使用Activity和Delegate與介面卡互動
阿新 • • 發佈:2019-01-08
在這個Demo裡,我們會分析如何通過委託模式(Delegation Pattern)幫助開發者把所有的業務邏輯從介面卡中移到Activity中。我們建立一個簡單的應用程式,通過該應用程式可以向列表中新增電話號碼,列表中每一行都有一個Remove按鈕,用於刪除電話號碼。
在介面卡中實現“Remove”按鈕的點選處理器,但是,並不在介面卡中實現刪除物件的方法。我們通過一個委託介面呼叫Activity的方法刪除物件。首先建立介面卡的程式碼,如下所示:
package com.example.huangfei.myapplication;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import java.util.List;
/**
* Created by huangfeihong on 2015/12/19.
*/
public class NumbersAdapter extends ArrayAdapter<Integer> {
//定義委託介面
public interface NumbersAdapterDelegate {
void removeItem(Integer value);
}
private Context mContext;
private LayoutInflater mInflater;
private NumbersAdapterDelegate mDelegate;
public NumbersAdapter (Context context, List<Integer> objects) {
super(context, 0, objects);
mContext = context;
mInflater = LayoutInflater.from(context);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null)
convertView = mInflater.inflate(R.layout.number_row, parent, false );
final Integer value = getItem(position);
TextView tv = (TextView) convertView.findViewById(R.id.numbers_row_text);
tv.setText(value.toString());
View button = convertView.findViewById(R.id.numbers_row_button);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (null != mDelegate) {//刪除物件
mDelegate.removeItem(value);
}
}
});
return convertView;
}
//為介面卡設定委託物件
public void setDelegate(NumbersAdapterDelegate delegate) {
mDelegate = delegate;
}
}
現在介面卡已經準備就緒,接下來分析Activity的程式碼:
package com.example.huangfei.myapplication;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;
import java.util.ArrayList;
public class MainActivity extends Activity implements NumbersAdapter.NumbersAdapterDelegate {
private static final String TAG = MainActivity.class
.getCanonicalName();
private ListView mListView;
private ArrayList<Integer> mNumbers;
private NumbersAdapter mAdapter;
private EditText mEditText;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mEditText = (EditText) findViewById(R.id.main_edittext);
mListView = (ListView) findViewById(R.id.main_listview);
mNumbers = new ArrayList<Integer>();
mAdapter = new NumbersAdapter(this, mNumbers);
mListView.setAdapter(mAdapter);
}
@Override
protected void onResume() {
super.onResume();
//註冊委託物件
mAdapter.setDelegate(this);
}
@Override
protected void onPause() {
super.onPause();
//取消註冊委託物件
mAdapter.setDelegate(null);
}
@Override
public void removeItem(Integer value) {
//從列表中移除指定項
mNumbers.remove(value);
Toast.makeText(this, "Removed object: " + value, Toast.LENGTH_SHORT).show();
mAdapter.notifyDataSetChanged();
}
public void addNumber(View v) {
String value = mEditText.getText().toString().trim();
try {
mNumbers.add(Integer.valueOf(value));
mEditText.setText("");
mAdapter.notifyDataSetChanged();
} catch (NumberFormatException e) {
Log.e(TAG, "Couldn't convert to integer the string: " + value);
}
}
}
委託模式在IOS開發中也被大量使用。比如,建立HTTP請求時,開發者可以設定一個委託物件,當請求處理完畢後指定一些操作。當編寫程式時,我們應時刻注意使用委託物件來組織程式碼。