安卓学习之广播的实践

《第一行代码》的学习。

模仿一个登陆流程，登陆后，点击退出发送广播强制退出，返回到登陆界面

实现的时候基本有下面几个步骤

一个ActivityCollector类管理所有的活动

一个BaseActivity 类作为所有活动的父类

一个LoginActivity继承于一个BaseActivity

MainActivity继承于一个BaseActivity显示登陆成功的界面

ActivityCollector类

public class ActivityCollector
{
public static List<Activity> activities = new ArrayList<Activity>();
public static void addActivity(Activity activity)
{
activities.add(activity);
}

public static void  removerActivity(Activity activity)
{
activities.remove(activity);
}

public static void finishAll()
{
for(Activity activity: activities)
{
if (!activity.isFinishing())
{
activity.finish();
}
}
}
}

+ BaseActivity 类

public class BaseActivity extends AppCompatActivity
{
private ForceOfflineReceiver receiver;

@Override
protected void onCreate(Bundle savedInstaceState)
{
super.onCreate(savedInstaceState);
ActivityCollector.addActivity(this);
}

@Override
protected void onResume()
{
super.onResume();
//这里注册一个广播，用于接收下线的消息
IntentFilter intentFilter = new IntentFilter();
intentFilter.addAction("com.magikid.broadcastbestpractice.FORCE_OFFLINE");
receiver= new ForceOfflineReceiver();
registerReceiver(receiver, intentFilter);
}

@Override
protected void onPause()
{
super.onPause();
//取消注册
if(receiver != null)
{
unregisterReceiver(receiver);
receiver = null;
}
}

@Override
protected void onDestroy()
{
super.onDestroy();
ActivityCollector.removerActivity(this);
}

class ForceOfflineReceiver extends BroadcastReceiver
{
@Override
public void onReceive(final Context context, Intent intent)
{
AlertDialog.Builder builder = new AlertDialog.Builder(context);
builder.setTitle("Warning");
builder.setMessage("You are forced to be offline. Please try to login again");
builder.setCancelable(false);
builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
ActivityCollector.finishAll();
Intent intent = new Intent(context, LoginActivity.class);
context.startActivity(intent);
}
});
builder.show();
}
}
}

LoginActivity类

public class LoginActivity extends BaseActivity {

private EditText accountEdit;
private EditText passwordEdit;
private Button login;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
accountEdit = (EditText)findViewById(R.id.account);
passwordEdit = (EditText)findViewById(R.id.password);
login = (Button)findViewById(R.id.login);

login.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v)
{
String account = accountEdit.getText().toString();
String password = passwordEdit.getText().toString();

if (account.equals("admin") && password.equals("123456"))
{
Intent intent = new Intent(LoginActivity.this,  MainActivity.class);

startActivity(intent);
finish();
}
else
{
Toast.makeText(LoginActivity.this, "account or password is invalid", Toast.LENGTH_SHORT).show();
}
}
});
}
}

//对应的layout
<TextView
android:layout_width="90dp"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:textSize="18sp"
android:text="Password"/>

<EditText
android:id="@+id/password"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:layout_gravity="center_vertical"/>
</LinearLayout>

<Button
android:id="@+id/login"
android:layout_width="match_parent"
android:layout_height="60dp"
android:text="Login"
/>

MainActivity类

public class MainActivity extends BaseActivity
{
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button forceOffline = (Button)findViewById(R.id.force_offline);
//点击按钮发送下线的广播
forceOffline.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v)
{
Intent intent = new Intent("com.magikid.broadcastbestpractice.FORCE_OFFLINE");
sendBroadcast(intent);
}
});
}

//对应的layout
<Button
android:id="@+id/force_offline"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Send force offline broadcast"
/>

主配置xml，将LoginActivity设置为默认启动界面

<activity android:name=".MainActivity">
</activity>
<activity android:name=".LoginActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.category.LAUNCHER"/>
</intent-filter>>
</activity>

一个简单的账号登录，模仿强制下线的Demo功能就完成了。主要是熟悉广播的试用