Question

Summary of preference is allowed only 2 lines .
If I want to display 3 lines or more in summary . How can I do ?

Answer 1

You can create you Preference class by extending any existing preference:

public class LongSummaryCheckboxPreference extends CheckboxPreference
{
    public LongSummaryCheckboxPreference(Context ctx, AttributeSet attrs, int defStyle)
    {
        super(ctx, attrs, defStyle);        
    }

    public LongSummaryCheckboxPreference(Context ctx, AttributeSet attrs)
    {
        super(ctx, attrs);  
    }

    @Override
    protected void onBindView(View view)
    {       
        super.onBindView(view);

        TextView summary= (TextView)view.findViewById(android.R.id.summary);
        summary.setMaxLines(3);
    }       
}

And then in preferences.xml:

 <com.your.package.name.LongSummaryCheckBoxPreference 
    android:key="@string/key"
    android:title="@string/title"
    android:summary="@string/summary" 
    ... />

The drawback is that you need to subclass all preference types you need 3 lines summary for.