TextUtils
//判断字符串不为空
String inputText = ...;
if (!TextUtils.isEmpty(inputText))
...
退出应用
@Override
public void onBackPressed() {
AlertDialog.Builder builder = new android.support.v7.app.AlertDialog.Builder(this);
builder.setTitle("提示");
builder.setMessage("确定注销吗");
builder.setNegativeButton("取消", null);
builder.setPositiveButton("确定", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
ActivityUtils.getInstance().popAllActivity();
LoginActivity.actionStart(MainActivity.this);
}
});
builder.show();
}
Intent传值
传值：FirstActivity
Intent intent = new Intent(FirstActivity.this, SecondActivity.class);
intent.putExtra(key, value);
startActivity(intent);
接收：SecondActivity
Intent intent = getIntent();
//类型必须一致，这里以Int为例，也可以采用别的类型
intent.getExtras().getInt(key);
//也可以是intent.getIntExtra(key, defaultValue);
Intent回调数据传值
请求：FirstActivity
//当然也可以传值给下一个活动，只是这里没写
Intent intent = new Intent(FirstActivity.this, SecondActivity.class);
// 第二个参数是请求码，只要是一个唯一值
startActivityForResult(intent, 1234);
回调：FirstActivity
protected void onActivityResult(int requestCode, int resultCode, Intent intent) {
switch (requestCode) {
case 1234:
if (resultCode == RESULT_OK) {
String returnedData = intent.getStringExtra(key);
}
break;
}
}
传值：SecondActivity
Intent intent = new Intent();
intent.putExtra(key, value);
//专门用于向上一个活动返回数据
//第一个参数用于向上一个活动返回结果码，
//一般只使用RESULT_OK或RESULT_CANCELED这两个值
//第二个参数则是把带有数据的Intent传递回去
setResult(RESULT_OK, intent);
//调用了finish()方法来销毁当前活动
finish();
用Bundle的Intent
Intent intent = new Intent(FirstActivity.this, SecondActivity.class);
Bundle bundle = new Bundle();
bundle.putSerializable(key, value);
//也可以用bundle.putParcelable(key, value);
//bundle也可以传除对象外的数据类型，只是这里用对象为例
//传对象的前提是对象必须序列化
//如用putParcelable，对象必须 implements Parcelable
//如用putSerializable，对象必须 implements Serializable
intent.putExtras(bundle);
startActivity(intent);
//获取数据
intent.getSerializableExtra(key);
intent.getParcelableExtra(key);
//bundle数组，以整形为例
bundle.putIntegerArrayList(key, value);
getIntent().getIntegerArrayListExtra(key);
onCreate的Bundle
使用场景：当一个活动进入停止状态，是有可能被系统回收的，这时重新回到被回收的活动，是不会执行onRestart()，而是执行onCreate()，活动中的临时数据和状态会丢失，怎么办呢？
public void onSaveInstanceState(Bundle outState, PersistableBundle outPersistentState) {
//5.0后一些特殊行为powered off 或者其他行为
//他会帮我们保存在outPersistentState中，一种更加坚固的保存数据方式
super.onSaveInstanceState(outState, outPersistentState);
outState.putString(key, value);
}
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.id.layout);
if (savedInstanceState != null) {
savedInstanceState.getString(value)
}
}
启动活动的最佳写法
FirstActivity:
SecondActivity.actionStart(FirstActivity.this, data1, data2);
SecondActivity:
public static void actionStart(Context context, String data1, String data2) {
Intent intent = new Intent(context, SecondActivity.class);
intent.putExtra(param1, data1);
intent.putExtra(param2, data2);
context.startActivity(intent);
}
新建线程
new Thread(new Runnable() {
@Override
public void run() {
//业务逻辑
}
}).start();
延时一秒
new Handler().postDelayed(new Runnable() {
public void run() {
//业务逻辑
}
}, 1000);
Fragment
//继承android.support.v4.app.Fragment
//不需要在build.gradle文件添加supoort-v4库的依赖
//因为appcompat-v7会将是supoort-v4库引入进来
public class LeftFragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater,
ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.activity_left_fragment, container, false);
}
}
//另一边同样的写法
//activity_mian.xml
//貌似Fragment的id必须添加
会动的Fragment
//FrameLayout的所有控件默认放在布局的左上角
//非常适合只在布局里放入一个碎片
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViewById(R.id.button).setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.button:
replaceFragment(new RightFragment());
break;
}
}
private void replaceFragment(Fragment fragment) {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction transaction = fragmentManager.beginTransaction();
transaction.replace(R.id.right_layout, fragment);
//模拟返回栈，接受一个名字描述返回栈的状态，一般传入null即可
transaction.addToBackStack(null);
transaction.commit();
}
Fragment和activity通信
//获取碎片实例
LeftFragment leftFragment = (LeftFragment)
getSupportFragmentManager().findFragmentById(R.id.left_fragment);
//获取当前碎片相关联的活动
MainActivity activity = (MainActivity) getActivity();
接受广播
//以监控网络变化为例
//清单文件添加对应权限
发送广播
public class MyBroadcastReceiver extends BroadcastReciver {
@Override
public void onReceive(Context context, Intent intent) {
Toast.makeText(context, "received in MyBroadcastReceiver", Toast.LENGTH_SHORT).show();
//有序广播的截断
//abortBroadcast();
}
}
//清单文件的application标签中对这个广播接收器进行修改
//静态注册
//enabled 是否启用
//exproted 是否允许这个广播接收器接收本程序以外的广播
//发送广播的触发点
Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onclick(View v) {
Intent intent = new Intent("com.example.broadcastter.MY_BROADCAST");
sendBroadcast(intent);
//如果是发送有序广播
//sendOrderedBroadcast(intent, null);
}
})
使用本地广播
//发送广播
private IntentFilter intFilter;
private LocalReciver localReciver;
private LocalBroadcastManager localBroadcastManager;
//获取实例
localBraodcastManager = LocalBroadcastManager.getInstance(this);
Intent intent = new Intent("com.example.broadcasttest.LOCAL_BROADCAST");
//发送本地广播
localBraodcastManager.sendBroadcast(intent);
@Override
protected void onDestroy() {
super.onDestroy();
localBroadcastManager.unregisterReceiver(localReceiver);
}
class LocalReceive extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
Toast.makeText(context, "received local broadcast", Toast.LENGTH_SHORT).show();
}
}
//接受广播
Intent intent = new Intent("com.example.broadcasttest.LOCAL_BROADCAST");
localBroadcastManager.sendBroadcast(intent);
将数据存储到文件中
//适合存储一些简单的文本数据或二进制数据
public void() {
String data = "Data to save";
FileOutputStream out = null;
BufferedWriter writer = null;
try {
//第一个参数是文件名，文件路径默认为/dada/data//files/
//MODE_PRIVATE表示文件同名时覆盖
//MODE_APPEND表示文件同名时添加
out = openFileOutput("data", Context.MODE_PRIVATE);
writer = new BufferedWriter(new OutputStreamWriter(out));
writer.write(data);
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (writer != null)
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
从文件中读取数据
public String load() {
FileInputStream in = null;
BufferedReader reader = null;
StringBuilder context = new StringBuilder();
try {
in = openFIleInput("data");
reader = new BufferedReader(new InputStreamReader(in));
String line = "";
while ((line = reader.readLine) != null) {
content.append(line);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (reader != null)
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return content.toString();
}
获取控件的宽和高
public class MyImageView extends android.support.v7.widget.AppCompatImageView {
public MyImageView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyImageView(Context context) {
super(context);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
}
}
