Android开发必看-详解Activity之间的数据传递

偏执的太偏执、 2022-07-12 03:00 244阅读 0赞

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。