Android开发必看-详解Activity之间的数据传递

2019-11-09 15:45:23

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Activity之间的数据传递

Activity单向数据传递

下面的；例子演示了从 OriginActivity activity 传递字符串“some data！” 到DestinationActivity activity. 注：这是两个活动之间发送数据的最直接的方法。

直接上代码（简单粗暴直接代码示例！）

OriginActivity

public class OriginActivity extends AppCompatActivity { @Override PRotected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_origin); // Create a new Intent object, containing DestinationActivity as target Activity. final Intent intent = new Intent(this, DestinationActivity.class); // Add data in the form of key/value pairs to the intent object by using putExtra() intent.putExtra(DestinationActivity.EXTRA_DATA, "Some data!"); // Start the target Activity with the intent object startActivity(intent); }}

DestinationActivity

public class DestinationActivity extends AppCompatActivity { public static final String EXTRA_DATA = "EXTRA_DATA"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_destination); // getIntent() returns the Intent object which was used to start this Activity final Intent intent = getIntent(); // Retrieve the data from the intent object by using the same key that // was previously used to add data to the intent object in OriginActivity. final String data = intent.getStringExtra(EXTRA_DATA); }}

其他的数据类型

对于其他的数据基本类型传递也是可以的，调用intent。putExtra（key，value）；但是取值时候要注明相应类型，比如传入的String，取值时候是getStringExtra（）以此类推。

传递对象

有两种方式

Serializable

Serializable这种方式直接实现Serializable接口，剩下的系统会帮我们做好。

代码如下（简单粗暴直接代码示例！）

intent.putExtra(DestinationActivity.EXTRA_DATA, myParcelableObject);bundle.putParcelable(DestinationActivity.EXTRA_DATA, myParcelableObject);final MyParcelableType data = intent.getParcelableExtra(EXTRA_DATA);

Parcelable

Parcelable是一个Android特定的接口，可以对自定义数据类型实现的（即你自己的对象/ POJO对象）。它是Android提供的，比Serializable更加高效。

代码如下（简单粗暴直接代码示例！）

bundle.putSerializable(DestinationActivity.EXTRA_DATA, mySerializableObject);final SerializableType data = (SerializableType)bundle.getSerializable(EXTRA_DATA);

Parcelable代码示例（依旧粗暴）

public class Foo implements Parcelable{ private final int myFirstVariable; private final String mySecondVariable; private final long myThirdVariable; public Foo(int myFirstVariable, String mySecondVariable, long myThirdVariable) { this.myFirstVariable = myFirstVariable; this.mySecondVariable = mySecondVariable; this.myThirdVariable = myThirdVariable; } // Note that you MUST read values from the parcel IN THE SAME ORDER that // values were WRITTEN to the parcel! This method is our own custom method // to instantiate our object from a Parcel. It is used in the Parcelable.Creator variable we declare below. public Foo(Parcel in) { this.myFirstVariable = in.readInt(); this.mySecondVariable = in.readString(); this.myThirdVariable = in.readLong(); } // The describe contents method can normally return 0. It's used when // the parceled object includes a file descriptor. @Override public int describeContents() { return 0; } @Override public void writeToParcel(Parcel dest, int flags) { dest.writeInt(myFirstVariable); dest.writeString(mySecondVariable); dest.writeLong(myThirdVariable); } // Note that this seemingly random field IS NOT OPTIONAL. The system will // look for this variable using reflection in order to instantiate your // parceled object when read from an Intent. public static final Parcelable.Creator<Foo> CREATOR = new Parcelable.Creator<Foo>() { // This method is used to actually instantiate our custom object // from the Parcel. Convention dictates we make a new constructor that // takes the parcel in as its only argument. public Foo createFromParcel(Parcel in) { return new Foo(in); } // This method is used to make an array of your custom object. // Declaring a new array with the provided size is usually enough. public Foo[] newArray(int size) { return new Foo[size]; } };}

Activty之间传递数据并且返回

举个栗子

MainActivity向DetailActivity传递数据，并且等待返回，MainActivity需要重写 onActivityResult(int requestCode, int resultCode, Intent data)方法，其中requestCode用于唯一标识请求的是DetailActivity，resultCode代表是请求的状态

粗暴的代码示例

MainActivity:public class MainActivity extends Activity { // Use a unique request code for each use case private static final int REQUEST_CODE_EXAMPLE = 0x9345; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); // Create an Intent to start DetailActivity final Intent intent = new Intent(this, DetailActivity.class); // Start DetailActivity with the request code startActivityForResult(intent, REQUEST_CODE_EXAMPLE); } // onActivityResult only get called // when the other Activity previously started using startActivityForResult @Override public void onActivityResult(int requestCode, int resultCode, Intent data) { super.onActivityResult(requestCode, resultCode, data); // First we need to check if the requestCode matches the one we used. if(requestCode == REQUEST_CODE_EXAMPLE) { // The resultCode is set by the DetailActivity // By convention RESULT_OK means that whatever // DetailActivity did was executed successfully if(resultCode == Activity.RESULT_OK) { // Get the result from the returned Intent final String result = data.getStringExtra(DetailActivity.EXTRA_DATA); // Use the data - in this case, display it in a Toast. Toast.makeText(this, "Result: " + result, Toast.LENGTH_LONG).show(); } else { // setResult wasn't successfully executed by DetailActivity // Due to some error or flow of control. No data to retrieve. } } }}DetailActivity:public class DetailActivity extends Activity { // Constant used to identify data sent between Activities. public static final String EXTRA_DATA = "EXTRA_DATA"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_detail); final Button button = (Button) findViewById(R.id.button); // When this button is clicked we want to return a result button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { // Create a new Intent object as container for the result final Intent data = new Intent(); // Add the required data to be returned to the MainActivity data.putExtra(EXTRA_DATA, "Some interesting data!"); // Set the resultCode as Activity.RESULT_OK to // indicate a success and attach the Intent // which contains our result data setResult(Activity.RESULT_OK, data); // With finish() we close the DetailActivity to // return back to MainActivity finish(); } }); } @Override public void onBackPressed() { // When the user hits the back button set the resultCode // as Activity.RESULT_CANCELED to indicate a failure setResult(Activity.RESULT_CANCELED); super.onBackPressed(); }}

注意事项

1.数据会立即返回，在调用finish（）之后，所以setResult()方法需要在finish（）之前调用，否否则数据不会返回。

2.确定你的Activity没有使用android:launchMode=”singleTask”启动模式，否则他会在一个单独的task，这样数据也不会返回。如果你的Activity使用singleTask启动，那么会立即调用onActivityResult()，并且返回result code o是Activity.RESULT_CANCELED.

3.谨慎的使用android:launchMode=”singleInstance”.在 Lollipop (Android 5.0, API Level 21)之前，不会返回数据。