多个Activity跳转的小结

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在android开发中Activity相当于web开发的页面，或者说如j2ee开发中对应的jsp页面。在开发jsp时，经常会遇到页面跳转的问题，在android也同样会遇到。以下的几个例子是我对android的Activity跳转的小结，也是最近做项目的小结。

第一个例子：demo1
Main—>SecondActivity—>Main
从流程上看就是从Main跳转到SecondActivity，再从SecondActivity返回到Main。也就是将子Activity的数据返回给父Activity。
代码如下：

public class Main extends Activity {private Button btn;private TextView request_text;private final int FIRST_REQUEST_CODE = 1;    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                request_text = (TextView)this.findViewById(R.id.request_text);                btn = (Button)this.findViewById(R.id.btn);        btn.setOnClickListener(new OnClickListener() {public void onClick(View v) {Intent i = new Intent(Main.this,SecondActivity.class);i.putExtra("request_text_for_main", "从Main传递到SecondActivity");startActivityForResult(i, FIRST_REQUEST_CODE);}});    }        protected void onActivityResult(int requestCode, int resultCode, Intent data) {    super.onActivityResult(requestCode, resultCode, data);    if(requestCode==FIRST_REQUEST_CODE && resultCode==Activity.RESULT_OK){    if(data != null) {    request_text.setText(data.getStringExtra("request"));    }    }    }}

public class SecondActivity extends Activity{private TextView request_text;private Button btn;private String text;public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.second);                request_text = (TextView)this.findViewById(R.id.request_text);                if (getIntent().getStringExtra("request_text_for_main") != null) {        text = getIntent().getStringExtra("request_text_for_main");        request_text.setText(text);        }                btn = (Button)this.findViewById(R.id.btn);        btn.setOnClickListener(new OnClickListener() {public void onClick(View v) {Intent i = new Intent();i.putExtra("request",text+"\n"+"从SecondActivity传递到ThirdActivity");setResult(Activity.RESULT_OK,i);finish();}});}}

图一

图一所示是demo初始化的样子，点击“第一次跳转”进入图二。

图二
图二显示从Main到SecondActivity这个过程，再点击“第二次跳转”即返回Main这个Activity。

图三
图三表示跳转结束，Button按钮上面的文字记录跳转的过程。

这个例子最主要是第一个Activity Main设置的onActivityResult()方法和startActivityForResult()方法。
在Main中通过startActivityForResult()调用SecondActivity，然后在onActivityResult()中获取其返回参数，或者说通过onActivityResult()进行回调。

SecondActivity中要返回第一个Main必须：
setResult(Activity.RESULT_OK,i);
finish();

第二个例子：demo2
Main—>SecondActivity—>ThirdActivity—>Main
这个例子的流程，比上一个更复杂一些，经历了3个Activity，最好跳转回第一个Activity。
代码如下：

public class Main extends Activity {private Button btn;private TextView request_text;private final int FIRST_REQUEST_CODE = 1;    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                request_text = (TextView)this.findViewById(R.id.request_text);                btn = (Button)this.findViewById(R.id.btn);        btn.setOnClickListener(new OnClickListener() {public void onClick(View v) {Intent i = new Intent(Main.this,SecondActivity.class);i.putExtra("request_text_for_main", "从Main传递到SecondActivity");startActivityForResult(i, FIRST_REQUEST_CODE);}});    }        protected void onActivityResult(int requestCode, int resultCode, Intent data) {    super.onActivityResult(requestCode, resultCode, data);    if(requestCode==FIRST_REQUEST_CODE && resultCode==Activity.RESULT_FIRST_USER){    if(data != null) {    request_text.setText(data.getStringExtra("request_text_for_third"));    }    }    }}

public class SecondActivity extends Activity{private TextView request_text;private Button btn;private final int SECOND_REQUEST_CODE = 2;private String text;public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.second);                request_text = (TextView)this.findViewById(R.id.request_text);                if (getIntent().getStringExtra("request_text_for_main") != null) {        text = getIntent().getStringExtra("request_text_for_main");        request_text.setText(text);        }                btn = (Button)this.findViewById(R.id.btn);        btn.setOnClickListener(new OnClickListener() {public void onClick(View v) {Intent i = new Intent(SecondActivity.this,ThirdActivity.class);i.putExtra("request_text_for_second", text+"\n"+"从SecondActivity传递到ThirdActivity");startActivityForResult(i, SECOND_REQUEST_CODE);}});}@Overrideprotected void onActivityResult(int requestCode, int resultCode, Intent data) {super.onActivityResult(requestCode, resultCode, data);if(requestCode==SECOND_REQUEST_CODE && data != null){setResult(Activity.RESULT_FIRST_USER, data);finish();}}}

public class ThirdActivity extends Activity{private TextView request_text;private Button btn;private String text;public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.third);                text = getIntent().getStringExtra("request_text_for_second");        request_text = (TextView)this.findViewById(R.id.request_text);        request_text.setText(text);                btn = (Button)this.findViewById(R.id.btn);        btn.setOnClickListener(new OnClickListener() {public void onClick(View v) {Intent i = new Intent();i.putExtra("request_text_for_third", text+"\n"+"从ThirdActivity再次传递到Main");setResult(Activity.RESULT_FIRST_USER, i);finish();}});}}

这个demo2比起前面的demo1的不同之处在于就是通过ThirdActivity进行跳转到Main。
在代码上的区别是：
(1)Main的onActivityResult()方法中,它的resultCode==Activity.RESULT_FIRST_USER而不是前面的resultCode==Activity.RESULT_OK
(2)SecondActivity中增加了onActivityResult()方法，该方法是用于回调ThirdActivity，并且该方法执行了跳转过程跳转到Main这个Activity。
(3) ThirdActivity和demo1的SecondActivity很类似。

第三个例子：demo3
Main—>SecondActivity—>ThirdActivity—>SecondActivity—>Main
这个过程看起来复杂，其实不然，最后一步是借助SecondActivity的另一个Button实现的。
代码如下：

public class Main extends Activity {private Button btn;private TextView request_text;private final int FIRST_REQUEST_CODE = 1;    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                request_text = (TextView)this.findViewById(R.id.request_text);                btn = (Button)this.findViewById(R.id.btn);        btn.setOnClickListener(new OnClickListener() {public void onClick(View v) {Intent i = new Intent(Main.this,SecondActivity.class);i.putExtra("request_text_for_main", "从Main传递到SecondActivity");startActivityForResult(i, FIRST_REQUEST_CODE);}});    }        protected void onActivityResult(int requestCode, int resultCode, Intent data) {    super.onActivityResult(requestCode, resultCode, data);    if(requestCode==FIRST_REQUEST_CODE && resultCode==Activity.RESULT_FIRST_USER){    if(data != null) {    request_text.setText(data.getStringExtra("final_request"));    }    }    }}

public class SecondActivity extends Activity{private TextView request_text;private Button btn,finalBtn;private final int SECOND_REQUEST_CODE = 2;private String text;public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.second);                request_text = (TextView)this.findViewById(R.id.request_text);                if (getIntent().getStringExtra("request_text_for_main") != null) {        text = getIntent().getStringExtra("request_text_for_main");        request_text.setText(text);        }                btn = (Button)this.findViewById(R.id.btn);        btn.setOnClickListener(new OnClickListener() {public void onClick(View v) {Intent i = new Intent(SecondActivity.this,ThirdActivity.class);i.putExtra("request_text_for_second", text+"\n"+"从SecondActivity传递到ThirdActivity");startActivityForResult(i, SECOND_REQUEST_CODE);}});                finalBtn = (Button)this.findViewById(R.id.finalBtn);        finalBtn.setOnClickListener(new OnClickListener() {public void onClick(View v) {Intent i = new Intent();i.putExtra("final_request", text+"\n"+"从SecondActivity最后传递到Main");setResult(Activity.RESULT_FIRST_USER,i);finish();}});}    protected void onActivityResult(int requestCode, int resultCode, Intent data) {    super.onActivityResult(requestCode, resultCode, data);    if(requestCode==SECOND_REQUEST_CODE && resultCode==Activity.RESULT_OK){    if(data != null) {    text = data.getStringExtra("request_text_for_third");    request_text.setText(text);    }    }    }}

public class ThirdActivity extends Activity{private TextView request_text;private Button btn;private String text;public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.third);                text = getIntent().getStringExtra("request_text_for_second");        request_text = (TextView)this.findViewById(R.id.request_text);        request_text.setText(text);                btn = (Button)this.findViewById(R.id.btn);        btn.setOnClickListener(new OnClickListener() {public void onClick(View v) {Intent i = new Intent();i.putExtra("request_text_for_third", text+"\n"+"从ThirdActivity再次传递到SecondActivity");setResult(Activity.RESULT_OK, i);finish();}});}}

比起前一个demo2其实没有更复杂之处，只是从ThirdActivity跳转回SecondActivity，而通过SecondActivity的另一个Button来跳转回Main的。

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