android入门学习 -- 2

2022-07-02 00:35:14

android入门学习

第三章

TextView

gravity指定文字对齐方式，可以使用|指定多个指
字体大小sp为单位

Button

textAllCaps大小写自动转换

EditText

hint提示文字
maxLines最大行数
获取EditText的输入内容editText.getText().toString()

ImageView

图片一般放在drawable目录下，指定分辨率
src设定图片目录
代码设置imageView.setImageResource(R.drawable.xxxx)

ProgressBar

可见属性android:visibility，可选值：visible可见，invisible不可见但占位，gone不可见不占位
在隐藏和显示之间来回切换

if (progressBar.getVisibility() == View.GONE) {
    progressBar.setVisibility(View.VISIBLE);
} else {
    progressBar.setVisibility(View.GONE);
}

style属性设定样式，圆形，水平

style="?android:attr/progressBarStyleHorizontal"

max属性设定进度条最大值
动态改变进度条进度

int progress = progressBar.getProgress();
progress += 10;
progressBar.setProgress(progress);

AlterDialog

在当前界面弹出一个对话框，屏蔽掉其他控件的交互，一般用于提示一些重要内容或警告

AlterDialog.Builder dialog = new AlterDialog.Builder(MainActivity.this);
dialog.setTitle("This is dialog");
dialog.setMessage("Something important.");
dialog.setCancelable(false);
dialog.setPositiveButton("OK", new DialogInterface.OnClickListener() {
    @override
    public void onClick(DialogInterface dialog, int which) {
    ...
    }
});

dialog.setNegaitiveButton("Cancel", new DialogInterface.OnClickListener() {
    @override
    public void onClick(DialogInterface dialog, int which) {
    ...
    }
});
dialog.show;

四种基本布局

  1. 线性布局LinearLayout
    常用，在线性方向上依次排列，不能在该方向上指定match_parents，否则就填满了
    layout_gravity指定控件在布局中的对齐方式，只有相反排列方向的对齐才会生效
    layout_weight使用比例的方式指定控件大小，需要将该方向的width/height指定为0dp，weight计算长度是按照所有控件的weight相加，然后用该控件weight/总的数值作为比例显示，还可以将一个设置为wrap，剩下的设置会占据剩余的长度
  2. 相对布局RelativeLayout
    可以相对于父布局，其他控件
  3. 帧布局
    所有控件默认放在右上角
  4. 百分比布局

引入布局

新建一个title.xml，将布局代码写入
在活动布局代码中写入<include layout="@layout/title" />
最后再活动中将系统自带标题栏隐藏掉

ActionBar actionBar = getSupportActionBar();
if (actionBar != null) {
    actionbar.hide();
}

创建自定义控件

比如创建一个返回按钮
新建TitleLayout继承自LinearLayout，成为自定义的标题栏控件

public class TitleLayout extends LinearLayout {
    
    public TitleLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        LayoutInflater.from(context).inflate(R.layout.title, this);

        //TODO: 点击事件的代码
    }
}

先构造，然后使用LayoutInflater.from()构造出一个对象，inflate动态加载布局文件，第一参数是布局文件id，第二参数是父布局，也就是TitleLayout，直接传入this
在布局文件中添加这个自定义控件

<com.example.packetname.TitleLayout
    android.layout_width="match_parent"
    android.layout_width="wrap_content" />

自定义控件的包名不能省略

ListView

新建一个ListView控件，宽高都设置为match_parent
然后再代码里设置一个String[]数组，并添加一个Adapter

ArrayAdapter<String> adapter = new ArrayAdapter<String>(getApplicationContext(), 
    android.R.layout.simple_list_item_1, data);
ListView listView = (ListView) findViewById(R.id.listView);
listView.setAdapter(adapter);

data是String[]数组，数据可以是数据库提供，也可以是网络下载
数组中的数据无法直接传递给ListView，还需要适配器，android中有很多适配器的实现类
ArrayAdapter是其中一种适配器，第一参数是上下文，第二参数是ListView子项布局的id，最后是适配的数据类型
最后调用ListView的setAdapter方法将构造好的适配器对象传递进入

定制ListView

效果：每个item显示一种水果名称和图片
先定义一个实体类

public class Fruit {
    private String name;

    private int imageId;

    public Fruit(String name, int imageId) {
        this.name = name;
        this.imageId = imageId;
    }

    public String getName() {
        return name;
    }
    
    public int getImageId() {
        return imageId;
    }
}

定义一个自定义布局fruit_item.xml，定义一个ImageView和TextView
再创建一个自定义的适配器，继承自ArrayAdapter，并将泛型指定为Fruit类

public class FruitAdapter extends ArrayAdapter<Fruit> {
    private int resourceId;
    
    public FruitAdapter(Contenxt context, int textViewResourceId, 
        List<Fruit> objects) {
        super(context, textViewResourceId, objects);
        resourceId = textViewResourceId;
    }

    @override
    public View getView(int position, View convertView, ViewGroup parent) {
        Fruit fruit = getItem(position); //获取当前实例
        View view = LayoutInflater.from(getContext()).inflater(resourceId, parent, false);
        ImageView fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
        TextView fruitName = (TextView) view.findViewById(R.id.fruit_name);
        fruitImage.setImageResource(fruit.getImageId());
        fruitName.setText(fruit.getName());
        return view;
    }
}

getView方法是每个子项被滚动到屏幕内的时候会被调用，getView中，getItem是获取当前项的Fruit

提升ListView的运行效率

getView中有一个convertView参数，用于将之前加载好的布局进行缓存，以便之后重用

if (convertView == null) {
    view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
} else {
    view = convertView;
}

还可以借助ViewHolder对这部分进行优化

class ViewHolder {
    ImageView fruitImage;

    TextView fruitName;
}
ViewHolder viewHolder;
if (convertView = null) {
    view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
    viewHolder = new ViewHolder();
    viewHolder.fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
    viewHolder.fruitName = (TextView) view.findViewById(R.id.fruit_name);
    view.setTag(viewHolder); //将ViewHolder存储在View中
} else {
    view = convertView;
    viewHolder = (ViewHolder) view.getTag(); //重新获取
}
viewHolder.fruitImage.setImageResource(fruit.getImageId());
viewHolder.fruitName.setText(fruit.getName());
return view;

ListView点击事件

listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        Fruit fruit = fruitList.get(position); //fruitList是List<Fruit>
        //TODO            
    }
});

RecyclerView

新增的控件，在app/build.gradle文件中，dependencies添加

implementation 'androidx.recyclerview:recyclerview:1.1.0'

布局中添加

    <androidx.recyclerview.widget.RecyclerView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/recycler_view"/>

Fruit类和fruit_item.xml

//Fruit class
public class Fruit {
    private String name;

    private int imageId;

    public Fruit(String name, int imageId) {
        this.name = name;
        this.imageId = imageId;
    }

    public String getName() {
        return name;
    }

    public int getImageId() {
        return imageId;
    }

}
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/fruit_image"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="10dp"
        android:id="@+id/fruit_name"/>

</LinearLayout>

新建一个适配器FruitAdapter类，继承自RecyclerView.Adapter，泛型指定为FruitAdapter.ViewHolder，是定义的一个内部类

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import java.util.List;

public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder> {

    private List<Fruit> mFruitList;

    /*
    * ViewHolder继承自RecyclerView.ViewHolder，传入一个View
    * view通常是子项的外层布局
    * */
    static class ViewHolder extends RecyclerView.ViewHolder {
        ImageView fruitImage;
        TextView fruitName;

        public ViewHolder(View view) {
            super(view);
            fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
            fruitName = (TextView) view.findViewById(R.id.fruit_name);
        }
    }

    public FruitAdapter(List<Fruit> fruitList) {
        mFruitList = fruitList;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item,
                parent, false);
        ViewHolder holder = new ViewHolder(view);
        return holder;
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Fruit fruit = mFruitList.get(position);
        holder.fruitImage.setImageResource(fruit.getImageId());
        holder.fruitName.setText(fruit.getName());
    }

    @Override
    public int getItemCount() {
        return mFruitList.size();
    }
}

最后是MainActivity中的代码

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private List<Fruit> fruitList = new ArrayList<>();

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

        initFruit();
        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);

        //LinearLayoutManager用于指定RecyclerView的布局方式
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);
        FruitAdapter adapter = new FruitAdapter(fruitList);
        recyclerView.setAdapter(adapter);
    }

    private void initFruit() {
        for (int i = 0; i < 2; i++) {
            Fruit apple = new Fruit("Apple", R.drawable.apple_pic);
            fruitList.add(apple);
            Fruit banana = new Fruit("Banana", R.drawable.banana_pic);
            fruitList.add(banana);
            Fruit orange = new Fruit("Orange", R.drawable.orange_pic);
            fruitList.add(orange);
            Fruit watermelon = new Fruit("Watermelon", R.drawable.watermelon_pic);
            fruitList.add(watermelon);
            Fruit pear = new Fruit("Pear", R.drawable.pear_pic);
            fruitList.add(pear);
            Fruit grape = new Fruit("Grape", R.drawable.grape_pic);
            fruitList.add(grape);
            Fruit pineapple = new Fruit("Pineapple", R.drawable.pineapple_pic);
            fruitList.add(pineapple);
            Fruit strawberry = new Fruit("Strawberry", R.drawable.strawberry_pic);
            fruitList.add(strawberry);
            Fruit cherry = new Fruit("Cherry", R.drawable.cherry_pic);
            fruitList.add(cherry);
            Fruit mango = new Fruit("Mango", R.drawable.mango_pic);
            fruitList.add(mango);
        }
    }
}

横向滚动的瀑布流布局

首先将fruit_item.xml中的元素改成垂直排列
再向主活动添加一句即可

layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);

RecyclerView还有网格布局GridLayoutManager和瀑布流布局StaggeredGridLayoutManager
例如瀑布流的实现：
将fruit_item.xml修改几处
首先将LinearLayout的宽度由100dp改成match_parent，因为瀑布流的布局的宽度是很据布局的列数来自动适配的，不是固定值，然后用layout_margin让子项之间留一些距离
接着修改MainActivity代码

StaggeredGridLayoutManager layoutManerger = new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL);

第一参数3是指布局分为3列，第二参数是指定布局的排列方向，最后再setLayoutManager即可

RecyclerView的点击事件

所有的点击事件都需要由具体的View去注册
修改FruitAdapter中的代码

        final ViewHolder holder = new ViewHolder(view);
        holder.fruitView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int position = holder.getAdapterPosition();
                Fruit fruit = mFruitList.get(position);
                Toast.makeText(v.getContext(), "u clicked view " + fruit.getName(), Toast.LENGTH_SHORT).show();
            }
        });

        holder.fruitImage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int position = holder.getAdapterPosition();
                Fruit fruit = mFruitList.get(position);
                Toast.makeText(v.getContext(), "u clicked image " + fruit.getName(), Toast.LENGTH_SHORT).show();
            }
        });

首先修改ViewHolder，添加fruitView变量保存子项最外层布局的实例，然后再onCreateViewHolder()方法中注册点击事件，这里为最外层布局和ImageView都注册了点击事件
点击图片就是Image的注册事件，点击文字因为没有注册，会被子项的最外层布局捕获

界面实践

制作Nine-Patch图片

一种特殊处理过的png图片，能够指定哪些区域可以被拉伸，哪些不可以
在drawable目录下右键图片，点击create 9-patch file即可创建
上边框和左边框便是拉伸的区域，下边框和左边框表示内容防止区域，鼠标拖动图片边缘绘制，按住Shift键拖动擦除

界面代码

界面

<?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"
    android:background="#d8e0e8">


    <androidx.recyclerview.widget.RecyclerView
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:id="@+id/msg_recycler_view"
        android:layout_weight="1"/>

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

        <EditText
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:id="@+id/input_text"
            android:hint="type something"
            android:maxLines="2"/>

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="send"
            android:textColor="#000"
            android:id="@+id/send"/>

    </LinearLayout>

</LinearLayout>

消息类Msg class

public class Msg {

    public static final int TYPE_RECEIVED = 0;
    public static final int TYPE_SENT = 1;

    private String content;

    private int type;

    public Msg(String content, int type) {
        this.content = content;
        this.type = type;
    }

    public String getContent() {
        return content;
    }

    public int getType() {
        return type;
    }


}

子项布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/left_layout"
        android:layout_gravity="left"
        android:background="@drawable/message_left">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_margin="10dp"
            android:textColor="#fff"
            android:id="@+id/left_msg"/>
    </LinearLayout>

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="right"
        android:background="@drawable/message_right"
        android:id="@+id/right_layout">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_margin="10dp"
            android:id="@+id/right_msg"/>

    </LinearLayout>

</LinearLayout>

MsgAdapter

public class MsgAdapter extends RecyclerView.Adapter<MsgAdapter.ViewHolder> {

    private List<Msg> mMsgList;

    static class ViewHolder extends RecyclerView.ViewHolder {
        LinearLayout leftLayout;
        LinearLayout rightLayout;

        TextView leftMsg;
        TextView rightMsg;

        public ViewHolder(View view) {
            super(view);
            leftLayout = (LinearLayout) view.findViewById(R.id.left_layout);
            rightLayout = (LinearLayout) view.findViewById(R.id.right_layout);
            leftMsg = (TextView) view.findViewById(R.id.left_msg);
            rightMsg = (TextView) view.findViewById(R.id.right_msg);
        }
    }

    public MsgAdapter(List<Msg> msgList) {
        mMsgList = msgList;
    }

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

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Msg msg = mMsgList.get(position);
        if (msg.getType() == Msg.TYPE_RECEIVED) {
            holder.leftLayout.setVisibility(View.VISIBLE);
            holder.rightLayout.setVisibility(View.GONE);
            holder.leftMsg.setText(msg.getContent());

        } else if (msg.getType() == Msg.TYPE_SENT) {
            holder.rightLayout.setVisibility(View.VISIBLE);
            holder.leftLayout.setVisibility(View.GONE);
            holder.rightMsg.setText(msg.getContent());

        }
    }

    @Override
    public int getItemCount() {
        return mMsgList.size();
    }
}

MainActivity

public class MainActivity extends AppCompatActivity {

    private List<Msg> msgList = new ArrayList<>();

    private EditText inputText;

    private Button send;

    private RecyclerView msgRecyclerView;

    private MsgAdapter adapter;

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

        initMsg();
        inputText = (EditText) findViewById(R.id.input_text);
        send = (Button) findViewById(R.id.send);

        msgRecyclerView = (RecyclerView) findViewById(R.id.msg_recycler_view);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        msgRecyclerView.setLayoutManager(layoutManager);
        adapter = new MsgAdapter(msgList);
        msgRecyclerView.setAdapter(adapter);

        send.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String content = inputText.getText().toString();
                if (!"".equals(content)) {
                    Msg msg = new Msg(content, Msg.TYPE_SENT);
                    msgList.add(msg);
                    adapter.notifyItemInserted(msgList.size() - 1);
                    //当有新消息时，刷新RecyclerView的显示
                    msgRecyclerView.scrollToPosition(msgList.size() - 1);
                    //定位到最后一行
                    inputText.setText(""); //清空输入框

                }
            }
        });
    }

    private void initMsg() {
        Msg msg1 = new Msg("Hello guy.", Msg.TYPE_RECEIVED);
        msgList.add(msg1);
        Msg msg2 = new Msg("Hello! Who is that?", Msg.TYPE_SENT);
        msgList.add(msg2);
        Msg msg3 = new Msg("This is Tom,. Nice to see you you you you you you you!!!!!!!!", Msg.TYPE_RECEIVED);
        msgList.add(msg3);
    }
}

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