Android学习之Fragment的各种实现功能（头部折叠，循环列表RecyclerView，左右滑动ViewPager）

Posted 2021-08-30 wangweizu99

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android学习杂记

四大组件之Service

1、服务开启的两种方式

startService：开启服务

开启服务后 服务就会长期的后台运行,即使调用者退出了.服务仍然在后台继续运行.服务和调用者没有什么关系, 调用者是不可以访问服务里面的方法.

bindService：绑定服务

服务开启后,生命周期与调用者相关联.调用者挂了,服务也会跟着挂掉.不求同时生,但求同时死.调用者和服务绑定在一起,调用者可以间接的调用到服务里面的方法.

2、滑动控件

NestedScrollView

折叠头部

<?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">

    <com.google.android.material.appbar.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="200dp">

        <com.google.android.material.appbar.CollapsingToolbarLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_scrollFlags="scroll|exitUntilCollapsed"
            app:titleEnabled="false">

            <ImageView
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:scaleType="centerCrop"
                android:src="@drawable/abc_vector_test"
                app:layout_collapseMode="parallax" />

            <androidx.appcompat.widget.Toolbar
                android:id="@+id/view_toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:layout_collapseMode="pin"
                app:popupTheme="@style/ThemeOverlay.AppCompat.Light">

                <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_gravity="center"
                    android:text="新闻详情" />
            </androidx.appcompat.widget.Toolbar>
        </com.google.android.material.appbar.CollapsingToolbarLayout>
    </com.google.android.material.appbar.AppBarLayout>

    <android.support.v4.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior">

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

            <TextView
                android:layout_width="match_parent"
                android:layout_height="50dp"
                android:text="hello world" />
            ...
            ...
        </LinearLayout>
    </android.support.v4.widget.NestedScrollView>
</android.support.design.widget.CoordinatorLayout>

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.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"
    tools:context=".MainActivity">

    <com.google.android.material.appbar.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="200dp"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">
        <com.google.android.material.appbar.CollapsingToolbarLayout
            android:layout_width="match_parent"
            android:layout_height="170dp"
            app:contentScrim="#999999"
            app:expandedTitleMarginBottom="100dp"
            app:layout_scrollFlags="scroll|exitUntilCollapsed"
            app:title="我是collapsebar的标题">

            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="第一个固定(pin)"
                android:textSize="40sp"
                app:layout_collapseMode="pin" />

            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_gravity="center"
                android:text="不设置,跟随滑动"
                android:textSize="40sp" />

            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_gravity="bottom"
                android:text="视察效果(parallax)"
                android:textSize="40sp"
                app:layout_collapseMode="parallax" />

            <androidx.appcompat.widget.Toolbar
                android:layout_width="match_parent"
                android:layout_height="30dp"
                android:layout_gravity="top"
                android:background="#600f"
                app:layout_collapseMode="pin">

                <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="我是toolbar" />
            </androidx.appcompat.widget.Toolbar>

        </com.google.android.material.appbar.CollapsingToolbarLayout>

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="appbar之内,collap之外"
            android:textColor="#0f0" />

    </com.google.android.material.appbar.AppBarLayout>

    <androidx.core.widget.NestedScrollView
        android:id="@+id/n_scroll_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior">

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

            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="哈"
                android:textColor="#0f0"
                android:textSize="200sp" />

            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="哈"
                android:textColor="#0f0"
                android:textSize="200sp" />

            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="哈"
                android:textColor="#0f0"
                android:textSize="200sp" />

            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="哈"
                android:textColor="#0f0"
                android:textSize="200sp" />
        </LinearLayout>
    </androidx.core.widget.NestedScrollView>

</androidx.coordinatorlayout.widget.CoordinatorLayout>

解释文章

3、常用属性大全

1、实现圆角矩形背景

<shape
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <!-- 填充的颜色 -->
    <solid android:color="#534F46" />
    <!-- 圆角的半径 -->
    <corners android:radius="10dp" />
</shape>

4、Fragment之间的通信之ViewModel

示例：

public class SharedViewModel extends ViewModel {
    private final MutableLiveData<Item> selected = new MutableLiveData<Item>();

    public void select(Item item) {
        selected.setValue(item);
    }

    public LiveData<Item> getSelected() {
        return selected;
    }
}

public class MasterFragment extends Fragment {
    private SharedViewModel model;

    public void onViewCreated(@NonNull View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        model = new ViewModelProvider(requireActivity()).get(SharedViewModel.class);
        itemSelector.setOnClickListener(item -> {
            model.select(item);
        });
    }
}

public class DetailFragment extends Fragment {

    public void onViewCreated(@NonNull View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        SharedViewModel model = new ViewModelProvider(requireActivity()).get(SharedViewModel.class);
        model.getSelected().observe(getViewLifecycleOwner(), item -> {
           // Update the UI.
        });
    }
}

模仿：

public class SharedViewModel extends ViewModel {
    private final MutableLiveData<String> strs = new MutableLiveData<String>();

    public void add(String str){
        strs.setValue(str);
    }

    public LiveData<String> getStrs(){
        return strs;
    }
}


public class Fragment1 extends Fragment {
    private SharedViewModel model;

    public Fragment1() {
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) {
        final View inflate = inflater.inflate(R.layout.fragment01, container, false);
        model = new ViewModelProvider(requireActivity(),new ViewModelProvider.NewInstanceFactory()).get(SharedViewModel.class);
        Button bt1=inflate.findViewById(R.id.bt1);
        bt1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                EditText et1 = inflate.findViewById(R.id.et1);
                model.add(et1.getText().toString());
            }
        });

        return inflate;
    }
    
    
    
    public class Fragment2 extends Fragment {
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) {
        View inflate = inflater.inflate(R.layout.fragment02, container, false);
        SharedViewModel model = new ViewModelProvider(requireActivity(),new 		            ViewModelProvider.NewInstanceFactory()).get(SharedViewModel.class);
        model.getStrs().observe(this, item -> {
            TextView t1 = inflate.findViewById(R.id.fragment2_t1);
            t1.setText(item);
        });
        return inflate;
    }
}

5、实现循环列表

建立RecyclerView适配器

public class LinearAdapter extends RecyclerView.Adapter<LinearAdapter.LinearViewHolder> {
    private Context mContext;
    private List<Integer> index=new ArrayList<Integer>();
    //展示的数据
    public LinearAdapter(Context context){
        this.mContext=context;
        for(int i=0;i<100;i++){
            index.add(i+1);
        }
    }

    //添加循环布局
    @Override
    public LinearAdapter.LinearViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        return new LinearViewHolder(LayoutInflater.from(mContext).inflate(R.layout.layout_linear_item,parent,false));
    }

    //可以为每个布局添加消息
    @Override
    public void onBindViewHolder(LinearAdapter.LinearViewHolder holder, int position) {
        holder.textView.setText(String.format("常用功能 %s", index.get(position)));
    }

    //item的总长度
    @Override
    public int getItemCount() {
        return 100;
    }

    //LinearViewHolder可以看作一个item的展示和内部逻辑处理，故而如果需要绑定事件，获取控件的时候要在itemView中获取
    //itemView由onCreateViewHolder方法LayoutInflater.inflatec创建
    class LinearViewHolder extends RecyclerView.ViewHolder{
        private TextView textView;
        public LinearViewHolder(View itemView){
            super(itemView);
            textView=(TextView) itemView.findViewById(R.id.tv_main);

            //简单事件处理
            textView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Toast.makeText(mContext,textView.getText().toString(), Toast.LENGTH_SHORT).show();
                }
            });
        }
    }

}

调用适配器

public class Fragment4 extends Fragment {
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) {
        View inflate = inflater.inflate(R.layout.fragment04, container, false);
        RecyclerView mRvMain = inflate.findViewById(R.id.rv_main);
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