public class MainActivity extends AppCompatActivity {
    public static final int REQUEST_CODE=200;
    public static final int REQUEST_CODE_PICK_IMAGE=300;
    private Button btn;
    private ImageView iv;
@Override
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
 
setContentView(R.layout.activity_main);
initView();
btn.setOnClickListener(new View.OnClickListener() {
            @Override
public void onClick(View v) {

                checkPerm();
}
        });
}
    private void checkPerm() {
        /**1.在AndroidManifest檔案中新增需要的許可權。
*
         * 2.檢查許可權
*這裡涉及到一個
 
API，ContextCompat.checkSelfPermission，
* 主要用於檢測某個許可權是否已經被授予，方法返回值為PackageManager.PERMISSION_DENIED
         * 或者PackageManager.PERMISSION_GRANTED。當返回DENIED就需要進行申請授權了。
* */
if(ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED
 
){ //許可權沒有被授予
/**3.申請授權
* @param
*  @param activity The target activity.（Activity|Fragment、）
* @param permissions The requested permissions.（許可權字串陣列）
* @param requestCode Application specific request code to match with a result（int型申請碼）
*    reported to {@link OnRequestPermissionsResultCallback#onRequestPermissionsResult(
             *    int, String[], int[])}.
             * */
ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
REQUEST_CODE);
}else{//許可權被授予
choosePhoto();
//直接操作
}

    }

    private void initView() {
        btn= (Button) findViewById(R.id.btn_open_pic);
iv= (ImageView) findViewById(R.id.iv);
}

    /***
     *
     * 4.處理許可權申請回調
*/
@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {

        if (requestCode == REQUEST_CODE)
        {
            if (grantResults[0] == PackageManager.PERMISSION_GRANTED)
            {

               //許可權被授予
choosePhoto();
} else
{
                // Permission Denied
Toast.makeText(MainActivity.this, "Permission Denied", Toast.LENGTH_SHORT).show();
}
            return;
}
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
}



    void choosePhoto(){
        /**
         * 開啟選擇圖片的介面
*/
Intent intent = new Intent(Intent.ACTION_PICK);
intent.setType("image/*");//相片型別
startActivityForResult(intent, REQUEST_CODE_PICK_IMAGE);
}


    @Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        switch (requestCode){
            case REQUEST_CODE_PICK_IMAGE:
                if (resultCode == RESULT_OK) {
                    try {
                        /**
                         * 該uri是上一個Activity返回的
*/
Uri uri = data.getData();
Bitmap bit = BitmapFactory.decodeStream(getContentResolver().openInputStream(uri));
iv.setImageBitmap(bit);
} catch (Exception e) {
                        e.printStackTrace();
Log.d("tag", e.getMessage());
Toast.makeText(this,"程式崩潰",Toast.LENGTH_SHORT).show();
}
                }
                break;
}

    }
}