I have problems with implementation of my custom PagerAdapter and using it with a ViewPager. This sample PagerAdapter has 10 items, every item is a button with it's index as text. When I run my program, I see a button with text '1' insted of '0'. And when I swipe to other items I get only blank views. When I swipe backwards sometimes I see a button with some number, but it disappears (maybe it is destroying and I remove it from the container), and sometimes I see a button with a number, but the number changes after the swipe (I think I create a new Button and I add it to the container, and for some reasons the viewpager shows this new button).
How can I fix this implementation? I haven't seen difference in examples.
My PagerAdapter implementation:
public class MyPagerAdapter extends PagerAdapter {
@Override
public int getCount() {
return 10;
}
@Override
public boolean isViewFromObject(View view, Object o) {
return o.getClass()==view.getClass();
}
@Override
public Object instantiateItem(ViewGroup container, int position) {
Button button = new Button(container.getContext());
ViewGroup.LayoutParams params = new ActionBar.LayoutParams(-1,-1);
button.setLayoutParams(params);
button.setText(String.valueOf(position));
container.addView(button);
return button;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((Button)object);
}
}
And my Activity:
public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ViewPager pager = (ViewPager) findViewById(R.id.pager);
pager.setAdapter(new MyPagerAdapter());
}
}
A PagerAdapter may implement a form of View recycling if desired or use a more sophisticated method of managing page Views such as Fragment transactions where each page is represented by its own Fragment. ViewPager associates each page with a key Object instead of working with Views directly.
Implement Swipe Views You can create swipe views using AndroidX's ViewPager widget. To use ViewPager and tabs, you need to add a dependency on ViewPager and on Material Components to your project. To insert child views that represent each page, you need to hook this layout to a PagerAdapter .
Implementation of PagerAdapter that represents each page as a Fragment that is persistently kept in the fragment manager as long as the user can return to the page. FragmentStatePagerAdapter. Implementation of PagerAdapter that uses a Fragment to manage each page.
Here is complete code:
xml layout:
<LinearLayout 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"
android:orientation="vertical"
tools:context="com.example.androidviewpagerapp.MainActivity" >
<android.support.v4.view.ViewPager
android:id="@+id/pager"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</LinearLayout>
MyPagerAdapter class:
import android.support.v4.view.PagerAdapter;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.Toast;
public class MyPagerAdapter extends PagerAdapter {
@Override
public int getCount() {
return 10;
}
@Override
public boolean isViewFromObject(View view, Object o) {
return o==view;
}
@Override
public Object instantiateItem(final ViewGroup container, int position) {
Button button = new Button(container.getContext());
ViewGroup.LayoutParams params = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
button.setLayoutParams(params);
button.setText(String.valueOf(position));
final int page = position;
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(container.getContext(), "You clicked: " + page + ". page.", Toast.LENGTH_SHORT).show();
}
});
container.addView(button);
return button;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((Button)object);
}
}
MainActivity:
import android.support.v4.view.ViewPager;
import android.app.Activity;
import android.os.Bundle;
public class MainActivity extends Activity {
ViewPager viewPager;
MyPagerAdapter myPagerAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
viewPager = (ViewPager)findViewById(R.id.pager);
myPagerAdapter = new MyPagerAdapter();
viewPager.setAdapter(myPagerAdapter);
}
}
You will see that Buttons are full screen. To avoid that you need to create some layout (like LinearLayout) and add button to that layout.
Example:
import android.support.v4.view.PagerAdapter;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.Toast;
public class MyPagerAdapter extends PagerAdapter {
@Override
public int getCount() {
return 10;
}
@Override
public boolean isViewFromObject(View view, Object o) {
return o==view;
}
@Override
public Object instantiateItem(final ViewGroup container, int position) {
Button button = new Button(container.getContext());
ViewGroup.LayoutParams params = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
button.setLayoutParams(params);
button.setText(String.valueOf(position));
LinearLayout layout = new LinearLayout(container.getContext());
layout.setOrientation(LinearLayout.VERTICAL);
ViewGroup.LayoutParams layoutParams = new ViewGroup.LayoutParams(
ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);
//add buton to layout
layout.addView(button);
final int page = position;
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(container.getContext(), "You clicked: " + page + ". page.", Toast.LENGTH_SHORT).show();
}
});
//to container add layout instead of button
container.addView(layout);
//return layout instead of button
return layout;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
//cast to LinearLayout
container.removeView((LinearLayout)object);
}
}
if you want to inflate views in pager you must have to implement two methods. instantiateItem and destroyItem
public class DialogPagerAdapter extends PagerAdapter {
private Context mContext;
//view inflating..
@Override
public Object instantiateItem(ViewGroup collection, int position) {
LayoutInflater inflater = LayoutInflater.from(mContext);
ViewGroup layout = (ViewGroup) inflater.inflate(R.layout.account_dialog_signin_viewpagers,
collection, false);
TextView tvLabel = (TextView) layout.findViewById(R.id.textView);
switch (position) {
case 0:
tvLabel.setText("Log In");
tvLabel.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
}
});
break;
case 1:
tvLabel.setText("Sign Up");
tvLabel.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
}
});
break;
case 2:
tvLabel.setText("Send Reset Link");
tvLabel.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//onOptionClickForgot.OnOptionClick();
}
});
break;
}
collection.addView(layout);
return layout;
}
@Override
public void destroyItem(ViewGroup collection, int position, Object view) {
collection.removeView((View) view);
}
@Override
public int getCount() {
return 3;
}
@Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
}
Simply call it like
viewPager.setAdapter(new DialogPagerAdapter);
xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="@dimen/dialog_button_height"
android:paddingLeft="@dimen/dimen_2"
android:paddingRight="@dimen/dimen_2"
android:minHeight="@dimen/dialog_button_height">
<TextView
android:id="@+id/textView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_centerInParent="true"
android:gravity="center"
android:text="@string/app_name"
android:textColor="@color/white"
android:textSize="@dimen/text_size_medium" />
</RelativeLayout>
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