android: visual issues on a custom slider - android

I created a custom slider that was working fine, but suddenly it started showing visual issues and i have no idea where to look to solve this problem.
the issue is the appearance of black borders/gradients around it. i tested on android 6 and android 4.0.3 as well. both are showing the same problem. on android 4.0.3, i can also see this problem around the actions in the toolbar when i press on them, it makes like a black gradient shadow.
any idea?
the code of my slider is:
public class StyledSeekBar extends SeekBar {
public StyledSeekBar(Context context) {
super(context);
this.init();
}
public StyledSeekBar(Context context, AttributeSet attrs) {
super(context, attrs);
this.init();
}
public StyledSeekBar(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
this.init();
}
#TargetApi(Build.VERSION_CODES.LOLLIPOP)
public StyledSeekBar(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
this.init();
}
/**
* Initializes the instance of this class.
*/
private void init(){
setThumb(getResources().getDrawable(R.drawable.apptheme_scrubber_control_selector_holo_light));
setIndeterminateDrawable(getResources().getDrawable(R.drawable.apptheme_scrubber_progress_horizontal_holo_light));
setProgressDrawable(getResources().getDrawable(R.drawable.apptheme_scrubber_progress_horizontal_holo_light));
}
}


it's no shadow. Looks like .png stretched. Try 9png


I found the solution! To fix this kind of issue, it is necessary to verify the 9-patch images and resolve all the bad patches. This can be done by using the draw9patch tool.

Related

My custom view failed to add to xml [duplicate]

When creating a custom view, I have noticed that many people seem to do it like this:
public MyView(Context context) {
super(context);
// this constructor used when programmatically creating view
doAdditionalConstructorWork();
}
public MyView(Context context, AttributeSet attrs) {
super(context, attrs);
// this constructor used when creating view through XML
doAdditionalConstructorWork();
}
private void doAdditionalConstructorWork() {
// init variables etc.
}
My first question is, what about the constructor MyView(Context context, AttributeSet attrs, int defStyle)? I'm not sure where it is used, but I see it in the super class. Do I need it, and where is it used?
There's another part to this question.

Long story short, No, but if you do override any constructor, then ensure to call super(...) with the exact same number of arguments (like, see Jin's answer for example why).
If you will add your custom View from xml also like :
<com.mypack.MyView
...
/>
you will need the constructor public MyView(Context context, AttributeSet attrs), otherwise you will get an Exception when Android tries to inflate your View.
If you add your View from xml and also specify the android:style attribute like :
<com.mypack.MyView
style="#styles/MyCustomStyle"
...
/>
the 2nd constructor will also be called and default the style to MyCustomStyle before applying explicit XML attributes.
The third constructor is usually used when you want all of the Views in your application to have the same style.

If you override all three constructors, please DO NOT CASCADE this(...) CALLS. You should instead be doing this:
public MyView(Context context) {
super(context);
init(context, null, 0);
}
public MyView(Context context, AttributeSet attrs) {
super(context,attrs);
init(context, attrs, 0);
}
public MyView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init(context, attrs, defStyle);
}
private void init(Context context, AttributeSet attrs, int defStyle) {
// do additional work
}
The reason is that the parent class might include default attributes in its own constructors that you might be accidentally overriding. For example, this is the constructor for TextView:
public TextView(Context context) {
this(context, null);
}
public TextView(Context context, #Nullable AttributeSet attrs) {
this(context, attrs, com.android.internal.R.attr.textViewStyle);
}
public TextView(Context context, #Nullable AttributeSet attrs, int defStyleAttr) {
this(context, attrs, defStyleAttr, 0);
}
If you did not call super(context), you would not have properly set R.attr.textViewStyle as the style attr.

MyView(Context context)
Used when instanciating Views programmatically.
MyView(Context context, AttributeSet attrs)
Used by the LayoutInflater to apply xml attributes. If one of this attribute is named style, attributes will be looked up the the style before looking for explicit values in the layout xml file.
MyView(Context context, AttributeSet attrs, int defStyleAttr)
Suppose you want to apply a default style to all widgets without having to specify style in each layout file. For an example make all checkboxes pink by default. You can do this with defStyleAttr and the framework will lookup the default style in your theme.
Note that defStyleAttr was incorrectly named defStyle some time ago and there is some discussion about whether this constructor is really needed or not. See https://code.google.com/p/android/issues/detail?id=12683
MyView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes)
The 3rd constructor works well if you have control over the base theme of the applications. That is working for google because they ship their widgets along side the default Themes. But suppose you're writing a widget library and you want a default style to be set without your users needing to tweak their theme. You can now do this using defStyleRes by setting it to the default value in the 2 first constructors:
public MyView(Context context) {
super(context, null, 0, R.style.MyViewStyle);
init();
}
public MyView(Context context, AttributeSet attrs) {
super(context, attrs, 0, R.style.MyViewStyle);
init();
}
All in all
If you're implementing your own views, only the 2 first constructors should be needed and can be called by the framework.
If you want your Views to be extensible, you might implement the 4th constructor for children of your class to be able to use global styling.
I don't see a real use case for the 3rd constructor. Maybe a shortcut if you don't provide a default style for your widget but still want your users to be able to do so. Shouldn't happen that much.

Kotlin seems to take away a lot of this pain:
class MyView
#JvmOverloads constructor(context: Context, attrs: AttributeSet? = null, defStyle: Int = 0)
: View(context, attrs, defStyle)
#JvmOverloads will generate all required constructors (see that annotation's documentation), each of which presumably calls super(). Then, simply replace your initialization method with a Kotlin init {} block. Boilerplate code gone!

The third constructor is much more complicated.Let me hold an example.
Support-v7 SwitchCompact package supports thumbTint and trackTint attribute since 24 version while 23 version does not support them.Now you want to support them in 23 version and how will you do to achieve this?
We assume to use custom View SupportedSwitchCompact extends SwitchCompact.
public SupportedSwitchCompat(Context context) {
this(context, null);
}
public SupportedSwitchCompat(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public SupportedSwitchCompat(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
private void init(){
mThumbDrawable = getThumbDrawable();
mTrackDrawable = getTrackDrawable();
applyTint();
}
It's a traditional code style.Note we pass 0 to the third param here. When you run the code, you will find getThumbDrawable() always return null how strange it is because the method getThumbDrawable() is its super class SwitchCompact's method.
If you pass R.attr.switchStyle to the third param, everything goes well.So why?
The third param is a simple attribute. The attribute points to a style resource.In above case, the system will find switchStyle attribute in current theme fortunately system finds it.
In frameworks/base/core/res/res/values/themes.xml, you will see:
<style name="Theme">
<item name="switchStyle">#style/Widget.CompoundButton.Switch</item>
</style>

If you have to include three constructors like the one under discussion now, you could do this too.
public MyView(Context context) {
this(context,null,0);
}
public MyView(Context context, AttributeSet attrs) {
this(context,attrs,0);
}
public MyView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
doAdditionalConstructorWork();
}

Custom/compound view: NoSuchMethodError for LinearLayout constructor

I have an Android library, LabelledSpinner which is essentially a compound view that holds a Spinner with TextViews, all in a LinearLayout.
However, when I run the app on Android 4 devices (my library supports Android 4 upwards), I get the following error:
java.lang.RuntimeException: Unable to start activity ComponentInfo{MyActivity}: android.view.InflateException: Binary XML file line #98: Error inflating class com.farbod.labelledspinner.LabelledSpinner
...
Caused by: java.lang.NoSuchMethodError: android.widget.LinearLayout.<init>
at com.farbod.labelledspinner.LabelledSpinner.<init>(LabelledSpinner.java:117)
at com.farbod.labelledspinner.LabelledSpinner.<init>(LabelledSpinner.java:112)
at com.farbod.labelledspinner.LabelledSpinner.<init>(LabelledSpinner.java:108)
...
Users of my library encountered the same issue.
Here are my constructors (you can also view the entire file on the GitHub repository) - note that this file extends LinearLayout:
public LabelledSpinner(Context context) {
this(context, null);
}
public LabelledSpinner(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public LabelledSpinner(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
initializeLayout(context, attrs);
}
#TargetApi(Build.VERSION_CODES.LOLLIPOP)
public LabelledSpinner(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
initializeLayout(context, attrs);
}
I think the error points specifically to the third constructor (the line references in the error aren't exactly clear to me).
I find it strange that I am given this error, as looking at the LinearLayout class, the constructors I am using are available:
public LinearLayout(Context context) {...}
public LinearLayout(Context context, #Nullable AttributeSet attrs) {...}
public LinearLayout(Context context, #Nullable AttributeSet attrs, int defStyleAttr) {...}
public LinearLayout(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
...
}
I am not getting this issue on Android Lollipop devices.

It turns out that in my case, my app was using an outdated version of the library (to be specific, I had not pushed the updates from my library to Bintray).
More information on the comment on the GitHub issue.

Android: Open Sliding Drawer in Graphical Layout in Eclipse?

Is it possible to open a SlidingDrawer when viewed inside the Eclipse graphical layout preview? By default it's closed when viewed so I cannot see what is happening with the layouts inside the SlidingDrawer.
If this isn't possible, what would be the best way to handle this problem? A separate layout file I guess?

I am not sure if there is a standard way to do this.
I currently use the following method: override SlidingDrawer.onFinishInflate() to force it open when in Eclipse layout preview.
import android.widget.SlidingDrawer;
public class MySlidingDrawer extends SlidingDrawer {
public MySlidingDrawer(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
public MySlidingDrawer(Context context, AttributeSet attrs) {
super(context, attrs);
}
#Override
protected void onFinishInflate() {
super.onFinishInflate();
if (isInEditMode()) {
open();
}
}
}
Then, of course, replace SlidingDrawer by my.package.MySlidingDrawer in layout.xml.

Do I need all three constructors for an Android custom view?

When creating a custom view, I have noticed that many people seem to do it like this:
public MyView(Context context) {
super(context);
// this constructor used when programmatically creating view
doAdditionalConstructorWork();
}
public MyView(Context context, AttributeSet attrs) {
super(context, attrs);
// this constructor used when creating view through XML
doAdditionalConstructorWork();
}
private void doAdditionalConstructorWork() {
// init variables etc.
}
My first question is, what about the constructor MyView(Context context, AttributeSet attrs, int defStyle)? I'm not sure where it is used, but I see it in the super class. Do I need it, and where is it used?
There's another part to this question.

Long story short, No, but if you do override any constructor, then ensure to call super(...) with the exact same number of arguments (like, see Jin's answer for example why).
If you will add your custom View from xml also like :
<com.mypack.MyView
...
/>
you will need the constructor public MyView(Context context, AttributeSet attrs), otherwise you will get an Exception when Android tries to inflate your View.
If you add your View from xml and also specify the android:style attribute like :
<com.mypack.MyView
style="#styles/MyCustomStyle"
...
/>
the 2nd constructor will also be called and default the style to MyCustomStyle before applying explicit XML attributes.
The third constructor is usually used when you want all of the Views in your application to have the same style.

If you override all three constructors, please DO NOT CASCADE this(...) CALLS. You should instead be doing this:
public MyView(Context context) {
super(context);
init(context, null, 0);
}
public MyView(Context context, AttributeSet attrs) {
super(context,attrs);
init(context, attrs, 0);
}
public MyView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init(context, attrs, defStyle);
}
private void init(Context context, AttributeSet attrs, int defStyle) {
// do additional work
}
The reason is that the parent class might include default attributes in its own constructors that you might be accidentally overriding. For example, this is the constructor for TextView:
public TextView(Context context) {
this(context, null);
}
public TextView(Context context, #Nullable AttributeSet attrs) {
this(context, attrs, com.android.internal.R.attr.textViewStyle);
}
public TextView(Context context, #Nullable AttributeSet attrs, int defStyleAttr) {
this(context, attrs, defStyleAttr, 0);
}
If you did not call super(context), you would not have properly set R.attr.textViewStyle as the style attr.

MyView(Context context)
Used when instanciating Views programmatically.
MyView(Context context, AttributeSet attrs)
Used by the LayoutInflater to apply xml attributes. If one of this attribute is named style, attributes will be looked up the the style before looking for explicit values in the layout xml file.
MyView(Context context, AttributeSet attrs, int defStyleAttr)
Suppose you want to apply a default style to all widgets without having to specify style in each layout file. For an example make all checkboxes pink by default. You can do this with defStyleAttr and the framework will lookup the default style in your theme.
Note that defStyleAttr was incorrectly named defStyle some time ago and there is some discussion about whether this constructor is really needed or not. See https://code.google.com/p/android/issues/detail?id=12683
MyView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes)
The 3rd constructor works well if you have control over the base theme of the applications. That is working for google because they ship their widgets along side the default Themes. But suppose you're writing a widget library and you want a default style to be set without your users needing to tweak their theme. You can now do this using defStyleRes by setting it to the default value in the 2 first constructors:
public MyView(Context context) {
super(context, null, 0, R.style.MyViewStyle);
init();
}
public MyView(Context context, AttributeSet attrs) {
super(context, attrs, 0, R.style.MyViewStyle);
init();
}
All in all
If you're implementing your own views, only the 2 first constructors should be needed and can be called by the framework.
If you want your Views to be extensible, you might implement the 4th constructor for children of your class to be able to use global styling.
I don't see a real use case for the 3rd constructor. Maybe a shortcut if you don't provide a default style for your widget but still want your users to be able to do so. Shouldn't happen that much.

Kotlin seems to take away a lot of this pain:
class MyView
#JvmOverloads constructor(context: Context, attrs: AttributeSet? = null, defStyle: Int = 0)
: View(context, attrs, defStyle)
#JvmOverloads will generate all required constructors (see that annotation's documentation), each of which presumably calls super(). Then, simply replace your initialization method with a Kotlin init {} block. Boilerplate code gone!

The third constructor is much more complicated.Let me hold an example.
Support-v7 SwitchCompact package supports thumbTint and trackTint attribute since 24 version while 23 version does not support them.Now you want to support them in 23 version and how will you do to achieve this?
We assume to use custom View SupportedSwitchCompact extends SwitchCompact.
public SupportedSwitchCompat(Context context) {
this(context, null);
}
public SupportedSwitchCompat(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public SupportedSwitchCompat(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
private void init(){
mThumbDrawable = getThumbDrawable();
mTrackDrawable = getTrackDrawable();
applyTint();
}
It's a traditional code style.Note we pass 0 to the third param here. When you run the code, you will find getThumbDrawable() always return null how strange it is because the method getThumbDrawable() is its super class SwitchCompact's method.
If you pass R.attr.switchStyle to the third param, everything goes well.So why?
The third param is a simple attribute. The attribute points to a style resource.In above case, the system will find switchStyle attribute in current theme fortunately system finds it.
In frameworks/base/core/res/res/values/themes.xml, you will see:
<style name="Theme">
<item name="switchStyle">#style/Widget.CompoundButton.Switch</item>
</style>

If you have to include three constructors like the one under discussion now, you could do this too.
public MyView(Context context) {
this(context,null,0);
}
public MyView(Context context, AttributeSet attrs) {
this(context,attrs,0);
}
public MyView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
doAdditionalConstructorWork();
}

Should I call super() or call this() for android custom view constructors?

When creating a custom view, I have noticed that many people seem to do it like this:
public MyView(Context context) {
super(context);
// this constructor used when programmatically creating view
doAdditionalConstructorWork();
}
public MyView(Context context, AttributeSet attrs) {
super(context, attrs);
// this constructor used when creating view through XML
doAdditionalConstructorWork();
}
private void doAdditionalConstructorWork() {
// init variables etc.
}
My problem with this is that it stops me from making my variables final. Any reason not to do the following?
public MyView(Context context) {
this(context, null);
// this constructor used when programmatically creating view
}
public MyView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
// this constructor used when creating view through XML
}
public MyView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
// this constructor used where?
// init variables
}
I've been able to create the view just fine through XML and through code, but I'm not sure if there are any drawbacks to this approach. Will this work in all cases?
There is another part to this question

The only drawback I can see (that no one seems to have mentioned) is that your second constructor loses the defStyle of the superclass, because you set it to zero. Look at the source code for any of Android's View classes, and you'll notice that the second constructor always has a specific defStyle defined.
For example, this is the second constructor of ListView:
public ListView(Context context, AttributeSet attrs) {
this(context, attrs, com.android.internal.R.attr.listViewStyle);
}
If you were to extend ListView using the second approach that you describe, com.android.internal.R.attr.listViewStyle would no longer be the defStyle, because you'd be bypassing that second super constructor and making it zero instead. I suppose you could resolve this by using the same defstyle as ListView, like so:
public MyView(Context context, AttributeSet attrs) {
this(context, attrs, android.R.attr.listViewStyle);
}
But it's not exactly the "purist" way, because you're artificially forcing it to have the same defStyle as ListView.
So, contrary to what the others said, I actually think you're better off using the first doAdditionalConstructorWork() approach outlined in your post, because that at least makes sure that the defStyle is set correctly.

Copied this from my answer for a similar question.
If you override all three constructors, please DO NOT CASCADE this(...) CALLS. You should instead be doing this:
public MyView(Context context) {
super(context);
init(context, null, 0);
}
public MyView(Context context, AttributeSet attrs) {
super(context,attrs);
init(context, attrs, 0);
}
public MyView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init(context, attrs, defStyle);
}
private void init(Context context, AttributeSet attrs, int defStyle) {
// do additional work
}
The reason is that the parent class might include default attributes in its own constructors that you might be accidentally overriding. For example, this is the constructor for TextView:
public TextView(Context context) {
this(context, null);
}
public TextView(Context context, #Nullable AttributeSet attrs) {
this(context, attrs, com.android.internal.R.attr.textViewStyle);
}
public TextView(Context context, #Nullable AttributeSet attrs, int defStyleAttr) {
this(context, attrs, defStyleAttr, 0);
}
If you did not call super(context), you would not have properly set R.attr.textViewStyle as the style attr.

Yup, that's a reasonable pattern to use so you don't have to repeat the custom work in every one of your constructors. And no, there don't appear to be any drawbacks to the method.

It purely depends on your requirement. Let us say if you want to use any methods in parent class without overriding their functionality in your custom view, then you need to use super() and instantiate parent class. If you dont need to invoke any methods in parent class all implementations are overridden in your custom view, then you don't need. Read A custom View Example section in this link.

Edit:
This is not Okay. See other answers to this question for reasons.
Original Answer:
It is Ok.
When we look at the source of TextView.java.
They have used the same hierarchy.
So you are Okay with this approach.

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