diff --git a/lib_base/src/main/java/com/android/base/app/fragment/RefreshLoadMoreStateLayoutImpl.kt b/lib_base/src/main/java/com/android/base/app/fragment/RefreshLoadMoreStateLayoutImpl.kt
index 0ba52b2..59c6599 100644
--- a/lib_base/src/main/java/com/android/base/app/fragment/RefreshLoadMoreStateLayoutImpl.kt
+++ b/lib_base/src/main/java/com/android/base/app/fragment/RefreshLoadMoreStateLayoutImpl.kt
@@ -2,10 +2,10 @@ package com.android.base.app.fragment
 
 import android.graphics.drawable.Drawable
 import android.view.View
-import com.android.base.app.ui.CommonId
 import com.android.base.app.ui.*
+import com.android.base.widget.StateProcessor
 
-internal class RefreshLoadMoreStateLayoutImpl private constructor(private val mLayout: View) : StateLayout, StateLayoutConfig {
+internal class RefreshLoadMoreStateLayoutImpl private constructor(layout: View) : StateLayout, StateLayoutConfig {
 
     companion object {
         fun init(view: View): RefreshLoadMoreStateLayoutImpl {
@@ -13,56 +13,72 @@ internal class RefreshLoadMoreStateLayoutImpl private constructor(private val mL
         }
     }
 
-    private var mMultiStateView: StateLayout = mLayout.findViewById<View>(CommonId.STATE_ID) as StateLayout
-    private var mRefreshView: RefreshLoadMoreView
+    private var _multiStateView: StateLayout? = layout.findViewById<View>(CommonId.STATE_ID) as? StateLayout
+    private var _refreshView: RefreshLoadMoreView
 
     val refreshView: RefreshLoadMoreView
-        get() = mRefreshView
+        get() = _refreshView
 
     init {
-        val refreshLayout = mLayout.findViewById<View>(CommonId.REFRESH_ID)
-        mRefreshView = RefreshLoadViewFactory.createRefreshView(refreshLayout)
+        val refreshLayout = layout.findViewById<View>(CommonId.REFRESH_ID)
+                ?: throw NullPointerException("You need to provide a refreshable layout with id R.id.base_refresh_layout in your xml.")
+
+        _refreshView = RefreshLoadViewFactory.createRefreshView(refreshLayout)
     }
 
-    override fun showLoadingLayout() = mMultiStateView.showLoadingLayout()
-    override fun showContentLayout() = mMultiStateView.showContentLayout()
-    override fun showEmptyLayout() = mMultiStateView.showEmptyLayout()
-    override fun showErrorLayout() = mMultiStateView.showErrorLayout()
-    override fun showRequesting() = mMultiStateView.showRequesting()
-    override fun showBlank() = mMultiStateView.showBlank()
-    override fun showNetErrorLayout() = mMultiStateView.showNetErrorLayout()
-    override fun showServerErrorLayout() = mMultiStateView.showServerErrorLayout()
+    override fun showLoadingLayout() = checkMultiStateView().showLoadingLayout()
+    override fun showContentLayout() = checkMultiStateView().showContentLayout()
+    override fun showEmptyLayout() = checkMultiStateView().showEmptyLayout()
+    override fun showErrorLayout() = checkMultiStateView().showErrorLayout()
+    override fun showRequesting() = checkMultiStateView().showRequesting()
+    override fun showBlank() = checkMultiStateView().showBlank()
+    override fun showNetErrorLayout() = checkMultiStateView().showNetErrorLayout()
+    override fun showServerErrorLayout() = checkMultiStateView().showServerErrorLayout()
 
-    override fun getStateLayoutConfig(): StateLayoutConfig = mMultiStateView.stateLayoutConfig
+    override fun getStateLayoutConfig(): StateLayoutConfig = checkMultiStateView().stateLayoutConfig
 
     override fun setStateMessage(state: Int, message: CharSequence?): StateLayoutConfig {
-        mMultiStateView.stateLayoutConfig.setStateMessage(state, message)
-        return mMultiStateView.stateLayoutConfig
+        checkMultiStateView().stateLayoutConfig.setStateMessage(state, message)
+        return checkMultiStateView().stateLayoutConfig
     }
 
     override fun setStateIcon(state: Int, drawable: Drawable?): StateLayoutConfig {
-        mMultiStateView.stateLayoutConfig.setStateIcon(state, drawable)
-        return mMultiStateView.stateLayoutConfig
+        checkMultiStateView().stateLayoutConfig.setStateIcon(state, drawable)
+        return checkMultiStateView().stateLayoutConfig
     }
 
     override fun setStateIcon(state: Int, drawableId: Int): StateLayoutConfig {
-        mMultiStateView.stateLayoutConfig.setStateIcon(state, drawableId)
-        return mMultiStateView.stateLayoutConfig
+        checkMultiStateView().stateLayoutConfig.setStateIcon(state, drawableId)
+        return checkMultiStateView().stateLayoutConfig
     }
 
     override fun setStateAction(state: Int, actionText: CharSequence?): StateLayoutConfig {
-        mMultiStateView.stateLayoutConfig.setStateAction(state, actionText)
-        return mMultiStateView.stateLayoutConfig
+        checkMultiStateView().stateLayoutConfig.setStateAction(state, actionText)
+        return checkMultiStateView().stateLayoutConfig
     }
 
     override fun setStateRetryListener(retryActionListener: OnRetryActionListener?): StateLayoutConfig {
-        mMultiStateView.stateLayoutConfig.setStateRetryListener(retryActionListener)
-        return mMultiStateView.stateLayoutConfig
+        checkMultiStateView().stateLayoutConfig.setStateRetryListener(retryActionListener)
+        return checkMultiStateView().stateLayoutConfig
     }
 
     override fun disableOperationWhenRequesting(disable: Boolean): StateLayoutConfig {
-        mMultiStateView.stateLayoutConfig.disableOperationWhenRequesting(disable)
-        return mMultiStateView.stateLayoutConfig
+        checkMultiStateView().stateLayoutConfig.disableOperationWhenRequesting(disable)
+        return checkMultiStateView().stateLayoutConfig
+    }
+
+    override fun getProcessor(): StateProcessor {
+        return checkMultiStateView().stateLayoutConfig.processor
+    }
+
+    override fun setMessageGravity(state: Int, gravity: Int): StateLayoutConfig {
+        checkMultiStateView().stateLayoutConfig.setMessageGravity(state, gravity)
+        return this
+    }
+
+    private fun checkMultiStateView(): StateLayout {
+        return _multiStateView
+                ?: throw IllegalStateException("Calling this function requires defining a view that implements StateLayout in the Layout")
     }
 
 }
\ No newline at end of file
diff --git a/lib_base/src/main/java/com/android/base/app/fragment/RefreshableStateLayoutImpl.java b/lib_base/src/main/java/com/android/base/app/fragment/RefreshableStateLayoutImpl.java
index 638f62d..5fe8cdb 100644
--- a/lib_base/src/main/java/com/android/base/app/fragment/RefreshableStateLayoutImpl.java
+++ b/lib_base/src/main/java/com/android/base/app/fragment/RefreshableStateLayoutImpl.java
@@ -10,6 +10,7 @@ import com.android.base.app.ui.RefreshView;
 import com.android.base.app.ui.RefreshViewFactory;
 import com.android.base.app.ui.StateLayout;
 import com.android.base.app.ui.StateLayoutConfig;
+import com.android.base.widget.StateProcessor;
 
 import static com.android.base.app.ui.CommonId.REFRESH_ID;
 import static com.android.base.app.ui.CommonId.STATE_ID;
@@ -149,6 +150,12 @@ final class RefreshableStateLayoutImpl implements RefreshStateLayout, StateLayou
         return this;
     }
 
+    @Override
+    public StateLayoutConfig setMessageGravity(int state, int gravity) {
+        checkMultiStateView().getStateLayoutConfig().setMessageGravity(state, gravity);
+        return this;
+    }
+
     @Override
     public StateLayoutConfig setStateIcon(@RetryableState int state, Drawable drawable) {
         checkMultiStateView().getStateLayoutConfig().setStateIcon(state, drawable);
@@ -179,6 +186,11 @@ final class RefreshableStateLayoutImpl implements RefreshStateLayout, StateLayou
         return this;
     }
 
+    @Override
+    public StateProcessor getProcessor() {
+        return checkMultiStateView().getStateLayoutConfig().getProcessor();
+    }
+
     private StateLayout checkMultiStateView() {
         if (mMultiStateView == null) {
             throw new IllegalStateException("Calling this function requires defining a view that implements StateLayout in the Layout");
diff --git a/lib_base/src/main/java/com/android/base/app/ui/StateLayoutConfig.java b/lib_base/src/main/java/com/android/base/app/ui/StateLayoutConfig.java
index 052f34a..7c5d154 100644
--- a/lib_base/src/main/java/com/android/base/app/ui/StateLayoutConfig.java
+++ b/lib_base/src/main/java/com/android/base/app/ui/StateLayoutConfig.java
@@ -4,6 +4,8 @@ import android.graphics.drawable.Drawable;
 import android.support.annotation.DrawableRes;
 import android.support.annotation.IntDef;
 
+import com.android.base.widget.StateProcessor;
+
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 
@@ -50,6 +52,8 @@ public interface StateLayoutConfig {
 
     StateLayoutConfig setStateMessage(@RetryableState int state, CharSequence message);
 
+    StateLayoutConfig setMessageGravity(@RetryableState int state, int gravity);
+
     StateLayoutConfig setStateIcon(@RetryableState int state, Drawable drawable);
 
     StateLayoutConfig setStateIcon(@RetryableState int state, @DrawableRes int drawableId);
@@ -60,4 +64,6 @@ public interface StateLayoutConfig {
 
     StateLayoutConfig disableOperationWhenRequesting(boolean disable);
 
+    StateProcessor getProcessor();
+
 }
diff --git a/lib_base/src/main/java/com/android/base/app/ui/UIEx.kt b/lib_base/src/main/java/com/android/base/app/ui/UIEx.kt
index d13e9e0..1c7ec40 100644
--- a/lib_base/src/main/java/com/android/base/app/ui/UIEx.kt
+++ b/lib_base/src/main/java/com/android/base/app/ui/UIEx.kt
@@ -4,6 +4,7 @@ package com.android.base.app.ui
 
 import com.android.base.app.BaseKit
 import com.android.base.utils.common.Checker
+import timber.log.Timber
 
 fun <T> RefreshListLayout<T>.processListResultWithStatus(list: List<T>?, onEmpty: (() -> Unit)? = null) {
     if (isLoadingMore) {
@@ -136,7 +137,11 @@ fun <T> RefreshStateLayout.processResultWithStatus(t: T?, onResult: ((T) -> Unit
     }
 }
 
-fun RefreshStateLayout.processErrorWithStatus(throwable: Throwable) {
+fun RefreshStateLayout.processErrorWithStatus(throwable: Throwable?) {
+    if (throwable == null) {
+        Timber.d("processErrorWithStatus called, but throwable is null")
+        return
+    }
     if (isRefreshing) {
         refreshCompleted()
     }
diff --git a/lib_base/src/main/java/com/android/base/data/Resource.java b/lib_base/src/main/java/com/android/base/data/Resource.java
index f0be229..251679e 100644
--- a/lib_base/src/main/java/com/android/base/data/Resource.java
+++ b/lib_base/src/main/java/com/android/base/data/Resource.java
@@ -15,13 +15,11 @@ public class Resource<T> {
     private final Throwable mError;
     private final Status mStatus;
     private final T mData; //data or default data
-    private final T mDefaultData; //data or default data
 
-    private Resource(Throwable error, T data, T defaultData, Status status) {
+    private Resource(Throwable error, T data, Status status) {
         mError = error;
         mStatus = status;
         mData = data;
-        mDefaultData = defaultData;
     }
 
     public boolean isSuccess() {
@@ -45,27 +43,33 @@ public class Resource<T> {
     }
 
     public static <T> Resource<T> success() {
-        return new Resource<>(null, null, null, Status.SUCCESS);
+        return new Resource<>(null, null, Status.SUCCESS);
     }
 
-    public static <T> Resource<T> success(@Nullable T t) {
-        return new Resource<>(null, t, null, Status.SUCCESS);
+    public static <T> Resource<T> success(@Nullable T data) {
+        return new Resource<>(null, data, Status.SUCCESS);
     }
 
     public static <T> Resource<T> error(@NonNull Throwable error) {
         return error(error, null);
     }
 
+    /**
+     * 创建一个 error 状态，且设置一个默认的数据
+     */
     public static <T> Resource<T> error(@NonNull Throwable error, T defaultValue) {
-        return new Resource<>(error, null, defaultValue, Status.ERROR);
+        return new Resource<>(error, defaultValue, Status.ERROR);
     }
 
     public static <T> Resource<T> loading() {
         return loading(null);
     }
 
+    /**
+     * 创建一个 loading 状态，且设置一个默认的数据
+     */
     public static <T> Resource<T> loading(T defaultValue) {
-        return new Resource<>(null, null, defaultValue, Status.LOADING);
+        return new Resource<>(null, defaultValue, Status.LOADING);
     }
 
     /**
@@ -74,9 +78,16 @@ public class Resource<T> {
      * @return Resource
      */
     public static Resource noChange() {
-        return new Resource<>(null, null, null, Status.NOT_CHANGED);
+        return new Resource<>(null, null, Status.NOT_CHANGED);
     }
 
+    /**
+     * 获取 Resource 中保存的数据，只有在 success 状态并且存在数据时下才能调用此方法，否则将抛出异常。
+     *
+     * @return Resource 中保存的数据。
+     * @throws UnsupportedOperationException 非 success 状态调用此方法。
+     * @throws NullPointerException          Resource 中没有保存数据时调用此方法。
+     */
     @NonNull
     public T data() {
         if (isError() || isLoading() || isNoChange()) {
@@ -88,17 +99,40 @@ public class Resource<T> {
         return mData;
     }
 
+    /**
+     * 获取 Resource 中保存的数据，如果不存在数据则返回 defaultData 所设置的默认数据，在不同状态下获取的数据具有不同的意义：
+     *
+     * <pre>
+     *     <li>success 状态下，返回一个成功操作所产生的数据</li>
+     *     <li>error 状态下，返回一个默认的数据，如果存在的话</li>
+     *     <li>loading 状态下，返回一个默认的数据，如果存在的话</li>
+     * </pre>
+     *
+     * @param defaultData 如果不存在数据则返回 defaultData 所设置的默认数据。
+     * @return Resource 中保存的数据。
+     */
     @Nullable
-    public T orElse(@Nullable T elseData) {
+    public T orElse(@Nullable T defaultData) {
         if (mData == null) {
-            return elseData;
+            return defaultData;
         }
         return mData;
     }
 
+    /**
+     * 获取 Resource 中保存的数据，在不同状态下获取的数据具有不同的意义：
+     *
+     * <pre>
+     *     <li>success 状态下，返回一个成功操作所产生的数据</li>
+     *     <li>error 状态下，返回一个默认的数据，如果存在的话</li>
+     *     <li>loading 状态下，返回一个默认的数据，如果存在的话</li>
+     * </pre>
+     *
+     * @return Resource 中保存的数据。
+     */
     @Nullable
-    public T defaultData() {
-        return mDefaultData;
+    public T get() {
+        return mData;
     }
 
     public Throwable error() {
@@ -112,7 +146,6 @@ public class Resource<T> {
                 "mError=" + mError +
                 ", mStatus=" + mStatus +
                 ", mData=" + mData +
-                ", mDefaultData=" + mDefaultData +
                 '}';
     }
 
diff --git a/lib_base/src/main/java/com/android/base/data/Resource.kt b/lib_base/src/main/java/com/android/base/data/Resource.kt
index 0ca07e0..91f1974 100644
--- a/lib_base/src/main/java/com/android/base/data/Resource.kt
+++ b/lib_base/src/main/java/com/android/base/data/Resource.kt
@@ -1,6 +1,6 @@
 package com.android.base.data
 
-
+/**when in loading*/
 inline fun <T> Resource<T>.onLoading(onLoading: () -> Unit): Resource<T> {
     if (this.isLoading) {
         onLoading()
@@ -8,6 +8,7 @@ inline fun <T> Resource<T>.onLoading(onLoading: () -> Unit): Resource<T> {
     return this
 }
 
+/**when error occurred*/
 inline fun <T> Resource<T>.onError(onError: (error: Throwable) -> Unit): Resource<T> {
     if (this.isError) {
         onError(error())
@@ -15,6 +16,7 @@ inline fun <T> Resource<T>.onError(onError: (error: Throwable) -> Unit): Resourc
     return this
 }
 
+/**when no change*/
 inline fun <T> Resource<T>.onNoChange(onNoChange: () -> Unit): Resource<T> {
     if (this.isNoChange) {
         onNoChange()
@@ -22,7 +24,7 @@ inline fun <T> Resource<T>.onNoChange(onNoChange: () -> Unit): Resource<T> {
     return this
 }
 
-/**success*/
+/**when succeeded*/
 inline fun <T> Resource<T>.onSuccess(onSuccess: (data: T?) -> Unit): Resource<T> {
     if (this.isSuccess) {
         onSuccess(this.orElse(null))
@@ -30,10 +32,20 @@ inline fun <T> Resource<T>.onSuccess(onSuccess: (data: T?) -> Unit): Resource<T>
     return this
 }
 
-/**success with data*/
+/**when succeeded and has data*/
 inline fun <T> Resource<T>.onSuccessWithData(onSuccess: (data: T) -> Unit): Resource<T> {
-    if (this.isSuccess && this.hasData()) {
-        onSuccess(this.data())
+    val t = this.get()
+    if (this.isSuccess && t != null) {
+        onSuccess(t)
     }
     return this
-}
\ No newline at end of file
+}
+
+val <T> Resource<T>?.isFailed
+    get() = this != null && this.isError
+
+val <T> Resource<T>?.isSucceeded
+    get() = this != null && this.isSuccess
+
+val <T> Resource<T>?.inLoading
+    get() = this != null && this.isLoading
\ No newline at end of file
diff --git a/lib_base/src/main/java/com/android/base/widget/SimpleMultiStateView.java b/lib_base/src/main/java/com/android/base/widget/SimpleMultiStateView.java
index 3f47d7e..f981ddb 100644
--- a/lib_base/src/main/java/com/android/base/widget/SimpleMultiStateView.java
+++ b/lib_base/src/main/java/com/android/base/widget/SimpleMultiStateView.java
@@ -26,7 +26,7 @@ import static com.android.base.app.ui.StateLayoutConfig.ViewState;
  */
 public class SimpleMultiStateView extends MultiStateView implements StateLayout {
 
-    private StateActionProcessor mStateActionProcessor;
+    private StateProcessor mStateProcessor;
     private StateListener mStateListener;
 
     public SimpleMultiStateView(Context context) {
@@ -45,8 +45,8 @@ public class SimpleMultiStateView extends MultiStateView implements StateLayout
 
         initProcessor(typedArray);
 
-        mStateActionProcessor.onInitialize(this);
-        mStateActionProcessor.onParseAttrs(typedArray);
+        mStateProcessor.onInitialize(this);
+        mStateProcessor.onParseAttrs(typedArray);
 
         typedArray.recycle();
     }
@@ -57,15 +57,15 @@ public class SimpleMultiStateView extends MultiStateView implements StateLayout
         if (!StringChecker.isEmpty(processorPath)) {
             try {
                 Class<?> processorClass = Class.forName(processorPath);
-                mStateActionProcessor = (StateActionProcessor) processorClass.newInstance();
+                mStateProcessor = (StateProcessor) processorClass.newInstance();
             } catch (ClassNotFoundException | IllegalAccessException | InstantiationException e) {
                 e.printStackTrace();
                 Timber.e("initProcessor() called can not instance processor: " + processorPath);
             }
         }
 
-        if (mStateActionProcessor == null) {
-            mStateActionProcessor = new StateActionProcessor();
+        if (mStateProcessor == null) {
+            mStateProcessor = new StateActionProcessor();
         }
     }
 
@@ -89,7 +89,7 @@ public class SimpleMultiStateView extends MultiStateView implements StateLayout
     }
 
     private void processStateInflated(@ViewState int viewState, @NonNull View view) {
-        mStateActionProcessor.processStateInflated(viewState, view);
+        mStateProcessor.processStateInflated(viewState, view);
     }
 
     @Override
@@ -139,7 +139,7 @@ public class SimpleMultiStateView extends MultiStateView implements StateLayout
 
     @Override
     public StateLayoutConfig getStateLayoutConfig() {
-        return mStateActionProcessor.getStateLayoutConfigImpl();
+        return mStateProcessor.getStateLayoutConfigImpl();
     }
 
 }
diff --git a/lib_base/src/main/java/com/android/base/widget/StateActionProcessor.java b/lib_base/src/main/java/com/android/base/widget/StateActionProcessor.java
index 1001b67..ba2032a 100644
--- a/lib_base/src/main/java/com/android/base/widget/StateActionProcessor.java
+++ b/lib_base/src/main/java/com/android/base/widget/StateActionProcessor.java
@@ -27,7 +27,7 @@ import static com.android.base.app.ui.StateLayoutConfig.SERVER_ERROR;
  * Email: ztiany3@gmail.com
  * Date : 2018-05-17 17:08
  */
-public class StateActionProcessor implements StateProcessor {
+public class StateActionProcessor extends StateProcessor {
 
     private OnRetryActionListener mOnRetryActionListener;
 
@@ -102,6 +102,7 @@ public class StateActionProcessor implements StateProcessor {
         private final int mState;
         private Drawable mDrawable;
         private CharSequence mMessage;
+        private int mMessageGravity;
         private CharSequence mActionText;
         private View mStateView;
         private TextView mMessageTv;
@@ -125,6 +126,7 @@ public class StateActionProcessor implements StateProcessor {
             setActionText(mActionText);
             setMessage(mMessage);
             setDrawable(mDrawable);
+            setMessageGravity(mMessageGravity);
         }
 
         void setDrawable(Drawable drawable) {
@@ -141,6 +143,13 @@ public class StateActionProcessor implements StateProcessor {
             }
         }
 
+        void setMessageGravity(int gravity) {
+            mMessageGravity = gravity;
+            if (mMessageTv != null) {
+                mMessageTv.setGravity(mMessageGravity);
+            }
+        }
+
         void setActionText(CharSequence actionText) {
             mActionText = actionText;
             if (mActionBtn == null) {
@@ -163,6 +172,12 @@ public class StateActionProcessor implements StateProcessor {
             return this;
         }
 
+        @Override
+        public StateLayoutConfig setMessageGravity(int state, int gravity) {
+            getViewInfoForState(state).setMessageGravity(gravity);
+            return this;
+        }
+
         @Override
         public StateLayoutConfig setStateIcon(@ViewState int state, Drawable drawable) {
             getViewInfoForState(state).setDrawable(drawable);
@@ -192,6 +207,12 @@ public class StateActionProcessor implements StateProcessor {
             mSimpleMultiStateView.setDisableOperationWhenRequesting(disable);
             return this;
         }
+
+        @Override
+        public StateProcessor getProcessor() {
+            return StateActionProcessor.this;
+        }
+
     };
 
-}
+}
\ No newline at end of file
diff --git a/lib_base/src/main/java/com/android/base/widget/StateProcessor.java b/lib_base/src/main/java/com/android/base/widget/StateProcessor.java
index f094a73..7821c8d 100644
--- a/lib_base/src/main/java/com/android/base/widget/StateProcessor.java
+++ b/lib_base/src/main/java/com/android/base/widget/StateProcessor.java
@@ -11,14 +11,14 @@ import com.android.base.app.ui.StateLayoutConfig;
  * Email: ztiany3@gmail.com
  * Date : 2018-05-17 17:25
  */
-interface StateProcessor {
+public abstract class StateProcessor {
 
-    void onInitialize(SimpleMultiStateView simpleMultiStateView);
+    protected abstract void onInitialize(SimpleMultiStateView simpleMultiStateView);
 
-    void onParseAttrs(TypedArray typedArray);
+    protected abstract void onParseAttrs(TypedArray typedArray);
 
-    void processStateInflated(@StateLayoutConfig.ViewState int viewState, @NonNull View view);
+    protected abstract void processStateInflated(@StateLayoutConfig.ViewState int viewState, @NonNull View view);
 
-    StateLayoutConfig getStateLayoutConfigImpl();
+    protected abstract StateLayoutConfig getStateLayoutConfigImpl();
 
 }