AndroidStudio學習筆記（五）小實戰

實戰

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1. 製作9-patch圖片
   使用draw9patch.bat文件製作。打開後導入圖片，可以在圖片的四個邊框繪製一個個的小黑點，在上邊框和左邊框繪製的部分表示當圖片需 要拉伸時就拉伸黑點標記的區域，在下邊框和右邊框繪製的部分表示內容會被放置的區域。使 用鼠標在圖片的邊緣拖動就可以進行繪製了，按住Shift鍵拖動可以進行擦除。
2. 添加RecyclerView依賴庫：
   implementation ‘com.android.support:recyclerview-v7:28.0.0’
3. 修改activity_main.xml中的代碼:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#d8e0e8" >

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

        <EditText android:id="@+id/input_text"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:maxLines="2" />
        <Button android:id="@+id/send"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="發送" />
    </LinearLayout>
</LinearLayout>

4. 新建Msg實體類:

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;
    }
}

5. 編寫RecyclerView子項的佈局，新建msg_item.xml，代碼如下:

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;
    }

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

    public void onBindViewHolder(ViewHolder holder, int position) {
        Msg msg = mMsgList.get(position);
        if (msg.getType() == Msg.TYPE_RECEIVED) {
            // 如果是收到的消息，則顯示左邊的消息佈局，將右邊的消息佈局隱藏
            holder.leftLayout.setVisibility(View.VISIBLE);
            holder.rightLayout.setVisibility(View.GONE);
            holder.leftMsg.setText(msg.getContent());
        } else if(msg.getType() == Msg.TYPE_SENT) {
            // 如果是發出的消息，則顯示右邊的消息佈局，將左邊的消息佈局隱藏
            holder.rightLayout.setVisibility(View.VISIBLE);
            holder.leftLayout.setVisibility(View.GONE);
            holder.rightMsg.setText(msg.getContent());
        }
    }

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

6. 要創建RecyclerView的適配器類，新建類MsgAdapter ，代碼如下:

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;
    }

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

    public void onBindViewHolder(ViewHolder holder, int position) {
        Msg msg = mMsgList.get(position);
        if (msg.getType() == Msg.TYPE_RECEIVED) {
            // 如果是收到的消息，則顯示左邊的消息佈局，將右邊的消息佈局隱藏
            holder.leftLayout.setVisibility(View.VISIBLE);
            holder.rightLayout.setVisibility(View.GONE);
            holder.leftMsg.setText(msg.getContent());
        } else if(msg.getType() == Msg.TYPE_SENT) {
            // 如果是發出的消息，則顯示右邊的消息佈局，將左邊的消息佈局隱藏
            holder.rightLayout.setVisibility(View.VISIBLE);
            holder.leftLayout.setVisibility(View.GONE);
            holder.rightMsg.setText(msg.getContent());
        }
    }

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

7. 最後修改MainActivity中的代碼，來爲RecyclerView初始化一些數據，並給發送按鈕加入事件響 應，代碼如下所示：

public class MainActivity extends AppCompatActivity {

    private List<Msg> msgList = new ArrayList<>();
    private EditText inputText;
    private Button send;
    private RecyclerView msgRecyclerView;
    private MsgAdapter adapter;
    private String MSG_Rec[]={
            "睡也是你，醒也是，無孔不入也是你。喫飯想你，走路想你，望穿秋水還是你~",
            "送你一朵花，做一枚髮卡，別在你的心間~",
            "我多希望人生如夢，夢裏都是詩，寫的是我和你~",
            "我感動得再也不說出話^o^只能簡單做一個復讀機了....."};

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


        initMsgs(); // 初始化消息數據

        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() {
            public void onClick(View v) {
                int temp;
                String content = inputText.getText().toString();
                if (!"".equals(content)) {
                    Msg msg = new Msg(content, Msg.TYPE_SENT);
                    msgList.add(msg);

                    //回覆消息2-4-6
                    temp = msgList.size()/2-1;
                    Msg msgRec;
                    if (temp<4){
                        msgRec = new Msg(MSG_Rec[temp], Msg.TYPE_RECEIVED);
                    }else {
                        msgRec = new Msg(content+"?", Msg.TYPE_RECEIVED);
                    }
                    msgList.add(msgRec);

                    adapter.notifyItemInserted(msgList.size() - 1);
                    // 當有新消息時， 刷新RecyclerView中的顯示
                    msgRecyclerView.scrollToPosition(msgList.size() - 1);
                    // 將 RecyclerView定位到最後一行
                    inputText.setText(""); // 清空輸入框中的內容
                }
            }
        });
    }

    private void initMsgs() {
        Msg msg1 = new Msg("hi~", Msg.TYPE_RECEIVED);
        msgList.add(msg1);
    }
}