title: Creating a three states checkbox on android
body: <p>I'm stuck in front of a big problem:
  I'd like to make three state checkbox on android.
  It's a checkbox upon a ListView with checkboxes. It should allows user to switch between three states:</p>
  
  <ul>
  <li>all checked</li>
  <li>none checked</li>
  <li>misc checked</li>
  </ul>
  
  <p>And optionally retain the misc state on change.</p>
  
  <p>If I'm right I should make a subclass of the CompoundButton class and implement a int mstate intead of the boolean mchecked.
  Then I should override the event listener, the functions to save the state, and the state getter and setter.</p>
  
  <p>My question is basically how can I implement that ?
  How to switch between the drawable states ? (I have implemented the middle_state in the xml) and how to correctly implement the event handler?</p>
  
  <p>Here is the implementation I started:</p>
  
  <pre><code>public class TriStateCheckBox extends CompoundButton{
      private int state;
  
      public TriStateCheckBox(Context context) {
          super(context);
      }
      public static interface onCheckChangedListener{
          void onCheckChanged(TriStateCheckBox view, int state);
      }
  
      public void onCheckChanged(TriStateCheckBox view, int state){
          this.state = state;
      }
  }
  </code></pre>
  
  <p>Here is the code of the stock CompoundButton:</p>
  
  <pre><code>/*
   * Copyright (C) 2007 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package android.widget;
  
  import com.android.internal.R;
  
  import android.content.Context;
  import android.content.res.TypedArray;
  import android.graphics.Canvas;
  import android.graphics.drawable.Drawable;
  import android.os.Parcel;
  import android.os.Parcelable;
  import android.util.AttributeSet;
  import android.view.Gravity;
  import android.view.ViewDebug;
  import android.view.accessibility.AccessibilityEvent;
  import android.view.accessibility.AccessibilityNodeInfo;
  
  /**
   * &lt;p&gt;
   * A button with two states, checked and unchecked. When the button is pressed
   * or clicked, the state changes automatically.
   * &lt;/p&gt;
   *
   * &lt;p&gt;&lt;strong&gt;XML attributes&lt;/strong&gt;&lt;/p&gt;
   * &lt;p&gt;
   * See {@link android.R.styleable#CompoundButton
   * CompoundButton Attributes}, {@link android.R.styleable#Button Button
   * Attributes}, {@link android.R.styleable#TextView TextView Attributes}, {@link
   * android.R.styleable#View View Attributes}
   * &lt;/p&gt;
   */
  public abstract class CompoundButton extends Button implements Checkable {
      private boolean mChecked;
      private int mButtonResource;
      private boolean mBroadcasting;
      private Drawable mButtonDrawable;
      private OnCheckedChangeListener mOnCheckedChangeListener;
      private OnCheckedChangeListener mOnCheckedChangeWidgetListener;
  
      private static final int[] CHECKED_STATE_SET = {
          R.attr.state_checked
      };
  
      public CompoundButton(Context context) {
          this(context, null);
      }
  
      public CompoundButton(Context context, AttributeSet attrs) {
          this(context, attrs, 0);
      }
  
      public CompoundButton(Context context, AttributeSet attrs, int defStyle) {
          super(context, attrs, defStyle);
  
          TypedArray a =
                  context.obtainStyledAttributes(
                          attrs, com.android.internal.R.styleable.CompoundButton, defStyle, 0);
  
          Drawable d = a.getDrawable(com.android.internal.R.styleable.CompoundButton_button);
          if (d != null) {
              setButtonDrawable(d);
          }
  
          boolean checked = a
                  .getBoolean(com.android.internal.R.styleable.CompoundButton_checked, false);
          setChecked(checked);
  
          a.recycle();
      }
  
      public void toggle() {
          setChecked(!mChecked);
      }
  
      @Override
      public boolean performClick() {
          /*
           * XXX: These are tiny, need some surrounding 'expanded touch area',
           * which will need to be implemented in Button if we only override
           * performClick()
           */
  
          /* When clicked, toggle the state */
          toggle();
          return super.performClick();
      }
  
      @ViewDebug.ExportedProperty
      public boolean isChecked() {
          return mChecked;
      }
  
      /**
       * &lt;p&gt;Changes the checked state of this button.&lt;/p&gt;
       *
       * @param checked true to check the button, false to uncheck it
       */
      public void setChecked(boolean checked) {
          if (mChecked != checked) {
              mChecked = checked;
              refreshDrawableState();
  
              // Avoid infinite recursions if setChecked() is called from a listener
              if (mBroadcasting) {
                  return;
              }
  
              mBroadcasting = true;
              if (mOnCheckedChangeListener != null) {
                  mOnCheckedChangeListener.onCheckedChanged(this, mChecked);
              }
              if (mOnCheckedChangeWidgetListener != null) {
                  mOnCheckedChangeWidgetListener.onCheckedChanged(this, mChecked);
              }
  
              mBroadcasting = false;            
          }
      }
  
      /**
       * Register a callback to be invoked when the checked state of this button
       * changes.
       *
       * @param listener the callback to call on checked state change
       */
      public void setOnCheckedChangeListener(OnCheckedChangeListener listener) {
          mOnCheckedChangeListener = listener;
      }
  
      /**
       * Register a callback to be invoked when the checked state of this button
       * changes. This callback is used for internal purpose only.
       *
       * @param listener the callback to call on checked state change
       * @hide
       */
      void setOnCheckedChangeWidgetListener(OnCheckedChangeListener listener) {
          mOnCheckedChangeWidgetListener = listener;
      }
  
      /**
       * Interface definition for a callback to be invoked when the checked state
       * of a compound button changed.
       */
      public static interface OnCheckedChangeListener {
          /**
           * Called when the checked state of a compound button has changed.
           *
           * @param buttonView The compound button view whose state has changed.
           * @param isChecked  The new checked state of buttonView.
           */
          void onCheckedChanged(CompoundButton buttonView, boolean isChecked);
      }
  
      /**
       * Set the background to a given Drawable, identified by its resource id.
       *
       * @param resid the resource id of the drawable to use as the background 
       */
      public void setButtonDrawable(int resid) {
          if (resid != 0 &amp;&amp; resid == mButtonResource) {
              return;
          }
  
          mButtonResource = resid;
  
          Drawable d = null;
          if (mButtonResource != 0) {
              d = getResources().getDrawable(mButtonResource);
          }
          setButtonDrawable(d);
      }
  
      /**
       * Set the background to a given Drawable
       *
       * @param d The Drawable to use as the background
       */
      public void setButtonDrawable(Drawable d) {
          if (d != null) {
              if (mButtonDrawable != null) {
                  mButtonDrawable.setCallback(null);
                  unscheduleDrawable(mButtonDrawable);
              }
              d.setCallback(this);
              d.setState(getDrawableState());
              d.setVisible(getVisibility() == VISIBLE, false);
              mButtonDrawable = d;
              mButtonDrawable.setState(null);
              setMinHeight(mButtonDrawable.getIntrinsicHeight());
          }
  
          refreshDrawableState();
      }
  
      @Override
      public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
          super.onInitializeAccessibilityEvent(event);
          event.setChecked(mChecked);
      }
  
      @Override
      public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
          super.onInitializeAccessibilityNodeInfo(info);
          info.setCheckable(true);
          info.setChecked(mChecked);
      }
  
      @Override
      protected void onDraw(Canvas canvas) {
          super.onDraw(canvas);
  
          final Drawable buttonDrawable = mButtonDrawable;
          if (buttonDrawable != null) {
              final int verticalGravity = getGravity() &amp; Gravity.VERTICAL_GRAVITY_MASK;
              final int height = buttonDrawable.getIntrinsicHeight();
  
              int y = 0;
  
              switch (verticalGravity) {
                  case Gravity.BOTTOM:
                      y = getHeight() - height;
                      break;
                  case Gravity.CENTER_VERTICAL:
                      y = (getHeight() - height) / 2;
                      break;
              }
  
              buttonDrawable.setBounds(0, y, buttonDrawable.getIntrinsicWidth(), y + height);
              buttonDrawable.draw(canvas);
          }
      }
  
      @Override
      protected int[] onCreateDrawableState(int extraSpace) {
          final int[] drawableState = super.onCreateDrawableState(extraSpace + 1);
          if (isChecked()) {
              mergeDrawableStates(drawableState, CHECKED_STATE_SET);
          }
          return drawableState;
      }
  
      @Override
      protected void drawableStateChanged() {
          super.drawableStateChanged();
  
          if (mButtonDrawable != null) {
              int[] myDrawableState = getDrawableState();
  
              // Set the state of the Drawable
              mButtonDrawable.setState(myDrawableState);
  
              invalidate();
          }
      }
  
      @Override
      protected boolean verifyDrawable(Drawable who) {
          return super.verifyDrawable(who) || who == mButtonDrawable;
      }
  
      @Override
      public void jumpDrawablesToCurrentState() {
          super.jumpDrawablesToCurrentState();
          if (mButtonDrawable != null) mButtonDrawable.jumpToCurrentState();
      }
  
      static class SavedState extends BaseSavedState {
          boolean checked;
  
          /**
           * Constructor called from {@link CompoundButton#onSaveInstanceState()}
           */
          SavedState(Parcelable superState) {
              super(superState);
          }
  
          /**
           * Constructor called from {@link #CREATOR}
           */
          private SavedState(Parcel in) {
              super(in);
              checked = (Boolean)in.readValue(null);
          }
  
          @Override
          public void writeToParcel(Parcel out, int flags) {
              super.writeToParcel(out, flags);
              out.writeValue(checked);
          }
  
          @Override
          public String toString() {
              return "CompoundButton.SavedState{"
                      + Integer.toHexString(System.identityHashCode(this))
                      + " checked=" + checked + "}";
          }
  
          public static final Parcelable.Creator&lt;SavedState&gt; CREATOR
                  = new Parcelable.Creator&lt;SavedState&gt;() {
              public SavedState createFromParcel(Parcel in) {
                  return new SavedState(in);
              }
  
              public SavedState[] newArray(int size) {
                  return new SavedState[size];
              }
          };
      }
  
      @Override
      public Parcelable onSaveInstanceState() {
          // Force our ancestor class to save its state
          setFreezesText(true);
          Parcelable superState = super.onSaveInstanceState();
  
          SavedState ss = new SavedState(superState);
  
          ss.checked = isChecked();
          return ss;
      }
  
      @Override
      public void onRestoreInstanceState(Parcelable state) {
          SavedState ss = (SavedState) state;
  
          super.onRestoreInstanceState(ss.getSuperState());
          setChecked(ss.checked);
          requestLayout();
      }
  }
  </code></pre>
  
  <p>Here is my xml state-liste implementation (working):</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;selector xmlns:android="http://schemas.android.com/apk/res/android"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"&gt;
  
      &lt;item android:state_checked="false"
            android:state_pressed="true"
            android:drawable="@drawable/btn_check_off_pressed" /&gt; &lt;!-- unchecked pressed --&gt;
  
      &lt;item android:state_checked="false"
            android:state_selected="true"
            android:drawable="@drawable/btn_check_off_selected" /&gt; &lt;!-- unchecked selected --&gt;
  
      &lt;item android:state_checked="true"
            android:state_pressed="false"
            android:state_focused="false"
            android:drawable="@drawable/btn_check_on" /&gt; &lt;!-- checked --&gt;
  
      &lt;item android:state_checked="true"
            android:state_pressed="true"
            android:drawable="@drawable/btn_check_on_pressed" /&gt; &lt;!-- checked pressed--&gt;
  
      &lt;item android:state_checked="true"
            android:state_selected="true"
            android:drawable="@drawable/btn_check_on_selected" /&gt; &lt;!-- checked selected--&gt;
  
      &lt;item android:state_middle="true"
            android:state_pressed="false"
            android:state_focused="false"
            android:drawable="@drawable/btn_check_middle" /&gt; &lt;!-- middle --&gt;        
  
      &lt;item android:state_middle="true"
            android:state_pressed="true"
            android:drawable="@drawable/btn_check_middle_pressed" /&gt; &lt;!-- middle pressed--&gt;
  
      &lt;item android:state_middle="true"
            android:state_selected="true"
            android:drawable="@drawable/btn_check_middle_selected"  /&gt; &lt;!-- middle selected--&gt; 
  
      &lt;item android:drawable="@drawable/btn_check_off" /&gt; &lt;!-- unchecked --&gt;
  &lt;/selector&gt;
  </code></pre>
  
  <p>And here is the stock xml implementation for the checkbox:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;!-- Copyright (C) 2008 The Android Open Source Project
  
       Licensed under the Apache License, Version 2.0 (the "License");
       you may not use this file except in compliance with the License.
       You may obtain a copy of the License at
  
            http://www.apache.org/licenses/LICENSE-2.0
  
       Unless required by applicable law or agreed to in writing, software
       distributed under the License is distributed on an "AS IS" BASIS,
       WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
       See the License for the specific language governing permissions and
       limitations under the License.
  --&gt;
  
  &lt;selector xmlns:android="http://schemas.android.com/apk/res/android"&gt;
  
      &lt;!-- Enabled states --&gt;
  
      &lt;item android:state_checked="true" android:state_window_focused="false"
            android:state_enabled="true"
            android:drawable="@drawable/btn_check_on" /&gt;
      &lt;item android:state_checked="false" android:state_window_focused="false"
            android:state_enabled="true"
            android:drawable="@drawable/btn_check_off" /&gt;
  
      &lt;item android:state_checked="true" android:state_pressed="true"
            android:state_enabled="true"
            android:drawable="@drawable/btn_check_on_pressed" /&gt;
      &lt;item android:state_checked="false" android:state_pressed="true"
            android:state_enabled="true"
            android:drawable="@drawable/btn_check_off_pressed" /&gt;
  
      &lt;item android:state_checked="true" android:state_focused="true"
            android:state_enabled="true"
            android:drawable="@drawable/btn_check_on_selected" /&gt;
      &lt;item android:state_checked="false" android:state_focused="true"
            android:state_enabled="true"
            android:drawable="@drawable/btn_check_off_selected" /&gt;
  
      &lt;item android:state_checked="false"
            android:state_enabled="true"
            android:drawable="@drawable/btn_check_off" /&gt;
      &lt;item android:state_checked="true"
            android:state_enabled="true"
            android:drawable="@drawable/btn_check_on" /&gt;
  
  
      &lt;!-- Disabled states --&gt;
  
      &lt;item android:state_checked="true" android:state_window_focused="false"
            android:drawable="@drawable/btn_check_on_disable" /&gt;
      &lt;item android:state_checked="false" android:state_window_focused="false"
            android:drawable="@drawable/btn_check_off_disable" /&gt;
  
      &lt;item android:state_checked="true" android:state_focused="true"
            android:drawable="@drawable/btn_check_on_disable_focused" /&gt;
      &lt;item android:state_checked="false" android:state_focused="true"
            android:drawable="@drawable/btn_check_off_disable_focused" /&gt;
  
      &lt;item android:state_checked="false" android:drawable="@drawable/btn_check_off_disable" /&gt;
      &lt;item android:state_checked="true" android:drawable="@drawable/btn_check_on_disable" /&gt;
  
  &lt;/selector&gt;
  </code></pre>