Android之Activity

一.初步认识

src

package cn.android.lyj;import android.app.Activity;import android.os.Bundle;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.TextView;public class TestActivity extends Activity {    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                Button button = (Button)findViewById(R.id.bt1);        button.setOnClickListener(new OnClickListener() {public void onClick(View v) {TextView textView = (TextView)findViewById(R.id.tv1);textView.setText("修改后");}});    }}

main.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:orientation="vertical" >    <TextView        android:id="@+id/tv1"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="@string/hello" /><Button     android:id="@+id/bt1"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:text="@string/bt_text" /></LinearLayout>

strings.xml

<?xml version="1.0" encoding="utf-8"?><resources>    <string name="hello">修改前text</string>    <string name="app_name">Test</string>    <string name="bt_text">修改text</string></resources>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="cn.android.lyj"    android:versionCode="1"    android:versionName="1.0" >    <uses-sdk android:minSdkVersion="10" />    <application        android:icon="@drawable/ic_launcher"        android:label="@string/app_name" >        <activity            android:label="@string/app_name"            android:name=".TestActivity" >            <intent-filter >                <action android:name="android.intent.action.MAIN" />                <category android:name="android.intent.category.LAUNCHER" />            </intent-filter>        </activity>    </application></manifest>

二.生命周期

注：缺少OnRestart(), 在OnStop()执行后当重新打开这个Activity时会被调用，OnRestart()——>onStart()——>onResume()

src

package cn.android.lyj;import android.app.Activity;import android.os.Bundle;import android.util.Log;public class TestActivity extends Activity {private static final String TAG = "LYJ";    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                Log.i(TAG, "onCreate()");    }        @Overrideprotected void onStart() {// TODO Auto-generated method stubsuper.onStart();Log.i(TAG, "onStart()");}@Overrideprotected void onResume() {// TODO Auto-generated method stubsuper.onResume();Log.i(TAG, "onResume()");}@Overrideprotected void onPause() {// TODO Auto-generated method stubsuper.onPause();Log.i(TAG, "onPause()");}@Overrideprotected void onStop() {// TODO Auto-generated method stubsuper.onStop();Log.i(TAG, "onStop()");}@Overrideprotected void onDestroy() {// TODO Auto-generated method stubsuper.onDestroy();Log.i(TAG, "onDestroy()");}}

main.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:orientation="vertical" >    <TextView        android:id="@+id/tv1"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="@string/hello" /></LinearLayout>

string.xml

<?xml version="1.0" encoding="utf-8"?><resources>    <string name="hello">测试生命周期</string>    <string name="app_name">Test</string>    </resources>

AndroidManifest.xml同上

二.运行结果：

启动运行：

分两种情况：

1.点击模拟器返回按钮——>会destory这个Activity

2.点击模拟器主页按钮——>用栈保存这个Activity,下次重新打开时不会再create

下次再打开这个Activity

三.细节

1. it is popped from the stack (and destroyed) and the previous activity resumes.

2. The two most important callback methods are.

a. onCreate() :  You must implement this method. The system calls this when creating your activity.

b. onPause() :   The system calls this method as the first indication that the user is leaving your activity (though it does not always   mean the activity is being destroyed). This is usually where you should commit any changes that should be persisted                            beyond the current user session (because the user might not come back).

3. ViewGroup继承自View.

4. An intent can also carry small amounts of data to be used by the activity that is started.