【Android UI】CoordinatorLayout实现带图片可拉伸的Toolbar

国际惯例，先看效果

步骤一：

在build.gradle中添加如下代码

dependencies {    compile fileTree(dir: 'libs', include: ['*.jar'])    compile 'com.android.support:appcompat-v7:23.0.1'    compile 'com.android.support:design:23.0.1'    compile 'com.android.support:recyclerview-v7:+'}

步骤二：

布局文件

<?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"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:fitsSystemWindows="true"    tools:context=".MainActivity">    <android.support.design.widget.AppBarLayout        android:layout_width="match_parent"        android:layout_height="172dp"        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">        <android.support.design.widget.CollapsingToolbarLayout            android:id="@+id/collapsing_toolbar"            android:layout_width="match_parent"            android:layout_height="match_parent"            android:fitsSystemWindows="true"            app:contentScrim="?attr/colorPrimary"            app:expandedTitleMarginEnd="64dp"            app:expandedTitleMarginStart="48dp"            app:layout_scrollFlags="scroll|exitUntilCollapsed">            <ImageView                android:id="@+id/backdrop"                android:layout_width="match_parent"                android:layout_height="match_parent"                android:fitsSystemWindows="true"                android:scaleType="centerCrop"                android:src="@drawable/cat"                app:layout_collapseMode="parallax" />            <android.support.v7.widget.Toolbar                android:id="@+id/toolbar"                android:layout_width="match_parent"                android:layout_height="?attr/actionBarSize"                app:layout_scrollFlags="scroll|enterAlways"                app:layout_collapseMode="pin"                app:popupTheme="@style/ThemeOverlay.AppCompat.Light"/>        </android.support.design.widget.CollapsingToolbarLayout>    </android.support.design.widget.AppBarLayout>    <android.support.v7.widget.RecyclerView        android:id="@+id/my_recycler_view"        android:layout_width="match_parent"        android:layout_height="match_parent"        app:layout_behavior="@string/appbar_scrolling_view_behavior">    </android.support.v7.widget.RecyclerView></android.support.design.widget.CoordinatorLayout>

步骤三：

Activity代码

public class MainActivity extends AppCompatActivity {    private RecyclerView mRecyclerView;    private RecyclerView.Adapter mAdapter;    private RecyclerView.LayoutManager mLayoutManager;    private String[] myDataset = {"A", "B", "C", "D", "E", "F", "G", "H", "J", "K", "L", "M", "N", "O", "P", "Q", "R"};    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);        setSupportActionBar(toolbar);        getSupportActionBar().setDisplayHomeAsUpEnabled(true);        CollapsingToolbarLayout collapsingToolbar =                (CollapsingToolbarLayout) findViewById(R.id.collapsing_toolbar);        collapsingToolbar.setTitle("Title");        mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);        // improve performance if you know that changes in content        // do not change the size of the RecyclerView        mRecyclerView.setHasFixedSize(true);        // use a linear layout manager        mLayoutManager = new LinearLayoutManager(this);        mRecyclerView.setLayoutManager(mLayoutManager);        // specify an adapter (see also next example)        mAdapter = new MyAdapter(myDataset);        mRecyclerView.setAdapter(mAdapter);    }    @Override    public boolean onCreateOptionsMenu(Menu menu) {        // Inflate the menu; this adds items to the action bar if it is present.        getMenuInflater().inflate(R.menu.menu_main, menu);        return true;    }    @Override    public boolean onOptionsItemSelected(MenuItem item) {        // Handle action bar item clicks here. The action bar will        // automatically handle clicks on the Home/Up button, so long        // as you specify a parent activity in AndroidManifest.xml.        int id = item.getItemId();        //noinspection SimplifiableIfStatement        if (id == R.id.action_settings) {            return true;        }        return super.onOptionsItemSelected(item);    }}

Adapter代码

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {    private String[] mDataset;    public static class ViewHolder extends RecyclerView.ViewHolder {        public TextView name;        public ViewHolder(View v) {            super(v);            name = (TextView)v.findViewById(R.id.name);        }    }    public MyAdapter(String[] myDataset) {        mDataset = myDataset;    }    @Override    public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {        View v = LayoutInflater.from(parent.getContext())                .inflate(R.layout.list_item, parent, false);        // set the view's size, margins, paddings and layout parameters        ViewHolder vh = new ViewHolder(v);        return vh;    }    @Override    public void onBindViewHolder(MyAdapter.ViewHolder holder, int position) {        String nameStr = mDataset[position];        holder.name.setText(nameStr);    }    @Override    public int getItemCount() {        return mDataset.length;    }}