Activity 基本使用

向另一个应用发送数据

1. 发起通话

Uri number = Uri.parse("tel:5551234");
Intent callIntent = new Intent(Intent.ACTION_DIAL, number);

2. 查看网页

Uri webpage = Uri.parse("https://www.android.com");
Intent webIntent = new Intent(Intent.ACTION_VIEW, webpage);

3. 发送带有附件的电子邮件

Intent emailIntent = new Intent(Intent.ACTION_SEND);
// 这个 intent 没有 URI, 所以要申明  "text/plain" 类型
emailIntent.setType(HTTP.PLAIN_TEXT_TYPE);
emailIntent.putExtra(Intent.EXTRA_EMAIL, new String[] {"jan@example.com"}); // 

emailIntent.putExtra(Intent.EXTRA_SUBJECT, "Email subject");
emailIntent.putExtra(Intent.EXTRA_TEXT, "Email message text");
emailIntent.putExtra(Intent.EXTRA_STREAM, Uri.parse("content://path/to/email/attachment"));

4. 创建日历活动

// 事件是在January 23, 2021 -- from 7:30 AM to 10:30 AM.
Intent calendarIntent = new Intent(Intent.ACTION_INSERT, Events.CONTENT_URI);
Calendar beginTime = Calendar.getInstance();
beginTime.set(2021, 0, 23, 7, 30);
Calendar endTime = Calendar.getInstance();
endTime.set(2021, 0, 23, 10, 30);
calendarIntent.putExtra(CalendarContract.EXTRA_EVENT_BEGIN_TIME, beginTime.getTimeInMillis());
calendarIntent.putExtra(CalendarContract.EXTRA_EVENT_END_TIME, endTime.getTimeInMillis());
calendarIntent.putExtra(Events.TITLE, "Ninja class");
calendarIntent.putExtra(Events.EVENT_LOCATION, "Secret dojo");

5. 创建 intent 来查看地图，验证是否存在可以处理该 intent 的应用，然后启动它

Uri location = Uri.parse("geo:0,0?q=1600+Amphitheatre+Parkway,+Mountain+View,+California");
Intent mapIntent = new Intent(Intent.ACTION_VIEW, location);
try {
    startActivity(mapIntent);
} catch (ActivityNotFoundException e) {
    // 如果没有对应的应用可以处理
}

6. 显示应用选择器

Intent intent = new Intent(Intent.ACTION_SEND);
String title = getResources().getString(R.string.chooser_title);
Intent chooser = Intent.createChooser(intent, title);
try {
    startActivity(chooser);
} catch (ActivityNotFoundException e) {
   // 如果没有对应的应用可以处理
}

更多示例可以访问官方文档：官方文档地址

获取Activity的结果的最佳做法

1. 直接在Activity 内部使用

ActivityResultLauncher<String> mGetContent = registerForActivityResult(new GetContent(),
    new ActivityResultCallback<Uri>() {
        @Override
        public void onActivityResult(Uri uri) {
           处理结果
        }
});

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    
    Button selectButton = findViewById(R.id.select_button);

    selectButton.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View view) {
         
            mGetContent.launch("image/*");
        }
    });
}

2. 封装到能够感知生命周期的类中（强烈推荐）

class MyLifecycleObserver implements DefaultLifecycleObserver {
    private final ActivityResultRegistry mRegistry;
    private ActivityResultLauncher<String> mGetContent;

    MyLifecycleObserver(@NonNull ActivityResultRegistry registry) {
        mRegistry = registry;
    }

    public void onCreate(@NonNull LifecycleOwner owner) {
       
        mGetContent = mRegistry.register(“key”, owner, new GetContent(),
            new ActivityResultCallback<Uri>() {
                @Override
                public void onActivityResult(Uri uri) {
                   // 处理结果
                }
            });
    }

    public void selectImage() {
        // 打开图片，选择图片
        mGetContent.launch("image/*");
    }
}

class MyFragment extends Fragment {
    private MyLifecycleObserver mObserver;

    @Override
    void onCreate(Bundle savedInstanceState) {
       
        mObserver = new MyLifecycleObserver(requireActivity().getActivityResultRegistry());
        getLifecycle().addObserver(mObserver);
    }

    @Override
    void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        Button selectButton = findViewById(R.id.select_button);
        selectButton.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View view) {
                mObserver.selectImage();
            }
        });
    }
}

3. 通用协定写法

ActivityResultLauncher<Intent> mStartForResult = registerForActivityResult(new StartActivityForResult(),
        new ActivityResultCallback<ActivityResult>() {
    @Override
    public void onActivityResult(ActivityResult result) {
        if (result.getResultCode() == Activity.RESULT_OK) {
            Intent intent = result.getData();
           处理结果
        }
    }
});

@Override
public void onCreate(@Nullable savedInstanceState: Bundle) {
    // ...

    Button startButton = findViewById(R.id.start_button);

    startButton.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View view) {
            // 指定跳转到某个页面处理事务，返回数据写在intent上
            mStartForResult.launch(new Intent(this, ResultProducingActivity.class));
        }
    });
}

如何让其他应用分享数据时能拉起你的应用进行操作

1. 添加 intent 过滤器

// 数据类型为文本或图像时处理 ACTION_SEND intent
<activity android:name="ShareActivity">
    <intent-filter>
        <action android:name="android.intent.action.SEND"/>
        <category android:name="android.intent.category.DEFAULT"/>
        <data android:mimeType="text/plain"/>
        <data android:mimeType="image/*"/>
    </intent-filter>
// 可以指定多个过滤器
    <intent-filter>
        <action android:name="android.intent.action.SENDTO"/>
        <category android:name="android.intent.category.DEFAULT"/>
        <data android:scheme="sms" />
        <data android:scheme="smsto" />
    </intent-filter>
</activity>

2. 处理其他应用发过来的数据

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    
    Intent intent = getIntent();
    Uri data = intent.getData();

    if (intent.getType().indexOf("image/") != -1) {
        // do something
    } else if (intent.getType().equals("text/plain")) {
        // do something
    }
}

3. 返回一些结果

Intent result = new Intent("com.example.RESULT_ACTION", Uri.parse("content://result_uri"));
setResult(Activity.RESULT_OK, result);
finish();

// 也可以直接指定结果值
setResult(RESULT_COLOR_RED);
finish();

在与其他应用交互时，软件包的可见性

关于一些特定交互相关，另写篇章阐述