If you’re using the Preferences API in Android, and want to confirm (show a dialog, perform a test, etc) before a Preference is updated, you need to find that Preference item and call setOnPreferenceChangeListener to a custom listener. This can work in conjunction with PreferenceManager.registerOnSharedPreferenceChangeListener, you just need to return false to have the Preference […]
Some Launchers will launch an app at it’s LAUNCH activity on top of the last point the user was at. Imagine: 1. User opens app. 2. The Launcher Activity is designated at Activity A, so that’s what opens. 3. User navigates several Activities deep and ends up at Activity D (A > B > C […]
The title isn’t exactly accurate – you can’t “restart” an app per se – but you can get pretty close:
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// presumably in an Activity; otherwise a Context instance will be needed for several methods Intent intent = getPackageManager().getLaunchIntentForPackage(getPackageName()); intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK); startActivity(intent); |
This starts the Activity specified in your manifest as the “LAUNCHER”, in a new task stack (history), and clear the existing stack.
In xml, you can use ?attr/actionBarSize, but if you need access to that value in Java…
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public int getActionBarSize() { TypedArray styledAttributes = getTheme().obtainStyledAttributes(new int[] { android.R.attr.actionBarSize }); int actionBarSize = (int) styledAttributes.getDimension(0, 0); styledAttributes.recycle(); return actionBarSize; } |
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package com.qozix.view; import android.view.View; import android.view.ViewGroup; import android.view.ViewParent; import java.util.ArrayList; import java.util.Collection; /** * Collection of utility functions for finding Views in a hierarchy. */ public class Finder { /** * Interface with method to determine if a particular View meets arbitrary criteria for inclusion in a * ViewFinder method's result set. */ public interface Qualifier { /** * Qualify boolean. * * @param view the view * @return the boolean */ boolean qualify(View view); } /** * Helper method to pre-cast Views to the type of the declared instance. * * @param <T> The Class reference (View subclass) the View should be cast to. * @param viewGroup The ViewGroup instance to search for the View specified by #id. * @param id The id of the View to be located within this Activity's view tree. * @return The View with the matching id. */ @SuppressWarnings("unchecked") public <T extends View> T findAndCast(ViewGroup viewGroup, int id) { return (T) viewGroup.findViewById(id); } /** * Utility * * @param qualifier * @param view * @return */ private static boolean qualifies(Qualifier qualifier, View view) { return qualifier == null || qualifier.qualify(view); } /** * Utility * * @param view the view * @return view group */ public static ViewGroup getContainingViewGroup(View view) { ViewParent viewParent = view.getParent(); if (viewParent instanceof ViewGroup) { return (ViewGroup) viewParent; } return null; } /** * Find first view. * * @param viewGroup the view group * @param qualifier the qualifier * @return the view */ public static View findFirst(ViewGroup viewGroup, Qualifier qualifier) { for (int i = 0; i < viewGroup.getChildCount(); i++) { View child = viewGroup.getChildAt(i); if (qualifies(qualifier, child)) { return child; } if (child instanceof ViewGroup) { View match = findFirst((ViewGroup) child, qualifier); if (match != null) { return match; } } } return null; } /** * Find all collection. * * @param viewGroup the view group * @return the collection */ public static Collection<View> findAll(ViewGroup viewGroup) { return findAll(viewGroup, null); } /** * Find all collection. * * @param viewGroup the view group * @param qualifier the qualifier * @return the collection */ public static Collection<View> findAll(ViewGroup viewGroup, Qualifier qualifier) { return findAll(viewGroup, qualifier, null); } /** * Find all collection. * * @param viewGroup the view group * @param qualifier the qualifier * @param out the out * @return the collection */ public static Collection<View> findAll(ViewGroup viewGroup, Qualifier qualifier, Collection<View> out) { if (out == null) { out = new ArrayList<>(); } for (int i = 0; i < viewGroup.getChildCount(); i++) { View child = viewGroup.getChildAt(i); if (qualifies(qualifier, child)) { out.add(child); } if (child instanceof ViewGroup) { findAll((ViewGroup) child, qualifier, out); } } return out; } /** * Get first child view. * * @param viewGroup the view group * @return the view */ public static View getFirstChild(ViewGroup viewGroup) { return viewGroup.getChildAt(0); } /** * Get first child view. * * @param viewGroup the view group * @param qualifier the qualifier * @return the view */ public static View getFirstChild(ViewGroup viewGroup, Qualifier qualifier) { for (int i = 0; i < viewGroup.getChildCount(); i++) { View child = viewGroup.getChildAt(i); if (qualifies(qualifier, child)) { return child; } } return null; } /** * Get last child view. * * @param viewGroup the view group * @return the view */ public static View getLastChild(ViewGroup viewGroup) { return viewGroup.getChildAt(viewGroup.getChildCount() - 1); } /** * Get last child view. * * @param viewGroup the view group * @param qualifier the qualifier * @return the view */ public static View getLastChild(ViewGroup viewGroup, Qualifier qualifier) { for (int i = viewGroup.getChildCount() - 1; i >= 0; i--) { View child = viewGroup.getChildAt(i); if (qualifies(qualifier, child)) { return child; } } return null; } /** * Get children collection. * * @param viewGroup the view group * @return the collection */ public static Collection<View> getChildren(ViewGroup viewGroup) { return getChildren(viewGroup, null); } /** * @param viewGroup * @param qualifier * @return */ public static Collection<View> getChildren(ViewGroup viewGroup, Qualifier qualifier) { return getChildren(viewGroup, qualifier, new ArrayList<>()); } /** * Get children collection. * * @param viewGroup the view group * @param qualifier the qualifier * @param out * @return the collection */ public static Collection<View> getChildren(ViewGroup viewGroup, Qualifier qualifier, Collection<View> out) { for (int i = 0; i < viewGroup.getChildCount(); i++) { View child = viewGroup.getChildAt(i); if (qualifies(qualifier, child)) { out.add(child); } } return out; } /** * Gets ancestors. * * @param view the view * @return the ancestors */ public static Collection<ViewGroup> getAncestors(View view) { return getAncestors(view, null); } /** * Gets ancestors. * * @param view the view * @param qualifier the qualifier * @return the ancestors */ public static Collection<ViewGroup> getAncestors(View view, Qualifier qualifier) { return getAncestors(view, qualifier, new ArrayList<>()); } /** * Gets ancestors. * * @param view the view * @param qualifier the qualifier * @param out * @return the ancestors */ public static Collection<ViewGroup> getAncestors(View view, Qualifier qualifier, Collection<ViewGroup> out) { ViewGroup parent = getContainingViewGroup(view); while (parent != null) { if (qualifies(qualifier, parent)) { out.add(parent); } parent = getContainingViewGroup(parent); } return out; } /** * Get siblings collection. * * @param view the view * @return the collection */ public static Collection<View> getSiblings(View view) { return getSiblings(view, null); } /** * Get siblings collection. * * @param view the view * @param qualifier the qualifier * @return the collection */ public static Collection<View> getSiblings(View view, Qualifier qualifier) { ViewGroup parent = getContainingViewGroup(view); if (parent == null) { return null; } Collection<View> siblings = new ArrayList<>(); for (int i = 0; i < parent.getChildCount(); i++) { View child = parent.getChildAt(i); if (child != view && qualifies(qualifier, child)) { siblings.add(child); } } return siblings; } /** * Get previous sibling view. * * @param view the view * @return the view */ public static View getPreviousSibling(View view) { return getPreviousSibling(view, null); } /** * Get previous sibling view. * * @param view the view * @param qualifier the qualifier * @return the view */ public static View getPreviousSibling(View view, Qualifier qualifier) { ViewGroup parent = getContainingViewGroup(view); if (parent == null) { return null; } for (int i = 0; i < parent.getChildCount(); i++) { View child = parent.getChildAt(i); if (child == view) { for (; i > 0; ) { View sibling = parent.getChildAt(--i); if (qualifies(qualifier, sibling)) { return sibling; } } } } return null; } /** * Get next sibling view. * * @param view the view * @return the view */ public static View getNextSibling(View view) { return getNextSibling(view, null); } /** * Get next sibling view. * * @param view the view * @param qualifier the qualifier * @return the view */ public static View getNextSibling(View view, Qualifier qualifier) { ViewGroup parent = getContainingViewGroup(view); if (parent == null) { return null; } for (int i = 0; i < parent.getChildCount(); i++) { View child = parent.getChildAt(i); if (child == view) { while (i < parent.getChildCount()) { View sibling = parent.getChildAt(++i); if (qualifies(qualifier, sibling)) { return sibling; } } } } return null; } /** * Get previous siblings collection. * * @param view the view * @return the collection */ public static Collection<View> getPreviousSiblings(View view) { return getPreviousSiblings(view, null); } /** * Get previous siblings collection. * * @param view the view * @param qualifier the qualifier * @return the collection */ public static Collection<View> getPreviousSiblings(View view, Qualifier qualifier) { ViewGroup parent = getContainingViewGroup(view); if (parent == null) { return null; } Collection<View> siblings = new ArrayList<>(); for (int i = 0; i < parent.getChildCount(); i++) { View child = parent.getChildAt(i); if (child == view) { break; } if (qualifies(qualifier, child)) { siblings.add(child); } } return siblings; } /** * Get next siblings collection. * * @param view the view * @return the collection */ public static Collection<View> getNextSiblings(View view) { return getNextSiblings(view, null); } /** * Get next siblings collection. * * @param view the view * @param qualifier the qualifier * @return the collection */ public static Collection<View> getNextSiblings(View view, Qualifier qualifier) { ViewGroup parent = getContainingViewGroup(view); if (parent == null) { return null; } Collection<View> siblings = new ArrayList<>(); boolean hasFoundReference = false; for (int i = 0; i < parent.getChildCount(); i++) { View child = parent.getChildAt(i); if (hasFoundReference && qualifies(qualifier, view)) { siblings.add(child); } if (child == view) { hasFoundReference = true; } } return siblings; } /** * Finds the first child in #rootView that is an instance of #clazz * * Use this instead of #findAll with an instanceof Qualifier in order to get typed returns, * e.g., Collection<TextView> textViews = ViewFinder.findAllByClass(someViewGroup, TextView.class); * * @param <T> The type of View subclass to search for. * @param viewGroup The View whose hierarchy should be examined for instances of #clazz. * @param clazz The Class to search for within #rootView. * @return The first child in #rootView this is an instance of #clazz. */ public static <T extends View> T findByClass(ViewGroup viewGroup, Class<T> clazz) { for (int i = 0; i < viewGroup.getChildCount(); i++) { View child = viewGroup.getChildAt(i); if (clazz.isInstance(child)) { return clazz.cast(child); } if (child instanceof ViewGroup) { T match = findByClass((ViewGroup) child, clazz); if (match != null) { return match; } } } return null; } /** * Returns a Collection of View subclasses instances of type T found within #rootView. * * Use this instead of #findAll with an instanceof Qualifier in order to get typed returns, * e.g., Collection<TextView> textViews = ViewFinder.findAllByClass(someViewGroup, TextView.class, null); * * @param <T> The type of View subclass to search for. * @param viewGroup The View whose hierarchy should be examined for instances of #clazz. * @param clazz The Class to search for within #rootView. * @param out A Collection of View subclasses of type T that will be populated with matches found in #rootView. * @return A Collection of View subclasses instances of type T found within #rootView. */ public static <T extends View> Collection<T> findAllByClass(ViewGroup viewGroup, Class<T> clazz, Collection<T> out) { for (int i = 0; i < viewGroup.getChildCount(); i++) { View child = viewGroup.getChildAt(i); if (clazz.isInstance(child)) { out.add(clazz.cast(child)); } if (child instanceof ViewGroup) { findAllByClass((ViewGroup) child, clazz, out); } } return out; } /** * Returns a Collection of View subclasses instances of type T found within #rootView. * * @param <T> The type of View subclass to search for. * @param viewGroup The View whose hierarchy should be examined for instances of #clazz. * @param clazz The Class to search for within #rootView. * @return A Collection of View subclasses instances of type T found within #rootView. */ public static <T extends View> Collection<T> findAllByClass(ViewGroup viewGroup, Class<T> clazz) { return findAllByClass(viewGroup, clazz, new ArrayList<>()); } } |
Add (or amend) your values/attrs.xml to include:
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<resources> <declare-styleable name="SeparatorLinearLayout"> <attr name="separator" format="reference" /> <attr name="separatorHeight" format="integer" /> <attr name="separatorWidth" format="integer" /> </declare-styleable> </resources> |
Some layout:
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<?xml version="1.0" encoding="utf-8"?> <com.qozix.widgets.SeparatorLinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="vertical" app:separator="?android:attr/listDivider"><!-- any drawable or color --> <TextView android:layout_width="match_parent" android:layout_height="wrap_content" android:padding="12sp" android:text="This is a row" /> <TextView android:layout_width="match_parent" android:layout_height="wrap_content" android:padding="12sp" android:text="This is a row" /> </com.qozix.widgets.SeparatorLinearLayout> |
And the class:
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package com.qozix.widgets; import android.content.Context; import android.content.res.TypedArray; import android.graphics.Canvas; import android.graphics.Rect; import android.graphics.drawable.Drawable; import android.util.AttributeSet; import android.view.View; import android.widget.LinearLayout; import com.qozix.widgets.R; /** * Created by michaeldunn on 8/15/16. */ public class SeparatorLinearLayout extends LinearLayout { private Drawable mSeparator; private Rect mSeparatorBounds = new Rect(); private int mSeparatorHeight; private int mSeparatorWidth; public SeparatorLinearLayout(Context context) { this(context, null); } public SeparatorLinearLayout(Context context, AttributeSet attrs) { this(context, attrs, 0); } public SeparatorLinearLayout(Context context, AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); setWillNotDraw(false); TypedArray typedArray = context.getTheme().obtainStyledAttributes(attrs, R.styleable.SeparatorLinearLayout, 0, 0); try { Drawable drawable = typedArray.getDrawable(R.styleable.SeparatorLinearLayout_separator); if (drawable != null) { setSeparator(drawable); } int drawableWidth = typedArray.getInt(R.styleable.SeparatorLinearLayout_separatorWidth, 0); if (drawableWidth != 0) { setSeparatorWidth(drawableWidth); } int drawableHeight = typedArray.getInt(R.styleable.SeparatorLinearLayout_separatorHeight, 0); if (drawableHeight != 0) { setSeparatorHeight(drawableHeight); } } finally { typedArray.recycle(); } } public void setSeparator(Drawable drawable) { mSeparator = drawable; if (mSeparator != null) { mSeparatorHeight = mSeparator.getIntrinsicHeight(); mSeparatorWidth = mSeparator.getIntrinsicWidth(); } } public void setSeparatorHeight(int separatorHeight) { mSeparatorHeight = separatorHeight; } public void setSeparatorWidth(int separatorWidth) { mSeparatorWidth = separatorWidth; } private void drawVerticalSeparators(Canvas canvas) { mSeparatorBounds.left = 0; mSeparatorBounds.right = canvas.getWidth(); for (int i = 0; i < getChildCount() - 1; i++) { View child = getChildAt(i); mSeparatorBounds.top = child.getBottom() - 1; mSeparatorBounds.bottom = mSeparatorBounds.top + mSeparatorHeight; drawDrawableToCanvas(canvas); } } private void drawHorizontalSeparators(Canvas canvas) { mSeparatorBounds.top = 0; mSeparatorBounds.bottom = canvas.getHeight(); for (int i = 0; i < getChildCount() - 1; i++) { View child = getChildAt(i); mSeparatorBounds.left = child.getRight() - 1; mSeparatorBounds.right = mSeparatorBounds.left + mSeparatorWidth; drawDrawableToCanvas(canvas); } } private void drawDrawableToCanvas(Canvas canvas) { mSeparator.setBounds(mSeparatorBounds); mSeparator.draw(canvas); } private void drawSeparators(Canvas canvas) { switch (getOrientation()) { case VERTICAL: drawVerticalSeparators(canvas); break; case HORIZONTAL: drawHorizontalSeparators(canvas); break; } } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); if (mSeparator != null) { drawSeparators(canvas); } } } |
The behavior here isn’t quite what I expected, or gather from the documentation. If you have <activity android:name=”.SomeActivity” android:launchMode=”singleTop” /> Then you start SomeActivity multiple times:
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private void doIt(){ startSomeActivity(); startSomeActivity(); } private void startSomeActivity(){ Intent intent = new Intent(this, SomeActivity.class); startActivity(intent); } |
You’ll get only one instance of SomeActivity at the top of the stack (as the singleTop launch mode promises), but you’ll notice that if you finish() or hit […]
Possibly useful in precomputing layout requirements…
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public static int getDefaultTextSize(Context context) { TypedValue typedValue = new TypedValue(); context.getTheme().resolveAttribute(android.R.attr.textAppearance, typedValue, true); int[] textSizeAttr = new int[] { android.R.attr.textSize }; TypedArray typedArray = context.obtainStyledAttributes(typedValue.data, textSizeAttr); int textSize = typedArray.getDimensionPixelSize(0, -1); typedArray.recycle(); return textSize; } |
When extending a typed class without specifying the type, just pass the type to the subclass’s erasure and specify that type in the reference to the superclass. E.g.,
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public class MyClass<E extends List> {} public class MySubClass<E extends List> extends MyClass<E> {} // E is already declared by the time we get to MyClass, so just reference it - instead of defining it - as a type param for the superclass |
As an example, consider the AOSP class RecyclerView.Adapter, which is declared as:
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public static abstract class Adapter<VH extends ViewHolder> |
A normal concrete implementation is fairly straightforward:
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public class MyAdapter extends Adapter<MyHolder> |
But what if you want […]
Probably unexpected behavior:
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public class Main { public static void main(String[] args) { mew SomeSub(); } public abstract static class SomeSuper { public SomeSuper(){ doInit(); } public abstract void doInit(); } public static class SomeSub extends SomeSuper { public int someIntMember = 3; public void doInit(){ System.out.println(someIntMember); // prints 0, not 3 } } } |
There’s not a direct way to work around this – often initialization or setup methods are used, sometimes with a Factory instance generator.