Api demo源码学习（11）--App/Activity/Reorder Activity

本节实现四个Activity中进行跳转，比较简单，唯一需要注意的是调用语句

intent.addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);

它的功能是，如果跳转后的Activity已存在，则不是新创建一个activity，而是回到原来已存在的Activity中。
Api demo中只在第四个Activity中调用了这个语句，效果不明显，如果我们在四个Activity中都添上这条语句，那无论我们点击多少次跳转（>=4次）,我们按返回键都只需要四次，依次返回四个Activity后就可以退出程序，因为每次跳转不是重新开一个新的Activity，而是将原来已存在的Activity拉到任务栈的顶端上来。

ReorderOnLaunchActivity.java

/** Called when the activity is first created. */
@Override
protected void onCreate(Bundle savedState) {
super.onCreate(savedState);

setContentView(R.layout.reorder_on_launch);

Button twoButton = (Button) findViewById(R.id.reorder_launch_two);
twoButton.setOnClickListener(mClickListener);
}

private final OnClickListener mClickListener = new OnClickListener() {
public void onClick(View v) {
Intent intent = new Intent(ReorderOnLaunchActivity.this, ReorderTwo.class);
intent.addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
startActivity(intent);
//finish();
}
};
}

ReorderTwo.java

public class ReorderTwo extends Activity {
@Override
protected void onCreate(Bundle savedState) {
super.onCreate(savedState);

setContentView(R.layout.reorder_two);

Button twoButton = (Button) findViewById(R.id.reorder_launch_three);
twoButton.setOnClickListener(mClickListener);
}

private final OnClickListener mClickListener = new OnClickListener() {
public void onClick(View v) {
Intent intent = new Intent(ReorderTwo.this, RecorderThree.class);
intent.addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
startActivity(intent);
//finish();
}
};

}

RecorderThree.java

public class RecorderThree extends Activity{
@Override
protected void onCreate(Bundle savedState) {
super.onCreate(savedState);

setContentView(R.layout.reorder_three);

Button twoButton = (Button) findViewById(R.id.reorder_launch_four);
twoButton.setOnClickListener(mClickListener);
}

private final OnClickListener mClickListener = new OnClickListener() {
public void onClick(View v) {
Intent intent = new Intent(RecorderThree.this, RecorderFour.class);
intent.addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
startActivity(intent);
//finish();
}
};

}

RecorderFour.java

public class RecorderFour extends Activity {
@Override
protected void onCreate(Bundle savedState) {
super.onCreate(savedState);

setContentView(R.layout.reorder_four);

Button twoButton = (Button) findViewById(R.id.reorder_second_to_front);
twoButton.setOnClickListener(mClickListener);
}

private final OnClickListener mClickListener = new OnClickListener() {
public void onClick(View v) {
Intent intent = new Intent(RecorderFour.this, ReorderTwo.class);
intent.addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
startActivity(intent);
//finish();
}
};

}

[align=left]最后别忘了在AndroidMenifest.xml中注册另外三个Activity。[/align]
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[align=left]以上即可。[/align]
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[align=left]下一节：Api demo源码学习（12）--App/Activity/Save & Restore State[/align]