But puting in drawable means that the image should be available everywhere, but somethimes (depends on your manifest settings) this could not be true, I mean you can turn of the compatibility mode.
also you can try dinamically at run time to set the image to the view
iv.setImageResource(R.drawable.somethig);

My situation was weird.Everything was correct until integrating FireBase Crash report to my Application.
I just added compile 'com.google.firebase:firebase-crash:11.0.1' & DrawableLeft vanished .When i went through the xml , noticed a warning (In lined below).
So added android:drawableStart & issue gone.
Still I am wondering about the relation of FireBase Crash reporting to the same.
Using left/right instead of start/end attributes Using Gravity#LEFT
and Gravity#RIGHT can lead to problems when a layout is rendered in
locales where text flows from right to left. Use Gravity#START and
Gravity#END instead.
Similarly, in XML gravity and layout_gravity attributes, use start
rather than left. For XML attributes such as paddingLeft and
layout_marginLeft, use paddingStart and layout_marginStart.
NOTE: If your minSdkVersion is less than 17, you should add both the
older left/right attributes as well as the new start/right attributes.
On older platforms, where RTL is not supported and the start/right
attributes are unknown and therefore ignored, you need the older
left/right attributes.
There is a separate lint check which catches that type of error.
(Note: For Gravity#LEFT and Gravity#START, you can use these constants
even when targeting older platforms, because the start bitmask is a
superset of the left bitmask. Therefore, you can use gravity="start"
rather than gravity="left|start".)

Check your image size. If you're using an unnecessarily large asset when actually deployed it might just not show despite looking correct in the designer.

Well ! in my case setting MinifyEnabled false and shrinkResources false is working fine now.
i was getting image from drawable. it was working pretty nice in debug version but after release version of apk it was showing sometime blank ImageView.
minifyEnabled false
shrinkResources true
**
See the Screenshots
**
Hope this may help anyone.

I had a similar problem where a drawable png was not showing up in Android Studio. Deleted the file and added it again in the drawable folder and it Worked for me.

Non-urgent Android layout id attribute quirk

I'm working on a couple of apps at the moment while I try to learn my way around the Android SDK. I had a bit of trouble recently with my layouts where I was defining, for example, an EditText element as such...
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<EditText
android:id="#+id/price_per_pack"
android:layout_width="100dip"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_toLeftOf="#id/price_per_pack"
android:layout_alignParentLeft="true"
android:textSize="12pt"
android:text="Price Per Pack"/>
</LinearLayout>
The application was compiling correctly, however when I attempted to start the activity which utilizes this layout nothing would happen. Through a process of elimination I identified the id attribute as the troublesome one and while playing about I discovered that changing
android:id="#+id/price_per_pack"
to
android:id="#+android:id/price_per_pack"
solved my problem and the application behaved as expected. My initial attempt at declaring the id attribute was based upon examples in the SDK documentation so I'm wondering if somebody could explain to me why I needed to make the above change to get it working?
I'm sure that it won't make any difference but I'm developing using the android-mode.el emacs plugin and have a completely up-to-date copy of the SDK.
Thanks in advance.

From Android Documentation:
With the android package namespace in place, we're now referencing an ID from the android.R resources class, rather than the local resources class.
It looks like you might have some syntax errors in your code posted.