Activity启动模式详解

来源：互联网发布：mac一键关闭所有程序编辑：程序博客网时间：2024/04/29 12:44

Activity的启动模式共有四种：standard，singleTop，singleTask，singleInstance！

1，standard：默认的启动模式，每当启动新的活动，它都会在返回栈中入栈，并处于栈顶，看代码：

public class FirstActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Log.d("FirstActivity", this.toString());        Button bt1 = ((Button) findViewById(R.id.bt1));        bt1.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                startActivity(new Intent(FirstActivity.this, FirstActivity.class));            }        });    }}

点击按钮：

03-07 13:56:37.235 31639-31639/cn.sh.changxing.firstcode D/FirstActivity: cn.sh.changxing.firstcode.FirstActivity@434463b8
03-07 13:56:50.655 31639-31639/cn.sh.changxing.firstcode D/FirstActivity: cn.sh.changxing.firstcode.FirstActivity@434c3e78

可以看到会创建不同的FirstActivity实例，此时需要连续按两次返回才能退出。

,2，singleTop：当启动的活动已经在栈顶时，则认为可以直接使用，不需要重新创建新的实例：

03-07 14:00:32.735 4163-4163/cn.sh.changxing.firstcode D/FirstActivity: cn.sh.changxing.firstcode.FirstActivity@434295d0

无论点击多少次按钮，都不会创建新的实例，并且按一次返回就能退出应用。

3，singleTask：不管活动在不在栈顶，都可以直接使用已经创建的实例，不需要重新创建新的实例，如果活动不在栈顶，则把当前在栈顶的活动移除，让该不在栈顶的活动重新回到栈顶，看代码：

FirstActivity中追加bt2：

public class FirstActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Log.d("FirstActivity", this.toString());        Button bt1 = ((Button) findViewById(R.id.bt1));        bt1.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                startActivity(new Intent(FirstActivity.this, FirstActivity.class));            }        });        Button bt2 = ((Button) findViewById(R.id.bt2));        bt2.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                startActivity(new Intent(FirstActivity.this, SecondActivity.class));            }        });    }    @Override    protected void onResume() {        super.onResume();        Log.d("FirstActivity", "onResume");    }}

SecondActivity：

public class SecondActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        Log.d("SecondActivity", this.toString());        setContentView(R.layout.activity_second);        Button a2Bt = ((Button) findViewById(R.id.a2_bt));        a2Bt.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                startActivity(new Intent(SecondActivity.this, FirstActivity.class));            }        });    }    @Override    protected void onDestroy() {        Log.d("SecondActivity", "onDestroy");        super.onDestroy();    }}

<activity    android:name=".FirstActivity"    android:launchMode="singleTask">    <intent-filter>        <action android:name="android.intent.action.MAIN" />        <category android:name="android.intent.category.LAUNCHER" />    </intent-filter></activity><activity android:name=".SecondActivity"></activity>

现在从FristActivity启动到SecondActivity，再从SecondActivity中启动FirstActivity

003-07 14:24:27.165 22287-22287/cn.sh.changxing.firstcode D/FirstActivity: cn.sh.changxing.firstcode.FirstActivity@435009e0
03-07 14:24:27.165 22287-22287/cn.sh.changxing.firstcode D/FirstActivity: onResume
03-07 14:24:33.765 22287-22287/cn.sh.changxing.firstcode D/SecondActivity: cn.sh.changxing.firstcode.SecondActivity@43523428
03-07 14:24:35.085 22287-22287/cn.sh.changxing.firstcode D/FirstActivity: onResume
03-07 14:24:35.450 22287-22287/cn.sh.changxing.firstcode D/SecondActivity: onDestroy

4：singleInstance：启动一个单独的返回栈来存放该活动，不管是哪个应用程序访问该活动，都共用同一个返回栈，也就解决了共享活动实例的问题。

<activity    android:name=".FirstActivity">    <intent-filter>        <action android:name="android.intent.action.MAIN" />        <category android:name="android.intent.category.LAUNCHER" />    </intent-filter></activity><activity android:name=".SecondActivity"    android:launchMode="singleInstance"/><activity android:name=".ThirdActivity"></activity>

以上把SecondActivity的launchMode设为singleInstance，并追加一个button启动活动ThirdActivity

public class SecondActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        Log.d("SecondActivity", this.toString());        setContentView(R.layout.activity_second);        Button a2Bt = ((Button) findViewById(R.id.a2_bt));        a2Bt.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                startActivity(new Intent(SecondActivity.this, FirstActivity.class));            }        });        Button a2Bt2 = ((Button) findViewById(R.id.a2_bt2));        a2Bt2.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                startActivity(new Intent(SecondActivity.this, ThirdActivity.class));            }        });    }    @Override    protected void onResume() {        super.onResume();        Log.d("SecondActivity", "onResume");    }    @Override    protected void onDestroy() {        Log.d("SecondActivity", "onDestroy");        super.onDestroy();    }}

操作流程：FirstActivity中启动SecondActiviy，再启动ThirdActivity，然后依次返回直至退出整个应用

03-07 14:36:53.520 9153-9153/cn.sh.changxing.firstcode D/FirstActivity: cn.sh.changxing.firstcode.FirstActivity@43431d70
03-07 14:36:53.525 9153-9153/cn.sh.changxing.firstcode D/FirstActivity: onResume
03-07 14:36:56.160 9153-9153/cn.sh.changxing.firstcode D/SecondActivity: cn.sh.changxing.firstcode.SecondActivity@434b06f0
03-07 14:36:56.200 9153-9153/cn.sh.changxing.firstcode D/SecondActivity: onResume
03-07 14:36:57.470 9153-9153/cn.sh.changxing.firstcode D/ThirdActivity: cn.sh.changxing.firstcode.ThirdActivity@434d56e0
03-07 14:36:59.105 9153-9153/cn.sh.changxing.firstcode D/FirstActivity: onResume
03-07 14:37:00.415 9153-9153/cn.sh.changxing.firstcode D/SecondActivity: onResume
03-07 14:37:03.220 9153-9153/cn.sh.changxing.firstcode D/SecondActivity: onDestroy

可以看到返回的时候是从ThirdActivity返回到FirstActivity，然后再返回到SecondActivity的。

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