Android应用程序四大组件之Activity(二)-优快云博客

Activity状态保存

1.onSaveInstanceState()/onCreate()/onRestoreInstanceState()

系统在回收当期Activity之前会调用onSaveInstanceState(),Back&Home两个键不会调用此方法.例如电子书程序,阅读到某一页内存不足被系统回收.可以通过此方法记录第几页.在程序重新启动时,在onCreate()里判断重新读取退出时第几页状态.它的参数Bundle是key-value形式

private final String SAVE_INSTANCE_TAG = "MainTestActivity.Saveinstancetag"; EditText editText = null; @Override protected void onSaveInstanceState(Bundle outState) { if(outState!=null){ outState.putString(this.SAVE_INSTANCE_TAG, "hello!!!!"); } System.out.println("onSaveInstanceState"); super.onSaveInstanceState(outState); } /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); System.out.println("onCreate"); editText = (EditText)findViewById(R.id.myEditText); if(editText!=null&&savedInstanceState!=null){ editText.setText(savedInstanceState.getString(SAVE_INSTANCE_TAG)); } if(savedInstanceState!=null){ System.out.println("savedInstanceState"+savedInstanceState); } }

onRestoreInstanceState()不一定是与onSaveInstanceState()成对使用的.调用此方法时.Activity定是被系统Destroy掉的.其Bundle参数值也可以传到onCreate()

@Override protected void onRestoreInstanceState(Bundle savedInstanceState) { // TODO Auto-generated method stub String tag= savedInstanceState.getString(this.SAVE_INSTANCE_TAG); super.onRestoreInstanceState(savedInstanceState); }

2.借助Activity Lifecycle+Preference

使用这种方式状态保存可以是.横竖屏幕切换,按Home or Back键之后再回来.

@Override protected void onPause() { // TODO Auto-generated method stub super.onPause(); // 写入 SharedPreferences SharedPreferences preferences = getSharedPreferences("name", MODE_PRIVATE); Editor editor = preferences.edit(); editor.putBoolean("boolean_key", true); editor.putString("string_key", "string_value"); editor.commit(); } @Override protected void onResume() { // TODO Auto-generated method stub super.onResume(); // 读取 SharedPreferences SharedPreferences preferences = getSharedPreferences("name", MODE_PRIVATE); preferences.getBoolean("boolean_key", false); preferences.getString("string_key", "default_value"); }

Activity之间通信

1.无参数Activity跳转

Intent intent = new Intent(Activity1.this, Activity2.class);
startActivity(intent);

2.向下一个Activity传递数据（使用Bundle和Intent.putExtras）

Intent intent = new Intent(); intent.setClass(Ex03_10Activity.this, Ex03_10_1.class); Bundle bundle = new Bundle(); bundle.putDouble("height", height); bundle.putString("sex", sex); intent.putExtras(bundle); startActivity(intent); //startActivityForResult(intent, 0);//数据的接收 Bundle bundle = this.getIntent().getExtras(); String sex = bundle.getString("sex"); double height = bundle.getDouble("height");

3.向上一个Activity返回结果（使用setResult，针对startActivityForResult(it,REQUEST_CODE)启动的Activity）

Intent intent=getIntent(); Bundle bundle2=new Bundle(); bundle2.putString("sex", "Man!"); intent.putExtras(bundle2); setResult(RESULT_OK, intent);

4.回调上一个Activity的结果处理函数（onActivityResult）

@Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { // TODO Auto-generated method stub switch (requestCode) { case RESULT_OK: Bundle bundle = data.getExtras(); String sex = bundle.getString("sex"); double height = bundle.getDouble("height"); et.setText(""+height); if(sex.equals("M")){ rb1.setChecked(true); }else{ rb2.setChecked(true); } break; default: break; } }

打电话
1. //叫出拨号程序
2. Uri uri = Uri.parse("tel:0800000123");
3. Intent it = new Intent(Intent.ACTION_DIAL, uri);
4. startActivity(it);
1. //直接打电话出去
2. Uri uri = Uri.parse("tel:0800000123");
3. Intent it = new Intent(Intent.ACTION_CALL, uri);
4. startActivity(it);
5. //用這個，要在 AndroidManifest.xml 中，加上
6. //<uses-permission id="android.permission.CALL_PHONE" />

传送SMS/MMS
1. //调用短信程序
2. Intent it = new Intent(Intent.ACTION_VIEW, uri);
3. it.putExtra("sms_body", "The SMS text");
4. it.setType("vnd.android-dir/mms-sms");
5. startActivity(it);
1. //传送消息
2. Uri uri = Uri.parse("smsto://0800000123");
3. Intent it = new Intent(Intent.ACTION_SENDTO, uri);
4. it.putExtra("sms_body", "The SMS text");
5. startActivity(it);
1. //传送 MMS
2. Uri uri = Uri.parse("content://media/external/images/media/23");
3. Intent it = new Intent(Intent.ACTION_SEND);
4. it.putExtra("sms_body", "some text");
5. it.putExtra(Intent.EXTRA_STREAM, uri);
6. it.setType("image/png");
7. startActivity(it);