Android 中的隐式与显式意图（ startActivity(intent) 崩溃）

Implicit vs Explicit Intent in Android ( startActivity(intent) crashes )

提问by coderplus

I'm new in this world. I have a problem when I use startActivity(intent). This is the Manifest:

我是这个世界的新手。我在使用 startActivity(intent) 时遇到问题。这是清单：

<activity
        android:name="com.example.counter.Splash"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

    <activity
        android:name="com.example.counter.MainActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.DEFAULT" />
        </intent-filter>

And this is the code:

这是代码：

 public class Splash extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);

    setContentView(R.layout.splash);

    Thread timer = new Thread(){
        public void run()
        {
            try
            {
                sleep(5000);

            }
            catch (InterruptedException e)
            {
                e.printStackTrace();
            }
            finally
            {

                Intent i=new Intent ("com.example.counter.MainActivity");
                startActivity(i);
            }
        }
    };

    timer.start();

}

I'd want to show Splash activity for 5 seconds and then show MainActivity. LogErrors: !https://www.dropbox.com/s/kg7xyp6h4b95itq/Screenshot%202014-02-08%2016.57.36.png

我想显示 Splash 活动 5 秒钟，然后显示 MainActivity。日志错误：！https://www.dropbox.com/s/kg7xyp6h4b95itq/Screenshot%202014-02-08%2016.57.36.png

回答by coderplus

There are two ways of doing what you are trying to do.

有两种方法可以做你想做的事情。

1. Using an implicit Intent
2. Using an explicit Intent

1. 使用隐式 Intent
2. 使用显式 Intent

Refer Intent Types

参考意图类型

1. Implicit Intent

1. 隐式 Intent

Declare Intent Filtersfor your Activityin your AndroidManifest.xml. By doing that the Androidsystem understands what kind of Intentsyour component(in this case your MainActivity) can handle.

声明Intent Filters你Activity在你的AndroidManifest.xml。通过这样做，Android系统了解Intents您的组件（在本例中是您的 MainActivity）可以处理的类型。

<activity
        android:name="com.example.counter.MainActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="com.example.counter.MainAction" />
            <category android:name="android.intent.category.DEFAULT" />
        </intent-filter>
<activity>

Now you will be able to launch your Activitywith the same Intent

现在您将能够以Activity相同的方式启动您的Intent

Intent i=new Intent ("com.example.counter.MainAction");
startActivity(i);

Such implicit Intentsare used when you don't explicitly know which Activity has to be started and you want the Android system to decide which component to start. If the system finds multiple components which can handle your Intent, it will allow the user to choose.

Intents当您不明确知道必须启动哪个 Activity 并且您希望 Android 系统决定启动哪个组件时，将使用这种隐式。如果系统找到多个可以处理您的 Intent 的组件，它将允许用户进行选择。

Note: it is possible that there are no applications that can handle your intent. In this case, your application will crash when you invoke startActivity(). To avoid this, before calling startActivity() you should first verify that there is at least one application registered in the system that can handle the intent. To do this use resolveActivity() on your intent object.

注意：可能没有应用程序可以处理您的意图。在这种情况下，当您调用 startActivity() 时，您的应用程序将崩溃。为了避免这种情况，在调用 startActivity() 之前，您应该首先验证系统中是否至少注册了一个可以处理意图的应用程序。为此，请在您的意图对象上使用 resolveActivity()。

1. Explicit Intent

2. 显式 Intent

In your case, you should use an explicit Intentas you already know which Activityyou want to start. So create an Intentby passing the context and the component(Activity) class you want to start.

在您的情况下，您应该使用显式，Intent因为您已经知道要从哪个Activity开始。因此，Intent通过传递上下文和要启动的组件（活动）类来创建一个。

Intent i=new Intent (this,MainActivity.class);
startActivity(i);

回答by nKn

You have to reference the classyou want to start. So you'd need something like:

你必须参考class你想要开始的。所以你需要这样的东西：

Intent newAct = new Intent(this, Splash.class);
startActivity(newAct);

What you're passing is an Actionthat is not understood as a class name.

你传递的是一个Action不被理解为类名的。

回答by Chintan Soni

I guess, Splashis your Launcher Activity, make following changes in your manifest file:

我想，Splash是您的启动器活动，在您的清单文件中进行以下更改：

<activity
    android:name="com.example.counter.Splash"
    android:label="@string/app_name" >
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />

        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

<activity
    android:name="com.example.counter.MainActivity"
    android:label="@string/app_name" >
</activity>

Make your activity this way:

以这种方式进行您的活动：

public class Splash extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.splash);

        /*Splach screen that display for 5 seconds when app start*/
        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                Intent i = new Intent(Splash.this, MainActivity.class);
                startActivity(i);
                finish();
            }
        }, 5000);

    }

}

I hope this should solve your problem now.

我希望这现在可以解决您的问题。

回答by Ali

I think you should be able to use (implicit Intent):

我认为你应该能够使用（隐式意图）：

Intent i=new Intent ("com.example.counter.MainActivity");

There is no reason to change it to (explicit intent):

没有理由将其更改为（明确意图）：

startActivity(new Intent(mContext, MainActivity.class));

but then you need to change the actionin intent filterof MainActivity from:

但你需要改变action在intent filterMainActivity从：

<action android:name="android.intent.action.MAIN" />

to:

到：

<action android:name="com.example.counter.MainActivity"/>

回答by MysticMagic?

You need to declare an activityin manifest file.

您需要在清单文件中声明一个活动。

Like this:

像这样：

<application
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name=".FirstActivity"
        android:label="@string/title_activity_main" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activty
        android:name="com.example.counter.MainActivity"/>
</application>

Hope it helps.

希望能帮助到你。

回答by la martir martir

i think it is better if you use Handler put this code at the splash Activity at the onCreate

我认为如果您使用 Handler 将此代码放在 onCreate 的启动 Activity 中会更好

new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                Intent intent = new Intent(getApplicationContext(), MainActivity.class);
                startActivity(intent);
                finish();
            }
        }, 1500); 

and if you want to open it one time it is good to use SharedPreferences

如果您想一次打开它，最好使用 SharedPreferences