Android控件開發之ToggleButton原理

在android平台上比較有特色的就是ToggleButton控件，雖然它的功能和CheckBox有些類似，但是他們的用處還是有一定的區別比如ToggleButton原本有圖片裝飾，通過ToggleButton可以很清楚的顯示某些狀態。它們均從Button為基類的CompoundButton中實現，其真假事件從Checkable來實現。

  public abstract class CompoundButton extends Button implements Checkable {
    private boolean mChecked; //狀態是否選中
    private int mButtonResource;
    private boolean mBroadcasting;
    private Drawable mButtonDrawable; //按鈕的圖標
    private OnCheckedChangeListener mOnCheckedChangeListener; //選中狀態改變監聽
    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(); //顯式的GC
    }

    public void toggle() {
        setChecked(!mChecked);
    }

    @Override
    public boolean performClick() {
              toggle();
        return super.performClick();
    }

    public boolean isChecked() {
        return mChecked;
    }

    public void setChecked(boolean checked) {
        if (mChecked != checked) {
            mChecked = checked;
            refreshDrawableState(); //更新當前狀態的按鈕圖標

            if (mBroadcasting) {
                return;
            }

            mBroadcasting = true;
            if (mOnCheckedChangeListener != null) {
                mOnCheckedChangeListener.onCheckedChanged(this, mChecked);
            }
            if (mOnCheckedChangeWidgetListener != null) {
                mOnCheckedChangeWidgetListener.onCheckedChanged(this, mChecked);
            }

            mBroadcasting = false;           
        }
    }

    public void setOnCheckedChangeListener(OnCheckedChangeListener listener) {
        mOnCheckedChangeListener = listener;
    }

    void setOnCheckedChangeWidgetListener(OnCheckedChangeListener listener) {
        mOnCheckedChangeWidgetListener = listener;
    }

   
    public static interface OnCheckedChangeListener {
        void onCheckedChanged(CompoundButton buttonVIEw, boolean isChecked);
    }

     public void setButtonDrawable(int resid) {
        if (resid != 0 && resid == mButtonResource) {
            return;
        }

        mButtonResource = resid;

        Drawable d = null;
        if (mButtonResource != 0) {
            d = getResources().getDrawable(mButtonResource);
        }
        setButtonDrawable(d);
    }

    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 boolean dispatchPopulateAccessibilityEvent(AccessibilityEvent event) {
        boolean populated = super.dispatchPopulateAccessibilityEvent(event);

        if (!populated) {
            int resourceId = 0;
            if (mChecked) {
                resourceId = R.string.Accessibility_compound_button_selected;
            } else {
                resourceId = R.string.Accessibility_compound_button_unselected;
            }
            String state = getResources().getString(resourceId);
            event.getText().add(state);
            event.setChecked(mChecked);
        }

        return populated;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        final Drawable buttonDrawable = mButtonDrawable;
        if (buttonDrawable != null) {
            final int verticalGravity = getGravity() & 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() { //android123提示狀態改變時需要更換按鈕的圖標
        super.drawableStateChanged();
       
        if (mButtonDrawable != null) {
            int[] myDrawableState = getDrawableState();
            
            mButtonDrawable.setState(myDrawableState);
           
            invalidate();
        }
    }

    @Override
    protected boolean verifyDrawable(Drawable who) {
        return super.verifyDrawable(who) || who == mButtonDrawable;
    }

    static class SavedState extends BaseSavedState {
        boolean checked;

             SavedState(Parcelable superState) {
            super(superState);
        }
        

        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<SavedState> CREATOR
                = new Parcelable.Creator<SavedState>() {
            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();
    }
}

從上面來看我們知道CompuundButton的實現相對繁瑣了些，主要是考慮狀態是否已經選中等情況的消息通知，android開發網提醒大家而ToggleButton相對CompuundButton增加的給用戶而言主要是開關的文字顯示。

public class ToggleButton extends CompoundButton {
    private CharSequence mTextOn;
    private CharSequence mTextOff;
   
    private Drawable mIndicatorDrawable;

    private static final int NO_ALPHA = 0xFF;
    private float mDisabledAlpha;
   
    public ToggleButton(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
       
        TypedArray a =
            context.obtainStyledAttributes(
                    attrs, com.android.internal.R.styleable.ToggleButton, defStyle, 0);
        mTextOn = a.getText(com.android.internal.R.styleable.ToggleButton_textOn);
        mTextOff = a.getText(com.android.internal.R.styleable.ToggleButton_textOff);
        mDisabledAlpha = a.getFloat(com.android.internal.R.styleable.ToggleButton_disabledAlpha, 0.5f);
        syncTextState();
        a.recycle();
    }

    public ToggleButton(Context context, AttributeSet attrs) {
        this(context, attrs, com.android.internal.R.attr.buttonStyleToggle);
    }

    public ToggleButton(Context context) {
        this(context, null);
    }

    @Override
    public void setChecked(boolean checked) {
        super.setChecked(checked);
       
        syncTextState();
    }

    private void syncTextState() {
        boolean checked = isChecked();
        if (checked && mTextOn != null) {
            setText(mTextOn);
        } else if (!checked && mTextOff != null) {
            setText(mTextOff);
        }
    }

    public CharSequence getTextOn() {
        return mTextOn;
    }

    public void setTextOn(CharSequence textOn) {
        mTextOn = textOn;
    }

    public CharSequence getTextOff() {
        return mTextOff;
    }

    protected void onFinishInflate() {
        super.onFinishInflate();
       
        updateReferenceToIndicatorDrawable(getBackground());
    }

    @Override
    public void setBackgroundDrawable(Drawable d) {
        super.setBackgroundDrawable(d);
       
        updateReferenceToIndicatorDrawable(d);
    }

    private void updateReferenceToIndicatorDrawable(Drawable backgroundDrawable) {
        if (backgroundDrawable instanceof LayerDrawable) {
            LayerDrawable layerDrawable = (LayerDrawable) backgroundDrawable;
            mIndicatorDrawable =
                    layerDrawable.findDrawableByLayerId(com.android.internal.R.id.toggle);
        }
    }
   
    @Override
    protected void drawableStateChanged() {
        super.drawableStateChanged();
       
        if (mIndicatorDrawable != null) {
            mIndicatorDrawable.setAlpha(isEnabled() ? NO_ALPHA : (int) (NO_ALPHA * mDisabledAlpha));
        }
    }
   
}