Android 探索Bottom sheets的使用

在Android Support Library 23.2版本推出之後，我們可以看到一些新的特性,例如AppCompat DayNight主題，BottomSheet等，其中BottomSheet控件用於從屏幕底部向上滑動，以顯示更多的內容。本篇文章是想總結一下我在學習BottomSheet過程中的一些筆記以及一些需要注意的地方。

首先我們來看一下效果圖

這個效果的實現很簡單，甚至基本不需要java代碼,我們只需要給這個可滑動的view添加BottomSheetBehavior 表現行爲即可，把這個behavior指定爲android.support.design.widget.BottomSheetBehavior就可以達到這種效果了，來看看代碼吧

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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="match_parent">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center_horizontal"
        android:orientation="vertical">

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="onClick1"
            android:text="方式一" />

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="onClick2"
            android:text="方式二" />

    </LinearLayout>

    <LinearLayout
        android:id="@+id/layout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:paddingLeft="15dp"
        android:paddingRight="15dp"
        android:background="#EFEFEF"
        app:layout_behavior="@string/bottom_sheet_behavior">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:minHeight="30dp"
            android:text="選取方式"
            android:textColor="?attr/colorAccent" />

        <Button
            android:id="@+id/photo"
            style="@style/Widget.AppCompat.Button.Borderless.Colored"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:minHeight="48dp"
            android:text="照片"
            android:textColor="@android:color/darker_gray" />

        <View
            android:layout_width="match_parent"
            android:layout_height="1dp"
            android:background="@android:color/darker_gray" />

        <Button
            android:id="@+id/camera"
            style="@style/Widget.AppCompat.Button.Borderless.Colored"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:minHeight="48dp"
            android:text="相機"
            android:textColor="@android:color/darker_gray" />

        <View
            android:layout_width="match_parent"
            android:layout_height="1dp"
            android:background="@android:color/darker_gray" />

        <Button
            android:id="@+id/tv_dialog_cancel"
            style="@style/Widget.AppCompat.Button.Borderless.Colored"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:text="取消"
            android:textColor="?attr/colorAccent" />
    </LinearLayout>

    <android.support.design.widget.FloatingActionButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="@dimen/fab_margin"
        android:onClick="fab"
        android:src="@android:drawable/ic_dialog_email"
        app:layout_anchor="@id/layout"
        app:layout_anchorGravity="right|top"
        app:pressedTranslationZ="10dp" />

</android.support.design.widget.CoordinatorLayout>

看到LinearLayout的behavior了吧，在這裏我們添加BottomSheetBehavior表現行爲而已，其他的地方沒有任何特殊的。LinearLayout裏面的佈局，至於定義成什麼樣就看你自己想怎麼寫啦。
雖說我們可以不需要任何java代碼就可以實現，不過這裏我們還是希望可以通過按鈕去控制它的一個顯示情況：

 public void fab(View view) {
        BottomSheetBehavior behavior = BottomSheetBehavior.from(findViewById(R.id.layout));
        if (behavior.getState() == BottomSheetBehavior.STATE_EXPANDED) {
            behavior.setState(BottomSheetBehavior.STATE_COLLAPSED);
        } else {
            behavior.setState(BottomSheetBehavior.STATE_EXPANDED);
        }
    }

代碼也很簡單，首先我們通過BottomSheetBehavior.from()方法來獲取到它的Behavior，然後通過getState方法來判斷現在的狀態，如果是展開的狀態，我們就讓它收縮起來；反之，則展開。
其中BottomSheet 有這麼幾種狀態：

• STATE_COLLAPSED ：被摺疊的狀態
• STATE_SETTING ：沉降，我的理解是視圖從脫離手指自由滑動到最終停下的這一小段時間
• STATE_EXPANDED ：完全展開的狀態
• STATE_HIDDEN ：被隱藏的狀態，默認是false，可通過app:behavior_hideable屬性設置
• STATE_DRAGGING ：被拖拽的狀態

Support Library 23.2中還提供了BottomSheetDialog和BottomSheetDialogFragment。BottomSheetDialog的用法與普通的dialog差不多，顯示的內容可以是列表，也可以是簡單的對話，當顯示的內容一滑入屏幕時，屏幕的其餘部分會變暗，以襯托Dialog重點。下面看下BottomSheetDialog的簡單使用：

 BottomSheetDialog dialog = new BottomSheetDialog(this);
        dialog.setContentView(R.layout.dialog_layout);
        dialog.show();

下面我們使用BottomSheetDialog結合RecyclerView來顯示一個含有一個列表的dialog，效果圖如下：

使用BottomSheetDialog的話，當我們點擊按鈕顯示的時候，它只會先出現一部分，我們拖動它的時候，它會佔滿屏幕，現在我們就來看一下代碼

package per.lijuan.bottomsheetdome;

import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.design.widget.BottomSheetBehavior;
import android.support.design.widget.BottomSheetDialog;
import android.support.v4.view.ViewCompat;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    public BottomSheetBehavior behavior;
    public RecyclerView recyclerView;
    public MyAdapter adapter;
    private BottomSheetDialog dialog;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
    }

    private void initView() {
        recyclerView = (RecyclerView) findViewById(R.id.recyclerview);
        recyclerView.setItemAnimator(new DefaultItemAnimator());
        recyclerView.setLayoutManager(new LinearLayoutManager(recyclerView.getContext()));

        adapter = new MyAdapter();
        adapter.setItemClickListener(new onItemClickListener(2));
        recyclerView.setAdapter(adapter);
        recyclerView.setVisibility(View.GONE);

        behavior = BottomSheetBehavior.from(recyclerView);
        behavior.setBottomSheetCallback(new BottomSheetBehavior.BottomSheetCallback() {
            @Override
            public void onStateChanged(@NonNull View bottomSheet, int newState) {
                if (newState == BottomSheetBehavior.STATE_COLLAPSED || newState == BottomSheetBehavior.STATE_HIDDEN) {
                    recyclerView.setVisibility(View.GONE);
                }
            }

            @Override
            public void onSlide(@NonNull View bottomSheet, float slideOffset) {
                recyclerView.setVisibility(View.VISIBLE);
                ViewCompat.setAlpha(recyclerView, slideOffset);
            }
        });
    }

    public void fab(View view) {
        BottomSheetBehavior behavior = BottomSheetBehavior.from(findViewById(R.id.layout));
        if (behavior.getState() == BottomSheetBehavior.STATE_EXPANDED) {
            behavior.setState(BottomSheetBehavior.STATE_COLLAPSED);
        } else {
            behavior.setState(BottomSheetBehavior.STATE_EXPANDED);
        }
    }

    public void onClick1(View view) {
        if (behavior.getState() == behavior.STATE_EXPANDED) {
            behavior.setState(BottomSheetBehavior.STATE_COLLAPSED);
        } else {
            behavior.setState(BottomSheetBehavior.STATE_EXPANDED);
        }
    }

    public void onClick2(View view) {
        RecyclerView recyclerView = (RecyclerView) LayoutInflater.from(this)
                .inflate(R.layout.list, null);
        recyclerView.setItemAnimator(new DefaultItemAnimator());
        recyclerView.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));
        MyAdapter adapter = new MyAdapter();
        recyclerView.setAdapter(adapter);

        dialog = new BottomSheetDialog(this);
        dialog.setContentView(recyclerView);
        dialog.show();
        adapter.setItemClickListener(new onItemClickListener(3));
    }

    public class onItemClickListener implements MyAdapter.ItemClickListener {
        private int index;

        public onItemClickListener(int index) {
            this.index = index;
        }

        @Override
        public void onItemClick(int position) {
            Toast.makeText(MainActivity.this, "您點擊了item" + position, Toast.LENGTH_LONG).show();
            if (index == 2) {
                behavior.setState(BottomSheetBehavior.STATE_COLLAPSED);
            } else if (index == 3) {
                dialog.dismiss();
            }
        }
    }
}

MyAdapter.class

package per.lijuan.bottomsheetdome;

import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

/**
 * 適配器
 * Created by lijuan on 2016/9/7.
 */
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        return new ViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item, parent, false));
    }

    @Override
    public void onBindViewHolder(final ViewHolder holder, final int position) {
        holder.mTextView.setText("item");
        holder.mTextView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mItemClickListener.onItemClick(position);
            }
        });
    }

    @Override
    public int getItemCount() {
        return 8;
    }

    class ViewHolder extends RecyclerView.ViewHolder {

        public TextView mTextView;

        public ViewHolder(View view) {
            super(view);
            mTextView = (TextView) view.findViewById(R.id.textview);
        }
    }

    public interface ItemClickListener {
        void onItemClick(int position);
    }

    public ItemClickListener mItemClickListener;

    public void setItemClickListener(ItemClickListener listener) {
        mItemClickListener = listener;
    }
}

list.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.RecyclerView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@android:color/white"/>

list_item.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="wrap_content"
    android:background="@android:color/white"
    android:orientation="vertical">

    <TextView
        android:id="@+id/textview"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="16dp"
        android:background="@android:color/white"
        android:gravity="center"
        android:text="Item"
        android:textSize="20sp" />

    <View
        android:layout_width="match_parent"
        android:layout_height="1dp"
        android:background="@android:color/darker_gray" />
</LinearLayout>

好了，本篇文章就這樣子啦，存在總結不到位的地方還望指導，感謝^_^

參考資料：https://material.google.com/components/bottom-sheets.html#

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