给ListView设置emptyView

给ListView设置emptyView

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使用ListView和GridView时，当列表为空时，默认是不显示任何内容的，这样对用户非常不友好，这时我们就需要通过setEmptyView(View emptyView)来设置当列表为空时的提示。

emptyView简单使用Demo

下面展示emptyView使用的简单Demo。

activity_empty_list_view.xml:

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    tools:context="com.littlejie.listview.EmptyListViewActivity">    <ListView        android:id="@+id/lv"        android:layout_width="match_parent"        android:layout_height="wrap_content"></ListView>    <!-- ListView的emptyView,默认不需设置其visiblity属性设置为GONE -->    <!-- 当ListView为空时,emptyView会自动被设置为GONE -->    <!-- 当ListView不为空时,emptyView会自动被设置为VIBISIBLE -->    <LinearLayout        android:id="@android:id/empty"        android:layout_width="match_parent"        android:layout_height="match_parent"        android:gravity="center"        android:orientation="vertical">        <TextView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout_gravity="center"            android:gravity="center"            android:text="Empty" />        <TextView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout_gravity="center"            android:gravity="center"            android:text="EmptyView可以是ViewGroup" />    </LinearLayout></LinearLayout>

EmptyListViewActivity.java:

public class EmptyListViewActivity extends Activity {    private ListView mLv;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_empty_list_view);        mLv = (ListView) findViewById(R.id.lv);        mLv.setAdapter(new ArrayAdapter<>(this,                android.R.layout.simple_list_item_1, generateString(0)));        mLv.setEmptyView(findViewById(android.R.id.empty));    }        private List<String> generateString(int num) {        List<String> list = new ArrayList<>();        for (int i = 0; i < num; i++) {            list.add("item " + i);        }        return list;    }}

运行结果如下：


emptyView复杂使用Demo

前一个Demo讲了emptyView的简单使用方法，那如果我们要自定义emptyView或者emptyView的布局跟ListView不在同一个布局文件中呢？恩，你可能会说：直接调用setEmptyView(View emptyView)不行嘛，难道有啥不一样？
看来，你还是too young too simple。直接调用的结果就是：emptyView根本就不会显示！！！
新建一个ComplexEmptyListViewActivity.java:

public class ComplexEmptyListViewActivity extends Activity {    private ListView mLv;    private EmptyView mEmptyView;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_complex_empty_list_view);        mLv = (ListView) findViewById(R.id.lv);        mLv.setAdapter(new ArrayAdapter<>(this,                android.R.layout.simple_list_item_1, Utils.generateString(0)));        mEmptyView = new EmptyView(this);        //此处是重点,如果不将mEmptyView添加进当前的ViewGroup,mEmptyView都不可见        //((ViewGroup) mLv.getParent()).addView(mEmptyView);        mLv.setEmptyView(mEmptyView);    }}

布局文件activity_complex_empty_list_view.xml:

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    tools:context="com.littlejie.listview.EmptyListViewActivity">    <ListView        android:id="@+id/lv"        android:layout_width="match_parent"        android:layout_height="wrap_content"></ListView></LinearLayout>

EmptyView:

public class EmptyView extends LinearLayout {    public EmptyView(Context context) {        super(context);        init(context);    }    public EmptyView(Context context, AttributeSet attrs) {        super(context, attrs);        init(context);    }    private void init(Context context) {        View view = LayoutInflater.from(context).inflate(R.layout.complex_empty_view, this);    }}

complex_empty_view.xml:

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical">    <TextView        android:layout_width="match_parent"        android:layout_height="match_parent"        android:gravity="center"        android:text="假装我是复杂的emptyView" /></LinearLayout>

运行demo，你会发现ListView为空时，根本就没显示emptyView。这是为什么呢？因为emptyView根本就没添加到当前Activity的布局中，所以即使设置了emptyView也不会显示，解决方法就是把emptyView添加到当前Activity的布局中（ComplexEmptyListViewActivity注释的内容）。

补充

1. 细心的可能已经发现，在两个demo中，我们都没去设置emptyView的visiblity属性，这是为什么呢？其实看下源码就知道了~

   当调用setEmptyView(View emptyView)方法时，ListView会调用到updateEmptyStatus(boolean empty)，在这里系统会跟empty去判断是否显示emptyView。恩，就这么简单~

   /** * Sets the view to show if the adapter is empty */@android.view.RemotableViewMethodpublic void setEmptyView(View emptyView) {    mEmptyView = emptyView;    // If not explicitly specified this view is important for accessibility.    if (emptyView != null            && emptyView.getImportantForAccessibility() == IMPORTANT_FOR_ACCESSIBILITY_AUTO) {        emptyView.setImportantForAccessibility(IMPORTANT_FOR_ACCESSIBILITY_YES);    }    final T adapter = getAdapter();    final boolean empty = ((adapter == null) || adapter.isEmpty());    updateEmptyStatus(empty);}/** * Update the status of the list based on the empty parameter.  If empty is true and * we have an empty view, display it.  In all the other cases, make sure that the listview * is VISIBLE and that the empty view is GONE (if it's not null). */private void updateEmptyStatus(boolean empty) {    if (isInFilterMode()) {        empty = false;    }    if (empty) {        if (mEmptyView != null) {            mEmptyView.setVisibility(View.VISIBLE);            setVisibility(View.GONE);        } else {            // If the caller just removed our empty view, make sure the list view is visible            setVisibility(View.VISIBLE);        }        // We are now GONE, so pending layouts will not be dispatched.        // Force one here to make sure that the state of the list matches        // the state of the adapter.        if (mDataChanged) {                       this.onLayout(false, mLeft, mTop, mRight, mBottom);         }    } else {        if (mEmptyView != null) mEmptyView.setVisibility(View.GONE);        setVisibility(View.VISIBLE);    }}